MYOPIA and GLAUCOMA

Careful examination and avoidance of trabeculectomy prescribed for moderate-to-high myopes with glaucoma

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The diagnosis and management of glaucoma in eyes with moderate-to-high myopia brings many challenges. Three leading glaucoma specialists shared their views on the optimum approach to such cases in a series of presentations at the 7th World Glaucoma Congress in Helsinki, Finland. Eyes with moderate-to-high myopia have an increased risk for glaucoma, but myopia can also sometimes masquerade as glaucoma. However, careful examination can distinguish between the two pathologies and ensure good treatment decisions, said Tin Aung PhD, FRCSed FRCSOphth, Singapore National Eye Centre and the National University of Singapore. “A concurrent diagnosis of moderate-to-high myopia does not fundamentally influence diagnosis and medical treatment,” he noted. He pointed out that in the Blue Mountain Eye Study, myopia of -6.D or more was associated with an increased risk of glaucoma and the higher the myopia the higher the risk. On the other hand, in eyes with myopia, a tilted disk or peripapillary atrophy (PPA) may mimic glaucomatous optic neuropathy. The key to glaucoma diagnosis in such cases is the detection of progression, because if there is progression, glaucoma is most likely the cause. He therefore recommended serial disc photography and added that research suggests that macular OCT measurements of the ganglion cell complex (GCC) and macular retinal ganglion cell-inner plexiform layer (GCIPL) may provide better glaucoma detection than standard retinal nerve fibre layer measurements. Regarding functional measurements, he noted that tilted discs and PPA in myopic eyes can themselves cause visual field defects. However, as with serial disc photography, progression detected by repeated visual field tests, will reveal if it is glaucoma. He added that whether a glaucoma patient is myopic or not, the aim of treatment will be the reduction of IOP. However, if surgery is indicated, minimally invasive glaucoma surgery may pose less risk of hypotony maculopathy in moderate-to-high myopes than would trabeculectomy. CAVEATS IN DIAGNOSIS Ki Ho Park MD, PhD, Seoul National University, agreed that a concurrent diagnosis of moderate-to-high myopia should not influence medical treatment of glaucoma. However, he stressed that there are many potential pitfalls in the diagnosis of glaucoma in such cases. “A diagnosis of glaucoma in moderate-to-high myopia patients is challenging because it is difficult to differentiate between glaucomatous changes and myopic changes. Disk tilt, peripapillary atrophy, chorioretinal atrophy and eyeball elongation make it difficult to detect glaucomatous structural change,” he said. He noted that eyes with moderate-to-high myopia typically have a large optic nerve head and an elongated disk with shallow cupping and extensive PPA. However, RNFL defects are less common than in glaucoma and, when present, the loss of thickness is more diffuse and less localised than it is in glaucoma. Sometimes the elongation of the myopic eye causes a temporal convergence of the superotemporal and inferotemporal RNFL, creating pseudo-RNFL defects by Optical Coherence Tomography (OCT), so-called “red disease”. Regarding treatment, Dr Park cited several studies showing that neither the presence nor degree of myopia appear to have any impact on the rate of progression. Therefore, a concurrent diagnosis of moderate-to-high myopia should not influence the estimation of the target IOP, he said. However, when surgery is indicated, trabeculectomy should be avoided, since myopia raises the risk for hypotony maculopathy, particularly in patients with other significant risk factors, such as young age, male gender and low scleral rigidity. Robert Chang MD, Stanford University, concurred with Dr Park regarding the avoidance of trabeculectomy in highly myopic eyes. He also reminded that the secondary Tubes vs Trabs study showed that tubes performed as well as trabeculectomy in terms of IOP reduction, but with a lower incidence of persistent hypotony. However, he took the position that a concurrent diagnosis of moderate-to-high myopia does influence both diagnosis and medical treatment. Dr Chang included several case examples illustrating the point of how high myopia can distort OCT results as well as affecting response to filtering surgery, both of which are well documented in the literature. “We also have to be wary of peripheral retinal changes as well as myopic degeneration changes in high myopes, so it’s a good idea to consult with your retinal surgeon. If it’s a straightforward case, you may also want to perform cataract surgery sooner for the marked visual improvement it can bring in very high myopes,” he added. Tin Aung: aung.tin@snec.com.sg Ki Ho Park : kihopark@snu.ac.kr David Chang: tmenzies@stanford.edu