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Editors Selection IGR 10-1
Perimetry: High-resolution multifocal pupillographic perimetry
Comment by Brad Fortune on:
27738 High-Resolution Multifocal Pupillographic Objective Perimetry in Glaucoma, Carle CF; James AC; Kolic M et al., Investigative Ophthalmology and Visual Science, 2011; 52: 604-610
This study by Carle et al. (155) follows from their previous work on the development of techniques for objective perimetry, including multifocal visual evoked potential (mfVEP) and more recently multifocal pupillographic objective perimetry (mfPOP). As Carle and colleagues review in their new paper, the essential technique of using the pupillary response to focal light stimuli as an objective method for performing perimetry has been the subject of previous studies by other groups dating back twenty years. One potentially strong advantage of such techniques is their objectivity, that is, their ability to assess visual sensitivity independently of the patient's subjective response criteria. This aspect generally leads to greater patient acceptance and often also increases reliability. Another important development by this group of investigators is the dichoptic stimulus presentation, which enables concurrent testing of both eyes. This and other advancements have helped to reduce the testing time to under six minutes (three minutes per eye). The authors also point out that the mfPOP technique is completely noncontact, and thus less invasive than the mfVEP and less complicated to administer. Given that the authors' previously successful work with mfPOP had been based on a stimulus pattern with 24 test regions per eye, the specific purpose of their new study was to assess performance of a higher-resolution stimulus pattern with 40 test regions per eye and to compare four different stimulus protocols, varying primarily in their temporal characteristics, for diagnostic accuracy in a group of 17 open-angle glaucoma patients with a wide range of disease severity and in 19 normal subjects.
The authors report that the temporal stimulus protocol having the most sparse presentation rate (the longest inter-stimulus intervals) provided the highest signal-to-noise ratio (SNR) as well as the best diagnostic performance for discriminating glaucomatous from normal eyes. It is interesting that this observation for mfPOP is similar to what had been discovered originally by this same group for mfVEP (and since confirmed by our and two other groups), especially since it is likely based on different physiological mechanisms. Nevertheless, this result is an important step forward in the development of mfPOP as the authors demonstrate the increased spatial resolution offers diagnostic advantages over their previous 24-region mfPOP stimulus pattern without any significant loss of SNR, due in large part to the temporally sparse stimulation paradigm. The mfPOP responses from the patients with glaucoma were significantly smaller in amplitude, had delayed peak times and were narrower (had shorter time courses) as compared to normal subjects. The diagnostic performance of the best mfPOP protocol was on par with several modes of subjective perimetry (e.g., standard white-on-white and frequency-doubling perimetry) carried out in the same cohort. Finally, another important advantage of mfPOP discussed by Carle and co-authors is that it is relatively less prone to uncorrected refractive error and lens opacities than some other forms of perimetry.
As the authors conclude, it will be important to study larger patient groups and for these encouraging results with mfPOP to be confirmed independently by other investigators. This is not trivial as the methods for presenting and controlling the stimulus, as well as for monitoring, synchronizing and processing the pupillary responses are all complex and technically demanding. The paper by Carle et al. Does not offer enough methodological detail for other laboratories to replicate the study identically, nor perhaps even for readers to fully evaluate the validity of the results. However, fortunately it appears that a mfPOP device is under commercial development, which may then offer opportunities for other groups to confirm its promising capabilities for glaucoma diagnosis and management.
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