Anatomy of the Lens
Macroscopic anatomy :
The lens is biconvex transparent avascular structure present in the
anterior Segment of the eyeball. It is enclosed in thin
capsule and is fixed in its place by the suspensory ligaments (the zonule
of Zinn)
Microscopic anatomy:
1. The lens capsule:
It is a thin highly elastic memberane. At the equator it give
attachment to the suspensory ligaments.
It is elastic so that it plays an essential role in accommodation.
It is a semipermeable membrane. It is thinner posteriorly than
anteriorly, so that complicated cataracts start in the posterior
subcapsular area.
2. The subcapsular epithelium:
It lines the anterior capsule and the equator but not the posterior capsule.
3. The lens substance :
It is formed of lens fibers. The newly formed fibers are laid outside
the older ones. The old fibers are pushed inwards and undergo a
process of sclerosis (decrease of water content ) to form the
nucleus. Thus the lens is formed of a central nucleus and an outer
soft cortex made of young fibers.
4. The nucleus :
It is formed of the following concentric
layers:
Embryonic nucleus.
Fetal nucleus: where there is Y suture, erect anteriorly and inverted
posteriorly.
Infantile nucleus.
Adult nucleus.
5. The cortex : it is always soft.
Functions of lens:
1. Refraction, its unaccommodated power is + 18D.
2. Accommodation
3. Protects the retina from ultraviolet rays.
CATARACT
It is any opacity within the crystalline lens.
Classification:
A. According to the etiology :
I. Congenital ( developmental ) cataract .
II. Acquired cataract:
-Traumatic cataract.
- Senile cataract
- Complicated cataract.
B. According to the consistency of lens:
I. Soft cataract : Both cortex and nucleous are soft.
II. Hard cataract : the nucleus is hard due to the normal progressive
decrease of water content of the nucleus during age.
C. According to the course of cataract :
I. stationary as congenital cataract.
II. Progressive as senile and complicated cataract.
D. According to site of opacity within the lens:
It may be :
Nuclear.
Anterior or posterior cortical
Anterior or posterior subcapsular.
Anterior or posterior polar.
CONGENITAL CATARACT
Definition :
It is opacity of the lens or its capsule dated since birth or shortly after
birth.
Etiology:
1. Hereditary , mostly autosomal dominant without systemic
abnormalities.
Maternal infection as rubella infection, toxoplasma and syphilis.
2. Maternal malnutrition as Vitamin D and calcium deficiency.
3. Associated with syndromes and mongolism.
Inborn errors of metabolism as galactosemia ( autosomal recessive)
Types:
1. Anterior polar cataract :
It occurs due to abnormal separation of lens vesicle from surface
ectoderm during embryonic development
2. Posterior polar cataract :
It occur due to persistent embryonic remnants of the hyaloids artery.
3. Zonular (lamellar) cataract
4. Coronary cataract :
5. Rubella cataract :
Occurs only when infection takes place
before 6 weeks of gestation.
6. Congenital nuclear cataract.
7. Blue dot cataract
8. Sutural cataract
MANAGEMENT OF CONGENITAL CATARACT
Diagnosis:
I. Symptoms and history taking from the mother:
Symptoms :
White pupil ( leukocoria)
Drop of vision.
Squint ( if unilateral ) or nystagmus (if bilateral)
The lens is examined through dilated pupil. Dilatation is done
By:
1. Atropine ointment , three times adays for 3 days before examination.
2. Other short acting atropine substitutes as cyclopentolate 1% are used
if there is atropine allergy.
ž The following should be know about the cataract in order to decide
the management.
1. Bilateral or unilateral.
2. Shape, type of cataract and its location ( posterior polar cataract cause
more drop of vision because they are to the nodal point).
3. Density of cataract ( either dense or faint) :
• With non significant opacities fundus can be clearly seen by both
direct and indirect ophthalmoscopes.
• With moderate opacities, funds can be seen with indirect
ophthalmoscope only.
• With very dense cataract, fundus will not be seen with any
opthalmoscope.
II. Examination of the eye :
It is done to find if there are contraindication of surgery or if there
another disease to be treated, for example:
1. Amblyopia and squint in unilateral cases or nystagmus in bilateral
cases.
2. Buphthalmos or microphthaloms.
3. Posterior segment anomalies .
4. Assessment of vision by preferential look and optokinetic
nystagmus
5. Retinal and optic nerve evaluation by objective methods:
Fundus examination if possible .
Ultrasonography B- scan if cataract is dense (it gives two dimensional
sections through the posterior segment of the eye).
Treatment
:
Indication and timing operation:
1. In bilateral dense cataract we interfere as early as possible, even in
the second day of life, to avoid nystagmus.
