EyeWorld Asia-Pacific September 2015 Issue

46 EWAP GLAUCOMA September 2015 Evolving views on IOP and glaucoma by Tony Realini, MD, MPH EyeWorld Contributing Writer Significant changes in our understanding of the role of IOP in the disease process I OP is, and will always be, a relevant component of any discussion about glaucoma. In recent years, however, its role in the disease process has undergone significant evolution. The history of IOP and glaucoma “Historically, IOP and glaucoma have been tightly bound and inexorably linked,” said M. Roy Wilson, MD , Wayne State University, Detroit. “The diagnosis and management of glaucoma have been based on our perspective of IOP for many years.” Not so long ago, elevated IOP was considered to be the very definition of glaucoma. Then it became a feature of the disease, which was recognized as a form of optic neuropathy. “Now it is considered a risk factor rather than a feature of the disease,” Dr. Wilson said. Color Doppler imaging measures blood ow velocity in retrobulbar blood vessels including the central retinal artery (pictured). Outcome parameters include peak systolic and end diastolic blood ow velocities and calculated vascular resistance index. Source: Alon Harris, MS, PhD IOP still matters This demotion in status does not diminish IOP’s role in the development and progression of glaucoma. “IOP is a causal risk factor for glaucoma at all levels of IOP,” said Paul Kaufman, MD, University of Wisconsin, Madison. “There is a dose- response relationship between IOP and the development of glaucoma. But age, central corneal thickness (CCT), and race are other significant risk factors for glaucoma.” Robert N. Weinreb, MD , University of California, San Diego, agreed. “IOP is clearly an important modifiable risk factor for glaucoma. The risk of glaucoma increases with the level of IOP.” Jeffrey Liebmann, MD , New York University, put it succinctly: “IOP plays a role in every eye with glaucoma.” IOP is not the whole story No one disputes the therapeutic benefit of IOP reduction. Major clinical trials have demonstrated the benefit of IOP reduction on the development of glaucoma in eyes with high IOP and on the progression of glaucoma in eyes Views from Asia-Pacific Daniel SU, MD Senior Consultant Eye & Retina Surgeons #13-03 Camden Medical Centre, 1 Orchard Boulevard, Singapore 248649 Tel. no. +65-67382999 Fax no. +65-67382111 drdanielsu@eyeretinasurgeons.com T his article provides an interesting perspective on the role of intraocular pressure (IOP) in glaucoma. Indeed, IOP does play a role in every eye with glaucoma. IOP is also the only risk factor that we can modify through treatment. However, the measurements we make at each clinic visit do not reveal the full picture behind the patient’s long-term IOP pro le. We still lack a convenient, reliable, and inexpensive way to monitor IOP over the 24-hour period in a manner similar to 24-hour blood pressure monitoring. Nor do we have a biologic marker to track a patient’s IOP pro le over a 3- or 6-month period like HbA1C in diabetes mellitus. These would give us greater insights into how well controlled our patients’ IOPs are in between clinic visits and help us titrate the treatment more appropriately. Ophthalmologists should consider two possible factors in glaucoma patients whose condition progresses despite low IOPs: excessive reduction of systemic blood pressure and obstructive sleep apnea (OSA). Some patients on antihypertensive medications may suffer from large nocturnal dips in blood pressure, resulting in inadequate ocular perfusion and possible progression of glaucoma. Such patients monitor their blood pressure daily and if it is found to be too low, the ophthalmologist should communicate with the physician and suggest that the antihypertensive treatment be lightened. This would allow slightly higher systemic blood pressure and better perfusion to the eyes. OSA causes obstruction of the airways during sleep and results in hypoxemia, leading to reduced oxygen delivery to ocular tissues. Ophthalmologists should ask patients who have worsening disease despite well-controlled IOP about snoring while sleeping, being awoken at night because of inability to breathe and daytime somnolence. Such patients should be evaluated with sleep studies and given continuous positive airway (CPAP) therapy while sleeping if OSA is present. Editors’ note: Dr. Su has no nancial interests related to his comments. with both normal and high IOP. But, as Harry Quigley, MD, Johns Hopkins University, Baltimore, pointed out, “IOP lowering is protective but limited. We don’t know the ideal target IOP for patients. Some get worse despite IOP reduction.” Dr. Liebmann added, “Knowledge of IOP is not required to diagnose glaucoma or to detect its progression.” Some of the weakness of association between IOP and glaucoma may arise from the limitations we face when measuring IOP. “There is no gold standard for IOP measurement,” Dr. Liebmann explained. What aspect of IOP matters? Another limitation of our understanding of IOP arises from its variability. What aspect of IOP