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Describe metabolic and drug-induced cataract.

Ophthalmology · 3rd Professional

Metabolic Cataract

Condition	Type of cataract and mechanism
Diabetes mellitus — true diabetic cataract	Rare; occurs in young type 1 patients with poorly controlled disease. Bilateral, rapidly progressive, sometimes maturing within days. Characteristic snowflake or "snowstorm" appearance — grey-white subcapsular flake-like opacities. Mechanism: excess glucose enters the sorbitol (polyol) pathway via aldose reductase; sorbitol cannot cross the lens membrane, accumulates, and draws water in osmotically, causing swelling, fibre rupture and opacification. May reverse with strict glycaemic control if treated early
Diabetes — accelerated senile cataract	Far commoner. An ordinary age-related cataract occurring earlier and progressing faster, with a predilection for the posterior subcapsular type
Transient refractive change in diabetes	Not a cataract, but often confused with one: hyperglycaemia causes lens swelling and a reversible myopic shift, and correction of the glucose causes a hypermetropic shift. Spectacles should not be prescribed until the glucose has been stable for several weeks
Galactosaemia	Galactose is converted by aldose reductase to galactitol.
Hypocalcaemia (tetanic cataract)	After parathyroidectomy, in hypoparathyroidism and in rickets. Punctate, iridescent, polychromatic subcapsular opacities separated from the capsule by a clear zone; often with other signs of tetany
WILSON disease	Copper deposition gives a sunflower (chalcosis-like) cataract — a central disc with radiating petals in the anterior capsule — together with the KAYSER-fleischer ring in Descemet membrane. Both may reverse with chelation
Myotonic dystrophy	Christmas-tree cataract — iridescent, needle-like, polychromatic crystals in the deep cortex. May be the presenting feature, and the diagnosis is made by looking for myotonia, ptosis and frontal balding
Others	LOWE syndrome; Fabry disease (cornea verticillata with a spoke-like cataract); mannosidosis; and hypothyroidism

Drug-induced and Physical Cataract

Agent	Type and features
Corticosteroids	The most important. A posterior subcapsular cataract, related to both dose and duration, and occurring by any route — oral, topical, inhaled, nasal and injected. Children are more susceptible. It is irreversible once established, though early changes may stabilise. This is a major and avoidable problem in India, where topical steroids are freely available and used for months by patients with allergic eye disease
Chlorpromazine and other phenothiazines	Fine anterior subcapsular stellate or star-shaped deposits, with pigmentation of the lids, conjunctiva and cornea; dose-related and stationary
Amiodarone	Small anterior subcapsular deposits; also cornea verticillata (a vortex keratopathy).
Miotics — echothiophate, pilocarpine	Anterior subcapsular vacuoles; a historical association from long-term glaucoma therapy
Busulfan, gold, allopurinol, statins	Reported associations of varying strength
Ionising radiation	Posterior subcapsular, appearing after a latent period of months to years; dose-dependent, and the lens is one of the most radiosensitive tissues in the body. Follows radiotherapy to the head and neck, and occupational exposure
Infrared (glass-blower’s or "heat" cataract)	In glass-blowers, furnace and foundry workers; causes true exfoliation of the anterior lens capsule.
Electrical injury and lightning	Anterior subcapsular opacities, appearing days to months after the injury
Ultraviolet-B	A well-established risk factor for cortical cataract, and highly relevant in India

Applied Aspects

Ask about steroids in every posterior subcapsular cataract, including inhalers, nasal sprays, skin creams and over-the-counter eye drops; patients do not volunteer these and do not regard them as medicines
Examine the lens of every child on long-term steroid, whatever the route; children are more susceptible and the change is irreversible
Do not refract an unstable diabetic; wait for several weeks of stable glucose, and explain why

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