Diseases of the Cornea

Diseases of the Cornea Indian Medical PG Question 1: Corneal vascularization is caused by which of the following?

• A. Graft rejection
• B. Chemical burn
• C. Contact lens use
• D. All of the above (Correct Answer)

Diseases of the Cornea Explanation: **Explanation:** Corneal vascularization (neovascularization) is a pathological condition where new blood vessels grow into the normally avascular cornea. This occurs when the balance between angiogenic factors (like VEGF) and anti-angiogenic factors is disrupted, usually due to inflammation, hypoxia, or limbal stem cell deficiency. **Analysis of Options:** * **Graft Rejection (Option A):** This is an inflammatory immune response. Neovascularization is both a risk factor for and a sign of corneal graft rejection. Vessels provide a pathway for immune cells to reach the donor tissue, leading to an "immune attack." * **Chemical Burn (Option B):** Alkali burns are particularly notorious. They cause extensive limbal stem cell damage and severe inflammation. The loss of the limbal barrier allows conjunctival vessels to encroach upon the cornea (conjunctivalization). * **Contact Lens Use (Option C):** Chronic use, especially with low-permeability lenses or overwear, leads to **corneal hypoxia**. The lack of oxygen triggers the release of vasoproliferative factors, causing superficial or deep stromal vessels to grow from the limbus. Since all three conditions are well-established causes of corneal neovascularization, **Option D** is the correct answer. **High-Yield Clinical Pearls for NEET-PG:** * **Pannus:** This refers to superficial vascularization accompanied by infiltration of granulation tissue (commonly seen in Trachoma and Phlyctenular keratoconjunctivitis). * **Micropannus:** Defined as vessel growth <2mm beyond the limbus (common in Trachoma). * **Ghost Vessels:** These are non-perfused, empty vascular channels that remain after the inciting inflammatory stimulus has subsided (classic in interstitial keratitis/Syphilis). * **Management:** Topical steroids or NSAIDs are used to reduce inflammation; anti-VEGF agents (e.g., Bevacizumab) are emerging treatments.

Diseases of the Cornea Indian Medical PG Question 2: Which of the following will be the most important adjuvant therapy in a case of fungal corneal ulcer?

• A. Atropine sulphate eye ointment (Correct Answer)
• B. Dexamethasone eye drops
• C. Pilocarpine eye drops
• D. Lignocaine eye drops

Diseases of the Cornea Explanation: ### Explanation In the management of a fungal corneal ulcer, **Atropine sulphate (1%) eye ointment** is the most critical adjuvant therapy alongside antifungal agents. **Why Atropine is the Correct Choice:** Fungal keratitis is almost always associated with **secondary anterior uveitis** and **iridocyclitis** due to the penetration of fungal toxins into the anterior chamber. Atropine acts as a potent **cycloplegic and mydriatic**, serving three vital functions: 1. **Relieves Ciliary Spasm:** It reduces the intense pain associated with the spasm of the ciliary body. 2. **Prevents Posterior Synechiae:** By keeping the pupil dilated, it prevents the iris from adhering to the lens. 3. **Increases Blood Supply:** By reducing congestion in the ciliary body, it improves ocular blood flow, which aids in the healing process. **Analysis of Incorrect Options:** * **B. Dexamethasone eye drops:** Steroids are strictly **contraindicated** in active fungal ulcers. They promote fungal growth, inhibit collagen synthesis (leading to perforation), and suppress the local immune response. * **C. Pilocarpine eye drops:** This is a miotic. It would worsen the pain by causing ciliary muscle contraction and increase the risk of forming small, fixed pupils (annular synechiae). * **D. Lignocaine eye drops:** While a local anesthetic, it is toxic to the corneal epithelium and inhibits wound healing. It should never be used for long-term pain management in ulcers. **Clinical Pearls for NEET-PG:** * **Drug of Choice (Medical):** Topical **Natamycin (5%)** is the first-line treatment for filamentous fungi (e.g., *Aspergillus*, *Fusarium*). * **The "Immune Ring":** Wessely’s ring (an immune ring of Ag-Ab complex) is often seen in fungal ulcers. * **Surgical Intervention:** If medical therapy fails or perforation is imminent, a **therapeutic penetrating keratoplasty (TPK)** is indicated.

Diseases of the Cornea Indian Medical PG Question 3: In microcornea, the diameter of the cornea is less than:

• A. 9 mm
• B. 10 mm (Correct Answer)
• C. 11 mm
• D. 8 mm

Diseases of the Cornea Explanation: **Explanation:** **Microcornea** is a congenital anomaly where the cornea is abnormally small but otherwise anatomically normal in structure and thickness. 1. **Why Option B is correct:** The standard clinical definition of microcornea is a horizontal corneal diameter of **less than 10 mm** in an adult, or **less than 9 mm** in a newborn. Since the question refers to the general diagnostic threshold, 10 mm is the established benchmark. The condition occurs due to an arrest in the growth of the cornea after the 5th month of gestation, while the rest of the eye may grow normally. 2. **Why other options are incorrect:** * **Option A (9 mm):** This is the threshold for a **newborn**. In an adult, a 9 mm cornea is already well within the range of microcornea. * **Option C (11 mm):** The average adult corneal diameter is approximately 11.5 to 12 mm. A diameter of 11 mm is considered a "small-normal" cornea but does not meet the pathological criteria for microcornea. * **Option D (8 mm):** While an 8 mm cornea is indeed microcorneal, it is not the *threshold* definition. 10 mm is the upper limit for the diagnosis. **High-Yield Clinical Pearls for NEET-PG:** * **Refractive Status:** Microcornea usually results in **hypermetropia** (flat cornea) and predisposes the patient to **closed-angle glaucoma** due to a crowded anterior segment. * **Associations:** It can occur in an otherwise normal eye (isolated) or as part of **Microphthalmos** (small globe). * **Systemic Associations:** Often linked with **Fetal Alcohol Syndrome**, Turner syndrome, and Ehlers-Danlos syndrome. * **Contrast with Megalocornea:** Megalocornea is defined as a horizontal diameter **>13 mm**.

