Refractive Surgery
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Direct answer
Three families of laser correction now serve most prescriptions: LASIK lifts a corneal flap (blade or femtosecond laser) and ablates the stromal bed beneath with an excimer laser; surface ablation (PRK and its variants) removes the epithelium and ablates the front of the stroma, trading slower comfort for no flap; and SMILE extracts a small lenticule through a keyhole incision with a femtosecond laser, flapless and with less dry eye. Candidacy is a checklist the exam expects verbatim: age 18 or older, refraction stable for at least a year, adequate corneal thickness on pachymetry with a residual stromal bed preserved (commonly at least 250 microns or so), normal topography — because keratoconus and forme fruste disease are absolute contraindications — and deferral in pregnancy, active autoimmune disease and uncontrolled dry eye. Corneal ectasia after surgery is the feared late complication; dry eye and night haloes are the common early ones.
What you must remember
- Candidacy checklist: age at least 18, documented refractive stability over a year, corneal topography free of ectatic patterns, pachymetry sufficient for the intended ablation, healthy ocular surface, and realistic expectations — presbyopia is not cured by laser.
- LASIK: a hinged flap of about 100 to 160 microns, excimer stromal ablation, flap repositioned without sutures; rapid visual recovery in a day or two; complications include flap displacement, flap striae, diffuse lamellar keratitis, epithelial ingrowth and infection.
- PRK and surface ablation: epithelium removed (mechanically or with alcohol), excimer applied to Bowman layer and stroma, bandage contact lens for days; slower recovery and haze risk, but preferred for thin corneas, epithelial basement membrane disease, and occupations with flap-trauma risk (contact sports, forces).
- SMILE (small incision lenticule extraction): femtosecond laser sculpts an intrastromal lenticule removed through a 2 to 3 mm incision — no flap, less corneal nerve section, less dry eye; currently used chiefly for myopia and myopic astigmatism.
- Ectasia: progressive thinning and bulging after ablation with irregular astigmatism; risk rises with suspicious topography, high correction, thin residual bed — prevention by case selection outranks treatment.
- Diffuse lamellar keratitis (DLK): granular inflammation at the flap interface in the first days after LASIK — "sands of the Sahara" on slit lamp; treated with intensive topical steroids, sometimes lifting and irrigating the flap.
- Beyond the cornea: phakic intraocular lenses serve high myopia with adequate endothelium and depth; refractive lens exchange suits presbyopic high errors; toric lenses handle astigmatism at cataract surgery.
- Dry eye and haloes: the commonest early complaints — dryness from nerve section settling over months, night haloes with large pupils; counsel before, not after.
Choosing between flap, surface and lenticule
A 26-year-old software engineer wants freedom from minus seven spectacles. Work the checklist as a consultation. Age and a year of stable refraction: satisfied. Topography decides: inferior steepening or skewed axes means refusing the laser regardless of tissue, and offering a phakic lens after checking anterior chamber depth and endothelium. Pachymetry reads 505 microns: a 110-micron flap plus a high ablation leaves a borderline residual bed, so surface ablation or SMILE — both flap-sparing — become the safer plans. His dry, screen-heavy workday tilts the argument toward SMILE, which disturbs fewer corneal nerves. Contrast a 22-year-old boxer: even with ample tissue, PRK beats LASIK because a fist can displace a flap years later. And a 52-year-old asking to "get rid of reading glasses" is counselled out of corneal laser: monovision with contact lenses can be trialled, and lens-based surgery is definitive. The operation is chosen last; the candidacy mathematics decide everything before the patient signs.
Where the exam frames it
Two stems dominate. The contraindication stem: a young patient with astigmatic progression, thin cornea and suspicious topography requests LASIK — the answer is to decline and evaluate for keratoconus, and candidates who pick "thinner flap LASIK" fall for the decoy. The complication stem pairs days with diseases: day one to three flap displacement or DLK, weeks for epithelial ingrowth, months for ectasia and dry eye — matching the timeline earns the mark. The PRK versus LASIK question is framed by cornea thickness and occupation, not by preference. Indian exam additions include radial keratotomy as the historic predecessor (spoke incisions, hyperopic drift) and the counselling point that the operated eye still ages: post-LASIK corneal biometry complicates future intraocular lens calculation — a nuance that impresses in a viva.
Frequently asked questions
What are the essential criteria before offering corneal laser refractive surgery?
Age 18 or older, stable refraction for at least a year, normal corneal topography, pachymetry sufficient to leave an adequate residual stromal bed, healthy surface, and realistic goals.
Why is keratoconus an absolute contraindication to LASIK?
Ablating an already weak, thinning cornea precipitates or accelerates corneal ectasia with irreversible irregular astigmatism.
What is diffuse lamellar keratitis?
Sterile granular inflammation at the LASIK flap interface in the first postoperative days, treated with intensive topical corticosteroids (and flap lift with irrigation in severe cases).
When is surface ablation preferred over LASIK?
For thin corneas where flap creation wastes tissue, in epithelial basement membrane dystrophy, and for occupations with high flap-trauma risk such as contact sports.
Can refractive surgery cure presbyopia?
No — corneal laser reshapes distance refraction while the ageing lens still loses accommodation; presbyopia is managed with monovision strategies or lens-based options.