Ophthalmology
Cornea and Corneal Blindness
Cornea for MBBS and NEET-PG: bacterial, fungal, herpetic and acanthamoeba keratitis, corneal ulcer, dry eye, keratoplasty and eye banking, mapped to NMC codes OP4.
MedNext Academy | 3 min read
Cornea and Corneal Blindness
Cornea for MBBS and NEET-PG: bacterial, fungal, herpetic and acanthamoeba keratitis, corneal ulcer, dry eye, keratoplasty and eye banking, mapped to NMC codes OP4.
This chapter covers the cornea from the infective ulcer to the transparent graft, teaching the pattern recognition that separates bacterial, fungal, herpetic and acanthamoeba keratitis. It links corneal oedema to endothelial function, sets out the causes and prevention of corneal blindness including vitamin A deficiency, and explains keratoplasty and eye banking.
High-yield: Cornea and Corneal Blindness
- A corneal ulcer is an epithelial defect with underlying stromal inflammation and stains green with fluorescein under a cobalt blue light.
- Bacterial keratitis in a contact lens wearer must raise suspicion of Pseudomonas, which causes a rapidly progressive, sight-threatening ulcer.
- A hypopyon is a layer of white cells settled in the anterior chamber and signals a severe, usually infective, keratitis or endophthalmitis.
- Fungal keratitis, often after vegetable-matter trauma, shows a dry ulcer with feathery margins and satellite lesions.
- Acanthamoeba keratitis is associated with contact lens use and water exposure and causes pain out of proportion to the signs with a ring infiltrate.
- Herpes simplex keratitis produces a branching dendritic ulcer, and topical steroids alone are contraindicated because they worsen the infection.
- A corneal scar is graded as nebula (faint), macula (moderate) or leucoma (dense white), which determines the visual impact.
- The corneal endothelium keeps the stroma dehydrated by its pump, so endothelial failure or a high intraocular pressure produces corneal oedema.
- Dry eye disease is tear-film instability with ocular surface inflammation and is assessed with tear break-up time and Schirmer's test.
- Vitamin A deficiency causes xerophthalmia, with Bitot's spots, corneal xerosis and, in the extreme, keratomalacia that melts the cornea.
- Keratoplasty may be optical to restore vision, therapeutic to control infection, or tectonic to restore integrity, and the corneal graft is uniquely favoured by the avascular, immune-privileged recipient bed.
- Corneal blindness is largely preventable, with ulceration, trauma, vitamin A deficiency and infection as leading causes.
- A tarsorrhaphy protects an exposed cornea, for example in facial nerve palsy with poor lid closure, by narrowing the palpebral aperture.
- Eye donation supplies corneal transplantation; eye banks screen donors and exclude tissue from those with rabies, septicaemia, leukaemia and certain viral infections.
Infective keratitis clues
- **Bacterial (Pseudomonas):** Contact lens wear, rapid progression, dense infiltrate, hypopyon.
- **Fungal:** Vegetable-matter trauma, dry ulcer, feathery margins, satellite lesions.
- **Herpes simplex:** Dendritic ulcer, reduced corneal sensation. Steroids alone contraindicated.
- **Acanthamoeba:** Contact lens and water exposure, severe pain, ring infiltrate.
NMC competencies in this chapter
- **OP4.1:** Corneal ulceration
- **OP4.2:** Infective keratitis differential diagnosis
- **OP4.3:** Corneal oedema
- **OP4.4:** Dry eye disease
- **OP4.5:** Corneal blindness and its prevention
- **OP4.6:** Keratoplasty
- **OP4.7:** Tarsorrhaphy
- **OP4.9:** Eye donation and eye banking
Frequently Asked Questions
How is a corneal ulcer diagnosed at the bedside?
By staining the cornea with fluorescein under a cobalt blue light: an epithelial defect stains bright green. A corneal scraping for microscopy and culture identifies the causative organism before starting targeted treatment.
Why are steroids dangerous in herpetic keratitis?
Topical steroids alone suppress local immunity and allow herpes simplex virus to replicate, worsening the dendritic ulcer and risking deeper stromal damage. Antiviral cover is needed first.
Why is the cornea an ideal tissue for transplantation?
The cornea is avascular and the recipient bed is relatively immune-privileged, so corneal grafts have a high success rate without systemic immunosuppression, unlike vascularised organ transplants.
How does vitamin A deficiency affect the eye?
It causes xerophthalmia with night blindness, Bitot's spots and corneal xerosis, and in severe deficiency keratomalacia, a melting of the cornea that is a major preventable cause of childhood blindness.
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