Fixation Stability and Scotoma Mapping for Patients With Low Vision

Abstract

Purpose To develop a simplified device that performs fundus perimetry techniques, such as fixation mapping and kinetic perimetry. Methods We added visual stimulation to a near infrared retinal imager, the Laser Scanning Digital Camera (LSDC). This device uses slit scanning illumination combined with a 2 dimensional CMOS detector, with continuous viewing of the retina. The CMOS read-out was synchronized with the slit scanning, thereby serving as a confocal aperture to reduce stray light in retinal images. Series of retinal images of 36 deg were automatically aligned to provide data for fixation maps and quantification of fixation stability. The LSDC and alignment techniques also provided fundus viewing with retinal location correction for scotoma mapping. Results First, fixation mapping was readily performed in patients with central scotoma or amblyopia. The automatic alignment algorithm allowed quantification of fixation stability in patients with macular pathologies that did not cause scotoma. Second, fixation stability was rapidly and quantitatively assessed by the automatic registration of a series of retina images. There was no significant difference in the fixation stability with automatic vs. manual alignment. Kinetic perimetry demonstrated that fundus imaging helped reduce the variability of perimetric data by identifying and preventing false positives due to eye motion. We found that the size of the blind spot was significantly larger for dark targets on brighter backgrounds than when the contrast was reversed (p < 0.045). This is consistent with incremental targets being detected partially or wholly due to scattered light falling on more sensitive retinal locations. Conclusions Fundus perimetry with the LSDC allows for a wide range of fixation and perimetry tasks.

Cones in ageing and harsh environments: the neural economy hypothesis

“…It does no good to scan light across the retina and then to use a sample‐and‐hold detector without a method to unmix the light from different retinal areas. The line scan technique can be used on a two dimensional detector, as long as there is a method for separating in space and/or time the light returning from two or more parts of the retina …”

“…As the targets are typically presented in Maxwellian view and with a small exit pupil, variation in intensity and other effects due to pupil size variations across subjects are minimised. While microperimetry or fundus perimetry are the best‐known applications, there are two broad types of methods for functional measurements, as detailed previously . One method includes projecting the stimuli or the stimulation beam onto the retina with one or more of the same beams used for imaging the fundus .…”

Confocal retinal imaging using a digital light projector with a near infrared VCSEL source

“…A low divergence 860nm VCSEL (RPMC Lasers Inc., O’Fallon MO) with a maximum output power of 750mW was used as the illumination source. A VCSEL was a reliable source used for NIR imaging with visual stimuli in the LSDC 8 , and the current VCSEL was selected for the DLO due to its relatively uniform and circularly symmetric output profile and low speckle noise. As compared to a typical high-power LED, the VCSEL has a smaller etendue and greater spatial coherence; this allows the VCSEL to remain collimated over greater distances, avoids the need for a custom total-internal-reflectance (TIR) prism, facilitates the addition of coherent sources at other wavelengths, and eliminates losses from pupil shaping.…”

“…Right. Registration coordinates are plotted in color to indicate the direction of a subject’s gaze over time (proceeding blue to red), as previously done with Aeon Imaging’s Laser Scanning Digital Camera 8 . Image registration and averaging is often used to improve signal to noise.…”

“…In this configuration, the rolling shutter acts as a flexible electronic aperture, which can be finely adjusted in position and width through software in real-time. 5–8 By temporally and spatially synchronizing the illumination lines to the rolling shutter exposure, the DLO acquires a line-confocal image of the entire field of view every frame. To image the retina, the illumination and detection pathways are combined using a beamsplitter, shown schematically in Figure 1.…”