Cataract
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Direct answer
Any opacity of the lens is a cataract, and painless, progressive blurring over months in an eye that is otherwise normal is its signature. Age-related cataract comes in three morphologies — cortical spoke opacities, nuclear sclerosis that browns the lens, and posterior subcapsular plaque that dazzles in bright light and blurs near work — and it remains the leading cause of blindness in India, responsible for roughly two-thirds of blindness in national surveys. Surgery is the only cure: phacoemulsification with foldable intraocular lens implantation through a 2 to 3 mm incision in urban practice, and manual small-incision extracapsular extraction at high-volume camps. Surgery is timed by the patient's visual needs, not by the cataract's ripeness.
What you must remember
- Posterior subcapsular cataract appears earliest and disables most, with glare in sunlight and poor near vision; causes include ageing, diabetes, steroid therapy and uveitis.
- Nuclear sclerosis shifts refraction myotically — the "second sight" of reading again without glasses before vision finally fails.
- Cortical cataracts cause monocular diplopia and spoke-like peripheral opacities seen against a red reflex.
- Congenital cataract associates with rubella (with salt-and-pepper retinopathy, deafness and cardiac disease), metabolic disease and familial forms; unilateral cases are operated by about six weeks of age, bilateral by eight to ten weeks, to forestall deprivation amblyopia.
- Optical biometry with keratometry and A-scan axial length feeds the SRK formula for intraocular lens power calculation — the Indian exam's favourite calculation method, with its A-constant.
- Acute postoperative endophthalmitis presents on days two to five with pain, hypopyon and vitritis; late posterior capsule opacification, the commonest long-term complication, is opened with Nd:YAG laser capsulotomy.
- Cystoid macular oedema (Irvine-Gass syndrome) explains unexplained vision loss weeks after uneventful surgery.
- Sight-threatening suprachoroidal haemorrhage is the feared intraoperative catastrophe; spectacle correction remains the rule because a monofocal IOL has no accommodation.
A routine case, worked end to end
A 68-year-old farmer can no longer read bus numbers; the right eye records 6/36, the left 6/18, both improving to only 6/24 with pinhole. Slit-lamp examination shows brunescent nuclear sclerosis with cortical spokes; the fundus, once dilated, is healthy. Proceed stepwise as the system does. Document that glare and visual handicap justify surgery on the worse eye, and clear general fitness for a largely topical-anaesthesia day procedure. Biometry measures keratometry and axial length, and the SRK formula returns an IOL power around 22 dioptres for a posterior chamber lens. Phacoemulsification fragments the nucleus ultrasonically, cortical aspiration cleans the bag, and a foldable lens is injected into the capsular bag through the self-sealing incision. Review at one day, one week and six weeks: vision should reach 6/9 with a mild astigmatic correction. If instead this farmer returned on day four with severe pain and a hypopyon, the pathway changes to vitreous tap with intravitreal antibiotics or vitrectomy depending on vision. If he returned in a year complaining of gradual re-blurring with a hazy posterior capsule behind a well-centred IOL, a five-minute Nd:YAG capsulotomy restores the view. One operation, three possible timelines — that is how a cataract question is constructed.
How the exam frames it
The FMGE pattern splits into recognition, timing and complications. Recognition: match the morphology (cortical, nuclear, posterior subcapsular) to its symptom — glare, second sight or monocular diplopia. Timing: when to operate on congenital cataract, and why the answer is weeks, not years. Complications: rank posterior capsule opacification as the commonest late problem and endophthalmitis as the feared early one. Programme knowledge adds marks: cataract is the backbone of the National Programme for Control of Blindness and Visual Impairment, high-volume surgery camps and government-sponsored IOL implantation having driven India's falling blindness prevalence.
Frequently asked questions
Which cataract causes the earliest glare and near-vision difficulty?
Posterior subcapsular cataract, because the opacity sits at the nodal point of the eye's optical axis and scatter is worst in bright light and miosis.
How is intraocular lens power calculated before surgery?
By keratometry for corneal power and A-scan or optical biometry for axial length, inserted into a formula such as SRK/SRK-T using the lens model's A-constant.
What is the treatment of posterior capsule opacification?
Nd:YAG laser posterior capsulotomy, a painless outpatient procedure that opens the opaque capsule behind the intraocular lens.
When should unilateral congenital cataract be operated?
Around six weeks of age, with bilateral cases by eight to ten weeks, followed by prompt aphakic correction and amblyopia therapy.
Which organism and timing define acute post-cataract endophthalmitis?
Typically coagulase-negative staphylococci or Staphylococcus aureus presenting two to five days after surgery with pain, hypopyon and vision loss.
Why does a patient with nuclear cataract sometimes read without glasses again?
Progressive nuclear sclerosis increases the lens's refractive power, producing a myopic shift called second sight — temporary, ending as the cataract matures.