Drug-induced cataract

What it is

Cataract has both systemic and ocular causes, and drugs stand in each of the two lists: steroids among the systemic causes and topical steroids among the ocular ones. The form tied to drugs is the subcapsular cataract, which is described as due to steroid use, sitting just deep to the lens capsule and lying in the visual axis.

Causes and risk

The majority of cataracts are age related or due to UV light. The rest of the causes are grouped:

• Systemic. Diabetes mellitus, steroids, infection such as congenital rubella, metabolic causes such as hypercalcemia, hyponatremia, hypokalemia and galactosemia, and myotonic dystrophy and Down's syndrome.
• Ocular. Trauma, uveitis, high myopia and topical steroids.

Diabetes affects the eye in several ways at once: retinopathy, refractive changes and acceleration of cataract, along with optic neuropathy and cranial nerve palsies causing diplopia.

How it presents

Cataract belongs to the gradual, not the acute, causes of visual loss, and the symptom named with it is glare. Four types are described:

• Nuclear, which changes the lens refractive index and is common in old age.
• Polar and cortical, which are localized, commonly inherited and lie in the visual axis.
• Subcapsular, due to steroid use, just deep to the lens capsule and in the visual axis.
• Dot opacities, common in normal lenses and also seen in diabetes and myotonic dystrophy.

Cataract is also one of the causes of monocular diplopia, the kind that occurs when one eye alone is open, along with a change in corneal shape such as keratoconus, uncorrected refractive astigmatism, corneal scarring and lens dislocation. Binocular diplopia, which disappears when one eye alone is open, belongs instead to cranial nerve palsy and to myasthenia gravis.