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Study does not support field improvement after IOP-reducing therapy
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In a study from Investigative Ophthalmology & Vision Science, researchers were unable to draw any association between therapeutic lowering of intraocular pressure and improvement in the visual field in treatment-naïve glaucoma patients from the Early Manifest Glaucoma Trial cohort.
Subjects with newly diagnosed glaucoma with normal to moderately elevated IOP were prospectively randomized either to IOP-lowering therapy for 129 patients or to no treatment in 126 patients. Before randomization, subjects underwent repeated standard automated perimetry (SAP) testing and Goldmann tonometry. Three months after randomization, patients again underwent SAP and tonometry.
Researchers calculated changes in visual fields as the difference in mean deviation (MD) values between the 3-month visit and baseline.
They found deterioration in MD was seen somewhat more often than improvement. In both treated and untreated eyes, 61% had a worse MD at the 3-month visit than at the baseline.
The numerical changes in MD were small and negative, indicating a slight deterioration; the mean change was -0.15 dB among treated and -0.44 dB among untreated eyes, according to the study.
The proportions of patients improving by at least 1 dB, at least 2 dB and at least 3 dB after 3 months were also the same or almost the same among untreated and treated eyes, researchers wrote.
Further, numeric changes in age-corrected threshold values at those points were small and negative, indicating slight deterioration, they said.
Mean baseline IOP was 20.7 mm Hg. At the 3-month visit mean IOP reduction was 24% for treated eyes and 0.8% for untreated eyes, according to the study.
Researchers found an IOP reduction in most treated eyes; 81% had an IOP reduction of at least 10%, 56% of those treated had a reduction of at least 20%, 29% had a reduction of at least 30%, 16% had a reduction of at least 40%, and 4% had an IOP reduction of at least 50%
In the untreated controls, IOP was reduced by at least 10% in 23% of control subjects, at least 20% in 5% and at least 30% in 1% of untreated controls.
Researchers found that the untreated mean baseline IOP, ranging from 13 mm Hg to 30 mm Hg, was not statistically significantly associated with change in MD.
“The result among treated patients suggests slightly more deterioration in eyes starting at a better MD level than among eyes starting with a worse MD level,” the researchers wrote. – by Abigail Sutton
Disclosure: Bengtsson is a consultant for Carl Zeiss. Please see the full study for all other authors’ financial disclosures.
Perspective
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Derek MacDonald, OD, FAAO
Elevated IOP is a strong risk factor for increased optic nerve head cupping and progressive glaucomatous field loss. Reversal of cupping may accompany a significant reduction in IOP, but this structural change has been attributed to mechanical laminar rebound and axonal thickening, and functional improvement rarely follows … or does it?
Bengtsson and colleagues found that the visual field did not improve after IOP reduction in the EMGT, but average baseline IOPs were relatively low and decreased modestly with treatment. Further, the logarithmic scale makes attentional visual field (AVF) analysis insensitive to early field loss, and reliance on global indices can mask focal defects. These limitations are compounded the subjective nature of psychophysical testing.
On the contrary, a growing body of evidence supports post-treatment improvement in pattern electroretinogram, or ERG, (an objective and linear assessment of retinal ganglion cell function) and local visual field sensitivity, suggesting that at least some retinal ganglion cells enter a period of reversible dysfunction preceding death during which treatment may “rescue” viable cells and restore function.
This emphasizes the importance of early diagnosis and robust IOP reduction, informed by functional assessment that relies on more than global indices and, ideally, on more than AVF analysis alone.
For some reason, I can’t help but picture a retinal ganglion cell on the wagon in Monty Python and the Holy Grail, … “I’m not dead yet …”
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