Introductory Ophthalmology

for Medical Students

A Syllabus for the Clerkship in Ophthalmology

Cynthia S. Chiu, MD Assistant Professor of Ophthalmology

Weill School of Medicine, Cornell University New York Presbyterian Hospital

with contributions by: D. Jackson Coleman, MD, Kip L. Dolphin, MD, and Thomas C. Lee, MD

Section 1: Ophthalmic Anatomy

The eye is an extension of the central nervous system. In fact, the retina is the only part of the brain you can visualize without the aid of neuro-imaging. The eye is designed much like a camera, and the tissues along its axis are translucent to allow the penetration of light. The anatomy of the globe can be divided into 3 layers: exterior, uvea, and interior, with associated attachments. The exterior layer consists of tissues that form the wall and the structure of the eye, and includes the cornea, conjunctiva, and sclera. The uveal layer is comprised of all the vascular structures, including the iris, ciliary body, choroid, and blood vessels. The interior layer contains the aqueous humor, the crystalline lens, the vitreous humor, and the neurosensory retina. Attached to the globe are the optic nerve, the extraocular muscles, and the cranial nerves.

The retina is an intricate network of neurons which, analogous to the film in a camera, absorbs the visual image. Histologically, the retina is organized into 8 layers; counter-intuitively light activates the outermost layer (closest to sclera) first, and then neurotransmission proceeds inward (toward the vitreous) until the axons of the ganglion cells coalesce into the optic nerve. Following the passage of light, the layers are: rod-cone outer segments, the outer nuclear layer (the cell bodies of the photoreceptors), the outer plexiform layer, the inner nuclear layer (the cell bodies of interneurons such as bipolar, amacrine, and horizontal cells), the inner plexiform layer, the ganglion cell layer, and the nerve fiber layer (the axons of the ganglion cells). Outside of the photoreceptor outer segments, the 8

th layer is the

retinal pigment epithelium, which maintains the health of the outer segments, helps recycle rhodopsin, and comprises the retinal blood-brain barrier. The orbit is a complicated 3-dimensional space made up of 7 bones: ethmoid, frontal, lacrimal, maxillary, palatine, sphenoid, and zygomatic. The important apertures of the orbit include the optic canal (for passage of the optic nerve and ophthalmic artery), the superior orbital fissure (for passage of CN III, IV, V, VI, sympathetic nerves, and the superior ophthalmic vein), and the inferior orbital fissure (for passage of the inferior ophthalmic vein and CN V). The supraorbital and infraorbital notch/foramens allows passage of CN V1 and V2 to innervate the frontal and maxillary regions, respectively.

Six extra-ocular muscles are attached to the globe, four recti (superior, inferior, medial, and lateral), and 2 obliques (superior and inferior). The eye and orbit are served by 6 cranial nerves. CN II is the optic nerve, transporting visual information to the brain. CN III provides motor input to the superior, medial, and inferior recti, the inferior oblique, and the eyelid retractors. CN III also provides parasympathetic innervation, via the ciliary ganglion, located just posterior to the globe. CN IV innervates the superior oblique. CN V provides sensory input to the eye and orbit. CN VI innervates the lateral rectus. CN VII provides motor input to the orbicularis oculi (eyelid protractor).

The lacrimal gland sits in the superotemporal quadrant of the orbit. In contrast, the nasolacrimal sac sits in a fossa along the inferonasal orbital rim. The nasolacrimal system begins with upper and lower canaliculi located along the nasal aspect of the eyelids. These canaliculi drain tears from the conjunctival fornices into the lacrimal sac. The sac is then drained by the nasolacrimal duct into the inferior meatus of the nose.

The visual pathway extends into the cranial cavity via the optic nerve. The optic nerves cross at the chiasm, where the nasal fibers (which actually serve the temporal visual field) decussate. From that point onward, each hemisphere contains neural signals from both eyes for the contralateral visual field. Posterior to the chiasm, the fibers form the optic tracts, then the optic radiations (located in the temporal and parietal lobes), and finally the visual cortex along the calcarine fissue of the occipital lobe.

References: 1. http://isgwww.cs.uni-magdeburg.de/~stefans/lehre/sfu/eye.jpg 2. http://anatomy.iupui.edu/courses/histo_D502/D502f04/lecture.f04/Eyef04/ret.jpg 3. http://www.cid.ch/DAVID/Bon/Bon20.html 4. http://www.chb-genomics.org/research/engle/images/nl-lateye.gif 5. http://eyelearn.med.utoronto.ca/OcuAnatLecture/images/Ocu_Anat_58.jpg 6. http://www.fz-juelich.de/ibi/ibi-1/datapool/page/181/figure%205-500.jpg

Section 2: Trauma and Ophthalmic Emergencies Subconjunctival Hemorrhage

Most simply put, a subconjunctival hemorrhage is a bruise under the conjunctiva. This occurs when a conjunctival capillary breaks and leaks blood into the subconjunctival space. Without a history of trauma, this commonly occurs with valsalva (cough, sneeze, screaming, etc.), eye rubbing, or may be spontaneous with a history of the use of aspirin, NSAIDs, or anti-coagulants. However, in the setting of trauma, if the hemorrhage is dense and opaque, a scleral rupture can be hidden beneath it, and the patient must be ruled-out for ruptured globe. Subconjunctival hemorrhages resolve spontaneously over 1-2 weeks, and unnecessary anti-coagulants should be held until recovery.

Corneal Abrasion A corneal abrasion is a break in the corneal epithelium. This can occur with both blunt (finger-poke) and shearing trauma (paper edge), or even prolonged exposure and drying (poor lid taping during general anesthesia). The corneal surface is the most densely innervated sensory surface of the body, and abrasions are exquisitely painful. Luckily, the corneal epithelium regenerates quickly, and with proper lubrication (antibiotic ointment) and analgesia, abrasions will heal spontaneously within days. Linear abrasions such as in this photo imply a foreign body under the eyelid, and these must be removed.

