Glaucoma: Optometry Helps Relieve the Pressure

For the past decade, intraocular pressure has taken something of a back seat in field of the glaucoma. In a provocative review, Van Buskirk and Cioffi encouraged the community to regard elevated intraocular pressure as a risk factor for glaucoma rather its cause. 1 The authors concluded, “Glaucomatous visual loss relates not to increase in intraocular pressure, or to any one risk factor but rather to a characteristic and recognizable optic neuropathy. Because the common denominator of glaucoma is the neuropathy, not the intraocular pressure, it makes more sense to divide populations into those with and without glaucomatous optic neuropathy.” Advances in visual assessment 2 and imaging 3 in glaucoma have also diminished the attention paid to intraocular pressure. Likewise, pharmaceutical agents for the treatment of glaucoma have been developed to treat the neuropathy independent of the control of pressure. 4 This apparent paradigm shift prompted a symposium entitled “IOP: The Forgotten Risk Factor” at the recent Annual Meeting of Association for Research in Vision and Ophthalmology. While intraocular pressure may be just one of many risk factors for glaucoma, it remains the most treatable. One important but unanswered question was whether treating a patient with elevated intraocular pressure, yet with no glaucomatous visual field loss or optic nerve damage, delayed or prevented the development of glaucomatous optic neuropathy. Fortunately, we now have the answer. The June issue of Archives of Ophthalmology reported the 5-year results from the Ocular Hypertension Treatment Study. 5 The results clearly demonstrate that treatment is effective in delaying or preventing glaucomatous visual field loss, optic disc damage, or both. The study examined 1636 people 40 to 80 years of age who had elevated intraocular pressure but no signs of glaucoma. Half were randomly assigned to daily eye drops and the other half assigned to observation without medication. The treatment reduced intraocular pressure by approximately 20%. The researchers noted that 4.4% of the treated patients developed glaucoma within five years. In comparison, 9.5% of those who did not receive eye drops developed glaucoma. The Ocular Hypertension Treatment Study represents a landmark for the profession of optometry. Although optometrists have been licensed to prescribe therapeutic pharmaceutical agents in most U.S. states for many years, this is the first federally-funded study of drug therapy in which we have participated on an equal footing with ophthalmology. One clinical center for the study was at the Eye Institute of the Pennsylvania College of Optometry under the direction of clinic principal investigator, G. Richard Bennett, MS, OD, FAAO. The College, Dr. Bennett, and all of the profession should be proud of this involvement. Furthermore, optometrists in 46 states are now able take advantage of these findings. In May, Governor Jeanne Shaneen signed legislation that allows optometrists in New Hampshire to prescribe for glaucoma. Ironically, Pennsylvania is a state with a relatively limited scope of optometric practice. Dr. Bennett was among those to caution professionals against over prescribing in ocular hypertensives. He stated, “This does not mean that eye care professionals should prescribe eye drops for all people who have elevated eye pressure with no sign of glaucoma.” It is important to note that even among the patients who did not receive treatment, fewer than 10% developed glaucoma. In deciding whether to treat individual patients the practitioner should take into account several other factors such as patient age, health status, and the potential for side effects and drug interactions. As anticipated, the Ocular Hypertension Treatment Study found that some patients are at greater risk than others. The likelihood of developing open-angle glaucoma was increased by older age, greater vertical and horizontal cup-disc ratios, greater Humphrey visual field pattern standard deviation, higher intraocular pressure, and thinner central corneal thickness. 6 In patients with thinner corneas, the measured intraocular pressure underestimates the true intraocular pressure. Thus, it is likely that the predicative value of corneal thickness is due to its effect on the measurement of intraocular pressure, although the finding that thinner corneas were observed in African American participants deserves further consideration. Those ocular hypertensives with excimer-induced corneal thinning may also be worthy our attention. 7 The Ocular Hypertension Treatment Study investigators recommend that corneal thickness be measured in the clinical evaluation of all patients with ocular hypertension. 6 A further important consideration is the cost of treatment. The Ocular Hypertension Treatment Study found that treatment reduced the five-year incidence of glaucoma by 5%. One can express this finding in an effort-to-yield measure: 100 patients need to be treated for 5 years to prevent five new cases for glaucoma, or more simply, 20 patients need to be treated for 5 years to prevent a single case. A question for the health economists is whether one case of glaucoma is worth 100 patient-years of prophylactic treatment? In this issue of Optometry and Vision Science Doyle and colleagues discuss the cost of glaucoma medical treatment. 8 They comment that treatment costs can vary dramatically. A patient may be treated binocularly with generic timolol once a day for less than $100 per year. In contrast the cost of other beta-blockers and alpha-agonists can exceed $500 per year. It is interesting to note that 5 years into the Ocular Hypertension Treatment Study, over 60% of the patients were using beta-blockers, nearly a half were using a prostaglandin analogue, and 40% were using two or more drugs. 5 We can look forward to further important findings from the Ocular Hypertension Treatment Study. The results combined with other ongoing clinical trials in glaucoma can only improve the quality of care that our patients will receive.