A cataract is opacity within the lens of the eye, and may affect either one or both eyes. The opacity changes the transparency and refractive index of the lens, resulting in the blurring of a person’s vision. According to the World Health Organisation (WHO, 2007), cataracts account for 47.9% of blindness worldwide. The reported prevalence of childhood cataracts ranges from 1-15 per 10,000 children.
This occurs at the centre of the lens, and interferes with distance vision. It is the most common type of cataract, and is usually the result of advancing age.
This begins at the outer rim of the lens, and gradually works towards the centre of the lens. It resembles the spokes of a wheel. It is most commonly found in patients with diabetes.
This affects the back of the lens, causing glare and blurring of vision. It is the most rapidly progressing type of cataract. Risk factors for the development of a subcapsular cataract are use of steroids, diabetes, and myopia.
The following are associated with acquired cataract in developed nations:
The lens of the eye is composed of specialised cells arranged in a highly ordered and complex manner. These cells are stratified epithelia and have a very high content of cytoplasmic protein; the crystallins. These proteins, along with the complex structure, impart transparency to the lens.
Unlike other epithelia, the lens does not shed nonviable cells. As such, it is particularly susceptible to the degenerative effects of aging on cell structure. The exact pathogenetic mechanisms of this are not known. It has, however been observed that most of the risk factors identified are environmental stressors that lead to the formation of toxins or the impairment of antioxidants.
With regards to the presentation of congenital cataracts:
Approximately one-third of congenital cataracts in children are inherited, one third are associated with systemic diseases, and one-third are idiopathic or sporadic.
Cataracts detected in infants and young children must be referred to a specialist as soon as possible in order to allow for normal visual development and to prevent blindness.
There is no proven therapy to prevent either cataract formation or its progression once it has developed. However, the following have been observed to be of benefit in decreasing risk:
Postoperative thickening of the lens capsule frequently occurs over time causing gradual deterioration of vision. This can be treated by splitting the capsule with a laser.
Postoperatively 95% of patients that have no other complications achieve a corrected acuity of 6/12.
The major risk factors that affect prognosis are diabetes and diabetic retinopathy. Diabetes causes fluctuating blood glucose levels. Occasionally, high blood glucose levels cause oedema and subsequent swelling of the lens. When the blood glucose diffuses, the swelling in the lens also reduces. This repeated action causes cataracts.
In paediatric cataracts, visual acuities of 20/20 to 20/40 may be achieved if cataracts are diagnosed and treated early.
Cataracts are lens opacities that can range in severity from unnoticed dots to total fogging of vision. Cataracts are by far the commonest cause of preventable blindness worldwide.
Age-related causes are most common, although there are also familial or congenital causes. Gradual painless deterioration of vision is the most common symptom reported, with other possible co-existing symptoms such as glare and problems with night driving dependent on the type of cataract.
Early symptoms can be alleviated with spectacles, but to correct vision, surgery is required. Surgery involves the insertion of an intraocular lens to replace the affected one. The exact technique used is determined by the aetiology and density of the cataracts. Phacoemulsification (a form of small incision surgery) is the most frequently used technique. Further investigations such as blood glucose, serum calcium, and liver biochemistry should be considered in order to diagnose any possible underlying metabolic disorder.
It is also worth noting that cataracts may not always be bilateral, and hence, eyes may be managed and treated individually according to the severity of the cataract within each eye.
http://www.careflash.com/video/cataracts (Cataracts explained in lay terms)
(Cataract surgery, Phacoemulsification) My favourite!
Kumar and Clark Clinical Medicine 7th edition
UpToDate articles "Cataract", "Cataract in children", and "Slit lamp examination"
All images taken from: http://en.wikipedia.org/wiki/Cataract_surgery
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