Corneal Foreign Body Metal, rust, and other particulate foreign bodies can become imbedded in the corneal stroma. These injuries often occur on-the-job, with metal work or explosions. Metal and rust are particularly toxic to the cornea and must be removed, usually with a tuberculin syringe needle or a drilling burr at the slit lamp. Care must be taken to remove as much foreign material as possible, while leaving enough corneal stroma to avoid perforation. Once a foreign body is found on the globe, the eye must be dilated to ensure there is no globe perforation or intraocular foreign bodies. To speed healing and prevent a secondary corneal ulcer, patients are treated with antibiotic ointment and frequent follow-up. Hyphema A hyphema is a layered blood clot within the anterior chamber. During blunt trauma, compressive forces cause fragile capillaries within the iris and ciliary body to break, and with sufficient bleeding, a clot will form. A hyphema is an indication that significant injury has occurred to the globe. Most hyphemas resolve spontaneously with topical steroids, cycloplegics (dilating drops), and activity restriction. However, these patients are prone to rebleeding, acute and chronic glaucoma, and permanent damage to the iris and angle. Very large clots filling the anterior chamber are called 8-ball hyphemas (after the black 8-ball in billiards) and may need surgical evacuation.

Acute Angle-Closure Glaucoma Angle-closure glaucoma usually occurs in middle-aged hyperopic (far-sighted) patients with cataracts. The combination of short globe length (common in hyperopes) and a large crystalline lens (cataract) can cause the pupil to become obstructed against the lens in a mid-dilated position. Aqueous humor is unable to circulate to the anterior chamber and pushes the peripheral iris forward, closing the angle, where fluid normally drains from the eye. Aqueous continues to accumulate behind the lens and iris, and the intraocular pressure increases dramatically, causing pain and loss of vision. Temporary therapy consists of pressure-lowering medications (topical and systemic), but definitive treatment is a laser iridotomy (hole in the iris) to create an opening by which aqueous can bypass the blockage to reach the drainage canals in the angle. Ruptured Globe In addition to penetrating injuries, the globe can rupture if sufficient blunt compressive force is applied. The structurally weakest areas of the globe are just posterior to the attachments of the extraocular muscles and at the limbus. In addition, prior surgical wounds, like those made for cataract surgery, are never as strong as native tissue and may open preferentially. Patients with suspected globe rupture should undergo thin-cut orbital CT, to evaluate the extent of injury. MRI is contraindicated due to the risk of metal foreign body. Treatment for ruptured globes is surgical exploration and repair. Systemic antibiotics and tetanus prophylaxis are also given. Retinal Detachment Patients with retinal detachment complain of vision loss, photopsias (flashing lights), and floaters. Though detachments can occur in the setting of trauma, they also occur spontaneously, especially in high myopia (near-sightedness) and with pre-existing retinal holes or tears. Retina that is detached for a prolonged period of time will atrophy and cause permanent visual loss, therefore surgical repair should be expedited. Depending on the size of the detachment, various surgical procedures can be used for repair: cryo (freezing), pneumo (injection of gas bubble), scleral buckle (silicone ring around the equator of the globe), and vitrectomy. Shaken Baby Syndrome Several factors lead to retinal injury in shaken baby syndrome. First of all, babies have large heads relative to their bodies, and weak neck support. Shaking results in a coup-contrecoup injury of the brain parenchyma, leading to contusions and intracranial hemorrhages. Increased intracranial pressure is translated down the optic nerve via the meninges. Squeezing the thorax causes increased venous pressure in the head. Both mechanisms increase pressure on the optic nerve and cause retinal vascular engorgement, leading to vitreous, retinal, and intraretinal hemorrhages. If the baby survives, treatment of the eye is mainly supportive, awaiting spontaneous reabsorption of the blood.

Endophthalmitis Infection within the globe can result from ocular injury (penetrating trauma or intraocular surgery) or hematogenous spread (sepsis). The common culprits are bacteria (staph, strep, Bacillus, and P.acnes) as well as ubiquitous fungi (yeasts from indwelling catheters). The vitreous is a nutritive jelly, much like agar, and bacterial seeding of the vitreous can quickly turn the eye into a self-contained abscess. Patients report loss of vision, pain, and redness. Treatment consists of vitreous culture and injection of broad spectrum intraocular antibiotics. Severe loss of vision may necessitate surgical removal of the vitreous abscess. Recovery is variable and depends on the virulence of the organism. Eyelid and Corneal Burns Both thermal and chemical burns cause devastating injury to the eyes. Early after injury, the eyelid skin can slough and the tissue becomes edematous from fluid third-spacing. As it heals, the skin contracts, and lid mal-positioning causes corneal exposure and thinning. Corneal and conjunctival defects also occur, and if limbal stem cells are damaged, these evolve into non-healing ulcers. Injury to the blood supply can cause ocular ischemia. Of chemical burns, alkaline agents cause more widespread damage due to deeper tissue penetration. Patients with chemical burns must undergo irrigation until the pH is neutralized. Aggressive lubrication and antibiotic prophylaxis are standard treatment. With severe inflammation, topical steroids can be used to minimize long-term scarring and contraction.

Orbital Cellulitis Infection of the orbit and periorbital tissues may extend from adjacent sinusitis or be inoculated by skin trauma. The pathogens most commonly implicated are staph, strep, and H.flu. It is important to differentiate between orbital and preseptal cellulitis; the former threatens the orbital apex, the cavernous sinus, and the CNS; the latter is limited to the skin. The orbital septum, a fibrous membrane which extends from periosteum to the eyelids, is the barrier which separates skin from deeper orbital contents. Proptosis, limited motility, and decreased vision are hallmarks of orbital involvement. Systemic antibiotics are used to treat both, but orbital infection requires long-term therapy. Orbital Fractures Compressive forces during trauma can cause orbital blow-out fractures. The bones which are thinnest and most prone to fracture are the postero-medial floor (the maxillary bone) and the medial wall (the lamina papyrecea). Large fractures of the orbital floor will permit the globe and orbital contents to sink inferiorly, resulting in enophthalmos and diplopia. Small fractures may entrap extraocular muscles, causing motility restriction, muscle atrophy, and nausea/bradycardia (pulling on extraocular muscles causes a vasovagal response). Fractures which are functionally or cosmetically significant are repaired using metal implants with antibiotic prophylaxis.

Orbital Compartment Syndrome The orbit is a fixed space, and the movement of the globe is limited posteriorly by the bony anatomy and anteriorly by the canthal tendons (which position the eyelids against the globe). Any mass (hemorrhage, abscess, tumor) which occupies space within the orbit will displace the globe forward, and a rapidly expanding mass will cause an orbital compartment syndrome. As pressure builds in a tense orbit, it can exceed the perfusion pressure of the globe and optic nerve, causing vision loss. Intraocular pressure also increases, causing acute glaucoma. A lateral canthotomy and cantholysis (to cut the tendons holding the globe back) will release the pressure and restore vision.

