Quick Answer
Corneal disorders and transplantation deliver 3-4 NEET PG questions per year across ophthalmology and image-based MCQs.
- Corneal anatomy — 5 layers (epithelium, Bowman, stroma, Descemet, endothelium); avascular; nourished by tears and aqueous.
- Bacterial keratitis — Pseudomonas is the classic contact-lens organism; fortified topical antibiotics hourly.
- Fungal keratitis — feathery margins, satellite lesions; natamycin 5 percent for filamentous; voriconazole for yeasts.
- HSV dendritic ulcer — fluorescein-stained branching pattern; topical ganciclovir or oral acyclovir; never steroids alone.
- Acanthamoeba — radial keratoneuritis + ring infiltrate; contact lens + water exposure; PHMB + chlorhexidine.
- Keratoconus — RGP → cross-linking → intracorneal ring segments → DALK.
- Transplant — DMEK for endothelial disease; DALK for stromal disease; PKP for full-thickness.
The cornea contributes about two-thirds of the eye's refractive power. When it clouds — infection, dystrophy or ectasia — vision loss is rapid and often reversible with the right pharmacology and surgery. India's estimated 1.2 million people with treatable corneal blindness make this a public-health issue too, driven by the Hospital Cornea Retrieval Programme (HCRP) and eye-bank networks at LV Prasad, Sankara Nethralaya and Aravind.
This NEETPGAI deep dive covers corneal anatomy, ulcerative keratitis of every stripe, keratoconus staging and treatment ladder, corneal dystrophies, and the modern keratoplasty spectrum (PKP → DSAEK → DMEK → DALK). Pair this with the ophthalmology high-yield topics guide and the common ophthalmology mistakes list for MCQ-focused revision.
Corneal anatomy and physiology
The cornea has five layers from anterior to posterior:
- Epithelium — stratified squamous, non-keratinised; regenerates from limbal stem cells.
- Bowman layer — acellular; does NOT regenerate — scars permanently.
- Stroma — 90 percent of corneal thickness; regularly arranged collagen fibrils give transparency.
- Descemet membrane — basement membrane of the endothelium; thickens with age.
- Endothelium — single hexagonal layer of cells; NON-mitotic in humans; pumps fluid out of the stroma to maintain clarity.
Key physiological facts:
- Avascular — nourished by tear film anteriorly and aqueous humour posteriorly; the limbal vasculature supplies the peripheral 1 mm.
- Innervated — long ciliary nerves (V1); most densely innervated tissue per surface area in the body.
- Endothelial cell density falls from about 4000 cells/mm² at birth to about 2500 by 60 years; below 500 the cornea decompensates.
Ulcerative keratitis — infectious causes
Bacterial keratitis
| Feature | Detail |
|---|
| Onset | Rapid (hours to 48 h) |
| Common organisms | Pseudomonas (contact lens), Staphylococcus, Streptococcus, Moraxella |
| Clinical | Dense yellow-white infiltrate, hypopyon, mucopurulent discharge, severe pain |
| Investigations | Corneal scraping → Gram + culture (blood agar, chocolate, thioglycolate) |
| Empirical therapy | Fortified topical cefazolin 5 percent + tobramycin 1.4 percent (or vancomycin + ceftazidime) alternating every 30 minutes for 24 h, then hourly; taper over 2 weeks |
| Newer option | Moxifloxacin 0.5 percent monotherapy for smaller peripheral ulcers |
Fungal keratitis (agricultural India high-yield)
| Feature | Detail |
|---|
| Onset | Indolent (days to weeks) after vegetable-matter trauma |
| Common organisms | Filamentous — Aspergillus, Fusarium (most common in India); yeast — Candida |
| Clinical | Feathery hyphal margins, satellite lesions, endothelial plaque, thicker hypopyon |
| Investigations | Scraping → KOH mount, Gram, lactophenol cotton blue, culture on SDA (Sabouraud) |
| Therapy — filamentous | Natamycin 5 percent topical hourly (WHO essential drug list) |
| Therapy — yeast/deep | Voriconazole 1 percent topical + oral voriconazole; intracameral voriconazole for endothelial plaque |
| India context | About 60 percent of infectious keratitis in southern and eastern India is fungal (unlike the West) |
Viral keratitis — HSV
| Feature | Detail |
|---|
| Epithelial (dendritic) | Branching ulcer with terminal bulbs on fluorescein staining (pathognomonic); rose bengal highlights infected epithelium |
| Stromal | Immunological — needs oral acyclovir + carefully monitored topical steroids |
| Endothelial (disciform) | Disc-shaped stromal oedema |
| Recurrence | 20-30 percent within 5 years (trigeminal ganglion reactivation) |
| Treatment | Topical ganciclovir 0.15 percent gel 5x/day OR oral acyclovir 400 mg 5x/day; long-term prophylaxis (400 mg BD) for frequent recurrences |
| Pitfall | Never use topical steroids alone in epithelial disease — worsens the ulcer |
Herpes zoster ophthalmicus (HZO)
- V1 dermatome shingles.
