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Letters to the Editor

Optic Nerve Head Drusen: The Relationship Between Intraocular Pressure and Optic Nerve Structure and Function: Comment

Katz, Bradley J. MD, PhD

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Journal of Neuro-Ophthalmology: March 2019 - Volume 39 - Issue 1 - p 143
doi: 10.1097/WNO.0000000000000730
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In their article, Nolan et al (1) retrospectively reviewed the records of 236 eyes of 146 patients with optic nerve head drusen (ONHD). The authors found no correlation between intraocular pressure (IOP) and perimetric mean deviation (PMD) as assessed by either Octopus or Humphrey automated perimetry. They found no correlation between IOP and mean retinal nerve fiber layer (RNFL) thickness. Based on these observations, they concluded that, “…lowering IOP in normotensive eyes may not be beneficial in preventing vision loss in patients with ONHD.”

As noted in the article, lowering IOP has been proposed as a means of slowing the loss of visual field in eyes with ONHD, but that there are no data to support this proposition. However, their conclusion that IOP-lowering therapy may be ineffective does not follow from the data presented: a noninterventional study by design cannot answer this question or lead to such a conclusion. To settle the issue of whether or not lowering IOP is beneficial, one would ideally design a prospective study in which eyes with ONHD were randomized to IOP-lowering therapy.

The authors acknowledge several limitations of their study. Among them is the fact that only one visual field and only one IOP measurement were considered for each eye. A limitation not listed is that each eye was considered a separate data point. This methodology does not take into account the fact that IOP, PMD, and RNFL thickness are likely to be correlated between the 2 eyes of a single individual. Based on these limitations and on the noninterventional design of the study, it is premature to conclude that IOP-lowering therapy is ineffective.

Patients with ONHD and visual field loss have few, if any, therapeutic options. Medical IOP-lowering therapy is relatively inexpensive and causes few side effects. Concluding that one should not offer these therapies to our patients with ONHD is without merit and potentially a disservice to patients.

The authors could have been more circumspect in their conclusions: there are no data to suggest that IOP-lowering therapy is effective or ineffective. In the absence of any data indicating that IOP-lowering therapy is harmful, physicians caring for these patients should openly discuss our uncertainty about the treatment of ONHD and, at least, offer to prescribe medical IOP-lowering therapy. In this way, patients and the physicians caring for them can continue to make informed decisions using the best data available.

REFERENCE

1. Nolan KW, Lee MS, Jalalizadeh RA, Firl KC, Van Stavern GP, McClelland CM. Optic nerve head drusen: the relationship between intraocular pressure and optic nerve structure and function. J Neuroophthalmol. 2018;38:147–150.
Copyright © 2018 by North American Neuro-Ophthalmology Society