2. Overview
Introduction to vertebrate eye lens
Embryonic development of lens
Cataracts introduction
Types & Clinical features of cataracts
Genetics behind cataracts
Population statistics
Prognosis & treatment
3. Lens Introduction
• Biconvex transparent
structure
• Focuses light on retina
Equator
• Ectodermal origin
Lens cortex
• Lens structure and function: capsule
Lens capsule
Lens epithelium Lens
Lens fibers Primary
Accommodation: nucleus
Epithelium
changing the power of the
lens
Crystallin proteins and
transparency
Fiber cell
4. • Central part of lens
• Forms by elongation of posterior epithelial lens vesicle
• Contains lens primary nucleus
• Anterior epithelium
• Cells anterior to central region
divide throughout lifetime
• Differentiate into fiber cells
• Elongates, looses their nuclei &
intracellular organelles
As part of continuous process
cells migrate toward center from
lens cortex and outer layers.
5.
6. Genetics of embryonic development
of lens
• Interactions of neural tube & epidermal thickenings called Placode
e.g. Olfactory, otic or lens placodes.
9. What is a cataract?
• A cataract is a clouding of the lens in the eye
• affects vision
• Most commonly associated with breakdown of the lens
microarchitecture
• Most cataracts are related to aging
• Cataracts are very common in older people
• Occur in either or both eyes
• Cannot spread from one eye to the other
• varying in degree from slight to complete opacity
• If lens is cloudy from a cataract, the image seen will be blurred
• Derives its name due to foggy or misty vision as near waterfall
10. Classification of Cataracts
On etiological basis
• Congenital cataracts
• Senile cataracts
• Secondary cataracts
• Traumatic cataracts
On the basis of Opacities (capsular/sub capsular)
• Polar cataract
• Pulverulent cataract
• Cerulean cataract
• Lamellar cataract
• Nuclear cataract
• Cortical cataract
• Sutural cataract
• Aculeiform cataract
• Total cataract
12. Causes
• Have multiple causes
• Often associated with breakdown of the lens
microarchitecture
• Includes vacuole formation
• Disarray of lens cells
• Cause large fluctuations in density resulting in light
scattering
• Accumulation of high molecular weight protein aggregates of
approximately 1000 Å or more
• Disruption of short-range ordered packing of the lens
crystallins
13. • Disruption of lens microarchitecture and protein denaturation are not
mutually exclusive events
• mutations in crystallins when sufficient to form aggregates, causes
Congenital cataracts
• environmental insults such as light, hyperglycemic or oxidative
damage contribute to age related cataract
• Mutations causing insult to epithelial cell resulting in disturbed
homeostasis if,
• Severe- congenital cataract
• Milder- senile along with environmental factors
• Inheritance pattern
Congenital- Mendelian inheritance
Senile- Complex pattern
• Exposure to compounds such that H2O2
14. • In general:
Congenital- infection, developmental defects or mutations
Senile- environmental, UV radiation or smoking or
formation of reactive
• Cataracts may also be part of multisystem genetic disorders such
as:
chromosome abnormalities
Lowe syndrome
neurofibromatosis type 2
15. Molecular basis
• A number of loci have been identified
• inheritance pattern of
autosomal dominant
autosomal recessive
X-linked
• 14 genes responsible for primary cataract have been identified
• 7 of these encode crystallins
• Allelic heterogeneity is seen for many Crystallin genes
• Crystallin mutations been found to cause
Misfolding & aggregation
Prevent protein-protein interactions that maintain lens
transparency
Decrease protein solubility & forms agglomerates
• Type of cataract may depend on time of gene expression during
lens development
16. • Connexin 50 & 46 mutations also lead to cataract
Hinder distribution of small molecules to fiber cells
Aberrant gap junctions form
Abnormal fiber cell production & formation
• Defective water transport protein
Change in solubility conditions in lens cell
E.g. MIP gene mutation
• Disruption of interaction between cytoskeletal proteins
E.g. BSFP2 and alphaA-crystallin
• Mutant transcription factors
PITX3, MAF, HSF4
19. Statistics (Indian)
• According to WHO, 47.8% of global blindness is due to cataract
in South Asia region
• prevalence of blindness in people >50 years of age (presenting
vision < 20/200) was observed to be 8.5%
• there is a declining trend over the period 1989-2001
• 51% of blindness is due to cataract in India
• in 2001, there were 7.75 million individuals whose blindness could
be attributed to cataract
• would increase to 8.25 million by 2020
• increase in the total number of cataract blind in the age group
above 70 years been observed
• From prevalence & CSR statistical data India would be placed
in a comfortable position for eliminating cataract blindness by
2020
20. Diagnosis, Treatment & Prognosis
• Visual acuity test: This eye chart test
measures how well subject see at
various distances.
• Dilated eye exam:
Drops are placed in eyes to
widen, or dilate, the pupils
special slit lamp used to examine
retina and optic nerve for signs of
damage and other eye problems
• Tonometry: to measure the pressure
inside the eye
21. Treatment
• symptoms of early cataract may be improved with new
eyeglasses, brighter lighting, anti-glare sunglasses, or
magnifying lenses
• cataract needs to be removed only when vision loss interferes
with everyday activities
• Only treatment is surgery
• Surgery is of two types-
Phacoemulsification, or phaco
Extracapsular surgery
• Natural lens removed, replaced
with IOL
22. Prognosis
• Risk with surgery
Infection & bleeding
Retinal detachment
• Cataract removal is one of of the safest and most effective types
of surgery
• In about 90 percent of cases, people who have cataract surgery
have better vision afterward
23. Cataract surgical rate (CSR) is a quantifiable measure of
the delivery of cataract services in a country. It is thus a
good indicator of how well a country is organizing its
efforts.
A CSR of 3000 was targeted under Vision 2020: the right to
sight, for India, by the year 2000.Current trends show that
this target has been achieved, but still there are regional
disparities across the country. But we are doing good.
24. References:
1. Congenital Cataracts and their Molecular Genetics-J. Fielding
Hejtmancik; Semin Cell Dev Biol. 2008 April; 19(2): 134–149
2. Current status of cataract blindness and Vision 2020: The right to
sight initiative in India-GVS Murthy et al; indian journal of
ophthalmology Year : 2008, Volume:56, Issue:6, Page : 489-494
3. Human molecular genetics: mechanism of inherited diseases- J J
Pasternak; 2nd edition, 2005
4. Death and DALY estimates for 2004 by cause for WHO Member
States;World Health Organization. who.int. 2004
5. Developmental Biology- Scott F. Gilbert ; 8th edition, 2006
6. http://www.nei.nih.gov/health/cataract/cataract_facts.asp
7. http://en.wikipedia.org/wiki/Cataract
8. http://eyeinstitutenc.com/cataract/
After the natural lens has been removed, it often is replaced by an artificial lens, called an intraocular lens (IOL). An IOL is a clear, plastic lens that requires no care and becomes a permanent part of your eye. Light is focused clearly by the IOL onto the retina, improving your vision. You will not feel or see the new lens.
