Cataracts

Published on 02/04/2015 by admin

Filed under Internal Medicine

Last modified 22/04/2025

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220 Cataracts

Instruction

Examine this patient’s eyes.

Salient features

History

• Drug history (steroids, chloroquine, phenothiazines, chlorambucil, busulfan)

• History of gradual deterioration of vision

• History of diabetes

• Inquire about smoking (JAMA 1992;268:989–94) and alcohol consumption (Arch Ophthalmol 1993;111:1130) as both cigarette smoking and heavy alcohol consumption increase the risk of cataract formation

• Family history is important even in age-related nuclear cataract as it explains about 50% variation in the severity of disease (N Engl J Med 2000;342:1786–90).

Examination

• Bilateral cataracts (shine light obliquely across the lens; Fig. 220.1, see also Fig. 201.3).

image image

Fig. 220.1 Cataracts. (A) Early. (B) White mature cataract.

(With permission from Kumar, Clark 2005.)

Proceed as follows:

• Tell the examiner that you would like to check the urine for sugar.

Diagnosis

This patient has premature bilateral cataracts (lesion) caused by diabetes mellitus (aetiology) and has had a gradual deterioration of vision (functional status).

Questions

Mention a few causes of cataracts

• Common causes:

• Old age (look for arcus senilis). The Framingham study reported that 13% of people aged 65–74 years and about 40% of those over the age of 75 years had cataracts.
• Diabetes mellitus (non-enzymatic glycosylation of lens protein is twice as high in diabetics as in age-matched controls and may contribute to the premature occurrence of cataracts).

• Uncommon causes:

• Trauma
• Metabolic: Cushing syndrome, Wilson’s disease (stellate cataracts), galactosaemia
• Chromosomal disorders: dystrophia myotonica, Turner syndrome
• Congenital infections (rubella or cytomegalovirus)
• Drugs (see above)
• Dermatological disorders: atopic dermatitis, ichthyosis
• Radiation: infrared (glass-blower’s cataract), X-ray, microwave radiation.

Advanced-level questions

How are cataracts treated?

Cataract extraction is performed by removing the lens nucleus and cortex from within the lens capsule (extracapsular). In most adults, a plastic lens is implanted within the capsule. Multifocal intraocular lens implants in some instances have reduced the need for both reading and distance spectacles. Lens extraction improves vision in 95% of instances. In the remaining, prior retinal disease or postoperative complications such as haemorrhage, glaucoma, infection or retinal detachment may be the cause. There are data suggesting that there is substantial benefit from bilateral cataract eye surgery in that it improves stereoacuity (Lancet 1998;352:925–9).

How is early cataract detected using direct ophthalmoscopy?

Examination of the red reflex with + 4 dioptres at approximately 20 cm from the patient will reveal a black opacity in the lens against the reddish hue of the reflex. If this opacity appears to move down on upward gaze, it is located in the posterior half of the lens, but if it appears to move up then it is located in the anterior half of the lens.

Is the use of inhaled steroids associated with cataracts?

The use of inhaled steroids is associated with nuclear and posterior subcapsular cataracts (N Engl J Med 1997;337:8–14).

What do you know about calpains in the pathogenesis of cataracts?

The transparency and refractive capacity of the lens depend on the short-range interactions, concentration and configuration of water-soluble proteins, the crystallins, within the fibre cells of the lens. The calpains are calcium-dependent cysteine proteases (proteolytic enzymes with cysteine in the catalytic site) that cleave crystallins. In rats, m-calpain is the major calpain involved in the animal model of cataractogenesis and it is the only calpain active in human lenses. It cleaves the N-terminal region of the lens proteins α-crystallin and β-crystallin, producing truncated crystallin aggregates that resist additional proteolysis and form cataracts. Aging leads to post-translational modifications of crystallins that also result in progressive loss of solubility and a tendency to aggregate. The potential involvement of calpains in some types of human cataract has led to suggestions that calpain inhibitors may be possible therapy.

Jacques Divel of Bernay, a small town in Brittany, devised extracapsular extraction of cataracts in 1748.

Harold Ridley, who worked at St. Thomas’s and Moorfields’s Eye Hospital in London, was the first to champion the insertion of artificial lens after removal of a cataract in the 1950s (Lancet 1999;354:1912).

Controversy over process patents swelled after ophthalmologist Samuel Pallin was awarded a patent in 1992 for a method of performing cataract surgery that did not require stitches. The US Congress amended the Patent Act in 1996 to address these concerns.

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