- Hutchinson sign — vesicles at the nasal tip → nasociliary nerve involvement → high risk of intraocular disease.
- Treat with oral acyclovir 800 mg 5x/day or valacyclovir 1 g TDS × 7 days ideally within 72 hours.
- Sequelae — post-herpetic neuralgia, pseudodendritic keratitis, iritis, secondary glaucoma, corneal anaesthesia (neurotrophic ulcer).
Acanthamoeba keratitis
| Feature | Detail |
|---|
| History | Contact lens + water exposure (tap water rinse, swimming, hot tub) |
| Clinical | Severe pain out of proportion to signs; radial keratoneuritis early; late ring infiltrate |
| Diagnosis | Confocal microscopy (double-walled cysts), PCR, culture on non-nutrient agar with E. coli overlay |
| Treatment | PHMB 0.02 percent + chlorhexidine 0.02 percent topical for months; hexamidine, propamidine adjuncts |
Think of Acanthamoeba when "bacterial" keratitis is not improving on antibiotics in a contact-lens wearer.
Keratoconus
Progressive, non-inflammatory stromal thinning and cone-shaped protrusion of the cornea. India — high prevalence in Kashmir, Ladakh, Punjab, and southern populations; associations include atopy and eye rubbing.
Signs
- Vogt striae — vertical stress lines in deep stroma; disappear with digital pressure.
- Fleischer ring — iron deposits at base of cone (best on cobalt blue filter).
- Munson sign — V-shaped indentation of lower lid on downgaze.
- Rizzuti sign — conical light reflection on nasal cornea by lateral limbal light.
- Scissoring reflex on retinoscopy.
- Corneal topography — inferior steepening, asymmetric bow-tie, high Kmax.
Management ladder
- Spectacle correction — early disease.
- Rigid gas-permeable (RGP) contact lenses — for moderate irregular astigmatism.
- Corneal collagen cross-linking (CXL) with riboflavin + UV-A — halts progression in eyes with thickness above 400 micrometres; strengthens stromal collagen via oxidative cross-links.
- Intracorneal ring segments (Intacs, Ferrara) — reshape the cornea in contact-lens intolerant patients without central scarring.
- Deep anterior lamellar keratoplasty (DALK) — for advanced disease with scarring; preserves recipient endothelium (lower rejection).
- Acute hydrops — sudden vision loss + oedema due to Descemet rupture; usually resolves with hypertonic saline + topical steroid over weeks; may leave scar needing DALK/PKP.
Corneal dystrophies
| Layer | Dystrophy | Feature |
|---|
| Epithelial | Cogan (map-dot-fingerprint) | Recurrent erosions |
| Bowman | Reis-Bücklers | Recurrent erosions, subepithelial reticular scarring |
| Stromal | Granular (Groenouw type I) | Discrete crumb-like opacities — hyaline (Masson trichrome) |
| Stromal | Lattice | Amyloid deposits (Congo red apple-green birefringence); TGFBI mutation |
| Stromal | Macular (Groenouw type II) | Diffuse cloudy stroma; mucopolysaccharide (Alcian blue/PAS); the only AR stromal dystrophy |
| Endothelial | Fuchs endothelial | Descemet guttate; progressive corneal oedema; needs DMEK/DSAEK |
| Endothelial | Posterior polymorphous | Vesicles at Descemet |
Mnemonic — Marilyn Monroe Always Gets Her Man In LA: Macular = MPS = Alcian blue; Granular = Hyaline = Masson trichrome; Lattice = Amyloid.
