Lens for undergraduate part 1 2015

Dr. Abdelmonem HamedFellow of Baylor of College of Medicine, USA

Professor of ophthalmology, Benha University, ARE

LENS

1

حامد المنعم عبد ادبنها جامعة ، العين وجراحة طب استاذ

بأمريكا بيلور طب كلية زميل

LENS

2

حامد المنعم عبد اد ، العين وجراحة طب استاذ

بنها جامعةبأمريكا بيلور طب كلية زميل

Part 1

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

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

4Prof . Dr. Abdelmonem Hamed

9 - 10 mm 4 mm

Lens Lens is suspended in eye by

Zonules of Zinn


Lens-Anatomy

1. Capsule


Transparent collagenese basement membrane

It allows a passage of small molecules both into and out of lens

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


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

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.


Lens - Functions

Focusing of light rays on the fovea through:

Prevents ultra-violet radiation from reaching the retina


accommodation Its refractive power

Accommodation

ciliary muscle contraction, the curvature of anterior surface , increase lens power.


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


Any opacity in the lens or its capsule is called cataract.

Cataract

Cataract Classification

According to age Congenital Infantile Juvenile Presenile Senile


According to stage Immature Mature Hypermature


According to morphology

Capsular (ant. & post. Polar) Sub capsular (ant. & post. subcap) Cortical Nuclear

Cataract Classification According to etiology

Not associated with ocular or systemic disease

Associated with ocular disease Associated with systemic disease

Risk Factors for Cataract Senility Sunlight (specially UV) Smoking Steroids Systemic diseases:

Deficiency of vitamin A,C, & E Diabetes


5S & 2 D

CONGENITAL CATARACT

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

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

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

Complications

Bilateral opacity: interferes with foveal development nystagmus

Unilateral cataract: squint , and amplyopia.

Types of congenital cataract

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.

2. Posterior polar cataract

Persistent hyaloid artery


Etiology

opacity at the posterior pole

Clinically

markedly diminished as the opacity is close to the nodal point

vision

3. Lamellar cataractmost common congenital cataract


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

4.Coronary cataract

Round opacities surround nucleus like a crown29Prof . Dr. Abdelmonem Hamed

5. Sutural cataract

Opacity follows shape of Y suture

Usually X-linked inheritance


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

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


Management of congenital Cataract Bilateral cataract

a. Bilateral Dense cataract – early surgery

b. Bilateral partial cataract –surgery @ the age of 2 years


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).

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)


Watch Irrigation and Aspiration

for congenital cataract@

https://www.youtube.com/watch?v=7eUy7h_xmZ8

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

Health & Medicine

Lens for undergraduate part 1 2015