Keratoconus: Symptoms, Diagnosis, and Why It Disqualifies LASIK

What Is Keratoconus?

Keratoconus is a progressive, non-inflammatory corneal ectasia (weakening and bulging) in which the normally dome-shaped cornea progressively thins and protrudes forward into a cone-like shape. The altered corneal geometry creates highly irregular astigmatism and forward displacement of the optical center, causing significantly distorted vision that cannot be fully corrected with standard glasses. The word "keratoconus" derives from the Greek for "cone-shaped cornea."

Keratoconus affects approximately 1 in 2,000 people, typically beginning in the late teens to early 20s. It is bilateral in most cases, though often asymmetric. The condition is associated with a history of eye rubbing (which may accelerate progression), atopic disease, and connective tissue disorders. There is a strong genetic component — first-degree relatives of keratoconus patients have significantly higher rates of the condition.

Symptoms and Vision Effects

Keratoconus symptoms evolve as the disease progresses:

• Progressive myopia that changes frequently and cannot be corrected to normal acuity
• Irregular astigmatism — glasses correction that seems "off" even when technically accurate
• Multiple images, ghost images, or monocular diplopia (seeing double with one eye)
• Halos, glare, and starbursts around lights
• Photophobia and eye rubbing
• Frequent prescription changes — a history of rapidly changing glasses prescription is a red flag for keratoconus screening

Diagnosis: Corneal Topography and Pentacam

Keratoconus diagnosis relies on corneal topography and tomography:

• Corneal topography (Placido disk): shows characteristic inferior steepening pattern with "crab claw" or "skewed axes" appearance; detects surface irregularities
• Pentacam / Scheimpflug tomography: measures anterior and posterior corneal elevation, pachymetry map, and Belin-Ambrósio deviation score; detects posterior surface changes that topography alone misses and identifies forme fruste keratoconus
• Aberrometry: shows large irregular higher-order aberrations, especially coma

These tests are performed as part of every thorough LASIK pre-operative evaluation, specifically to screen for keratoconus that would contraindicate surgery.

Disease Progression

Keratoconus progression varies widely. Some patients remain stable for years; others progress rapidly. Progression is more common in younger patients (under 30) and those with a history of eye rubbing or atopy. Corneal crosslinking (CXL) is the only proven intervention to halt keratoconus progression by stiffening the corneal collagen. Early CXL (before vision-threatening cone formation) preserves the best long-term prognosis.

Why LASIK Is Absolutely Contraindicated in Keratoconus

LASIK removes corneal stromal tissue to reduce corneal thickness and change its curvature. A keratoconus cornea is already abnormally thin and structurally weak in the apex region. Removing additional tissue from an already compromised cornea dramatically accelerates ectatic progression — the cornea weakens further, bulges more severely, and vision deteriorates rapidly. This outcome (iatrogenic ectasia — ectasia caused by the surgery) can be devastating and may eventually require corneal transplantation.

Even patients with very mild, early keratoconus detected only on topography screening (and not yet causing visual symptoms) are at high risk for accelerated ectasia after LASIK. This is why corneal topography screening is mandatory in any responsible LASIK pre-operative evaluation, and why detecting even subclinical keratoconus is grounds for declining LASIK. See LASIK disqualifying conditions.

Forme Fruste Keratoconus

Forme fruste keratoconus refers to very early, subclinical keratoconus detectable on topography or tomography but not yet causing measurable vision symptoms or correction requirements. It represents the "frustrated" form of the disease — present but not yet fully expressed. Pentacam elevation maps and Belin-Ambrósio scoring can identify these patients even when traditional topography appears borderline. Forme fruste keratoconus is considered an absolute contraindication to LASIK at most responsible centers, though some expert centers perform LASIK + simultaneous crosslinking in very carefully selected cases.

Treatment Alternatives for Keratoconus Patients

Treatment	Purpose	Stage
Corneal collagen crosslinking (CXL)	Halt progression	Progressive keratoconus
Scleral contact lenses	Optical correction of irregular astigmatism	All stages
Rigid gas permeable lenses	Optical correction	Mild to moderate
Toric soft lenses	Partial correction	Very mild only
ICL (phakic IOL)	Reduce spectacle dependence	Stable cases with sufficient corneal thickness
Penetrating keratoplasty (corneal transplant)	Replace cornea	Advanced, contact lens intolerant
DALK (deep anterior lamellar keratoplasty)	Replace stroma, preserve endothelium	Advanced, preferred over PK