What is Keratoconus?

Keratoconus is a progressive, non-inflammatory disorder of the cornea in which the central or inferior cornea progressively thins and bulges forward into a cone shape. The change in corneal shape produces a high degree of irregular astigmatism, distortion of the image entering the eye, and a steady reduction in vision that cannot be fully corrected with ordinary spectacles. It typically begins in the late teens or early twenties, progresses through the third decade and may stabilise thereafter — though the rate of progression and the severity vary widely between patients and even between the two eyes of the same patient.

Keratoconus is among the most common causes of visual impairment in young people in India. Habitual eye-rubbing, atopic disease (asthma, eczema, allergic conjunctivitis), connective tissue disorders and a positive family history are the main associations. Modern imaging — particularly swept-source OCT tomography with the Anterion — allows detection long before any clinical sign is visible at the slit lamp, and modern treatment with corneal collagen crosslinking can halt progression in over 95 % of eyes.

How the Keratoconic Cornea Differs from Normal

The healthy cornea is a smooth, dome-shaped, transparent tissue about 540 µm thick centrally. Its strength comes from approximately 200 lamellae of type I collagen running parallel to the corneal surface. In keratoconus, these collagen lamellae become fragmented, the keratocytes are reduced, and there is loss of structural enzymes such as the lysyl oxidase that normally crosslinks collagen. The result is a cornea that is biomechanically weaker than normal and progressively yields under the constant pressure of the aqueous humour, producing the characteristic apical thinning and conical protrusion shown below.

Symptoms

Keratoconus is initially silent and may be detected only on routine refraction. As the disease progresses, the patient typically notices:

• Frequent change of spectacle prescription — particularly with rapidly increasing astigmatism in one or both eyes during the teenage and early adult years.
• Distorted, smeared or “ghost” images — straight lines appear bent, headlights and street-lamps streak at night, and there are multiple overlapping images (monocular diplopia or polyopia).
• Reduced best-corrected visual acuity in spectacles — even with the most accurate cylinder, vision is no longer sharp.
• Glare, halos and increased sensitivity to bright lights.
• Constant eye-rubbing, often associated with allergy.
• Acute hydrops (rare, in advanced disease) — sudden severe pain and dramatic loss of vision due to a break in Descemet’s membrane and abrupt corneal swelling.

Risk Factors and Associations

Diagnosis — From Slit-Lamp to Anterion

Early keratoconus has no slit-lamp signs and may even have normal acuity in spectacles. Diagnosis depends increasingly on corneal imaging. The cornerstone investigation at Suraj Eye Institute is swept-source OCT tomography with the Anterion, which generates a four-map refractive display of corneal curvature, anterior elevation, posterior elevation and pachymetry. Posterior elevation and the inferior–superior pachymetric asymmetry are the earliest and most specific signs of subclinical keratoconus.

Other diagnostic findings

• Slit-lamp signs: Vogt’s striae (fine vertical lines in the posterior stroma at the cone apex), Fleischer ring (iron deposit at the base of the cone), apical scarring in advanced cases, and Munson’s sign (cone protrusion deforming the lower lid on down-gaze).
• Retinoscopy: Scissoring reflex — pathognomonic and visible in early disease.
• Corneal biomechanics: Corvis ST and Ocular Response Analyzer measure dynamic corneal deformation under an air-puff and identify biomechanical weakness before geometric change.

Staging — The Amsler-Krumeich Classification

Treatment — A Step-Wise Approach

1. Stop the rubbing

The first prescription is behavioural. Patients are counselled to stop eye-rubbing entirely; allergic disease is treated aggressively (topical mast-cell stabilisers, antihistamines and a short course of steroids if needed) so the urge to rub is removed. This single measure can stabilise mild disease.

2. Spectacles and soft contact lenses

For early disease, glasses or soft toric contact lenses give acceptable vision. Once astigmatism becomes irregular, the spherocylindrical correction in spectacles can no longer focus light to a single point and a rigid lens is needed.

3. Specialty contact lenses

Rigid gas-permeable (RGP), Rose K, hybrid (rigid centre / soft skirt) and full-scleral lenses provide the regular optical surface that the keratoconic cornea cannot. Scleral lenses vault the entire cornea and rest on the sclera — they are the workhorse for moderate-to-advanced keratoconus and avoid mechanical trauma to the cone.

4. Corneal Collagen Crosslinking (CXL / C3R)

Crosslinking is the only treatment that halts the disease. Riboflavin (vitamin B2) is instilled onto the cornea after epithelial debridement (the classical “epi-off” Dresden protocol) or through the intact epithelium (“epi-on”). The cornea is then exposed to ultraviolet-A (365 nm) light for 30 minutes (standard) or 10 minutes (accelerated). Riboflavin in the presence of UV-A generates oxygen free radicals that form covalent crosslinks between collagen fibrils, increasing biomechanical stiffness by 300–400 %. Five-year studies show progression is halted in > 95 % of treated eyes, and there is a small flattening of K-max in many patients. CXL is offered to any patient with documented progression on serial Anterion, and proactively to teenagers in whom rapid progression is otherwise the rule.

5. Intracorneal ring segments (ICRS / Intacs)

Synthetic rings implanted in the corneal periphery flatten the central cone and can improve contact lens tolerance and spectacle correction. Best suited to moderate disease with clear central cornea and contact-lens intolerance.

6. Keratoplasty — DALK and PK

Around 10–20 % of patients eventually require corneal transplantation. Deep Anterior Lamellar Keratoplasty (DALK) is the procedure of choice — the patient’s healthy endothelium is retained, eliminating endothelial rejection and giving long graft survival. Penetrating keratoplasty (PK) is reserved for failed DALK, deep central scarring or post-hydrops patients. Both procedures are performed routinely at Suraj Eye Institute.

Prognosis

The visual outlook in keratoconus has been transformed by Anterion screening and crosslinking. The classical natural history — relentless progression to corneal scarring and transplantation — is now uncommon for patients diagnosed in adolescence. With behavioural counselling, allergy control and timely crosslinking, the great majority of patients retain functional vision throughout life with spectacles or specialty contact lenses, and only a minority ultimately need keratoplasty. Late-onset keratoconus (after age 30) and stable late disease may need only optical correction.

Frequently Asked Questions

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