Retinal detachment after photorefractive keratectomy

Abstract

I would like to comment on the recent article by Ruiz-Moreno and coauthors1 about retinal detachment after photorefractive keratectomy (PRK). The authors are to be commended for reporting the results of a retrospective study to analyze the incidence and characteristics of retinal detachment (RD) in myopic patients treated by PRK. The authors conclude, “The RDs appeared in a group with a myopic SE (−11.4 D) higher than the median SE in the overall series (−4.71 D), but our RD incidence was not greater than those previously published.” Their results suggest that patients with a higher degree of myopia are more prone to develop an RD after PRK. However, myopic eyes tend to develop lattice degeneration, retinal breaks, and RDs.2 Retinal breaks or detachments may not always be caused by PRK. They are part of the natural history of the myopic eye, and an expected complication regardless of refractive surgery. The questions are, Does the PRK procedure increase the risk of RD in myopic patients? Is the risk of RD after PRK increased in eyes with higher degrees of myopia? A theory for the cause of retinal detachment after refractive surgery with the excimer laser is that with each application of the excimer laser beam, a shock wave is transmitted to the eye and absorbed by the vitreous. If this is true, it would be expected that eyes with higher degrees of myopia would be more prone to develop an RD since higher total energy levels of laser would be used during the procedure. This might have been the case with the RD cases after PRK reported by Ruiz-Moreno and coauthors. The pulsed energy applied to the cornea during PRK is a potential source of damage to the vitreous and retina.3 When the excimer laser light ablates tissue, energy is released anteriorly as a plume of ablated tissue and is thrown into the air in front of the cornea. In addition, it has been reported that particulate matter is ejected from the cornea for up to 18 inches. Such a powerful force might also be associated with backward force into the vitreous. Hahn and coauthors4 showed that many of the ablation particles launched into the air are water spherules. The particle diameter is 100 to 800 μm. Posteriorly, energy is transmitted in the form of a shock wave. This wave at least will mean types of laser spheres may be on the order of 10 atmospheres of pressure. The effect of shock waves and posteriorly radiated energy on the vitreous' integrity is unknown. Although RD after PRK for the correction of myopia is infrequent,1,5 it is important that the patient is well informed and understands that preoperative and postoperative visits to a retina and vitreous specialist are necessary. Again, Ruiz-Moreno and coauthors are to be commended for an interesting paper and for providing additional information about the incidence of RD after refractive surgery to correct myopia. Fernando J. Arevalo MD aCaracas, Venezuela