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Editors Selection IGR 16-4

Visual Function Tests: Postillumination pupil responses

Comment by Chris Johnson on:

47976 Intrinsically photosensitive (melanopsin) retinal ganglion cell function in glaucoma, Feigl B; Mattes D; Thomas R et al., Investigative ophthalmology & visual science, 2011; 52: 4362-4367

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Feigl et al. (1835) evaluated sustained, post-illumination pupil responses (PIPR) to ten-second presentations of a 7.15- degree diameter short wavelength (488 nm) and long wavelength (610 nm) high intensity light stimulus in 25 glaucoma patients and 16 age-matched healthy participants with normal visual function. The purpose of this investigation was to determine whether glaucomatous damage affected intrinsically photosensitive (Melanopsin) retinal ganglion cell function. The difference between the pupil response to blue and red stimuli was smaller for the glaucoma patients than for the normal control participants, and the advanced glaucoma patients had a smaller difference between red and blue pupil responses in comparison to the early glaucoma patients. However, the kinetics (time to the plateau of the PIPR) was not different for the two groups. These findings indicate that patients with moderate and severe glaucomatous damage exhibit sensitivity loss for the intrinsically photosensitive retinal ganglion cells, which suggests that this procedure may be useful in monitoring glaucomatous progression. In general, this was a carefully performed investigation that was well designed, accounted for many possible confounding factors, and utilized an appropriate statistical analysis procedure. The authors are to be congratulated for their efforts in this regard. It would be helpful to readers if the local pattern of visual field loss (and the criteria for classifying glaucomatous visual field properties), the presence or absence of other ocular, neurologic or systemic diseases were present in the glaucoma patients, and other clinical factors were specified in greater detail. In future investigations, it will be informative to determine which of the many classes of intrinsically photosensitive retinal ganglion cells are adversely affected by glaucoma (assuming tests can be developed to differentiate among these types), whether duration or type of medical treatment is related to this effect, whether individual measurement of optical media (mostly lens) transmission properties enhance our understanding of this effect, the relationship of PIPR deficits to optic disc damage and visual field loss, and the relationship of PIPR to risk factors for development and progression of glaucoma.

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