Cataract and Cataract Surgery
On this page
Direct answer
A cataract is any opacity of the crystalline lens, presenting as painless, progressive blurring of vision with glare and, in nuclear sclerosis, a myopic shift. Age-related cataract is the commonest form and the leading cause of treatable blindness in India; treatment is surgical — phacoemulsification with foldable intraocular lens implantation is the standard, with manual small-incision cataract surgery (SICS) an effective, low-cost alternative. There is no medical treatment that reverses cataract.
What you must remember
- Age-related types: nuclear sclerosis (brunescent nucleus, myopic shift and second sight), cortical spoke opacities and posterior subcapsular cataract, which blurs vision most in bright light and on near effort because of posterior pole involvement.
- Maturity in cortical cataract: immature cataract retains a clear zone with an iris shadow, mature cataract is fully opaque with no iris shadow, intumescent cataract is swollen and may raise pressure, and hypermature Morgagnian cataract has liquefied cortex with a shrunken nucleus sinking inferiorly.
- Systemic and other causes: diabetes accelerates cataract (snowflake opacities), galactosaemia produces an oil-droplet lens, hypoparathyroidism causes tetany cataract, chronic corticosteroid use causes posterior subcapsular opacity, and uveitis, trauma and radiation are important secondary causes.
- Congenital cataract: may be genetic, maternal rubella (with a pearly dense lens, microphthalmia and salt-and-pepper retina) or metabolic; dense bilateral cataract must be operated within the first weeks to months of life to prevent deprivation amblyopia, followed by posterior capsulotomy, anterior vitrectomy and aphakic correction.
- Surgical options: intracapsular extraction removes the whole lens with its capsule and is now rarely used; extracapsular surgery preserves the posterior capsule for lens implantation; phacoemulsification fragments the nucleus with ultrasound through an incision of about three millimetres or less, with foldable lens implantation and sutureless closure.
- IOL basics: power is calculated from keratometry and axial length by formulas such as SRK; lenses are made of PMMA, acrylic or silicone, and placed in the capsular bag; the first implant was performed by Harold Ridley.
- Complications: posterior capsular opacification is the commonest late complication and is treated by Nd:YAG laser capsulotomy; intraoperative posterior capsule rupture, cystoid macular oedema, endophthalmitis, retinal detachment, iris damage and IOL decentration are the others to list.
Common confusion
Two errors recur in examinations. First, students equate maturity with visual acuity — a posterior subcapsular cataract can devastate reading vision while still "immature" on slit lamp maturity grading. Second, phacomorphic glaucoma (a swollen intumescent lens causing angle closure) is confused with phacolytic glaucoma (leakage of lens proteins from a hypermature cataract causing open-angle inflammation); both need lens extraction but through different medical preparation. Also remember that in SICS the incision is a self-sealing scleral tunnel, not the 180-degree section of older extracapsular surgery.
Exam-focused takeaway
In theory, prepare types and maturity of cataract as one long answer and congenital cataract with its rubella associations as a short note; diagrams of phaco steps or the Morgagnian lens fetch marks. In viva, expect the iris shadow test for maturity, the timing of congenital surgery, IOL power determinants and why Nd:YAG is used for capsulotomy. In the posting, examine each cataract for maturity and fundus glow, watch a phaco and a SICS in the theatre, and follow the post-operative review of vision and intraocular pressure, since that is where complications declare themselves.
Frequently asked questions
What are the symptoms of age-related cataract?
Painless progressive blurring, glare from lights, fading of colours, monocular diplopia early on, and a myopic shift in nuclear sclerosis that may temporarily improve reading without glasses.
How is immature cataract distinguished from mature cataract?
On slit lamp examination an immature cataract has some clear cortex and throws an iris shadow on oblique illumination, while a mature cataract is completely opaque and casts no iris shadow.
What is phacoemulsification?
Extracapsular surgery in which an ultrasonic probe fragments the nucleus through a small self-sealing incision, after which cortical matter is aspirated and a foldable intraocular lens is implanted in the capsular bag.
How is the power of an intraocular lens calculated?
By biometry — keratometry of the cornea and ultrasonic axial length fed into formulas such as the SRK regression formula, with the intended post-operative refraction chosen by the surgeon.
What is posterior capsular opacification and its treatment?
Proliferation of lens epithelial cells on the intact posterior capsule, months to years after surgery, causing visual decline; treated by Nd:YAG laser posterior capsulotomy.
Why must dense congenital cataract be operated early?
Because light deprivation during the sensitive period of visual development causes irreversible deprivation amblyopia; bilateral dense cataract is ideally operated within the first two months of life.