Corneal transplantation
Modern keratoplasty is layer-selective wherever possible.
| Procedure | Layer replaced | Best for | Advantage |
|---|
| PKP (penetrating keratoplasty) | Full thickness | Any full-thickness scar or opacity | Universal |
| DALK (deep anterior lamellar keratoplasty) | Epithelium + stroma (spare endothelium) | Keratoconus, stromal scars | Lower rejection (no endothelial rejection) |
| DSAEK (Descemet stripping automated endothelial keratoplasty) | Endothelium + Descemet + 100-150 micrometres posterior stroma | Fuchs, pseudophakic bullous keratopathy | Small incision, faster recovery |
| DMEK (Descemet membrane endothelial keratoplasty) | Endothelium + Descemet only (about 15 micrometres) | Fuchs, aphakic/pseudophakic bullous keratopathy | Best visual acuity, lowest rejection |
Graft rejection
- Classic triad — pain, redness, photophobia (RSVP: redness, sensitivity to light, vision drop, pain).
- Khodadoust line — endothelial rejection line marching across the graft.
- Treatment — intensive topical steroids (prednisolone acetate 1 percent hourly), oral prednisolone, topical tacrolimus.
- Rejection rates — PKP about 20 percent at 5 years; DALK 5-10 percent (no endothelial rejection); DMEK less than 5 percent.
Eye banking in India
- Hospital Cornea Retrieval Programme (HCRP) — hospital-based systematic donation model coordinated by NPCBVI; over 65,000 annual retrievals.
- Storage — McCarey-Kaufman (MK) medium short-term; Optisol-GS up to 14 days at 4°C.
- Donor exclusions — HIV, HBV, HCV, sepsis, prion disease, intraocular malignancy, unknown-cause encephalitis.
- Age limits — practically 3-70 years, with liberalisation for endothelial keratoplasty.
- India leaders — LV Prasad Eye Institute (Hyderabad), Sankara Nethralaya (Chennai), Aravind Eye Care (Madurai), RP Centre AIIMS (New Delhi), Ramayamma International Eye Bank at LVPEI.
NEET PG MCQ traps
- Bowman layer does NOT regenerate — heals as scar.
- Corneal endothelium does NOT divide in humans.
- Pseudomonas keratitis — contact lens; rapid, severe.
- Fungal keratitis — feathery, satellite; natamycin 5 percent for filamentous.
- Dendritic ulcer — HSV pathognomonic; fluorescein stains; rose bengal highlights.
- Never use topical steroids alone in HSV epithelial disease.
- Hutchinson sign — tip of nose vesicles → nasociliary V1 → intraocular involvement risk.
- Acanthamoeba — contact lens + water; radial keratoneuritis + ring infiltrate; PHMB + chlorhexidine.
- Vogt striae, Fleischer ring, Munson sign — keratoconus triad.
- Cross-linking — riboflavin + UV-A; halts keratoconus progression above 400 micrometres.
- Granular dystrophy — hyaline (Masson trichrome).
- Lattice dystrophy — amyloid (Congo red).
- Macular dystrophy — mucopolysaccharide (Alcian blue), AR, only Groenouw II.
- Fuchs dystrophy — Descemet guttata → oedema → DMEK/DSAEK.
- DMEK — best visual outcome for endothelial failure; hardest technique.
- DALK — best for keratoconus with scarring; no endothelial rejection.
- Khodadoust line — endothelial rejection line.
- RSVP — red, sensitive, vision drop, pain (rejection symptoms).
- Optisol-GS — corneal preservation up to 14 days.
- HCRP — hospital-based donor programme under NPCBVI.
Recent updates and India context
- Epithelium-on ("accelerated") cross-linking — trials suggest comparable outcomes to Dresden protocol with lower discomfort; adoption is patchy in Indian centres.
- Bowman layer transplantation — a lamellar option for advanced keratoconus in eyes not suitable for DALK; pioneered by LV Prasad Eye Institute for Indian patients.
- Fungal keratitis burden — India accounts for a disproportionate share globally; the WHO essential medicines list added natamycin partly on Indian trial data (Mycotic Ulcer Treatment Trial, MUTT, established natamycin superior to voriconazole for Fusarium).
- NPCBVI 2024-25 — Hospital Cornea Retrieval Programme rollout expanded to district hospitals; national keratoplasty pool aims to clear India's estimated 1.2 million corneal blind wait-list.
- Simple limbal epithelial transplantation (SLET) — a low-cost autologous limbal stem cell technique developed at LV Prasad Eye Institute for unilateral chemical burns and limbal stem cell deficiency; standard globally now.