References: 1. http://dro.hs.columbia.edu/ced3/conjhemb.jpg 2. http://www.alanoptics.per.sg/abrasion.jpg 3. http://www.varga.org/corneal_foreign_body_2.jpg 4. http://www.opt.pacificu.edu/ce/catalog/10310-SD/Trauma%20Pictures/Hyphema.jpg 5. http://a248.e.akamai.net/7/248/430/20041208092715/www.merckfrosst.ca/e/health/glaucoma/glaucoma/ classify/images/glauc_closed.jpg 6. http://eyelearn.med.utoronto.ca/Lectures04-05/Trauma/Images/26Open11.jpg 7. http://www.eyeweb.org/atlas/retina/rd.jpg 8. http://pedsccm.wustl.edu/All-Net/media/gif/neurogif/trauma/5-retinalhem-abn.jpg 9. http://eyelearn.med.utoronto.ca/Lectures04-05/RedEye/images/RedEye_042.jpg 10. http://www.kernoweb.myby.co.uk/salamanders/images/burnface.jpg 11. http://eyelearn.med.utoronto.ca/PBLcases/new_ca4_small.jpg 12. http://www.uth.tmc.edu/radiology/test/er_primer/face/images/zcorn02.JPG 13. http://www.caep.ca/004.cjem-jcmu/004-00.cjem/vol-4.2002/vol-4.image/049-f1.jpg

Section 3: Primary Care Ophthalmology Refractive Error In healthy eyes, good distance vision depends on a

combination of factors: the power of the cornea and lens, which are responsible for bending (refracting) light, must be paired with a globe of the right length for an image to be focused on the retina. If the power of the cornea and lens are fixed, the image will be focused to a discrete point. If the length of the eye is such that the retina coincides with this focal point, a sharp image will be perceived. This perfect system is called emmetropia. However, if the globe is too long and the focal point lies anterior to the retina, the image will defocus and blur by the time it falls on the retina. This is called myopia, or near-sightedness. Myopic patients can see better up close because as they bring the object of regard closer to the eye, the focal point of the image moves posteriorly to the retina until the image is clear. Luckily adding lenses in front of the eye, in the form of glasses or contacts, can correct for refractive error. If the globe is too short and the focal point lies posterior to the retina, the image will also be blurred when it reaches the retina. This is called hyperopia, or far-sightedness. Young hyperopic patients can move the focal point forward by increasing the power of their native lenses (by stimulating cholinergic input to the ciliary muscles) in a process called accommodation. Astigmatism occurs when the shapes of cornea and lens are not perfectly spherical, that is, when the curvature is greater in one axis compared to another. This causes light to bend differently along different planes and there can be two separate focal points. Just as before, when the focal points do not both coincide with the retina, a blurred image results. The closer a patient brings the object to the eye, the more posterior the image will be focused (see above under myopia). An object which is too close has an image that falls behind the retina. The process of accommodation increases the power of the lens to decrease the focal distance and pull the image forward until it is sharply focused on the retina. However, the human lens continues to grow with age and over time it becomes less flexible. Past the age of 40, the process of accommodation weakens significantly and patients have difficulty seeing at near. This is called presbyopia. At this stage patients need reading glasses, and if they also wear a distance correction, they require bifocals.

Conjunctivitis Pink eye is the lay term for conjunctivitis, or inflammation of the conjunctiva which is usually the transparent lining of the globe. With inflammation, the conjunctiva becomes edematous and the blood vessels become dilated. The most common causes of conjunctivitis are viral, bacterial, and allergic. The same viruses that cause the common cold (adenovirus, enterovirus, etc) can also infect the eye, causing teary/mucous discharge and irritation. Bacterial infections are most often caused by strep, staph, and H.flu, but may also be caused by gonococcus and Chlamydia. The discharge is much thicker, more copious and purulent. Patients with allergic disease complain of itching and teary discharge. In all cases a history is important for diagnosis. Bacterial infection is treated with topical antibiotics (or systemic if gonococcal or chlamydial). Allergic disease is treated with topical and systemic antihistamines and mast cell stabilizers. There is no treatment for viral conjunctivitis, but patients are given contact precautions as it is highly contagious. Blepharitis Inflammation of the eyelids leads to chronic irritation, foreign body sensation, and dryness. There are specialized oil-secreting glands at the eyelid margins which can become congested with lipid and infected with skin flora. Shed skin cells, oil, and bacteria can accumulate at the base of the lashes. Treatment for blepharitis includes warm compresses, eyelid scrubs, and artificial tears. Severe cases associated with rosacea require systemic tetracyclines. Chalazion A stye, or hordeolum, is a small abscess that develops within an eyelid oil gland. If it persists, a localized granuloma, or chalazion, develops. Medical treatment consists of warm compresses and antibiotic ointment, to try to elicit the pus to the surface and induce spontaneous drainage. If the chalazion fails to open on its own, surgical curettage is necessary. Chalazia can be prevented if the underlying condition, usually blepharitis, is well-controlled, and therefore daily compresses and eyelid hygiene are recommended. Contact Dermatitis An allergic dermatitis can develop from foreign soaps, lotions, or makeup applied around the eye. The skin becomes inflamed, with tissue edema, erythema, and discomfort. The skin often has a corrugated appearance. Differentiating from a preseptal cellulitis requires a careful history, but often contact dermatitis extends over a wider area (wherever the inciting substance was applied) and the redness is more prominent. The offending agent should be discontinued immediately. Often this alone is enough. With more severe cases, a mild ophthalmic steroid cream can be used to quiet the inflammation.

