LASIK-Associated Visual Field Loss in a Glaucoma Suspect FREE

We report a case of visual field loss first noted after laser in situ keratomileusis (LASIK). One similar case has been described.¹ Since LASIK involves brief iatrogenic elevation of intraocular pressure (IOP), we are concerned about the possible rare instances of this occurrence in future patients.

A 47-year-old high myope received a diagnosis of ocular hypertension in 1979 with an IOP of 30 OU. Her mother and sister had glaucoma. Treatment with 0.5% timolol maleate maintained her IOP in the high teens except for an occasional IOP in the low 20s. Findings on Humphrey 24-2 visual field testing were normal on June 4, 1997 (Figure 1).

On June 16, 1999, an experienced surgeon (R.S.R.) performed LASIK for correction of 10.5 diopters (D) of myopia in the right eye and 9.5 D of myopia in the left. Pachymetry measured a 473-µm thickness OU preoperatively and a 360-µm thickness OD and 390-µm thickness OS postoperatively. During the week postsurgery the patient noted a new paracentral scotoma in her left eye. On June 25, 1999, visual field testing showed the presence of a previously undocumented scotoma superotemporal to fixation in the left eye (Figure 2). A notch was noted on the corresponding aspect of the optic nerve. Latanoprost was added as treatment for both eyes and the patient was sent for glaucoma consultation.

On August 23, 1999, uncorrected vision was 20/20 OD and 20/25 OS. Her IOP was 12 mm Hg 3 hours after treatment with 0.5% timolol and latanoprost OD and 17 mm Hg 3 hours after latanoprost therapy OS. Pupils were normal with no afferent defect. Five iris transillumination defects were present in the left eye; none were present in the right. No Kruckenberg spindle was present in either eye. Posner gonioscopy revealed an angle open to the ciliary body band for 360° in both eyes with marked pigmentation of the posterior trabecular meshwork in the left eye more than in the right eye. The cup-disc ratio was 0.6 OD and 0.7 OS with peripapillary atrophy and temporal sloping in both eyes. The diagnosis of open-angle glaucoma with a component of pigment dispersion was made. The patient was relieved to consider the possibility that the visual field change may have occurred in association with the LASIK procedure, rather than due to concurrent progression of the underlying disease.

The IOP has measured in the low teens OU when treated with 0.5% timolol and latanoprost, though her readings may be falsely low owing to her thin corneas. Visual field testing on December 1, 1999, showed no progression of the scotoma (Figure 3).

An experienced LASIK surgeon can limit the duration of the iatrogenic increase in IOP during LASIK to approximately 10 seconds. During this time a mechanical suction ring achieves a pressure of approximately 80 mm Hg. Although the brevity of the pressure elevation suggests that most optic nerves could tolerate the procedure, the severity of the pressure elevation suggests that, at least occasionally, mechanical compression or ischemia may damage an optic nerve. The stress of pressure elevation in LASIK is of shorter duration but greater magnitude compared with gravity inversion² or high-resistance wind instrument playing,³ activities that have been associated with elevated IOP and abnormal visual fields.

Inspection of the optic nerve prior to LASIK may allow identification of some of the patients who are at risk. Features of the optic nerve that may be of concern are the same variables that identify early glaucomatous optic nerve damage: vertical cup–disc diameter ratio corrected for optic disc size, total neuroretinal rim area, rim–disc area ratio, and cup–disc area ratio corrected for disc size.⁴ Patients with glaucoma, a family history of glaucoma, as well as glaucoma suspects should be cautioned of this risk prior to the performance of LASIK. For many of these patients, photorefractive keratectomy, intrastromal corneal ring segments, or continued use of contact lenses or eyeglasses may offer satisfactory vision without subjecting the optic nerve to the small but real risk of pressure-associated visual field loss.