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No association between contrast sensitivity, IOP reduction in patients with ocular hypertension, researchers find
In evaluating the relationship between intraocular pressure and contrast sensitivity in patients with ocular hypertension, Anderson and colleagues found no relationship between the two.
As a result of this finding, the researchers disclosed in a recent Ophthalmology study that previous sensitivity changes in glaucomatous patients indicate reversible glaucoma-induced dysfunction.
In their comparative case series, researchers analyzed 1,310 participants from the Ocular Hypertension Treatment Study (OHTS): 692 eyes that had been treated and 618 eyes that had not received treatment. They also utilized data from the second phase of OHTS in which the control eyes received treatment and the treatment eyes continued receiving treatment, as detailed in the study.
Results showed that treated eyes had a decrease in IOP, but no significant change in mean deviation or pattern standard deviation.
"We show that reduction of elevated IOP in eyes without glaucoma does not produce a significant change in contrast sensitivity using automated perimetry," the authors concluded. "Our results provide a necessary control required to strengthen the argument that previous studies showing visual field improvement with IOP reduction in glaucoma have demonstrated glaucoma-induced dysfunction rather than simply a general relationship between IOP and contrast sensitivity."
Perspective
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For nearly 3 decades, researchers have hypothesized that lowering IOP in glaucomatous eyes may improve visual function, suggesting that initial reversible retinal ganglion cell (RGC) dysfunction may precede subsequent irreversible RGC death. Anderson and Stainer, through retrospective analysis of the OHTS 1 and 2 data sets, demonstrate that IOP reduction in nonglaucomatous eyes has no impact on standard automated perimetry mean deviation (SAP MD), indirectly suggesting that improved visual function is more than an IOP or pharmacologic effect common to any eye.
While the Early Manifest Glaucoma Trial showed that initial post-treatment IOP was a strong predictor of future progression, one wonders whether a similar post hoc analysis of that data set may provide direct evidence of improved visual function following IOP reduction in glaucomatous eyes (Leske and colleagues).
These results speak to the importance of early diagnosis and appropriate intervention at the stage of reversible retinal ganglion cell axonal injury (whether precipitated by hypoxia, glutamate toxicity, mitochondrial dysfunction, neurotrophic deprivation, glial activation, autoimmunity or a combination of these or other mechanisms) rather than irreversible cell body death. They also pique curiosity as to what constitutes appropriate intervention – neuroprotection, anyone?
Reference:
Leske MC, et al. Arch Ophthalmol 2003;121:48-56.
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Ophthalmology. 2014; doi: 10.1016/j.ophtha.2014.04.014.