Cataract Cataracts can be congenital or acquired. Simply put, a cataract is the clouding of the crystalline lens, which results in scattering, or diffraction, rather than focusing, or refraction, of light. Congenital cataracts are caused by insults to the fetus in utero. For senile cataracts, lens fibers continue to add to the diameter of the lens over time, much like the trunk of a tree. In addition, as patients age, lens proteins become less soluble and precipitate, causing the lens to change color and opacify. Symptoms caused by cataract include blurred vision, difficulty with reading, and glare. Treatment is by surgical removal, by a process called phacoemulsification (highly concentrated ultrasound with vacuum) and, in adults, replacement with an artificial intraocular lens. Glaucoma Although the mechanism is not well understood, glaucoma is a disease caused by elevated intraocular pressure or vascular instability which causes damage to the optic nerve. Acute glaucoma causes pain and rapid visual loss. However, chronic glaucoma is often painless and patients can lose a considerable number of optic nerve fibers, and subsequently much peripheral vision, before they present. The hallmark of glaucoma is a cupped nerve, where nerve tissue is lost and consequently a large central crater is formed (normally the central depression is less than 30-40%). Visual field testing reveals loss of peripheral, and sometimes central, vision. The goal of treatment is to reduce the intraocular pressure, and this can be accomplished with topical medications (aqueous suppressants and outflow stimulants), laser treatment, and filtering surgery. Macular degeneration Age-related macular degeneration (ARMD) is an idiopathic disease that causes central visual loss in elderly patients. In the dry form, a yellow substance called lipofuscin deposits under the RPE in discrete lesions called drusen. Drusen cause dysfunction and atrophy of the RPE. Since the RPE is vital to the normal functioning of the retinal photoreceptors and the blood-retinal barrier, visual loss ensues. Dry ARMD is a slowly progressive disease with no known cure. Recent studies have shown a diet rich in anti-oxidant vitamins and smoking cessation can slow the course of disease. If there is enough damage to the RPE and the underlying Bruchs membrane, choroidal vessels will break through and gain access to the retina and subretinal space. This choroidal neovascularization is comprised of abnormally leaky capillaries which are fragile and prone to bleeding. If this occurs, the disease transitions to the wet form of macular degeneration. Macular hemorrhages can cause instant and grave visual loss. Photodynamic therapy (laser treatment combined with a drug which targets abnormal choroidal vessels) can retard the progression of disease but may not restore vision. Several new drugs targeting stimulants to new vessel growth, namely VEGF, are showing promising results.

Migraine Migraines are thought to originate from vasospasm of the cerebral arteries. In addition to debilitating headache, nausea, photophobia, and phonophobia, migraines can be accompanied by visual or other sensory auras. It is important to recognize that the symptoms arise from the visual cortex in the occipital lobe and not from the eyes. Visual auras usually begin as scintillating scotomas, shimmering curtains or colored geometric patterns. As the migraine progresses, the positive visual phenomena can expand to cover the visual field. In some patients, negative phenomena can cause a hemianopia (or blackout of half the visual field)! Treatment is aimed at recognition of symptoms and serotonin agonists in conjunction with neurological consultation. Strabismus In normal alignment of the eyes, the corneal light reflex is centered in both pupils. Good alignment is necessary for normal development of visual acuity and stereopsis, or depth perception. Any misalignment results in competition between the fovea of the two eyes (since the brain cannot reconcile two different images both supposedly at the center of vision). This causes one eye to develop a central scotoma, or blind spot. Thus strabismus during childhood results in amblyopia, or poor visual development of one eye. Strabismus in adulthood (due to trauma, thyroid disease, or sensory deprivation) can cause diplopia and cosmetic concerns. In children, patching for amblyopia (to strengthen the weaker eye) should accompany surgical realignment. Adults who do not opt for surgery can try prism glasses and patching.

References: 1. http://www.merck.com/media/mmhe2/figures/fg226_1.gif 2. http://www.cibavision.com/images/products/astigmatism.jpg 3. http://www.chall.com/Chall1/conjunctivitis_lg.gif 4. http://www.ueseyecare.com/images/photos/blepharitis_l.jpg 5. http://www.eyesearch.com/chalazion.jpg 6. http://www.allergycapital.com.au/Images/EyeDerm.jpeg 7. http://technology.kingston.ac.uk/dirc/medical/images/catara2.jpg 8. http://www.eyeatlas.com/box/96glaucoma_cupping.jpg 9. http://www.ohiovalleyeye.com/images/macdegen_K45_dry.jpg 10. http://macula.org/images/retina_wet.jpg 11. http://www.perret-optic.ch/optometrie/symptomes_diagnostiques/symptomes/symptomes_image/ opto_migraine_ophtalmic.gif 12. http://www.eyedr4kids.com/images/exotropia.jpg

Section 4: Ophthalmology Associated with Systemic Disease Thyroid Ophthalmopathy Autoimmune thyroid disease is a systemic disorder that

spans the spectrum from hyper- to hypo-thyroid. Orbital disease does not necessarily parallel the exocrine abnormalities; in fact, orbital disease can precede hormonal changes by months, or lag behind by years! The cardinal features of thyroid ophthalmopathy include: exophthalmos, eyelid retraction (which causes corneal exposure and injury) and abnormally thickened extraocular muscles (which cause strabismus, limited motility, and diplopia). Rarely visual loss can occur due to optic nerve compression by hypertrophied extraocular muscles. Primary treatment is to stabilize the exocrine abnormality. Treatment of eye disease includes lubrication, orbital decompression (inducing orbital fractures to reduce the proptosis), and strabismus and eyelid surgery. Stevens-Johnson Syndrome Mucosal sloughing and scar formation are the hallmarks of Stevens-Johnson Syndrome, which can be caused by reaction to systemic medications or viral infections. The initial phase of injury is much like a burn: tissue necrosis and third-spacing of fluid. Later stages are cicatricial (meaning scar-forming) and aberrant bands of conjunctiva, or synechiae, and corneal neovascularization can cause permanent visual loss. Treatment is supportive with aggressive lubrication and antibiotic prophylaxis. Topical steroids may quiet the inflammation and minimize long-term scarring. Corneal transplant or keratoprosthesis (artificial cornea) are options to restore vision. Herpes Simplex Over ninety percent of Americans are sero-positive for herpes simplex virus (HSV). After initial infection, the virus stays dormant in the sensory ganglia and can reactivate and travel down the sensory nerves to erupt as a vesicular rash. The virus can infect the eye directly from branches of the trigeminal nerve, or by contact from adjacent infected areas. In addition to a vesicular eyelid dermatitis, HSV can cause a viral conjunctivitis, corneal ulcers, uveitis (intraocular inflammation), and retinal necrosis. HSV corneal ulcers have a characteristic branching appearance like the dendrites of a neuron. When deeper corneal tissues are affected, dense scarring and neovascularization can develop, causing loss of vision. Treatment of HSV ocular infection is by antiviral antibiotics (acyclovir) and topical steroids for immunosuppression. The inflammatory response to virus often causes more damage than the infection alone. Patients with recurrent outbreaks are given low dose acyclovir for long-term prophylaxis. Visual loss due to corneal scarring can be treated with corneal transplant.

