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Editors Selection IGR 16-3

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Comment by Ivan Goldberg on:

59604 Short-Term Enhancement of Visual Field Sensitivity in Glaucomatous Eyes Following Surgical Intraocular Pressure Reduction, Wright TM; Goharian I; Gardiner SK et al., American Journal of Ophthalmology, 2015; 159: 378-85.e1

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In this prospective, case-controlled cohort study of 30 eyes of 30 glaucoma patients who underwent trabeculectomy or insertion of a glaucoma drainage device compared with 41 eyes of 28 patients who continued stably on medical therapy, Wright and co-workers set out to determine whether or not intra-ocular pressure (IOP) reduction improved visual field (VF) sensitivities in the short-term. Matched for age and VF mean deviation, the two groups were followed with serial VFs for three months post-surgery or for 18 months with ongoing stable medications.

Whereas surgery reduced IOP from a group mean of about 18 to 10 mmHg, stable medical treatment maintained cohort mean IOP at about 13.7 mmHg.

Localized VF sensitivities were recorded for all tested points, for 16 central and for 36 peripheral points. In the operated eyes, an average of six of all points improved compared with three in the medical group; for the central 16, 1.8 points improved following surgery compared with 0.8 without and for the peripheral 36, 4.6 points improved compared with 2.6. With VF sensitivity fluctuations, as anticipated, some points also deteriorated: again more often in the surgical versus the medical group, suggesting greater variability following surgery.

In the surgery versus medical groups, VF Mean Deviation improved in ten eyes versus six and Pattern Standard Deviation, in nine eyes versus three.

Asked the investigators: what clinical parameters were associated with VF improvements in the surgery group? Favorable were trabeculectomy over glaucoma drainage device, an associated improvement in ocular perfusion pressure (OPP) and greater improvement in eyes with worse pre-surgical damage. Factors that seemed to play no part included eye laterality, patient age, baseline IOP or absolute IOP reduction achieved.

As quoted by the authors, despite the relatively small sample size, the presence of some confounders and the lack of an established baseline VF sensitivity variability, these results support Spaeth's report that IOP reduction leads to an improved VF sensitivity¹ as well as the suggestion by Caprioli² and by Musch et al.³ that the most damaged areas of the VF seem to show the most benefit. These findings also conform with similar indications of partial reversibility of glaucoma damage when assessed electro-physiologically.

At any one time in a glaucoma-affected eye there would seem to be populations of retinal ganglion (RGCs)and their support cells that are fully functional, that are dysfunctional but redeemable if a noxious element is reduced or removed, that are irreversibly damaged and non-functioning and are at various stages of degeneration. Surgical reduction of IOP would seem to allow dysfunctional RGCs to return to more normal activities, at least in the short term.

This all seems to underline the complex relationship between IOP levels and VF sensitivities. Nonetheless, to have potential reversibility of glaucoma damage result from risk factor (IOP) reduction is exciting and promising, particularly from a neuroprotection perspective.

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