- Cultivated oral mucosal epithelial transplantation (COMET) — for bilateral limbal stem cell deficiency (Stevens-Johnson, chemical burns).
- Bioengineered corneal implants — a 2022 Swedish trial of pig-collagen implants offered a scaleable alternative; India regulatory pathway is under discussion given the vast unmet need.
Frequently asked questions
How do you differentiate bacterial, fungal and Acanthamoeba keratitis clinically?
Bacterial keratitis progresses rapidly over 24-48 hours with dense yellow-white infiltrate, mucopurulent discharge and hypopyon — Pseudomonas in contact lens wearers, Staphylococcus, Streptococcus and Moraxella most common. Fungal keratitis is more indolent, with feathery filamentous margins, satellite lesions, endothelial plaque and thicker hypopyon — think Aspergillus or Fusarium after vegetable-matter trauma, common in agricultural India. Acanthamoeba keratitis presents with severe pain out of proportion to signs, radial keratoneuritis and a late ring infiltrate; contact-lens wear with water exposure (swimming, tap water rinse) is the classic history. Confocal microscopy and PCR clinch the diagnosis when routine cultures are negative.
What is the pathognomonic finding in HSV epithelial keratitis and how do you treat?
The pathognomonic finding is a branching dendritic ulcer with terminal bulbs, stained by fluorescein and often better visualised with rose bengal. Treatment is topical ganciclovir 0.15 percent gel five times daily or acyclovir ointment, or oral acyclovir 400 mg five times daily. Never use topical steroids alone in epithelial disease — they worsen the ulcer. Debridement of infected epithelium accelerates healing. Stromal keratitis (immunologically mediated) needs combined topical steroid plus oral acyclovir prophylaxis to prevent recurrence. Recurrences follow the trigeminal ganglion, seen in about 20-30 percent within 5 years.
What are the surgical options for keratoconus and how do you sequence them?
Sequencing depends on severity. Early keratoconus with tolerable spectacle correction — hard rigid gas permeable (RGP) contact lenses. Progressive disease in an eye with corneal thickness above 400 micrometres — corneal collagen cross-linking (CXL) with riboflavin and UV-A halts progression. Contact-lens intolerance without central scarring — intracorneal ring segments (Intacs, Ferrara rings) reshape the cornea. Advanced disease with acute hydrops or central scarring — deep anterior lamellar keratoplasty (DALK), which preserves recipient endothelium and reduces rejection risk. Full-thickness penetrating keratoplasty (PKP) is now second-line for keratoconus given DALK outcomes.
How does DMEK differ from DSAEK and PKP in corneal transplantation?
PKP (penetrating keratoplasty) is full-thickness replacement — 8 mm trephine, 16 interrupted or double running sutures — traditional but high astigmatism and rejection risk. DSAEK (Descemet stripping automated endothelial keratoplasty) replaces the diseased endothelium plus about 100-150 micrometres of posterior stroma via a small limbal incision — quicker rehabilitation, better refractive outcome. DMEK (Descemet membrane endothelial keratoplasty) transplants only Descemet membrane plus endothelium (about 15 micrometres) — near-normal cornea, best visual outcome and lowest rejection, but technically demanding. DALK spares recipient endothelium and suits stromal disease like keratoconus.
What is the HCRP and how has it changed corneal donation in India?
The Hospital Cornea Retrieval Programme (HCRP) is India's structured in-hospital corneal donation model — trained transplant coordinators counsel families of deceased patients in mortuaries and ICUs about corneal donation, obtain consent, and coordinate retrieval within 6-12 hours of death. Introduced in the mid-2000s under the National Programme for Control of Blindness and Visual Impairment (NPCBVI), HCRP shifted the donor base from voluntary eye pledge to hospital-based systematic retrieval, driving India's annual corneal collection to over 65,000 tissues. LV Prasad Eye Institute, Sankara Nethralaya, Aravind and AIIMS network centres run high-volume HCRP models and lead the wait-list clearance for the estimated 1.2 million Indians with treatable corneal blindness.
This content is for educational purposes for NEET PG exam preparation. It is not a substitute for professional medical advice, diagnosis, or treatment. Clinical information has been reviewed by qualified medical professionals.
Written by: NEETPGAI Editorial Team
Reviewed by: Pending SME Review
Last reviewed: July 2026