Herpes Zoster After chickenpox infection, the herpes zoster virus (HZV) also remains dormant in the sensory ganglia. Reactivation of HZV manifests as shingles, a painful vesicular rash which, unlike HSV, strictly respects the dermatomes. Virus latent in the trigeminal ganglion can erupt in the V1 or V2 dermatomes, and can infect the eye. Like HSV, HZV can cause conjunctivitis, corneal ulcers, uveitis, and retinal necrosis. When the eye is involved, topical and oral acyclovir limit viral replication while topical steroids are used to treat the inflammation. Though HZV does not recur in the eye, corneal scarring can cause permanent visual loss. If this occurs, corneal transplant is an option. Post-herpetic neuralgia is a chronic and debilitating condition that is induced by sensory nerve damage during the initial shingles outbreak, and can be treated with neurontin or tricyclic antidepressants. Uveitis Inflammation within the eye has many etiologies. Any cause of systemic inflammation (autoimmune disease, infection, neoplasm) can also cause ocular disease. Uveitis is characterized by pain, visual loss, glaucoma, tissue necrosis, and scarring. Patients should undergo a diagnostic work-up to evaluate for autoimmune and infectious etiologies. Uveitis can affect many different ocular tissues. Scleritis is focal inflammation of the ocular wall, causing redness and tenderness to touch. Iritis/iridocyclitis is inflammation within the anterior chamber (white blood cells leaking from the iris and ciliary body), and is commonly seen in juvenile rheumatoid arthritis and HLA-B27 related diseases (ankylosing spondylitis, Reiters, etc). Patients can present with loss of vision, photophobia, and acute glaucoma. With severe iritis, white blood cells can layer into a precipitate called a hypopyon. Posteriorly, retinitis, retinal vasculitis, and choroiditis can occur in patients with systemic lupus erythematosus, sarcoid, and various infectious organisms such as tuberculosis, syphilis, and cytomegalovirus. Scarring and necrosis here not only lead to visual loss but also to secondary complications such as retinal detachment. Optic neuritis, or inflammation along the optic nerve, is often associated with multiple sclerosis. When the orbit, extraocular muscles, and lacrimal gland are involved, the term inflammatory orbital pseudotumor is used (to be distinguished from pseudotumor cerebri). Treatment of uveitis can be difficult with topical steroids alone if the patient has concurrent systemic disease. Though topical treatment is the first line of therapy for intraocular disease, addition of systemic immunosuppressives such as methotrexate, Cytoxan, Imuran, and Embrel are often needed to keep the inflammation under control. Patients are frequently co-managed with rheumatologists.

Ocular Side Effects from Systemic Medications Numerous systemic medications can induce ocular changes and toxicity. For example, tetracyclines and oral contraceptives can cause idiopathic intracranial hypertension (pseudotumor cerebri) which can cause papilledema and optic neuropathy. Plaquenil can induce an irreversible maculopathy; amiodarone can leave vortex-shaped corneal opacities. Topamax can cause a uveal effusion syndrome leading to acute angle closure glaucoma. Rifabutin can cause severe uveitis and a hypopyon. Cessation of the inciting drug can reverse the ocular injury in many, but not all, cases. In the photo, systemic steroid use and radiation to the head and neck can both induce cataract formation, but these cataracts require surgery to restore vision. Diabetic Retinopathy Diabetes induces systemic microvascular ischemia, and the end-organs most severely involved are the eyes, kidneys, and peripheral nerves. Both juvenile- and adult-onset diabetics get ocular complications; the longer a patient has had diabetes, the greater the chances of vision-threatening retinopathy. Poor glucose control leads to cytostructural changes in the retinal vasculature. In the non-proliferative form of retinopathy, small vessel ischemia and infarcts lead to hemorrhages, cotton-wool spots (infarcts of the nerve fiber layer), and microaneurysm formation. These abnormal blood vessels also leak fluid, causing distortion of the retinal architecture and vision loss. More severe diabetes and chronic ischemia induce the proliferative form of retinopathy, with the development of retinal, optic disc, and anterior segment neovascularization. Abnormal retinal vessels extend up into the vitreous cavity and can cause large hemorrhages as well as tractional retinal detachments. Abnormal iris and angle vessels cause neovascular angle-closure glaucoma. Patients with both diabetes and hypertension get accelerated disease. Primary treatment is with strict glucose and blood pressure control. Once patients present with visual loss or neovascularization, laser photocoagulation of the retina can treat or slow the disease. Vitrectomy and retinal detachment repair are surgical options. New drugs targeted at the stimulants for neovascularization, namely VEGF, are currently being introduced and are showing promising results. Hypertensive Retinopathy Hypertension also causes systemic ischemia and ocular complications. Signs of chronic hypertension include attenuated and tortuous retinal vessels, hemorrhages, and cotton-wool spots. Retinal macroaneurysms can develop, which then leak fluid or rupture and bleed, causing acute vision loss. Severe malignant hypertension can cause papilledema and retinal and choroidal ischemia, which can occur in other acute hypertensive states such as pre-eclampsia. Treatment is with acute and long-term blood pressure control.

