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Keratoconus Management and Contact Lens
Cornea
1. Clinical Analogy & Overview
Exam pearl
- Clinical Analogy: Think of the normal cornea as a perfectly tensioned trampoline - uniform collagen weave providing symmetric curvature. Keratoconus is what happens when some of the cross-links in that trampoline fabric progressively fail: the weakened zone bulges forward under intraocular pressure, thinning and steepening asymmetrically. Like a trampoline with a worn patch, it deforms most where the structural integrity is lowest - the inferior-central cornea.
- Keratoconus (KC) is a bilateral, asymmetric, progressive, non-inflammatory ectatic disorder of the cornea characterised by paracentral thinning, anterior protrusion, and irregular myopic astigmatism leading to progressive visual deterioration. It is the most common primary corneal ectasia worldwide, with an estimated prevalence of 1:2000 in the general population.
| Parameter | Detail |
|---|---|
| Prevalence | 1:2000 general; up to 1:500 in South Asian populations |
| Onset | Puberty (10-25 years); progression halts ~4th decade |
| Sex | Slight male predominance (M:F = 1.5:1) |
| Laterality | Bilateral ~97%; highly asymmetric; fellow eye subclinical in 50% |
| Genetics | most commonly autosomal dominant with variable penetrance; also reported as autosomal recessive and multifactorial; VSX1, SOD1, LOX gene mutations implicated |
| Associations | Atopy, Down syndrome, Leber congenital amaurosis, eye rubbing, contact lens wear, Marfan syndrome, mitral valve prolapse |
| Parameter | Detail |
|---|---|
| Prevalence | 1:2000 general; up to 1:500 in South Asian populations |
| Onset | Puberty (10-25 years); progression halts ~4th decade |
| Sex | Slight male predominance (M:F = 1.5:1) |
| Laterality | Bilateral ~97%; highly asymmetric; fellow eye subclinical in 50% |
| Genetics | most commonly autosomal dominant with variable penetrance; also reported as autosomal recessive and multifactorial; VSX1, SOD1, LOX gene mutations implicated |
| Associations | Atopy, Down syndrome, Leber congenital amaurosis, eye rubbing, contact lens wear, Marfan syndrome, mitral valve prolapse |
2. Pathophysiology
Molecular Basis
- Collagen degradation: Collagen degradation: Elevated matrix metalloproteinases (MMP-1, MMP-9) degrade stromal collagen. Concurrent decrease in TIMP (tissue inhibitor of metalloproteinases) shifts the MMP:TIMP balance toward destruction.
- Oxidative stress: Oxidative stress: Reduced catalase and SOD-1 activity → accumulation of reactive oxygen species (ROS) → keratocyte apoptosis → stromal thinning.
- Collagen cross-linking deficit: Collagen cross-linking deficit: Reduced lysyl oxidase activity → impaired pyridinoline cross-link formation between collagen fibrils → biomechanical weakening.
- Epithelial role: Epithelial role: Keratoconus epithelium shows disrupted hemidesmosomes, increased IL-1, TNF-α; epithelial cytokines drive underlying keratocyte apoptosis in a feed-forward loop.
- Structural consequence: Structural consequence: Bowman's layer ruptures → scar formation → progressive ectasia. Collagen lamellae slip and delaminate (reduced inter-lamellar cohesion).
Histopathology
| Layer | Histopathological Finding |
|---|---|
| Epithelium | Iron deposition (Fleischer ring); irregular thickness; disrupted BM |
| Bowman's Layer | Fragmentation, breaks, and scarring (PATHOGNOMONIC) |
| Stroma | Thinning, collagen fibril disorganisation, reduced fibril diameter, keratocyte loss |
| Descemet's Membrane | Folds and rupture in acute hydrops → endothelial gap → aqueous influx |
| Endothelium | Polymegethism, pleomorphism in advanced cases |
| Layer | Histopathological Finding |
|---|---|
| Epithelium | Iron deposition (Fleischer ring); irregular thickness; disrupted BM |
| Bowman's Layer | Fragmentation, breaks, and scarring (PATHOGNOMONIC) |
| Stroma | Thinning, collagen fibril disorganisation, reduced fibril diameter, keratocyte loss |
| Descemet's Membrane | Folds and rupture in acute hydrops → endothelial gap → aqueous influx |
| Endothelium | Polymegethism, pleomorphism in advanced cases |
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Keep reading Keratoconus Management and Contact Lens
13 more sections are included with the Clinical plan.
- Clinical Features
- Investigations & Grading Systems
- Contact Lens Options in Keratoconus
- Corneal Crosslinking (CXL)
- Intrastromal Corneal Ring Segments (ICRS)
- Phakic IOL in Keratoconus