Abstract
Purpose :
The human eye’s perception of infrared light arises from two-photon absorption at the retinal photoreceptor cells, which can be activated by a pulsed laser source. The infrared light produces color perception that corresponds to approximately half of the wavelength of the laser emission. The mechanism of IR vision has only recently been elucidated. The goal of this study was to determine a normative level for infrared light sensitivity in different age groups of healthy subjects.
Methods :
We enrolled 40 subjects aged 20 to 60 years (10 for each decade of life) without any history of ocular or systematic diseases. Only eyes with Snellen visual acuity of 0.8 or better and a spherical equivalent of less than ±4.00D were included. The participants received a complete eye examination to confirm eligibility. Optical coherence tomography and light scattering assessment were also performed. All participants were dark-adapted for 30 minutes. Sensitivity was measured at seven test loci (up to 15°) with the Goldmann size III stimulus and the method of adjustment. In a custom-made procedure, measurements were performed in compliance with ANSI Z136.1 and EN 60825−1 standards using a femtosecond laser (1045nm, 63MHz repetition frequency, 250 fs pulse duration). Images of the fundus were recorded with scanning laser ophthalmoscopy. Sensitivity values were expressed in decibels (dB) on a 0 (1mW) to 30 (1μW) dB scale.
Results :
There was a slight loss of -0.6 dB per decade in the cumulative threshold, but regression analysis showed the lack of a significant correlation between age and sensitivity. The intergroup analysis confirmed that infrared vision did not significantly differ between the four decades of life. The sensitivity level did not significantly correlate with visual acuity, spherical equivalent, retinal thickness or straylight parameter. The comparison of values measured at the seven locations showed a significant difference between the central (19.7 ±2.2dB) and the peripheral retina (22.5 ±2.4dB).
Conclusions :
We confirmed that infrared vision can be successfully measured in a clinical setting. Unlike visible-light sensitivity, this infrared perception proves independent of age. We proposed a norm for infrared sensitivity in healthy individuals, which can be considered a reference in future studies on various ocular pathologies.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.