Retinal Artery Occlusions Acute painless visual loss is usually an indication of a vascular catastrophe. Occlusion of the retinal arteries, whether by embolus, atherosclerotic disease, or vascultis, is analogous to a stroke in the eye. Like the brain there is loss of function and tissue edema. The recovery of vision is variable, but due to the intense metabolic demands of the retina, more often than not the damage is irreparable. Occlusion of the central retinal artery causes severe and widespread visual loss. Involvement of a branch retinal artery can cause central visual loss if it is located in the macula (central retina) or a scotoma (blind spot) if located more peripherally. Emboli that can be visualized within the vessel lumen are called Hollenhorst plaques. Patients with such plaques must undergo embolic work-ups including carotid dopplers and cardiac echograms. Treatment is by modification of risk factors. Giant Cell Arteritis One cause of retinal artery occlusion in elderly patients is giant cell, or temporal, arteritis (GCA). GCA is a systemic vasculitis that can lead to blindness, stroke, and myocardial infarction. Symptoms worrisome for GCA include sudden visual loss, temporal headache, scalp tenderness, pain with chewing, proximal limb myalgias, loss of appetite, and weight loss. Elevated sedimentation rate and C-reactive protein help make the diagnosis. Patients are treated with high dose systemic steroids with a slow taper. Temporal artery biopsy, performed by the ophthalmologist, provides the histological diagnosis for vasculitis. Retinal Vein Occlusion Another vascular event marked by acute painless visual loss is the occlusion of a retinal vein. On fundus exam, large flame-shaped hemorrhages and tortuous vessels are pathognomonic. Similar to arterial occlusions, ischemia and tissue edema set in. However, the causes of vein occlusions are quite different. Diabetes, hypertension, and hypercoagulable states (such as polycythemia vera, anticardiolipin antibodies, pregnancy, etc) are the most common etiologies. In addition, vein occlusions may be caused by intrinsic ocular factors, such as glaucoma and venous compression by overlying arteries (in the setting of hypertension). Widespread ischemia, as with a central vein occlusion, can cause retinal and anterior segment neovascularization, which is treated with laser. Otherwise, treatment is by modification of risk factors. Sickle Cell Retinopathy In low oxygen environments, the erythrocytes of patients with sickle cell change morphology (sickle) and cause systemic vascular occlusions. In the retina, these infarcts cause bleeding and retinal neovascularization (in response to the ischemia) in a characteristic pattern called the sea fan. Like other proliferative retinopathies, sea fans can cause vitreous hemorrhages and tractional retinal detachments. Treatment is by laser photocoagulation and by stabilizing the patients overall health.

Retinopathy of Prematurity Premature babies have underdeveloped lungs at birth and are given supplemental oxygen therapy. However, their retinas are also immature, and excess oxygen causes the retinal vascular pattern to change. Neovascularization occurs, with scaffolding of fibrovascular sheets into the vitreous. Left untreated, these fibrovascular membranes contract and cause retinal detachment. Premature babies under 2000 grams must be monitored for the development of retinopathy of prematurity (ROP). Once ROP begins, treatment with laser or cryo (freezing) to the peripheral retina is performed to induce regression of abnormal vessels. These children must be monitored long-term for the development of high myopia and strabismus that accompany ROP. Retinoblastoma The most common malignant intraocular tumor of childhood is retinoblastoma. The retinoblastoma gene normally functions as a tumor suppressor. When one allele is knocked out, either by a germline or somatic mutation, damage to the second allele will result in the formation of a white calcific tumor. Both eyes can be affected, as can the pineal gland, which also contains photoreceptor elements. Affected children most commonly present with leukocoria (white pupil) and strabismus. Small tumors confined to the retina can be treated with laser and cryo. Large tumors which threaten to metastasize can be treated with chemo- and radio-therapy, or by enucleation (removal of the eye). Siblings and parents should also be examined. Unfortunately, patients with retinoblastoma often develop other malignancies such as osteogenic sarcomas, especially in the areas previously treated with radiation.

Papilledema The strict definition of papilledema is elevated intracranial pressure causing bilateral optic nerve edema. The causes of papilledema include hydrocephalus, infection (meningitis, encephalitis), space-occupying mass, and idiopathic intracranial hypertension (pseudotumor cerebri). Though visual acuity may not be affected initially, over time papilledema can cause death of optic nerve fibers and optic neuropathy and vision loss will result. Treatment focuses on the inciting etiology. In cases of idiopathic intracranial hypertension, intractable papilledema can be treated by optic nerve fenestration, a surgical procedure to create a window in the meninges that line the optic nerve.

Optic Neuritis Optic neuritis is the inflammation of the optic nerve. It can be caused by many autoimmune, toxic, and infectious processes, but it is commonly associated with multiple sclerosis (MS). MS is an autoimmune disorder that targets myelin, and is characterized by waxing and waning neurological deficits and white matter lesions on MRI. Optic neuritis presents with vision loss and pain with eye movements. Often optic disc edema can be seen in the affected eye. The natural course of disease is spontaneous improvement, however patients with severe vision loss can be treated with high-dose intravenous steroids to accelerate recovery. Stroke Cerebral infarct along the visual pathways will cause various patterns of visual loss, depending on the location of injury. All lesions posterior to the optic chiasm will cause bilateral visual field defects; the more posterior the lesion, the more congruous the field defects will appear. To determine the location of the stroke, the rule is as follows: defects correspond to lesions in the opposite hemisphere, and superior defects point to inferior lesions (and vice versa). Optic tract lesions (C) can produce homonymous hemianopias. Since fibers which serve the superior visual field travel inferiorly to the temporal lobes (D), lesions here create superior quadrantanopias or segmental defects. Thus parietal lobe lesions produce inferior defects. Occipital lobe lesions (E) can involve or spare the center of vision, depending on the area involved. Though little can be done to recover loss field, visual rehabilitation and training can help patients cope with their limited peripheral vision.

References: 1. http://www.revoptom.com/handbook/images/62a.jpg 2. http://www.uveitis.org/images/sjs2.JPG 3. http://www.hkmj.org.hk/skin/images/108-1.jpg 4. http://eyemicrobiology.upmc.com/Images/Sub/PhotoEyeDendrite.jpg 5. http://www.opt.pacificu.edu/ce/catalog/Steroids%20Yudcovitch/Figure12.jpg 6. http://www.nova.edu/~albert/ScleritisWeb.jpg 7. http://e-learning.studmed.unibe.ch/augenheilkunde/systematik/aderhaut/images/iritis2.jpg 8. http://archopht.ama-assn.org/cgi/content/full/117/9/1260/FIGEPE80058F1 9. http://hubnet.buffalo.edu/ophthalmology/site/Home/Eye_Disorders/Posterior_subcapsular_cataract.jpg 10. http://www.neec.com/images/photos/diabetic%20retinopathy%20figure%203.jpg 11. http://www.tedmontgomery.com/the_eye/eyephotos/pics/DiabeticRetinopathyProliferative.jpg 12. http://hubnet.buffalo.edu/ophthalmology/site/Home/Eye_Disorders/Hypertensive_retinopathy.jpg 13. http://www.omnieyespecialists.com/images/eye_brao.jpg 14. http://www.mrcophth.com/pathology/gca2.jpg 15. http://www.scielo.br/img/revistas/abo/v66n6/18991f1.jpg 16. American Academy of Ophthalmology, Basic and Clinical Science Course 2001, Section 12 Retina. 17. http://www.nei.nih.gov/photo/eye_exam/images/exam13_preview.jpg 18. http://akimichi.homeunix.net/~emile/aki/medical/Image/retinoblastoma-1.jpeg 19. http://www.escrs.org/eurotimes/March2003/images/ivf2.jpg.jpg 20. http://smtp1.jobsoned.com/emailimages/op/042103/opearls2.jpg 21. http://www.stroke-information.net/hydrocephalus111.jpg 22. http://www.opt.indiana.edu/riley/ONhEdema.jpg 23. http://splweb.bwh.harvard.edu:8000/pages/ppl/mark/ms/gifs/ms1.gif 24. http://www.ttuhsc.edu/eye/Faculty%20Presentations/Visual%20Field%20Testing%20Tech%20Seminar_ files/slide0036_image002.jpg