2. In unilateral cataract surgery is indicated as early as
possible to avoid amblyopia ( except in cases that
does not affect vision significantly as anterior polar or very faint
cataract)
Methods of surgical removal of congenital cataract :
The irrigation aspiration technique:
Pars plana lensectomy :
Methods of optical correction of childhood aphakia:
It is of ultimate importance to correct aphakia for both far and near
vision. Far vision correction is done by the following methods:
1. Glasses:
Their power is measured by postoperative retinoscopy.
2. Contact lenses:
1. They give excellent visual correction and can
2. tolerated in unilateral as well as bilateral
3. aphakia.
3. IOL implantation
SENILE CATARCT
Definition :
It is acquired lens opacity occurring in old age in the absence of a
local or systemic disease. It affects both sexes equally.
The general features of senile cataract are :
• Always bilateral ( one eye precedes the other)
• Progressive to maturity and hypermaturity
• Hard nucleus
• No local or systemic disease can be found.
Types:
It may be either:
• Subcapsular cataract.
• Cortical cataract.
• Nuclear cataract
A. Subcapsular cataract
It may be either:
1. Anterior subcapsular cataract.
2. Posterior subcapsular cataract : it is very close to the nodal point, so
that it causes marked drop of vision especially with miosis
B. Senile cortical cataract
It is slowly progressive process of opacification of anterior, posterior
and equatorial cortex. It runs in 4 stages, incipient, immature, mature and
the hypermature cataract.
C. Senile nuclear cataract
There is exaggeration of the physiological process of dehydration of
the lens nucleus. This will lead to increasing the refractive index of the
nucleus ( causing myopic shift) followed by opacification of the nucleus.
MANGEMENT OF SENILE CATARACT
A. Cataract extraction is done only after evaluation of the retinal
condition, then optical correction of aphakia has to be done.
Evaluation of retina and optic nerve functions :
1. Subjective evaluation :
a. Visual acuity should be matching with the density of cataract. It
should be at least HM or PL with very dense cataract .No PL means
damage of the retina optic nerve ( hopeless surgery ).
b. Normal colour perception
c. Light projection test : it is done in cases of mature cataract for
assessment of the visual filed. The patient is asked to fix his eye to his own
finger in a dark room. A focused low intensity light is presented to his eye
from 50 cm distance from various directions. The patient should identify the
correct direction of light even with a very dense cataract . Bad light
projection means unhealthy retina or optic nerve and poor surgical
prognosis.
2. Objective evaluation :
a. Fundus examination if the cataract is not dense.
b. Ultrasonography : the A – scan is used to measure the antero-
posterior diameter of the eye for IOL power calculation.
Surgical techniques :
A. Indication and timing of operation :
1. To improve vision:
2. Emergency treatment of lens induced glaucoma in cases of :
Phacolytic glaucoma.
Phacomorphic glaucoma.
Lens subluxaion, anterior dislocation or posterior dislocation.
B. Choice of operation:
If the zonule is intact we do ECCE or phaco – emulsification.
If there is subluxation or dislocation we do ICCE.
I. ECCE(extra capsular cataract extraction) :
1. Anterior capsulotomy.
2. Delivery of the nucleus through a 8 – 10 mm incision.
3. Irrigation / aspiration of the cortex is done by a double way cannula.
The posterior capsule is left intact for implantation of IOL.
ž Advantages :
Low incidence of vitreous loss and retinal detachment.
Posterior chamber IOL can implanted inside the posterior capsule.
ž Disadvantages :
Large incision leading to astigmatism.
After cataract which can be treated by YAG laser capsulotomy.
If lens matter remain it will cause uveitis and glaucoma.
2. phaco – emulsification :
1. anterior capsulomy.
2. Emulsification of the nucleus by ultrasonic waves together with its
aspiration.
3. irrigation and aspiration of the cortex.
The posterior capsule is left intact for IOL implantation
3. ICCE (intra capsular cataract extraction) :
1. very large incision.
2. peripheral iridectomy should be done to avoid secondary angle
closure glaucoma due to pupillary block by the vitreous face.
3. Removal of the lens within its intact capsule, usually by cryo.
Disadvantages :
- No posterior chamber IOL implantation.
- High incidence of retinal detachment and vitreous loss.
- Very large incision ( nearly half of the limbus) leading to high
astigmatism.
* Indications :
- Hard cataract with subluxation or dislocation.
Optical correction of aphakia :
1. Glasses according to postoperative retinoscopy ( average power is +
10 D. for far vision and +13 D. for near vision) the disadvantages of
aphakic glasses are :
a. Marked magnification of image about 30 ٪so that they are
contraindicated in cases of unilateral aphakia because they lead to
intolerable aniseikonia and binocular diplopia.
b. Field contraction, prismatic effect and image distortion.
c. Bad cosmetic appearance.
2. Contact lenses : the power is measured by retinoscopy (+ 13 for far
vision in average, For near vision + 3 D. glasses are added) they cause
image magnification about 10% which can be tolerated in unilateral
aphakia. Disadvantages of contact lenses are:
• Need special care.
• Corneal ulcers.
• Giant papillary conjunctivitis .
• IOL: the power is calculated preoperatively by a special equation
using the corneal refractive power ( measured by keratometer) and
axial length of the eye ( measured by ultrasonography A- scan) the
average powers are about +20D for PC-IOL. Or +18 for AC- IOL..
For near vision we add +3 glasses).
Complications of cataract surgery:
I. Intraoperative complications:
1. Retrobulbar hematoma due to local anaesthesia. Intraocular
hemorrhage that may be severe and expulsive.
2. Rupture of the posterior capsule during ECCE.
3. Vitreous loss especially in ICCE.
II. Early postoperative complications :
1. Uveitis due to surgical trauma or remnants of lens mater.
2. Transient glaucoma
3. Corneal edema that may persist requiring keratoplasty.
4. Prolapse of iris.
5. Macular edema especially in cases of vitreous loss.
6. Endophthalmitis.
III. Late postoperative complications:
1. Astigmatism due to large or bad incisions.
2. Opacification of posterior capsule. It is opened by YAG laser.
3. Persistent glaucoma or corneal edema.
4. . Retinal detachment especially in cases of ICCE or vitreous loss.
LENS INDUCE GLAGUCOMA
A. Secondary acute angle closure glaucoma due to pupillary block :
1. Lens intumescences in the senile cataract
2. Anterior lens dislocation
3. Subluxated lens may be incarcerated in the pupil.
B. phacolytic glaucoma:
It occurs in HMSC because lens proteins leak through the rarefied
capsule these lens proteins will be engulfed by macrophages that will
block the trabecular pores causing acute secondary open angle glaucoma.
It has all the symptoms and signs of acute congestive glaucoma .It
differs from acute PACG in that: the angle is open
.
Exfoliation syndromes :
1. True exfoliation syndrome :
It is a rare disease occurring in cases of chronic exposure to infra- red .
There is continuous sheding of flecks from the lens capsule that will
block the trabeculm causing secondary chronic open angle glaucoma.
2. Pesudo exfoliation syndrome :
There is deposition of white flecks ( looking like dandruff) on the lens,
iris and trabeculum causing secondary chronic open angle glaucoma.
This material is formed of abnormal basement memberane of iris and
ciliary body, so that, it is not treated by lens extraction . It is treated
medically and surgically as primary open angle glaucoma.
TRAUMATIC CATARACT
Etiology:
• Blunt trauma ( concussion cataract) : the opacity is cortical and rosette
shaped it occurs due to rupture of the posterior capsule ( the thinnest
area of the lens capsule).
• Perforating trauma leading to injury of the capsule.
• IOFP (intra ocular foreign body).
i. An iron FB causes siderotic cataract.
ii. A copper FB causes sunflower cataract.
Management:
1. Meticulous ocular examination:
• The aim is to detect any other ocular complication secondary to the
trauma in addition to the cataract.
• An IOFB should be removed if necessary.
• Any wound should be sutured properly.
• Ultrasonography if the cataract is dense to detect vitreous hemorrhage
or retinal detachment following the trauma.
2. Cataract extraction and IOL implantation:
• Irrigation aspiration or pars plana lensectomy in cases of soft cataract.
• ECCE in cases of hard cataract.
3. Regular postoperative follow up:
To detect late complications of trauma that may affect the eye.
AFTER CATARACT
After cataract is opacity in the pupillary area immediately following
cataract operation or trauma. It is formed of:
Parts of anterior and posterior capsule.
Lens fibers left behind during surgery.
Proliferation of remaining subcapsular epithelium.
Treatment:
No interference is necessary if the vision is not affected .
If the after cataract is thick. Surgical intervention is necessary
ECTOPIA LENTIS
Displacement of the lens from its normal position. The lens may be
partially displaced ( subluxation) or totally displaced ( dislocation)
SUBLUXATION OF THE LENS
Displacement of crystalline lens within the pupillary area due to
tearing of a portion of the suspensory ligament ( zonule)
Etiology:
Congenital e.g Marfan's syndrome: subluxated lens, RD, tall stature,
arachnodactyly ( long finger)
Acquired
i. Traumatic
ii. Degenerative e.g. hypermatue cataract
iii. Metablolic e.g. homocystinuria.
Symptoms :
Decreased vision due to myopic astigmatism.
Uniocula diplopia.
Treatment:
If no complications : glasses to correct the error of refraction.
If complications occur: Extraction of the subluxated lens either by a
scoop plus anterior vitrectomy or by pars – plana lensectomy.
DISLOCATION OF THE LENS
Displacement of the lens from its place due to total tearing or absence
of the zonules.
Etiology
As in subluxated lens
Types :
Anterior dislocation in the anterior chamber.
Posterior dislocation in the vitreous