Two-Photon Microperimetry: A media opacity-independent retinal function assay

Abstract

Humans perceive light in the visible portion of electromagnetic radiation. However, visible light is scattered and attenuated by optical media opacities. Because all conventional visual function tests rely on visible light, test results are reduced in patients with optical media opacities like corneal scars, cataracts, and vitreous hemorrhages. Infrared (IR) light has greater penetrance through tissue than visible light. Two-photon IR visual stimulation, a recently pioneered technology, should enable testing of retinal visual function and produce results that are less susceptible to media opacities. The effects of simulated media opacities on visual performance in young healthy volunteers and the change in visual function in healthy phakic patients of two age ranges (20-40 and 60-80-year-old) were studied using conventional testing and 2-photon infrared visual stimulation. All subjects completed visual function testing using cone contrast threshold (CCT) testing, conventional microperimetry, visible light microperimetry from a novel device (2PM-Vis), and infrared 2-photon microperimetry (2PM-IR). Retinal sensitivity measured by 2PM-IR demonstrated lower variability than all other devices relying on visible spectrum stimuli. Retinal sensitivity decreased proportionally with the transmittance of light through each filter. CCT scores and retinal sensitivity decreased with age in all testing modalities. Visible spectrum testing modalities demonstrated larger test result differences between young and old patient cohorts; this difference was inversely proportional to the wavelength of the visual function test. 2PM-IR mitigates media opacities which may mask small differences in retinal sensitivity when tested with conventional visual function testing devices.One Sentence SummaryTwo photon infrared visual function testing produces results that are less susceptible to media opacities than conventional tests.

In vivo imaging of the human eye using a 2-photon-excited fluorescence scanning laser ophthalmoscope

“…The visual field test done by the clinical instrument (MAIA, photopic conditions) before TPEF shows typical visual sensitivity with an average threshold of 27.7 dB, and a value of 27.4 dB one month after TPEF imaging. We also performed perimetry in photopic and scotopic conditions, using both single-photon and two-photon isomerization of visual pigments (7,34,35). Small changes of visual sensitivity with aging were reported earlier in scotopic perimetry testing (36), therefore we decided to use it as another test of retinal function.…”

Seeing invisible light: 2-photon microperimetry to measure visual function

“…As described by Wei et al, a stimulus pattern formed by either two-photon infrared or visible light was projected onto the retina. 9 Test subjects were asked to adjust the intensity of the stimulus by scrolling either up or down on a computer mouse, which would either increase or decrease the intensity of the stimulus entering the eye. 9 When the visibility threshold was reached and the subject could no longer see the stimulus, the subject was asked to click on the mouse, thereby recording the threshold power that could be detected.…”

“… 9 Test subjects were asked to adjust the intensity of the stimulus by scrolling either up or down on a computer mouse, which would either increase or decrease the intensity of the stimulus entering the eye. 9 When the visibility threshold was reached and the subject could no longer see the stimulus, the subject was asked to click on the mouse, thereby recording the threshold power that could be detected. 9 The same procedure was performed four more times, and an average threshold sensitivity for all five replicate tests was calculated.…”

“… 9 When the visibility threshold was reached and the subject could no longer see the stimulus, the subject was asked to click on the mouse, thereby recording the threshold power that could be detected. 9 The same procedure was performed four more times, and an average threshold sensitivity for all five replicate tests was calculated. 9 Conventional microperimetry (cMP, Nidek MP-3, San Jose, CA) assessed macular sensitivity using a Goldmann III stimuli over an intensity range from 0 to 34 dB under mesopic conditions.…”

“… 9 The same procedure was performed four more times, and an average threshold sensitivity for all five replicate tests was calculated. 9 Conventional microperimetry (cMP, Nidek MP-3, San Jose, CA) assessed macular sensitivity using a Goldmann III stimuli over an intensity range from 0 to 34 dB under mesopic conditions. Although multiple stimuli across the macula were tested, only the foveal sensitivity was included in our assessment.…”