Volume Perimetry

Abstract

Purpose Volume scotomas are three-dimensional regions of space that are not visible to the observer. Volume perimetry maps volume scotomas. Volume scotomas predicted from combining monocular visual fields assume known fixation locus (mainly foveal). However fixation loci are not always known, especially with central field loss. Here we demonstrate methods for measuring and calculating volume scotomas and discuss their practical implications. Methods Three patients (bitemporal hemianopia, binasal scotoma, and central field loss (CFL)) were evaluated. Slices through the volume scotomas were measured at three distances: at the plane of fixation, at a plane anterior to fixation (representing anterior volume perimetry), and a plane posterior to fixation (representing posterior volume perimetry). For anterior volume perimetry, patients fixated on a screen 100cm away through a beamsplitter that reflected the perimetric stimulus (at 50cm). For posterior volume perimetry, patients fixated on a near target (50cm) while perimetric stimuli were presented on a screen 150cm beyond the fixation. At the plane of fixation, monocular visual fields under binocular viewing conditions were measured using a computerized dichoptic perimeter. Results Posterior and anterior volume scotomas were documented in patients with bitemporal hemianopia and binasal scotomas respectively. The CFL patient demonstrated both anterior and posterior volume scotomas. Scotoma magnitude was considered to determine its effect on visual function. Conclusions Direct measurement of volume scotomas can be performed. Anterior and posterior volume visual fields can vary substantially from conventional binocular perimetry measured at the fixation plane, revealing blind areas not otherwise identified. These volume scotomas are likely to impair functional vision such as driving (for bitemporal hemianopes) and near work with small hand tools (for binasal scotomas). Patients with CFL will have impaired functional vision for both distance and near tasks. Consideration of volume scotomas can help provide more effective vision rehabilitation and counseling.

A Depth-Dependent Integrated VF Simulation for Analysis and Visualization of Glaucomatous VF Defects

“…Complicated procedures impractical for clinical practice are needed to perform real VVF testing as demonstrated previously. 9 In contrast, our simulation can estimate BVF on any object distance plane given any chosen fixation plane using real patient's data instantaneously.…”

“… 8 Conversely, the presence of an impaired BVF location at the fixation plane does not mandate impaired vision at the same location for every other depth plane. 9 It is, therefore, possible that objects appearing at impaired locations on distance planes different from the current fixation plane are at risk of being undetected by patients, which could lead to reduced efficiency in daily functioning and even accidents.…”

“…Direct measurement of VVF at representative planes has only been reported in one recent article. 9 Three slices of VF at the plane of fixation, a plane anterior to fixation, and a plane posterior to fixation were measured in three patients with a complicated set up. 9 The study found that anterior and posterior VVFs could vary substantially from conventional binocular perimetry measured at the fixation plane, revealing impaired areas not otherwise identified.…”

“… 9 Three slices of VF at the plane of fixation, a plane anterior to fixation, and a plane posterior to fixation were measured in three patients with a complicated set up. 9 The study found that anterior and posterior VVFs could vary substantially from conventional binocular perimetry measured at the fixation plane, revealing impaired areas not otherwise identified. The study, however, did not recruit typical glaucoma patients, and consequently cannot shed light on typical VVF defects likely to be experienced by people with glaucoma, the most common cause of VF loss.…”

New Challenges in Low-Vision Research

“…3 The measurement of three-dimensional scotomas (volume scotomas) will allow clinicians to better evaluate the impaired functional vision for tasks at different distances. 4 …”