Treating a hyperopic shift after refractive surgery

Abstract

In the article on refractive changes after excimer laser phototherapeutic keratectomy (PTK),1 the authors conducted a commendable study of 112 eyes and reported a mean hyperopic shift of 3.42 diopters (D) ± 1.14 (SD) (range 1.00 to 5.25 D) at 12 months. In addition, nearly 90% of the eyes had an increase in the best corrected visual acuity (BCVA) after PTK. It is important to understand that although PTK will help to clear superficial corneal pathology and improve the BCVA in the affected eye, it will induce a significant hyperopic error and thus lead to a decrease in the uncorrected visual acuity. This could lead to an unacceptable anisometropia, especially if the corneal pathology is unilateral. Thus, many patients may subsequently require contact lenses or a refractive surgical procedure. The hyperopic shift should be dealt with at the time of surgery. This can be done by doing a hyperopic photorefractive keratectomy procedure after the PTK (making a personal nomogram for the amount of ablation performed during PTK and the expected hyperopic shift). The second option is to do an antihyperopia treatment at the end of the PTK procedure. The PTK ablation is performed with a 6.0 mm optical zone as usual. After the PTK is completed, a circular disk of sterile filter paper or a soft contact lens trephined to a diameter of 4.0 mm is placed on the central cornea and an additional 50 to 100 pulses of energy are delivered, keeping the optic zone constant at 6.0 mm. This leads to a 1.0 mm peripheral annulus of treatment, which helps to undo the hyperopic shift induced by PTK. Another (less accurate) option is to use methylcellulose 2.5% to coat the central 4.0 mm of the cornea and then perform the laser ablation so that mainly peripheral tissue is ablated. I hope the development of new hyperopic reduction software will help us overcome this universal complication of an otherwise rewarding procedure. Tanuj Dada MD aNew Delhi, India