High degenerative axial myopia is defined as an eye having an axial length greater than 26 mm—sometimes even exceeding 34 mm—and a spherical equivalent less than or equal to -6.00 D. Such degree of myopia is mostly associated with degenerative changes that involve the sclera, choroid, retina, and vitreous.
The incidence of retinal detachment is higher in myopic eyes than in emmetropic eyes (3.2% [myopia greater than -6.00 D] vs 0.71%, respectively).1,2 The yearly incidence of retinal detachment is approximately 0.015% in eyes with up to -4.75 D of myopia, 0.07% in eyes with -5.00 to -9.75 D, and 0.075% in eyes with myopia greater than -10.00 D.3,4 The risk of retinal detachment in myopic eyes is anywhere from 15 to 110 times greater in patients with -15.00 D to -20.00 D of myopia. Premature posterior vitreous detachment in patients aged 40 to 60 years with peripheral retinal degenerations and moderate-to-high myopia may be a predisposing factor to more frequent development of retinal disease.
IATROGENIC FACTORS INDUCED
Over the past few years, PRK and LASIK have been increasingly used to correct low-to-high myopia.5-7 The placement of phakic IOLs in the anterior chamber is yet another technique for the correction of high myopia; however, in these instances, refractive surgery induces iatrogenic factors that may lead to an increased incidence of retinal disease and detachment. Possible iatrogenic factors include (1) the impact of the excimer laser's shock waves on the eye during PRK and LASIK, (2) intraocular pressure (IOP) changes induced by the suction ring to stabilize the eye during LASIK, (3) hypotonia induced during anterior chamber phakic IOL implantation, and (4) an inflammatory reaction induced by any kind of surgery.
The incidence of retinal detachment after PRK is between 0.08% and 0.15%.8,9 It is difficult to consider PRK an etiopathogenic factor for retinal disease because of the mean lapse time between refractive surgery and retinal detachment after PRK, as well as its low incidence of occurrence; however, we must consider the theoretical risk of shock waves from the laser and the inflammatory reaction after surgery.
Retinal detachments after PRK have most frequently occurred in highly myopic patients, for which reason it seems that the appearance of retinal detachment relates to the intrinsic risk of myopia. Corneal changes induced by PRK (eg, haze, optical aberrations produced by keratectomy) do not make visualization of the fundus difficult, either in identifying retinal tears or for retinal surgery.
The appearance of retinal detachment after LASIK is similar to PRK (0.06–0.36%).9 In eyes where LASIK was used to correct myopia, the risk of retinal detachment is initially a result of the myopia itself. Additionally, the risk in these myopic eyes could be increased by the manipulation associated with the laser procedure. During this technique, the suction ring inadvertently increases IOP by more than 65 mm Hg. The authors proposed that the sudden increase in IOP may exert a mechanical stretch on the vitreous base. Mechanical stress is also induced into the eye via the laser's shock waves. Upon examination of the retinal detachment in those patients with myopia, we determined that LASIK did not increase the difficulty of identifying or locating a break in the peripheral retina.
The most important consideration is whether IOL implantation may induce a higher risk of retinal disorders—especially retinal detatchment—among highly myopic phakic patients. Theoretically, this risk might be determined by high myopia itself, but it may also be influenced by iatrogenic factors induced by refractive surgery. Several reports have described retinal detachment after phakic IOL implantation.10,11 In highly myopic patients, the appearance of retinal detachment in three separate series (5.16%, 4.8%, 4.08%) was higher than that in the literature (3.2%) for myopia greater than -6.00 D.9,12,13 The lapse of time between anterior chamber phakic IOL implantation and the appearance of retinal detachment is variable, and for this reason the relationship is unclear.
Retinal detachment in the first 6 months after refractive surgery could be considered a consequence of the procedure; however, the increased risk of retinal detachment may also be attributed to high myopia—especially if the axial length is greater than 30.24 mm—or IOL-induced changes in the myopic eye. Additionally, if high myopia is corrected with a phakic anterior chamber IOL, visualization of the peripheral retina is very poor, and surgical treatment of retinal detachment is difficult.
The appearance of retinal detachment in high myopia after refractive surgery is related to the pathology and not the surgery, although the refractive surgery may condition some aspects.
AFTER CATARACT SURGERY
The relationship between cataract and high myopia has been previously reported.14,15 A cataract in high myopic patients, which is mostly posterior subcapsular or nuclear, tends to be more frequent, appears at an earlier age, and progresses more rapidly than a cataract in a nonmyopic patient. As a result, myopic patients often need cataract surgery at a younger age. Additionally, refractive lens exchange for purely refractive purposes is more frequently used, especially around the age when presbyopia develops, with its physiological changes that decrease the optical quality of the lens. Some authors report that the retinal changes in high myopia increase the risk of retinal detachment after cataract surgery, an issue aggravated by certain factors including youth, axial length, history of retinal detachment surgery in the contralateral eye, predisposing retinal lesions, the surgical technique, and posterior capsule integrity.
Although studies support and confirm the potential hazard that lens removal has on the development of retinal detachment, especially in high myopic patients,14 other clinical studies16-18 do not support such risk and report low postoperative risk of retinal detachment (1–4%). Some authors also suggest that the risk of retinal detachment may increase with the time.18
Retinal detachment as a complication after cataract surgery has a low rate of incidence in high-myopic patients, but the incidence is still doubled when compared with unoperated high myopic or normal patients after cataract surgery.
José M. Ruiz-Moreno, MD, PhD, is a Professor in the División de Oftalmología, School of Medicine (Campus de San Juan), Universidad Miguel Hernández, Alicante, Spain. Dr. Ruiz-Moreno states that he has no financial interest in the products or companies mentioned. He may be reached at firstname.lastname@example.org.
Francisco L. Lugo Quintás, MD, is a collaborator in the División de Oftalmología, School of Medicine (Campus de San Juan), Universidad Miguel Hernández, Alicante, Spain. Dr. Quitás states that he has no financial interest in the products or companies mentioned. He may be reached at email@example.com.