Keratoconus

👁️‍🗨️ Keratoconus

🔍 Definition

Keratoconus is a progressive, non-inflammatory thinning and ectasia (bulging) of the cornea, leading it to assume a conical shape, which results in irregular astigmatism and impaired vision.

🧠 "Keratoconus" literally means cone-shaped cornea.

 

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🧬 Pathophysiology

• Progressive thinning of the central or paracentral cornea

• Leads to forward bulging and cone-shaped protrusion

• Causes irregular astigmatism → distorted and blurry vision

• Often bilateral but asymmetric

🔧 Underlying Mechanism

• Defective collagen structure or enzymes

• Leads to weakening of stromal lamellae

• Often associated with increased oxidative stress

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📊 Epidemiology

Feature	Detail
Onset	Usually puberty to early 20s
Gender	Slight male predominance
Progression	Slowly progressive, may stabilize by 30s
Prevalence	~1 in 2,000 (varies by population)

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🧪 Risk Factors

• Genetic predisposition (family history)

• Eye rubbing (strongest environmental factor)

• Atopy: allergies, asthma, eczema

• Connective tissue disorders: Marfan, Ehlers-Danlos

• Down syndrome

• Leber’s congenital amaurosis

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👀 Symptoms

Symptom	Notes
Blurry or distorted vision	Due to irregular astigmatism
Increased light sensitivity	Especially to glare or halos
Frequent eyeglass changes	Progressive refractive error
Monocular diplopia	Double vision in one eye
Difficulty seeing at night	Early sign

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🔬 Signs on Examination

Sign	Detail
Scissoring reflex	On retinoscopy due to irregular cornea
Oil droplet reflex	Bright red reflex in the pupil (ophthalmoscopy)
Fleischer ring	Iron deposits around cone base (seen on slit lamp)
Vogt’s striae	Fine vertical stress lines in deep stroma
Munson’s sign	V-shaped indentation of lower lid on downgaze (advanced)
Corneal thinning	Most pronounced at apex of cone

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🧪 Diagnosis

🔹 Corneal Topography (Gold Standard)

• Detects early irregular astigmatism

• Maps the cone and curvature

• Shows inferior steepening and asymmetry

🔹 Pachymetry

• Measures corneal thickness

• Thinning at apex of the cone

🔹 Pentacam / Scheimpflug Imaging

• 3D imaging of the anterior segment

• Detects posterior corneal elevation (early sign)

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🔄 Progression Stages (Amsler-Krumeich Classification)

Stage	Key Features
Stage 1	Mild astigmatism, normal vision with glasses
Stage 2	Irregular astigmatism, decreased BCVA
Stage 3	Thinning <450 μm, visual distortion
Stage 4	Severe scarring, very thin cornea, corneal opacity

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💊 Management

🧼 Early / Mild Disease

Option	Purpose
Glasses	For mild astigmatism
Soft toric lenses	For low-grade irregular astigmatism

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🧴 Moderate Disease

Option	Purpose
Rigid Gas Permeable (RGP) lenses	Improve visual acuity by reshaping tear film
Hybrid lenses	Soft skirt + RGP center (more comfortable)
Scleral lenses	Vault over cornea, excellent vision & comfort

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🔬 Corneal Collagen Cross-Linking (CXL)

• First-line to halt progression

• Uses riboflavin (vitamin B2) drops + UV-A light

• Strengthens collagen bonds in stroma

• Ideal in progressive keratoconus, especially <35 years old

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🔧 Advanced Disease

Treatment	Notes
Intracorneal Ring Segments (ICRS)	Implanted to flatten cone and improve shape
Corneal transplant (PK or DALK)	Reserved for cases with scarring or failure of lenses

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⚠️ Complications

• Corneal hydrops: Acute rupture of Descemet’s membrane → edema, pain, sudden vision drop

• Corneal scarring

• Progressive vision loss

• Social/psychological impact in teens/young adults

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🧠 Mnemonic: "KERA"

• Kone-shaped cornea

• Ectasia + thinning

• RGP lenses help early

• Advanced cases → cross-linking, rings, or graft

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📌 Patient Tips

• Avoid rubbing eyes

• Wear protective eyewear (especially with sports)

• Regular follow-ups for topography

• Early detection in family members

• Educate about cross-linking before vision loss

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Would you like:

• A visual diagram of corneal shape changes in keratoconus?

• A patient handout version for education?

• Or a quick revision flashcard summary?