Cataract is defined as clouding or progressive thickening of the lens. It is mainly a disease of the elderly and it is the leading cause of blindness worldwide. There are three types of cataracts, the subcapsular cataract, when it occurs at the back of the lens; nuclear when it is in the nucleus and cortical when it starts peripherally and works its way to the center.
The patient will complain of decreased visual acuity. This is the most common complaint and only when the visual acuity is affected significantly is a cataract considered clinically relevant. Another frequent complaint is increased glare from oncoming headlights at night and brightly lit environment during the day. Patient with cataract may also experience varying degrees of myopia due to the increase in diopteric power of the lens, patient will report an improvement in their near vision and a decreased need for their reading glasses. This improved vision is unfortunately temporary and will disappear as the cataract worsens.
The cataract is also staged at presentation with the use of a visual acuity chart. A patient who cannot see better than 20/200 is said to have a mature cataract.
A thorough history and physical examination is enough to make a diagnosis a cataracts. However, laboratory investigations may be required to screen for underlying diseases like blood sugar for diabetes mellitus. Also, laboratory tests are an essential part of pre-surgical work up so the baseline investigations should be carried out and clotting factors to prevent perioperative bleeding.
Imaging studies are ordered when a dense cataract obscures the view of the posterior part of the eye when a posterior pole pathology is suspected.
There are special tests that could also be requested there is suspicion of coexisting ocular disease e.g a Maddox rod test in a patient with suspected macular problems.
The treatment for cataract is surgical and there has been no proven medical remedy till date and the definitive surgical remedy is lens extraction and replacement with an intraocular lens and there are various techniques for this procedure.
The intracapsular cataract extraction or ICCE involves the extraction of the entire lens and posterior capsule. This procedure is contraindicated in children and young adults.
Extracapsular cataract extraction or ECCE involves the removal of the lens through an opening in the anterior capsule and preserving the posterior capsule. This procedure has a number of advantages over ICCE.
Phacoemulsification is a more modern technique. It involves the use of an ultrasonically driven needle to break the lens down to tinier bits and aspirate these bits through a needle port. It offers some advantages over the ECCE like smaller incisions and faster wound healing.
The prognosis following surgery is very favorable if there are no accompanying ocular diseases prior to surgery that could affect vision. Cystoid macular edema is the main cause of morbidity following cataract surgery. In patients with diabetes and diabetic retinopathy, the visual prognosis is not very good.
The precise cause of the changes that occur in the lens with age is not known, however many factors have been implicated as contributory including chronic illnesses like diabetes and hypertension, ultraviolet light, smoking, previous eye injury, positive family history, prolonged corticosteroid use, previous eye surgery, alcoholism, hormone replacement therapy and use of statins (cholesterol lowering drugs).
Congenital cataracts could be caused by intrauterine infections like rubella, syphillis and cytomegalovirus, genetically transmitted syndromes and metabolic disorders.
Cataract is the leading cause of blindness worldwide and is responsible for as much as 51% of the world's blindness. As at 2004, it was estimated that about 53.8million of the world’s population experience some form of disability due to cataract. Of that number, 52.2million are in developing and underdeveloped countries. This is probably due to the inadequacy of surgical services in those countries or barriers in assessing these services. The incidence of senile cataract increases with advancing age and as much as 67% in patients aged 70 and over. The costs of treating cataract yearly is estimated at 6.8 billion dollars making it a public health concern.
Cataract affects more women than men and there is no documented evidence to show racial predilection.
The pathophysiology of cataract cuts across many factors and involves intricate interactions between various physiological processes. The weight and thickness of the lens increases as it ages while the accommodative power decreases, a process called nuclear sclerosis then occurs. It is when the central nucleus of the lens becomes compressed and hardened due to the addition of cortical layers in a concentric pattern. Another mechanism is the decrease in epithelial cell density due to the accumulation of small scale epithelial losses which eventually leads to loss of lens transparency. Also, there could be progressive oxidative damage to the lens. Another mechanism is the when soluble low molecular weight cytoplasmic lens proteins are converted to soluble high molecular weight aggregates.
Cataract is usually a visible opacity in the lens. When it located on the visual axis, it will lead to visual loss. Although there are other types of cataracts like secondary, traumatic, congenital and radiation cataracts, the commonest type is the one related to aging also known as senile cataracts. Visual loss in cataract is gradual and it can affect either or both eyes. It cannot be transmitted from one eye to the other.