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Editors Selection IGR 13-3

Function Measurement: Multifocal pupillographic PM

Comment by Harry Wyatt on:

46813 Multifocal pupillographic perimetry with white and colored stimuli, Maddess T; Ho Y-L; Wong SSY et al., Journal of Glaucoma, 2011; 20: 336-343

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This is a further study of the authors' device for multifocal pupillographic perimetry (mfPOP), which uses the pupillary light reflex (PLR) to 'objectively' assess visual fields. At each test location, response amplitude to a fixed stimulus is estimated and compared to normal database values. One constraint on the technique's usefulness is the amount of amplitude variation between normal subjects (SDb-norm), which determines the deviation from the normal mean that reliably indicates abnormality, and also the number of potentially discriminable levels of abnormality. Whatever reduces SDb-norm increases the technique's potential usefulness. Maddess et al. (1310) considered that if short wavelength (blue) light contributed significantly to the PLR during mfPOP, between-subject variation could result partly from between-subject variation of age-related pre-photoreceptor changes. Using stimuli with different blue content, they characterized the shape of the stimulus/response curves ‐ compressive functions they call 'saturation'. The somewhat tepid conclusion is that the results 'seem to provide no reason not to use [yellow] stimuli.' Since relatively transient PLR responses to moderate stimuli show 'luminance'-type spectral sensitivity (L+M cone-driven), the absence of much blue contribution agrees with expectation. A second conclusion is that 'very saturating luminances should be avoided' because operating further along the compressive function makes it harder to discriminate normal from abnormal, or degrees of abnormality. However, useful stimuli must also be strong enough to elicit responses some particular number of SDb-norms above just-detectable. Another reason for avoiding very strong stimuli is that they can stimulate locations beyond the nominal test location due to light spread. The PLR is particularly vulnerable to this, since light incident anywhere on the retina can contribute to the single output. [For those reading the paper, don't be misled by a reference on page 337 to stimuli with '1 and 4 presentations/s/ region (MI1 and MI4)'; MI1 is the higher-frequency stimulus giving smaller responses (Fig. 3).]

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