Diseases of the Cornea Indian Medical PG Question 4: Which of the following is NOT a sign of graft rejection?

• A. Krachmer spots
• B. Khodadoust line
• C. Oedema
• D. Foster spot (Correct Answer)

Diseases of the Cornea Explanation: **Explanation:** The correct answer is **Foster spot** because it is a clinical feature of **Pathological Myopia**, not corneal graft rejection. A Foster-Fuchs spot is a pigmented, circular lesion in the macula caused by subretinal neovascularization and subsequent scarring/hemorrhage. **Understanding Graft Rejection Signs:** Corneal graft rejection is an immunological response (Type IV hypersensitivity) against the donor tissue. It can involve different layers of the cornea: * **Krachmer spots (Option A):** These are subepithelial infiltrates seen in **stromal rejection**. They represent a localized inflammatory response and are similar in appearance to the infiltrates seen in epidemic keratoconjunctivitis. * **Khodadoust line (Option B):** This is the hallmark sign of **endothelial rejection**. It is a linear precipitate of lymphocytes (keratic precipitates) on the endothelium that moves across the graft, destroying endothelial cells and leading to graft failure. * **Oedema (Option C):** Corneal edema (thickening and loss of clarity) is a primary sign of **endothelial rejection**. When the pump function of the endothelium is compromised by the immune attack, the stroma becomes hydrated. **High-Yield Clinical Pearls for NEET-PG:** * **Wessely Ring:** An immune ring in the corneal stroma (antigen-antibody complex) often seen in viral keratitis or graft rejection. * **Timeframe:** Graft rejection typically occurs at least 2 weeks after surgery (sensitization period). * **Management:** The mainstay of treatment is intensive **topical corticosteroids** (e.g., Prednisolone acetate 1%). * **Epithelial Rejection:** Characterized by an elevated epithelial line (rejection line) that stains with fluorescein.

Diseases of the Cornea Indian Medical PG Question 5: Corneal endothelial cell counting is performed using which instrument?

• A. Tachymetry
• B. Pachymetry
• C. Specular microscope (Correct Answer)
• D. Perimetry

Diseases of the Cornea Explanation: ### Explanation **Correct Answer: C. Specular microscope** The **corneal endothelium** is a single layer of non-regenerating hexagonal cells responsible for maintaining corneal dehydration (deturgescence) via an active Na+/K+ ATPase pump. **Specular microscopy** is a non-invasive photographic technique that allows for the visualization and analysis of these cells. It provides critical data including: * **Endothelial Cell Density (ECD):** Normal adult count is 2000–3000 cells/mm². * **Polymegathism:** Variation in cell size (Coefficient of Variation). * **Pleomorphism:** Variation in cell shape (Percentage of hexagonality). **Analysis of Incorrect Options:** * **A. Tachymetry:** This is a distractor term. In general engineering, it refers to distance measurement, but it has no standard application in clinical ophthalmology. * **B. Pachymetry:** This instrument measures **corneal thickness**. While thickness is an indirect indicator of endothelial function (as a failing pump leads to edema/thickening), it does not count individual cells. * **D. Perimetry:** This is used for mapping the **visual field** (e.g., Humphrey Field Analyzer), primarily used in the diagnosis and management of glaucoma and neurological visual defects. **High-Yield Clinical Pearls for NEET-PG:** * **Critical Threshold:** If the endothelial cell count falls below **500 cells/mm²**, the cornea loses its ability to remain clear, leading to corneal edema and bullous keratopathy. * **Guttata:** Specular microscopy shows these as "dark spots" or "holes" in the endothelial pattern, characteristic of **Fuchs' Endothelial Dystrophy**. * **Surgical Clearance:** Specular microscopy is mandatory before certain procedures like ICL (Implantable Collamer Lens) implantation to ensure the endothelium is healthy enough to tolerate the intraocular surgery.

Diseases of the Cornea Flashcard 1 of 5

Question: Which stain is used to identify granular dystrophy of the cornea? _____

Answer: Masson's trichrome

Diseases of the Cornea Flashcard 2 of 5

Question: The following result on Placido disk test will be seen in _____

Answer: keratoconus

Diseases of the Cornea Flashcard 3 of 5

Question: The following result on Placido disk test will be seen in _____

Answer: corneal astigmatism

Diseases of the Cornea Flashcard 4 of 5

Question: Causes of interstitial keratitis: (Think granulomatous diseases, protozoal, mycobacterial) _____

Answer:

Diseases of the Cornea Flashcard 5 of 5

Question: Corneal thickness is best measured by a _____

Answer: pachymeter