Lens for undergraduate part 1 2015
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Transcript of Lens for undergraduate part 1 2015
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Dr. Abdelmonem HamedFellow of Baylor of College of Medicine, USA
Professor of ophthalmology, Benha University, ARE
LENS
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حامد المنعم عبد ادبنها جامعة ، العين وجراحة طب استاذ
بأمريكا بيلور طب كلية زميل
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LENS
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حامد المنعم عبد اد ، العين وجراحة طب استاذ
بنها جامعةبأمريكا بيلور طب كلية زميل
Part 1
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Lens
Transparent, spheroid structure
RI = 1.39. It does not have nerve,
or blood vessels. Biconvex ,
anterior surface (r=10mm) posterior surface
(r=6mm). Prof . Dr. Abdelmonem Hamed 3
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Lens
Diameter : 9 - 10 mm Thickness is 4 mm in
adults. Its weight is about 65
milligrams at the birth and up-to 258 mg by 80 years of age.
Power= 15 – 18 D
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9 - 10 mm 4 mm
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Lens Lens is suspended in eye by
Zonules of Zinn
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Lens-Anatomy
1. Capsule
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Transparent collagenese basement membrane
It allows a passage of small molecules both into and out of lens
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Lens-Anatomy
2. Lens Epithelium :single layer of cells lining the anterior capsule. It is gradually become elongated towards the equator.
Function of he lens epithelium: Formation the lens fibers regulate the transport of metabolite
to & from the lens secrete the lens capsule
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Lens - AnatomyThe Nucleus:
consists of(i) Embryonic nucleus ( formed in lens vesicle) (ii) Fetal nucleus: ( formed before birth )(iii) Infantile nucleus: (From birth to puberty). (iv) Adult nucleus: (early adult life).
Lens Cortex(i) It is located peripheral to nucleus(ii) formed after sexual maturation. 8
i
iiiiiiv
cortex
Prof . Dr. Abdelmonem Hamed
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Lens - Sutures
Anterior and posterior Y – shaped suture lines are formed at the junction of lens fibres.
They are formed by overlap of ends of secondary fibers in each growth shell.
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Lens - Functions
Focusing of light rays on the fovea through:
Prevents ultra-violet radiation from reaching the retina
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accommodation Its refractive power
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Accommodation
ciliary muscle contraction, the curvature of anterior surface , increase lens power.
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Watch Video of accommodation
@ https://www.youtube.com/watch?
v=DMPyD1mcNW0
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Lens - Crystalline
Lens fibres contain high concentrations of crystalline.
Crystalline represent the major protein of the lens (constitute 90% of total protein content of lens).
Prof . Dr. Abdelmonem Hamed
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Any opacity in the lens or its capsule is called cataract.
Cataract
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Cataract Classification
According to age Congenital Infantile Juvenile Presenile Senile
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Cataract Classification
According to stage Immature Mature Hypermature
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Cataract Classification
According to morphology
Capsular (ant. & post. Polar) Sub capsular (ant. & post. subcap) Cortical Nuclear
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Cataract Classification According to etiology
Not associated with ocular or systemic disease
Associated with ocular disease Associated with systemic disease
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Risk Factors for Cataract Senility Sunlight (specially UV) Smoking Steroids Systemic diseases:
Deficiency of vitamin A,C, & E Diabetes
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5S & 2 D
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CONGENITAL CATARACT
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Causes Of Congenital Cataracti. Maternal malnutrition of mother.
ii. Maternal infection by virus, e.g. rubella in the first trimester.
iii. Deficient oxygenation, e.g. placenta praevia.
Definition: Lens opacity, which is present at birth or shortly after.
CONGENITAL CATARACT
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Symptoms:
Given by mother. 1. Defective vision.2. White pupil
(leucocoria).3. Abnormal movements
of the eye due to squint or nystagmus.
عن كلهاطريق
االم
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Signs:
1. By tourch light: White reflex within pupil. 2. By Ophthalmoscopic examination: cataract3. Another Congenital anomalies:
Dental anomalies. Microphthalmos. Mental retardation. Congenital heart disease Microencephaly. Deafness
عن كلهاالطبيب
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Complications
Bilateral opacity: interferes with foveal development nystagmus
Unilateral cataract: squint , and amplyopia.
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Types of congenital cataract
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1. Anterior polar
1. delayed formation of AC Irritation of the subcapsular epithelium cataract
Etiology (touch between cornea & ant. Capsule of lens)
2. perforation of a corneal ulcer, as in ophthalmia neonatorum.
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2. Posterior polar cataract
Persistent hyaloid artery
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Etiology
opacity at the posterior pole
Clinically
markedly diminished as the opacity is close to the nodal point
vision
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3. Lamellar cataractmost common congenital cataract
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Definition:lens opacity involving one or more lamellae of the lens.
i
Etiology Malnutrition of mother and lack of
vitamins during pregnancy lamellar cataract + erosion of permanent teeth.
iiiiiiv
cortex
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Lamellar cataract looks like (steering wheel) Why this happen?Vitamin D deficiency formation of opaque lens fibers.
On recovery from this deficiency, formation of clear lens fibers, pushing the opaque fibers onward, opaque lamella.
Riders are due to unequal recovery of the equatorial cells at the same time
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4.Coronary cataract
Round opacities surround nucleus like a crown29Prof . Dr. Abdelmonem Hamed
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5. Sutural cataract
Opacity follows shape of Y suture
Usually X-linked inheritance
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6. Blue dot opacities
• Blue dot cortical opacities•Do not affect VA
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7. Total cataractit is due to rubella infection to the pregnant mother in the first trimester
The cataract extraction operation is risky due to:Associated cardiac anomaly (risk of GA)The virus remains dormant inside the lens
for 3 years which may lead to postoperative endophthalmitis
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Management of Developmental Cataract Fixation develops between 2-4 months
of age. Uniocular cataract
if vision is affected early surgery, (to avoid amblyopia and).
if vision is not affected:*No treatment
*Mydriatics- if opacity is central
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Management of congenital Cataract Bilateral cataract
a. Bilateral Dense cataract – early surgery
b. Bilateral partial cataract –surgery @ the age of 2 years
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P.S. the risks of cataract operation before 6 months are:AC is shallow.Pupil will not dilate properly (dilator muscle is not
well developed).
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Management of congenital CataractOperative procedure
1. Irrigation and Aspiration with primary posterior capsulotomy as well as anterior vitrectomy
2. Lensectomy (Pars plana or anterior route)
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Watch Irrigation and Aspiration
for congenital cataract@
https://www.youtube.com/watch?v=7eUy7h_xmZ8
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Management of congenital Cataract
Post-operative visual rehabilitation:
1. (younger than 2 yrs) Contact lens –for uniocular cataract Glasses - In bilateral cataract .
2. (older than 2 yrs) insert IOL
PS. Occlusion therapy for treatment of amblyopia.
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Thank you