Fundamental of Opthalmology

Faraza JavedPhD Pharmacology

Diagnostic Tests in Opthalmology

What is ophthalmology? Opthalmos=eye Logos=word, thought, discourseThe science of eyes is opthalmology

The branch of medicine concerned with the eyes Anatomy Function Disease

Fundamentals of Opthalmology

The visual system A coordinated pair of eyes

The appropriate protective mechanisms

The necessary neural apparatus to interpret visual information

To produce a clear image of the external world and transmit this to visual cortex of brain

Structure of Eyeball

Fibrous coat Cornea, sclera

Vascular coat (uveal tissue) Iris, ciliary body, choroid

Nervous coat Retina

Sclera Collagen Variable thickness

1mm around optic nerve head,

0.3mm posterior to muscle insertions

Tough, opaque, mainly avascular

Outer wall of the eyeball -protects intraocular contents, preserve shape

Attachments for the extraocular muscles

Cornea - anatomy 500-700 µm thick Transparent, avascular Forms approximately the

anterior 1/6 of the outer coat of the eye and is continuous posteriorly with the sclera

5 layers: Epithelium Bowman’s membrane Stroma Descemet’s membrane Endothelium

Iris and pupil (Vascular Coat)

Attached to ciliary body

Forms pupil at center

Pupil movements Mydriasis (Dilation):

Dilator pupillae muscles Low-intensity light,

excitement, fear Sympathetic

Miosis (Constriction): Sphincter pupillae

muscle Bright light,

accommodation Parasympathetic

Ciliary body

Connects the iris and the choroid

Functions: Aqueous humor

production Suspension of lens,

accommodation

Aqueous Humour production Active secretion by the

epithelium of the ciliary processes of the ciliary body

Function: Carries O2, nutrients to

lens, cornea and waste products away

Maintain shape of eye by intraocular pressure

Flushes away blood, macrophages, inflammatory cells

Lens

Transparent, biconvex structure

Radially arranged zonule fibers that insert into the lens around its equator connect the lens to the ciliary body

Can change diopteric power but amplitude of accommodation reduces with age

Choroid Highly vascularised

structure between the sclera and the retina

Vessel layer, capillary layer provides O2 + nutrition

to the outer retinal layer,

Temperature homeostasis

Conduct blood vessels Absorb excess light

Vitreous body

Clear gel-like structure that fills the posterior eye

98% water+ 2% collagen, hyaluronic acid, soluble proteins

Transmission of light onto the retina, cushion to the eyeball during trauma, nutritive and supportive role in retinal metabolism

Retina (Neural Layer)

Converts light into nerve impulses

Multilayered 2 functional layers:

Neurosensory retina Retinal pigment

epithelium (RPE)

1. Retinal pigment epithelium (RPE)

Single layer Microvilli at the apex where

the photoreceptors attach Functions:

Melanin pigments which absorb light (antireflection)

Participate in turnover of photoreceptors

Recycle vitamin A to form photosensitive pigments

2. Neurosensory retina

3 main groups of neuronal cells: photoreceptors, bipolar cells, ganglion cells

Photoreceptor cells (rods + cones) undergo photochemical changes (phototransduction)

Bipolar cells relay nerve impulse to ganglion cells

Ganglion cell exit at optic disc to become optic nerve

Optic disc

The location where ganglion cell axons exit the eye to form the optic nerve

Yellowish orange color 1.5mm diameter (may

vary), vertically oval Central retinal vessels

enter and leave the eye here

Retinal blood supply Retinal arteries supply O2

+ nutrients to the inner layers of the retina

Outer layers (RPE-outer nuclear) supplied by choroidal capillaries

SuperiorSuperior and inferior branches, which split into nasal, temporal branches.

Capillaries with nonfenestrated endothelium, prevent large molecules and toxins to permeate; this forms the inner blood retinal barrier

Optic nerve

Contains over 1 million fibres Nerve fibres are

myelinated only after leaving the eye

Surrounded by cerebrospinal fluid in the anterior extension of the subarachnoid space

Protected by the same meningeal layers of the brain

There are many diseases, disorders, and age-related changes that may affect the eyes and surrounding structures. The sharpness of vision is reduced despite use of the best glasses. The amount of light that reaches the back of the retina is reduced, and this wear and tear results in the development of cataract, macular degeneration or glucoma.

Such conditions cause damage to the eye's optic nerve and gets worse over time. It's often linked to a buildup of pressure inside the eye. The increased pressure, called intraocular pressure, can damage the optic nerve, which transmits images to your brain. If the damage continues, it can lead to retinal cell degeneration and permanent vision loss.

Opthamological Method

Tonometery

Tonometry measures the pressure within your eye. During tonometry, eye drops are used to numb the eye. Then a doctor or technician uses a device called a tonometer to measure the inner pressure of the eye. A small amount of pressure is applied to the eye by a tiny device or by a warm puff of air.

The range for normal pressure is 12-22 mm Hg. Most glaucoma cases are diagnosed with pressure exceeding 20mm Hg. However, some people can have glaucoma at pressures between 12 -22mm Hg. Eye pressure is unique to each person.

Opthalmoscopy This diagnostic procedure helps the doctor

examine your optic nerve for glaucoma damage. Eye drops are used to dilate the pupil so that the doctor can see through your eye to examine the shape and color of the optic nerve.

The doctor will then use a small device with a light on the end to light and magnify the optic nerve. If intraocular pressure is not within the normal range or if the optic nerve looks unusual, doctor may ask to have one or two more glaucoma exams: perimetry and gonioscopy.

Perimetry Perimetry is a visual field test that

produces a map of your complete field of vision. This test will help a doctor determine whether your vision has been affected by glaucoma. During this test, you will be asked to look straight ahead and then indicate when a moving light passes your peripheral (or side) vision. This helps draw a "map" of your vision.

After glaucoma has been diagnosed, visual field tests are usually done one to two times a year to check for any changes in your vision.

Gonioscopy This diagnostic exam helps determine whether

the angle where the iris meets the cornea is open and wide or narrow and closed. During the exam, eye drops are used to numb the eye. A hand-held contact lens is gently placed on the eye.

This contact lens has a mirror that shows the doctor if the angle between the iris and cornea is closed and blocked (a possible sign of angle-closure or acute glaucoma) or wide and open (a possible sign of open-angle, chronic glaucoma).

Pachymetry Pachymetry is a simple, painless test to measure

the thickness of your cornea. A probe called a pachymeter is gently placed on the front of the eye (the cornea) to measure its thickness. Pachymetry can help your diagnosis, because corneal thickness has the potential to influence eye pressure readings.

With this measurement, doctor can better understand IOP reading and develop a treatment plan. The procedure takes only about a minute to measure both eyes.

Electroretinography

Electroretinography allows to examine the function of the light-sensing cells (photoreceptors) in the retina by measuring the response of the retina to flashes of light. Eye drops numb the eye and dilate the pupil. A recording electrode in the form of a contact lens is then placed on the cornea, and another electrode is placed on the skin of the face nearby.

The eyes are then propped open. The room is darkened, and the person stares at a flashing light. The electrical activity generated by the retina in response to the flashes of light is recorded by the electrodes.Electroretinography is particularly useful for evaluating diseases, such as retinitis pigmentosa, in which the photoreceptors are affected.

Thanks