University of Iowa Health Care

Ophthalmology and Visual Sciences

Laser Refractive Surgery:

From One Medical Student to Another

3. Pre-op Examination

(Sakimoto et al. 2006, AAO 2007)

Since laser vision correction is an elective procedure, selection of the appropriate surgical candidates is paramount. Preoperative assessment begins with obtaining the patient's ophthalmic history and general medical history. Important aspects of the medical history to ask about are listed in Table 1.

Table 1.
Patient History /
Active Ocular Infection or Intra-ocular Inflammation
Significance /

History of Herpes Simplex Keratitis

A possible contraindication since application of the laser can potentially reactivate the herpes simplex virus


A suction ring is used to hold the eye in place and elevates the intraocular pressure. However, patients with well-controlled glaucoma may be candidates.


Contraindication due to unpredictable results


Ocular trauma can cause LASIK flap dislocation. Patients who are at higher risk for eye injuries, such as patients who play contact sports, should consider PRK instead of LASIK.


Should be stable for 1 year prior to surgery. Patients under the age of 21 should wait, as their refraction may not be stable.


Certain medications can affect the cornea and are contraindicated for laser vision correction. (e.g., isotretinoin, amiodarone, sumatriptan)

Pregnant or Nursing

Women who are pregnant or nursing may have unstable refractions. Laser vision correction should be postponed until after pregnancy or for several months after nursing.

Patient Expectations

Patients with unrealistic expectations are not good candidates for refractive surgery.

Systemic Immunologic Disorders

Patients with systemic autoimmune disease, such as rheumatoid arthritis or systemic lupus erythematosus, are at risk for poor wound healing.

A comprehensive eye exam should be performed. This should include a manifest and cycloplegic refraction, corneal topography, pachymetry, slit-lamp examination of the anterior segment, measurement of intraocular pressure, assessment for dry eye syndrome, and a dilated fundus examination (Table 2). Before the assessment, patients who wear contacts should not wear their contact lenses for at least 2 weeks (for soft contact lenses) or 4 weeks (for rigid gas permeable contact lens wearers). A contact lens holiday is necessary because contact lenses can warp or alter the shape of the cornea.

Table 2.



Visual Acuity and Refraction

An accurate and stable preoperative refraction is important in determining if a patient is eligible for refractive surgery. Patients with a high amount of refractive error may not be good candidates for refractive surgery. Cycloplegic refraction eliminates the ability to accommodate yielding a more accurate refraction.

Corneal Topography

Laser vision correction is contraindicated in patients with irregular astigmatism and ectasia (bulging of the cornea, such as keratoconus) because these conditions may result in unpredictable refractive outcomes and worsening ectasia.


Pachymetry is the measurement of corneal thickness. Laser vision correction reshapes the cornea by removing stroma. Only a certain amount of stromal tissue can be safely removed to ensure that the cornea remains stable in shape. Insufficient corneal thickness for the proposed ablation depth is a contraindication to laser vision correction.


Pupil size is measured under dim and bright light. Although this is controversial, some surgeons attempt to make the treatment diameter greater than the largest pupil size to help prevent post-op glare and halos.

Assessment for Dry Eye Syndrome

Dry eye syndrome is a common post-operative complication after laser vision correction. Dry eye syndrome should be treated and controlled before laser vision correction. There are various methods to clinically detect dry eye syndrome, including Schirmer's tear production test.

Back | Next

last updated: 11/29/2011

Written by Reid Turner

Illustrated by Steve McGaughey

Faculty supervision and review by Anna Kitzmann, MD

Turner R, McGaughey S, Kitzmann A. Laser Vision Correction: From one Medical student to another. November 29, 2011; Available from: tutorialsLaser-Vision-Correction-tutorial/

Share this page: