Understanding Cataract

Cataract is opacity of the crystalline lens.
The lens is the part of our eye that helps us focus image of objects in our retina for clear vision. To
achieve this, the lens has to be clear and transparent but in certain conditions, this transparency is lost
leading to blurring or absolute loss of vision.

Cataract is the commonest cause of blindness globally. It contributes about 51% of blindness and 65.2
million of global burden of blindness. 1
In Nigeria, according to national blindness survey, it contributes about 43% of the burden of blindness. 2 It
is important to note that blindness from cataract is reversible through surgical intervention
Causes 3
The causes of cataract can be congenital or acquired
Congenital causes
A) Maternal causes
i)Maternal infection: maternal infection at the early stage of pregnancy can cause cataract.eg Rubella,
toxoplasmosis, cytomegalovirus infection etc.
ii)It can happen in children whose mother took high and/or prolonged dose of corticosteroid,
thalidomide etc.
iii)maternal exposure to radiation either as occupational hazard or therapy.
iv)Malnutrition: Malnutrition in the early stage of pregnancy can increase the risk of congenital cataract

B) Fetal factors

i) It can be hereditary and mode of inheritance is dominant e.g., coronary cataract etc.
iii)It can happen as part of chromosomal anomaly like down’s syndrome characterized by short stature,
flat occiput, single palmar crease etc.
iii)It could due to metabolic diseases like galactosemia
iv)Birth trauma
i)Age: Commonest cause of cataract is age. Senile cataract can start at about age of 50 years.
ii)Presenile cataract can occur earlier than that and could be caused by:
a) Diabetes Mellitus
b) Myotonic dystrophy: Characterized by difficulty in relaxation of muscle after voluntary contraction.
c)Syndermatotic cataract: These are cataract associated with skin diseases e.g., atopic dermatitis,
vasculare atrophicus, scleroderma and keratotis follicularis. x
iii)Drugs e.g. steroids, allopurinol, busulphan, Gold
iv)Trauma: It can be blunt or penetration trauma, electric shock or lightening
v)Exposure to radiation e.g., infrared (glass blowers’ cataract) X-ray
vi)Secondary cataract like chronic anterior uveitis, Glaucomflecken 4 (pathognomonic of past acute angle-
closure glaucoma) etc.
Anything that disrupts the NA + K + ATPase pump that maintains the balance of water and electrolyte in
the lens will cause cataract. This could be biological, mechanical or chemical.
Example of biological is aging. Aging affects the concentration of reduced glutathione which prevents
oxidative stress that causes degeneration and also affects the pump mechanism.
Example of Mechanical is trauma.
Example of chemical is diabetes. In diabetics, glucose tends to diffuse from aqueous humor to lens due
to hyperglycemia. In the lens, they are converted to aldose which causes osmotic pull of water into the
lens and disrupts the water/electrolyte balance causing change in refractive index(refraction) initially
and later causes cataract.
Clinical Features
i)Painless progressive diminution of vision.
ii)Glares: Dazzling of bright light like direct sunlight y day and car headlamp by night
iii)Haloes: Scattering of light in spectrum of lights especially in the immature stage.
iv)Complicated cataract like intumescent, phacolytic etc. may be painful.

It is important to know other things that may look like cataract especially in children
i)Retinoblastoma: Tumour of eye. It requires quick intervention to save eye and life.
ii)Retinopathy of prematurity especially in preterm babies
iii)Hyperplastic primary vitreous
iv)Coats disease
In adults, retinal detachment and vitreous haemorrhage may lead to loss of fundal red reflex just like
mature cataract
When cataract is fully mature, the definitive treatment is surgery. Recently sutureless small incision
cataract surgery and phaecoemulsification are becoming popular in developing nations. The success rate
is close to 100%. Cataract blindness is reversible by surgery
In Children
Surgery should be carried out as soon as it is noticed especially when in one eye because of suppression
of the affected eye and subsequent amblyopia. If both eyes are affected, surgery should also be done as
soon as possible to avoid stimulus deprivation amblyopia. Surgery is followed by eye patch of
unoperated eye as would be advised by the surgeon.
Complication of surgery
Anaesthetic complications: Retrobulbar haemorrhage, globe penetration etc. from local anaesthesia
Posterior capsular rent, vitreous loss, nucleus drop etc.
Acute post op endophthalmitis, Iris prolapse, dislocation of intraocular lens etc.
Late post op
Posterior capsular opacity, Macular oedema, Retinal detachment etc.
Evaluation of intervention
Cataract surgery is one of the most cost-effective health interventions. We can monitor the extent of
cataract surgery services using the cataract surgery rate (CSR) and cataract surgery coverage (CSC). 5 CSR
is the number of cataract surgery per million population per year.it evaluates uptake of cataract
services. It is about 2700/million in the USA but about 300/million in African and in Nigeria. 6 CSC is the

number of surgeries (Phakiks and pseudophakiks ) divided by the sum of surgeries and those awaiting
surgeries. 7 It evaluates the performance of cataract program. In Nigeria CSC for eyes is 5.6% for females
and 24.5% for males. 4
1)Blindness and Visual Impairment. World Health Organization; October, 2019. Available from:
2)Mohammed M. Abdull, Selvaraj Sivasubramaniam, Gudlavalleti VS, Murthy, Clare Gilbert, Tafida
Abubakar, Christian Ezelum, et al. Causes of Blindness and Visual Impairment in Nigeria: The Nigeria
National Blindness and Visual Impairment Survey. Invest Ophthalmol Vis Sci 2009; 50:4114 20.
3) Khurana AK. Comprehensive Ophthalmology 4 th Edition. New age international publishers 2007.182-
4) Khanski JJ, Bowlin B. Clinical Ophthalmology :A Systematic Approach.Elsevier 2011.273
5) Vision 2020, The Right to Sight: Global Initiative for the Elimination of Avoidable Blindness. (Disease
Control and Prevention of Visual Impairment). Action Plan 2006 2011; 2020. p. 10-4. [Last cited 0n 2020
Jul 2020].
6) The World Health Report: Life in the 21st Century – A Vision for All. Geneva: World Health
Organization; 1998. p. 47-8.
7) Gullapalli N. Rohit K, Ahishek P. Global burden of cataract. Curr Opin Ophthalmol 2011;22:4-9

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