Am I a Candidate for LASIK? What the Assessment Involves

Laser vision correction is one of the most commonly performed elective surgical procedures worldwide, with an excellent safety record in appropriately selected patients. The key phrase is appropriately selected. A thorough pre-operative assessment is essential — and occasionally results in a recommendation not to proceed with LASIK, or to consider an alternative procedure.

Why Patient Selection Matters

The complications most feared in refractive surgery — including post-LASIK ectasia, where the cornea progressively bulges after treatment — are almost always preventable with rigorous pre-operative screening. Modern assessment technology allows us to detect subtle corneal shape abnormalities that would not have been visible a decade ago.

Spending time getting the assessment right is in the patient's best interest. A well-selected patient has an extremely high probability of an excellent outcome.

Key Factors in LASIK Candidacy

1. Age and Prescription Stability

The prescription must be stable for at least 12 months — typically two successive refractions showing no change — before LASIK is performed. Operating on a prescription that is still changing leads to regression and dissatisfaction. Most surgeons prefer to treat patients aged 21 or older; myopia often stabilises in the early-to-mid twenties.

For patients over approximately 45, the natural loss of accommodation (presbyopia) means that achieving excellent uncorrected distance vision will come at the cost of near vision without reading glasses. This tradeoff must be explicitly discussed.

2. Corneal Topography and Tomography

This is the most critical part of the assessment. Corneal topography maps the curvature of the corneal surface; tomography adds a measurement of the posterior (back) surface and corneal thickness at all points.

We are looking for:

• A normal, regular corneal shape
• Absence of keratoconus or forme fruste (subclinical) keratoconus
• Adequate and even corneal thickness
• Normal posterior corneal elevation

Irregular topography patterns, even in the absence of symptoms, may indicate an underlying ectatic tendency that contraindicates LASIK.

3. Corneal Thickness

Average corneal thickness is approximately 540 microns. The minimum safe residual stromal bed thickness after LASIK (flap creation + ablation) is generally 250–300 microns, depending on surgeon preference and risk tolerance.

A simple calculation: if your cornea is 500 microns thick, a standard 110-micron flap leaves 390 microns. Treating -4.00 dioptres of myopia removes approximately 55–65 microns. Residual bed = approximately 325–335 microns — safely above the threshold.

For thinner corneas or higher prescriptions, the arithmetic may not work — in which case PRK (no flap, therefore more tissue preserved in the ablation zone) may be the safer alternative.

4. Dry Eye

LASIK transects corneal nerves in the flap creation, temporarily impairing the corneal sensation that drives reflex tearing. Pre-existing dry eye disease is significantly worsened post-LASIK and can result in persistent discomfort and blurred vision.

Dry eye is assessed via the Ocular Surface Disease Index questionnaire, slit-lamp examination, and tear film quality measurements. Patients with significant dry eye may be advised to undertake dry eye treatment before surgery, or may be better served by PRK (which causes less severe dry eye) or an alternative procedure.

5. Pupil Size

In mesopic (dim light) conditions, the pupil may dilate larger than the optical treatment zone of the laser — particularly with older laser platforms. This can cause halos and glare at night. Modern lasers with larger treatment zones have largely mitigated this concern, but large pupils in dim light remain a factor for patients with demanding night vision requirements (pilots, shift workers, etc.).

LASIK vs PRK

Some patients who are not candidates for LASIK are suitable for PRK (photorefractive keratectomy). PRK uses the same excimer laser to reshape the cornea, but without a flap — the surface epithelium is removed and the stroma is treated directly. PRK:

• Eliminates the risk of flap-related complications
• Is preferred for thin corneas and for contact sport participants
• Has equivalent long-term visual outcomes to LASIK
• Involves a longer recovery — approximately 5–7 days of surface discomfort while the epithelium regenerates, and 2–4 weeks to functional vision rather than the 24–48 hours typical of LASIK

The Consultation

A LASIK consultation at Northern Eye Consultants involves a comprehensive assessment as described above. Results are reviewed in detail and a recommendation is made — including whether LASIK, PRK, refractive lens exchange, or no intervention is most appropriate for your situation.

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Dr Ross MacIntyre performs LASIK, PRK and refractive assessments at Northern Eye Consultants, Bundoora. Book a refractive assessment →