Section 5: Ophthalmic Surgeries Cataract Surgery Most cataracts in the United States are removed with

small incision, sutureless surgery. Patients are kept awake and receive local anesthesia to the eye, in the form of topical lidocaine jelly or an orbital injection. Two small wounds are created in the peripheral cornea. After the anterior lens capsule is removed, the cataract itself is emulsified and vacuumed out using an ultrasonic probe approximately the size of a large pen. Once the cataract is removed, an artificial lens is folded and injected into the same lens capsular bag. The artificial lens is specially designed with a central optic (the actual lens) and two haptics (arms) which unfold and hold the lens in place. Post-operatively the eye is treated with topical antibiotics and steroids and protected while the sutureless wounds heal. Most patients have significant visual improvement by the first post-operative day.

Glaucoma Surgery Filtration surgery is performed when medications have failed to reduce the intraocular pressure to a level that is safe for the optic nerve. The goal of glaucoma surgery is to create an alternative path by which intraocular fluid can drain from the eye and be reabsorbed by the venous circulation. The traditional trabeculectomy involves creating a partial thickness flap in the sclera, which covers a hole connecting the anterior chamber to the outside world. The flap helps keep the efflux of fluid partially controlled, so that hypotony does not develop. Aqueous leaves the eye through the hole (sclerotomy), travels under the flap and under the conjunctiva, to be reabsorbed posteriorly by the ophthalmic veins. When the scleral tissue is not healthy, artificial valves can be implanted to act as a conduit for aqueous removal. Strabismus Surgery Realignment of the eyes can be done by mechanically repositioning the extraocular muscles. Weak muscles are shortened or moved forward to increase their actions. Overactive muscles are shifted more posteriorly to cause relaxation and weakening. Strabismus surgery is usually performed on two muscles at a time, either corresponding muscles on both eyes (both strengthened or weakened) or antagonist muscles on the same eye (one strengthened while the other weakened). In adult patients with complex strabismus (such as thyroid disease), temporary knots can be tied in the operating room, to be more finely adjusted in the recovery room, with the patient awake and able to cooperate.

Vitrectomy and Retina Surgery Access to the posterior segment of the globe is by endoscopic surgery. A magnifying lens is placed on top of the cornea to provide view of the vitreous and retina. Small ports in the sclera are created, through which fine instruments and a light source are inserted. The vitreous is a thick tenacious jelly which must be cut and evacuated before the retina can be approached. Once the retina is repaired, the vitreous cavity can be filled with a variety of different liquids and gases to help position the retina for healing. Surgery to the optic disc can also be performed via this endoscopic approach, though such procedures are still mostly experimental. Dacryocystorhinostomy Chronic naso-lacrimal duct obstruction leads to excess tearing and the potential for recurrent infection. To bypass the blockage, a small opening in the nasal bone is made adjacent to the lacrimal sac, and the mucosa of the sac and the nasal cavity are joined. Then, silicone tubes are passed through the lacrimal canaliculi, into the new opening, and then retrieved from the nose and tied. These tubes stay in place for several weeks while the new passageway heals, to help maintain patency of the openings, before they are removed. Temporal Artery Biopsy To make the diagnosis of giant cell arteritis and justify long-term steroid treatment, ophthalmologists are often asked to perform temporal artery biopsies. The temporal artery is identified either by palpation or by Doppler ultrasonography. The skin and subcutaneous fascia are dissected until the artery is identified. The artery is then carefully isolated and ligated before excising a specimen for pathology. Histologically, hallmarks for vasculitis include granulomatous inflammation, obliteration of the vessel lumen, and disruption of the elastic lamina.

Laser Surgery There are numerous applications for laser photocoagulation in ophthalmology. In refractive surgery, laser energy is used to remodel the cornea and to change its refractive power, to give patients clear vision without the use of spectacles or contact lenses. In the anterior segment, laser is used to perforate the iris (in acute angle closure glaucoma), to remodel the drainage structures of the eye (in chronic glaucoma), to open a clear window in lens capsule opacities (behind an artificial lens), and to cut buried sutures. In the posterior segment, laser is used to treat proliferative retinopathies, including diabetic disease, sickle cell disease, and ROP. By coagulating selected sections of retina, there is decreased retinal metabolic demand, and decreased production of the chemical stimulants to neovascularization (such as VEGF). A new form of laser is now the standard of care in macular degeneration. Photodynamic therapy is the combination of an intravenous drug which specifically targets abnormal new vessels, followed by selective activation of the drug in the eye through laser light. In orbital surgery, laser is also used during dacryocystorhinostomy and in eyelid skin resurfacing.

