Ocular Hypertension and Glaucoma

An estimated 9%–28% of patients with myopia have primary open-angle glaucoma (POAG). Consequently, it is likely that some patients with glaucoma will request refractive surgery.

Of particular concern in patients with ocular hypertension or POAG is the effect of the acute rise in intraocular pressure (IOP) to more than 65 mm Hg when suction is applied while the stromal flap is cut for LASIK or the epithelial flap for epipolis LASIK (epi-LASIK). There have been reports of new visual field defects arising immediately after LASIK that are attributed to mechanical compression or ischemia of the optic nerve head from the temporary increase in IOP.

Evaluation of a patient with ocular hypertension or POAG includes a complete history and ocular examination with peripheral visual field testing and corneal pachymetry. A history of poor IOP control, nonadherence to treatment, maximal medical therapy, or prior surgical interventions may suggest progressive disease, which may contraindicate refractive surgery. The surgeon should also note the status of the angle, the presence and amount of optic nerve cupping, and the degree of visual field loss, especially if split fixation is present.

Several reports have confirmed that central corneal thickness affects the Goldmann applanation tonometry (GAT) and the Tono-Pen (Reichert Technologies, Depew, NY) measurement of IOP (see the section Glaucoma After Refractive Surgery in Chapter 11). The principle of applanation tonometry assumes a corneal thickness of 520 μm. Studies have demonstrated that thinner-than-normal corneas give falsely low IOP readings, whereas thicker corneas give falsely high readings. For example, IOP is underestimated by approximately 5.2 mm Hg in a cornea with a central thickness of 450 μm. Although all reports agree that central corneal thickness affects GAT IOP measurement, there is no consensus on a specific formula to compensate for this effect in clinical practice.

In the treatment of myopia, LASIK and surface ablation procedures remove tissue to reduce the steepness of the cornea; this sculpting process creates a thinner central cornea, which leads to artifactually low IOP measurements postoperatively. Such inaccurately low central applanation tonometry measurements hinder the diagnosis of corticosteroid-induced glaucoma after keratorefractive procedures, resulting in optic nerve cupping, visual field loss, and decreased visual acuity (Fig 10-4).

Because of the difficulty that PRK and LASIK cause in the accurate measurement of IOP, these refractive procedures should not be considered for a patient whose IOP is poorly controlled. Furthermore, patients should be advised of the effect of refractive surgery on their IOP measurements and urged to inform future ophthalmologists about their surgery. Patients should be referred to a glaucoma specialist when indicated.

Patients with ocular hypertension can often safely undergo refractive surgery. Such patients must be counseled preoperatively that refractive surgery treats only the refractive error and not the natural history of the ocular hypertension, which can sometimes progress to glaucoma, accompanied by optic nerve cupping and visual field loss. The ophthalmologist should pay particular attention to the risk factors for progression to glaucoma, including older age, reduced corneal thickness, increased cup–disc ratio, family history of glaucoma, and elevated IOP. Each patient needs to understand that after excimer laser ablation, it is more difficult to accurately assess IOP.

The decision about whether to perform refractive surgery in a patient with glaucoma is controversial. There are no long-term studies on refractive surgery in this population. LASIK is contraindicated in any patient with marked optic nerve cupping, visual field loss, or visual acuity loss. The refractive surgeon may ask the patient to sign an ancillary consent form that documents the patient’s understanding that POAG may cause progressive vision loss independent of any refractive surgery and that IOP elevation during a LASIK or epi-LASIK procedure, or following LASIK or surface ablation (often due to a corticosteroid response), can cause glaucoma progression.

Figure 10-4 Glaucomatous optic nerve atrophy in a patient with “normal” intraocular pressure (IOP) after laser in situ keratomileusis (LASIK). A, Fundus photograph demonstrating increased cup–disc ratio in a patient who received a diagnosis of glaucoma 1 year after LASIK. The patient had decreased vision, with corrected distance visual acuity of 20/40 and IOP of 21 mm Hg. B, Humphrey 24-2 visual field with extensive inferior arcuate visual field loss corresponding to thinning of the superior optic nerve rim. C, Optical coherence tomography image demonstrates marked optic nerve cupping.

(Parts A and B courtesy of Jayne S. Weiss, MD; part C courtesy of Steven I. Rosenfeld, MD.)

The surgeon should be aware that placement of a suction ring may not be possible if there is a functioning filtering bleb or a tube shunt. In rare cases in which both filtering surgery and LASIK are being planned, it is preferable to perform LASIK before the filter is placed. Suction time should be minimized to decrease the chance of optic nerve damage from the transient increase in IOP. Alternatively, PRK or laser subepithelial keratomileusis (LASEK) may be preferable because each avoids the IOP rise associated with LASIK flap creation. The surgeon must exercise caution when using postoperative corticosteroids because of their potential for elevating IOP. The patient should be informed as to when to resume postoperative topical medications for glaucoma. Finally, to avoid trauma to the flap, IOP should generally not be checked for at least 72 hours.

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Excerpted from BCSC 2020-2021 series: Section 13 - Refractive Surgery. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.