Abundant evidence underlines pressure dependency of glaucoma damage

Chicago-While results of epidemiologic studies indicate that only one-third of glaucoma damage is attributable to excess IOP over the normal distribution, much more of glaucoma damage appears to be pressure-dependent and therefore preventable, especially in patients whose IOP is higher than average, said Paul F. Palmberg, MD, PhD.

Dr. Palmberg delivered the Robert N. Shaffer Lecture during a combined meeting with Prevent Blindness America held during the annual meeting of the American Academy of Ophthalmology. He is known for introducing the term “target pressure” in 1989, and he spoke on “How much of glaucoma damage is pressure-dependent?”

Dr. Palmberg said that although epidemiologic studies have found a weak relationship between IOP and glaucomatous damage, closer examination of the data from those trials reveals that low normal pressures may be protective. He went on to review findings from a number of clinical studies published over the last two decades supporting that concept. The best evidence derives from the large, prospective, multicenter, National Eye Institute-sponsored randomized clinical trials. Collectively, those studies demonstrate that aggressive intervention to lower IOP to a target level is helpful in patients with advanced glaucoma, normal-tension glaucoma, and those with early disease.

Dr. Palmberg concluded by crediting Paul Chandler, MD, as first suggesting the importance of seeking lower target pressures in some glaucoma patients in a 1960 landmark paper in the American Journal of Ophthalmology.

“It turns out we are back to the future and that Paul Chandler said it best when he suggested that patients with advanced glaucoma with damage at both poles require an IOP below the average normal to be stable, eyes with limited cupping confined to one pole of the disc appear to withstand tension better, and perhaps can do well with an IOP in the mid-to-upper normal range, while those with a normal appearing disc may be able to withstand ocular hypertension for years without sustaining glaucomatous damage. The appearance of the disc may be the best guide as to the effect of IOP on the eye and how to manage glaucoma,” he said.