References: 1. http://www.drloden.com/Pages/Pics/cataract.gif 2. http://www.avclinic.com/Lens_implant_-from_Pfizer.jpg 3. http://www.asianbizguide.com/website/a-i/g/genehan/diagram.gif 4. http://eyelearn.med.utoronto.ca/Lectures04-05/Paediatric/images/Paediatric_20.jpg 5. http://www.eyemdlink.com/images/illustrations/small/vitrectomy.jpg 6. http://www.eyemdlink.com/images/illustrations/small/dcr_tube.jpg 7. http://www.gaileyeyeclinic.com/images/dr3.gif 8. http://www.eyemdlink.com/images/illustrations/small/focal_laser_amd.jpg

Section 6: Equipment and Diagnostic Studies Used in Ophthalmology The Slit Lamp The translucency of ocular tissues makes the eye an ideal

organ to examine by visualization. The slit lamp microscope is specially designed to allow for a magnified and stereoscopic view. Anterior segment structures (the eyelids, cornea, conjunctiva, iris, anterior chamber, and lens) can be seen directly. Combining the slit lamp with a hand-held lens allows visualization of the posterior segment (the optic nerve, posterior vitreous, and central retina. Contact lenses can be applied to examine the angle and the peripheral retina. An applanation tonometer attached to the slit lamp is used to check intraocular pressure. Procedures such as corneal foreign body removal and suture placement can be performed with the patient positioned in the slit lamp. Hospitalized patients are often supine and unable to sit at the slit lamp. In these situations, a penlight or portable slit lamp exam can suffice, but the exam is significantly less detailed. The Direct and Pan-Optic Ophthalmoscopes Most ophthalmologists prefer to examine patients with the pupils pharmacologically dilated. However, when the pupil is small, a direct or pan-optic ophthalmoscope can be used to view the optic nerve and retina. Even with the pupils dilated, the view of the optic disc is greatly magnified with the direct scope, so this is preferred by many neuro-ophthalmologists. These instruments are small, battery-charged, and portable, making them ideal for use at the bedside. The pan-optic is a recent innovation on the direct ophthalmoscope to give a wider field of view. However both scopes are used in the same way. With the scope positioned in front of the patients pupil, the physician dials in power until the retinal vessels are in focus. Then with small adjustments to the viewing angle, the vessels can be traced proximally to the optic nerve or more distally to examine the peripheral retina. Hemorrhages and retinal emboli can be visualized in this way. The major disadvantages to the direct scope are the necessity for close proximity to the patient and the small field of view. The Indirect Ophthalmoscope For a stereoscopic view of the retina, the indirect ophthalmoscope can be used. A hand-held lens is positioned a few centimeters above the cornea, and through a dilated pupil, a three-dimensional, wide-field image of the retina can be seen. With additional techniques such as scleral depression (indenting the wall of the eye towards the vitreous), the far retinal periphery can be examined. Laser photocoagulation can be combined with indirect ophthalmoscopy to treat peripheral lesions not accessible to traditional slit lamp lasers.

The Goldmann Applanation Tonometer The gold standard for measuring intraocular pressure is the Goldmann tonometer. It was designed to balance the force exerted outward by the cornea (the wall of the ocular water balloon) and the force inward by the applanation tip mounted on an adjustable pressure gauge. A yellow dye called fluorescein is applied to the cornea and, with the cobalt blue light from the slit lamp, the cornea makes a green meniscus against the applanation tip. The size of the meniscus varies depending on the force applied by the tip, and the gauge is adjusted until the two forces are equalized. The reading at the point of equalization is the intraocular pressure. The Tono-Pen The Tono-Pen is another contact method by which the intraocular pressure is measured. It is portable for use in supine patients, and will still function even for eyes with corneal surface diseases where the Goldmann applanator cannot be used. It is also a better choice for children, since it requires less cooperation. A rubber sleeve is placed over the metal tip for protection. Once the pen is calibrated, the tip is gently tapped against the central cornea until the pressure is displayed digitally on the handle. The Goldmann Perimeter Visual fields can provide important diagnostic information for patients with glaucoma and neuro-ophthalmic disorders. The Goldmann Perimeter is a manual, operator-driven visual field machine. The patient is instructed to look at a central fixation point and lights of different sizes and intensities are presented to his peripheral vision. The targets are first positioned in non-seeing areas and are moved toward central fixation. When the patient first notices the target, he sounds the buzzer, and that point is marked on the field map by the operator. Point by point the visual field is plotted out. By connecting the points for a set size/intensity of light, a contour map of visual field is made. Targets which are larger and brighter are better visualized in the periphery. As the size and intensity of the target decrease, the field constricts. Glaucomatous defects and hemianopias are easy to demonstrate, as shown by the example.

The Humphrey Visual Field Analyzer The Humphrey is a second visual field machine which is automatic and operator-independent. The patient interacts with a computer, and based on complex algorithms, he is tested for selected patterns of visual field loss. Like the Goldmann, the targets vary in intensity, but unlike the Goldmann, they are all the same size. The bowl of the Humphrey has a fixed array of targets, which activate in a seemingly random sequence. Once a defect is detected, the Humphrey is programmed to carefully test the points surrounding the defect to elicit any possible patterns consistent with optic nerve or CNS disease. In addition, the Humphrey is better able to test the center of fixation and has special programs to detect central scotomas (blind spots). Unlike the contour map generated with the Goldmann perimeter, the printout from the Humphrey shows field loss as decreased sensitivity on a numerical scale which is then translated graphically into gray-scale.

The Fluorescein Angiogram Retinal disease is often vascular in etiology. Diabetic retinopathy with macular edema and neovascularization, macular degeneration with choroidal neovascular membranes, and central retinal artery occlusions are prime examples. In fluorescein angiography, fluorescein dye is injected intravenously and circulates to the retina where it gets activated by blue light mounted on a camera. Photos are taken as retinal and choroidal vessels fill. Thus retinal perfusion can be traced chronologically, and any abnormal vessels prone to leakage can be identified. In addition, emission of fluorescent light from the dye can identify retinal lesions that cannot be visualized directly due to blood or other media opacity. Even after most of the fluorescein has left the retinal circulation, the staining pattern which remains can also be diagnostic for many retinal diseases.

References: 1. http://stleye.com/images/Mentor%20GH12%20Slit%20Lamp-5-step%20mag.JPG 2. http://www.suncoastretina.com/images/illustrations/directOphth.jpg 3. http://www.mortonmedical.co.uk/vet_images/panoptic_big.jpg 4. http://www.medisave.co.uk/images/heine-omega-180.jpg 5. http://www.eyeinstitute.net/goldmantono_big.gif 6. http://www.pomonline.com/images/14opht2.jpg 7. http://www.eyetec.net/group3/images/goldman1.jpg 8. http://www.goodhope.org.uk/departments/eyedept/images/case3lfield.jpg 9. http://www.bpei.med.miami.edu/site/disease/images/visfield.jpg 10. http://www.bpei.med.miami.edu/site/disease/images/visfield2full.jpg 11. http://www.eyesondiabetes.org.au/upload/741631408_diag&mgt04.jpg 12. http://www.djo.harvard.edu/files/2960_353.jpg