Laser Refractive Surgery:

From One Medical Student to Another

4. LASIK and PRK

There are two main surgical techniques used to performlaser vision correction: LASIK and PRK. The major difference between these surgeries is the way in which access is gained to the anterior corneal stroma. In LASIK, a 100-200 µm corneal flap is created using a microkeratome (blade) or femtosecond laser (Sakimoto et al. 2006). In PRK, access to the stroma is gained by removing the epithelium of the cornea mechanically (by a brush or blade), chemically (i.e. with alcohol), or by laser (AAO 2007). After stroma is exposed (either by making a flap (LASIK) or by removing the epithelium (PRK)), the patient is asked to fixate on a central light. An eye-tracker is engaged to adjust for any eye movements during the ablation, and a pre-programmed excimer ablation, based on the patient's preoperative refractive error, is performed in seconds to minutes.

Patients are typically given an anxiolytic (i.e. diazepam) prior to surgery to help them relax during the procedure. To decrease infection risk and inflammation, patients generally are treated with an antibiotic drop and steroid drop for about one month after surgery. The patient is examined postoperatively at the following intervals: post-op day 1, 1 week, 1 month, 3 months, 6 months, and 1 year. Illustrations of these surgeries can be seen in Figure 5 and Figure 6.

Figure 5. LASIK: A femtosecond laser creates a flap with a hinge. The flap is lifted and the excimer laser sculpts the stroma. The flap is replaced and adheres on its own without sutures. Vision typically improves within 24 hours, and there is minimal post-operative pain.

Table 3. LASIK vs. PRK (AAO 2007)

Item	LASIK	PRK
Initial examination	Similar to PRK	Similar to LASIK
Procedural difference	Corneal flap made with a microkeratome or femtosecond laser	Surface epithelium removed by a variety of methods (blade, alcohol, brush, or laser)
Excimer laser procedure	Similar to PRK	Similar to LASIK
Postoperative discomfort	Usually minimal	Significant pain for the first several days postoperatively. Patients are given narcotics to control the postoperative pain.
Visual recovery	Starts improving at one day	Starts to improve over the first week, but continues to improve over the first month and may take up to 3 months to achieve the final postoperative visual acuity.
Possible Complications	Glare/halo/ghosting Residual refractive error Corneal flap problems	Glare/halo/ghosting Residual refractive error Corneal haze

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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. EyeRounds.org. November 29, 2011; Available from: EyeRounds.org/ tutorialsLaser-Vision-Correction-tutorial/

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• Introduction
• Anatomy
• Pre-op Examination
• LASIK and PRK
• Complications
• Web Resources
• References

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