Download LENS - Peshawar Medical College, Peshawar Dental College

LENS
It is a highly organized
transparent spheroid structure
that has evolved to perform
refraction of the light entering
in the eye. It does not posses
nerve, blood vessels or
connective tissue.
Anatomy of LENS
Biconvex Lens
Diameter varies from 8.8 to 9.2 (9mm)
Lens grow in size continuously throughout life.
Its weight is about 60 mgm at the birth and
up-to 250 mgm by 80 years of age.
Antero-posterior thickness changes with
accommodation. Thickness is 4.75 – 5 mm
(4.5mm) (un-accommodated) in adults.
Circumference is known as equator
Anatomy of LENS
Lens is suspended in eye by Zonules
which are inserted on anterior
surface and equatorial lens capsule
and attached to ciliary body(Pars
Plicata- Ciliary Processes) .
 Zonular fibres are series of fibrillin
rich fibre.
Anatomy of LENS
Histologically lens consists of three
major components:

1. Capsule – is a thick collagenese
basement membrane which is transparent,
elastic acellular envelop, thick at anterior preequatorial region (21 micron m), thinnest at
the posterior pole (4 micron m). Anterior pole
is approximately 14 micron m thick.
Anatomy of LENS

2. Lens Epithelium – It is a single layer of
cells lining the anterior capsule and extends to
the equatorial lens bow.
Zone of epithelial cells:
a. Central – cells do not actively divide,
they divide under pathological conditions
only.
b. Pre-equatorial germinal zone : cells
rarely divide.
Anatomy of LENS
C. Germinal zone: constitute of the
stem cell population. The newly formed
cells from germinal zone are forced into
transitional zone where they elongate
and differentiate to form mass of the
lens. The lens capsule regulate the
transport of metabolite, nutrients and
electrolytes to the lens fibers.
Anatomy of LENS

