Posterior Subcapsular Cataracts: How they are Caused and Possible Treatment

The lens is a rounded clear structure within the eye whose job is to focus light clearly onto the retina for crisp vision. Over time, with age and oxidative damage from sunlight and other toxins, the lens can accumulate opacity, leading to the formation of cataract. A cataract occurs when sufficient opacity has accumulated within the lens to cause visual impairment. Cataracts can cause blurred vision, increasing difficulty with reading or recognizing objects from afar, difficulty with color appreciation, and glare in certain light conditions.

Cataracts can be divided into different types, depending on where in the lens the opacity has developed; although often these types overlap and co-exist. These include:

• Nuclear cataracts

Nuclear cataracts develop within the center of the lens, its nucleus.

• Cortical cataracts

Cortical cataracts develop around the rim, towards the edges (periphery) of the lens, its cortex.

• Posterior subcapsular cataracts

Posterior subcapsular cataracts are a special kind of cataract that are characterized by relatively rapid progression and significant visual influence. As the name suggests, they are located posteriorly; at the very back of the lens, just inside the capsule that supports and surrounds the lens. Despite being at the very back of the lens, they are located centrally along the visual axis, which means that light that enters the eye through the pupil goes through a posterior subcapsular cataract on its way to the retina.

This location within the eye, at the very back of the lens and in the middle of the visual axis, is known as the eye’s “nodal point”; this point is important for the geometric optics of the eye, as all light entering the eye goes through this small region. That is the reason why posterior subcapsular cataracts are so visually disabling, even when they do not appear to be so large.

Because the posterior subcapsular cataract’s influence is magnified at the nodal point of the eye, the scattering of light is quite significant from them. People with posterior subcapsular cataracts often describe significant problems with glare, such as at dawn, or dusk, or with oncoming headlights while driving at night. They often advise me they have lost confidence driving at night; it is pleasing to be able to reassure them that after their cataracts are treated, they should be able to drive at night again, so important for confidence and independence.

All cataracts are associated with ageing, but posterior subcapsular cataracts are more sensitive to metabolic disturbances. Compared to nuclear and cortical cataracts, they are more frequently associated with, and occur at an earlier age, in:

• Type 2 diabetes

• Malnutrition

• Excessive alcoholism

• Previous intraocular inflammation

• Previous ocular trauma

• Certain congenital metabolic disorders

Like all cataracts, posterior subcapsular cataracts can be effectively treated by cataract surgery, in which the cataract is removed, and a clear, artificial intraocular lens inserted in its place, restoring the vision. Some types of cataracts (e.g. nuclear cataracts) can be managed in the early stages by altering the power of a person’s eye glasses; unfortunately, posterior subcapsular cataracts are not as amenable to treatment in this way, and once they cause significant visual problems, are best managed surgically.