Near-infrared light sensitivity as a new tool to assess retinal function in age-related macular degeneration

Abstract

Purpose : Human eye's perception of near-infrared (NIR) light results from the two-photon absorption by retinal photoreceptors. In such a setting, pulsed NIR laser produces color sensation that corresponds (closely but not precisely) to the so-called visible spectrum with half of the wavelength used. The mechanism of NIR vision has recently been elucidated, and its clinical application sought. In this case-control study, we determined retinal sensitivity to NIR in patients with age-related macular degeneration (AMD) and compared it to visible-light microperimetry.

Methods : We recruited 24 AMD patients and 20 healthy controls and measured their visual function in one (better) eye. The NIR threshold was assessed using a two-photon excitation setup, which employs a femtosecond laser to project 1045-nm stimuli with ultrashort pulses. An array of neutral-density filters attenuates the laser power to meet the safety requirements of ANSI Z136.1-2014. Retinal sensitivity to visible light was measured using an MP-1 microperimeter (Nidek Technologies Srl). A customized 12-degree grid consisting of 44 retinal loci was applied. Best-corrected visual acuity (VA) and the logarithm of straylight were secondary outcome measures.

Results : The median (interquartile range) age of AMD and control subjects was 77.2 (71.8 to 79.9) years and 71.3 (67.8 to 78.3) years, respectively. AMD resulted in decreased logMAR VA, i.e., 0.09 (0.04 to 0.22), which in normal eyes was -0.04 (-0.06 to 0.02). A comparable level of straylight was found in the two populations with 1.18 (1.07 to 1.45) log(s) in the study and 1.16 (1.01 to 1.30) log(s) in the healthy group. The NIR threshold of AMD and control groups differed significantly (Mann-Whitney, P=.0001): 7.9 (7.1 to 9.5) dB vs. 10.5 (9.5 to 10.7) dB. In visible-light microperimetry, retinal sensitivity was also significantly decreased (Mann-Whitney, P=.0001) in AMD (14.4; 11.1 to 15.3 dB) compared to the controls (17.5; 16.5 to 18.3 dB).

Conclusions : We demonstrated that NIR retinal sensitivity in AMD patients is significantly impaired compared to healthy subjects, similarly to standard microperimetry. Although further research is needed, this proof-of-concept study suggests that this (new) functional parameter can be used in AMD patients' retinal-function assessment beyond standard VA measurements.

This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.