Reflections on refractive surgery

Chennai: Refractive surgery is a surgical procedure performed to correct the refractive error (spectacle power) of the eye. It is usually done to get rid of or reduce dependence on glasses and contact lenses.

It can be performed in a patient with stable refraction (glass power) after the age of 18-21 years. Complete medical history along with detailed eye examination is mandatory in all candidates, special Investigations like corneal topography, Anterior Segment Optical Coherence Tomography (ASOCT) are performed to evaluate the shape, thickness and curvature of the cornea and other dimensions of the eye.

According to Dr Ramya S, senior consultant, ophthalmologist, Dr Agarwal’s Eye Hospital, Chennai, after acquiring all the details, the eye surgeon makes a decision regarding the available options of refractive surgery for the patient.

The current refractive procedures can be classified as corneal procedures and lens based surgery, she says and adds corneal procedures include laser assisted power correction and this can be further divided as three types.

PRK (Photorefractive Keratectomy): This procedure involves careful removal of the top most layer of the cornea also known as epithelium, this is followed by Excimer laser (wavelength 193 nm) delivery which reshapes the corneal surface – to correct the refractive power of the eye. A contact lens is placed for a few days to support the healing of the eye, the epithelium is very thin (50 microns) and usually grows back within three days.

LASIK (Flap Based Procedure): This is a very popular procedure and involves creation of a flap (100-120 micron) in the superficial layer of the cornea. This flap can be created by two methods.

Refractive Lenticule Extraction: This is the most advanced refractive surgery and requires only Femtosecond laser (the same laser as described in FEMTO-LASIK. Refractive power of the eye is corrected by using femtosecond laser to create a lenticule (of predetermined size and thickness) within the layers of the cornea.This lenticule can then be extracted in two ways