3. Lens substance: It constitute the main
mass of the lens. It is divided intoa. Nucleus
b. Cortex
Nucleus: consists of
(i) Embryonic nucleus (it contains primary
lens fibres that are formed in lens vesicle)
Anatomy of LENS
(ii) Fetal nucleus: it contains embryonic
nucleus and all fibres added to the lens before
birth
(iii) Infantile nucleus: it contains embryonic ,
fetal nucleus together with all the fibres added
up-to the age of 4 years.
(iv) Adult nucleus: composed of all fibres
added before sexual maturation
The nucleus consists of densely compacted lens
fibres and higher refractive index than cortex.
LENS Anatomy
Cortex
Capsule
3
4
3 – Adult Nu
4 - Infantile Nu
5 – Foetal Nu
6 – Embryonic Nu.
24 May 2017
5
6
9
Lens Cortex
It is located peripherally and is composed
of secondary fibres formed continuously
after sexual maturation. It is further
divided into:
Deep cortex
Intermediate cortex
Superficial cortex
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).
Crystalline has the following constituents:
Alpha
Beta and,
Gamma
Lens - Functions
The lens serves two major
functions:
Focusing of visible light rays on the
fovea
Preventing damage from ultraviolet radiation by reaching the
retina
Lens – Physiology
Lens function and transparency is
dependant on the supply of appropriate
nutrient to its various structures.
Metabolic needs of a adult lens is met by
the aqueous and vitreous.
There is continuous transport of ions into
and out of the lens.
Lens – Physiology
The transparency is dependent on highly
organized structure of lens, dense packing of
crystalline. Avascularity, absence of pigments
and optimal hydration.
By act of accommodation it changes focusing
power. Accommodation occurs by increasing
the curvature of anterior surface thereby
changing refractive power of lens.
 Light transmission and elasticity of lens
decreases with age.
CATARACT
Any opacity in the lens or its capsule, whether
developmental or acquired is called cataract.
Developmental opacities are usually partial
and stationary, whereas acquired opacities are
progressive. They progress until the entire lens
is involved, but exceptions are well known in
both types.
Classification of Cataract
Classification based on Etiology
Classification based on
Morphology
Classification based on Maturity
Classification based on the Age
of onset
Classification based on Etiology
Developmental
Acquired
Developmental
Hereditary
Intrauterine causes
o
o
o
o
Rubella
Toxoplasmosis
CMV
Steroids
Acquired Cataract
1.
2.
3.
4.
Age related (senile)
Secondary cataract (Chronic Uveitis, ACG)
Cataract associated with ocular diseases
Cataract associated with systemic diseases
(pre-senile) (Diabetes, galactosemia etc)
5. Traumatic Cataract
6. Drug induced cataract (Steroids and others)
Classification based on Morphology
Capsular (Ant and Post)
Subcapsular (Ant and Post)
Nuclear
Cortical
Classification based on Maturity
Immature
Mature
Hypermature
Morgagnian
Classification based on the Age of
onset
Congenital
Infantile
Juvenile
Presenile
Senile
Risk Factors for Cataract
 Senility
 Sunlight (specially UV –A and UV-B component)
 Severe Diarrheal dehydration
 Vitamin A,C, E deficiency
 Diabetes
 Smoking
 Corticosteroids
 Genetic
Pathogenesis of Cataract
Caused by degeneration and opacification of
existing lens fibres, formation of aberrant
fibres or deposition of other material in their
place.
Factors causing disturbance of critical intra –
and extra-cellular equilibrium of water and
electrolyte or deranges the colloid system
within the fibres tends to bring about
opacification.
Pathogenesis of Cataract
Fibrous metaplasia of fibres (in complicated
cataract)
Epithelial cell necrosis (Glaucomflecken)
Deposition of abnormal products of
metabolism, drugs or metals.
Pathogenesis of Cataract
Biochemical Processes
o Hydration
o Denaturation of Lens Proteins
o Sclerosis
Pathogenesis of Cataract
The Changes in the Epithelial Cells
and the Capsule
Changes in the Lenticular Fibres
Sclerosis
Symptoms of Cataract
1. Blurring of vision
2. Frequent change of glasses due to rapid
change in refractive index of the lens
3. Painless, progressive gradual diminution of
vision due to reduction in transparency of the
lens
4. Second sight or myopic shift in case of nuclear
cataract causing index myopia, improving near
vision.
Symptoms of Cataract
5. Loss or marked diminution of vision in bright
sunlight or bright light beam in central
posterior subcapsular cataract.
6. Monocular diplopia or polyopia in presence of
cortical spoke opacities
7. Glare in posterior subcapsular cortical
cataract due to increased scattering of light
Symptoms of Cataract
8. Colored haloes around the light as seen
in cortical cataract due to irregular
refractive index in different parts of the
lens.
9. Color shift , reds are accentuated
10. Visual field loss, generalized reduction
in sensitivity due to loss of transparency
Disturbances in Vision
Appearance of Black Spots
Reduction of Visual Fields
Uni ocular Polyopia
Lenticular Myopia
Changes in Colour values
Differential Diagnosis of painless
gradual diminution of vision
Chronic open angle glaucoma
Macular degeneration
Optic atrophy
Corneal dystrophy
Retinopathy associated with systemic
disorders (hypertension or diabetes)
Assessment
Visual Acuity
Direct Distant Ophthalmoscopy
(Fundal Glow)
Light Reflex
Slit Lamp Examination
Management
Medical
Surgical
Medical Management
Refraction
Dark Glasses
Surgical Management
Indications
Visual Improvement
Medical Indications
Cosmetic Indications
Surgical Management
Couching
Intracapsular Cataract Extraction
(ICCE)
Extracapsular Cataract Extraction
(ECCE)
Phacoemulsification
Clinical Rotation of
rd
3
Year
Surgical Techniques
Complications
Management of complications
Ectopia Lentis
Aquired
(Trauma, Large eye ball, High
Myopia)
Hereditary
o Marfans Syndrome
o Homocystinuria
o Weil Marchesani Syndrome
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