Clinical Application of Infrared-Light Microperimetry in the Assessment of Scotopic-Eye Sensitivity

Abstract

The eye can see pulsed near-infrared (IR) radiation with the color corresponding to half of the wavelength used. Until recently, the technology required for measuring IR vision was confined to optical laboratories and was not studied clinically. The current investigation sought to determine the values for IR thresholds in a healthy population. Methods: IR-light threshold was measured in 45 healthy participants, aged from 21 to 70 years. Ten patients with retinal pathology were included for comparison. Ocular media clarity was assessed with a straylight parameter. The sensitivity of dark-adapted eyes (expressed on a 0-26 dB scale) were tested using an IR microperimeter. The device consists of a femtosecond laser that emits 1045 nm light to project a stimulus at the retina. Results: All participants were able to see the IR stimulus, which they perceived as green, and all performed the test. Measurements at seven locations revealed lower sensitivity at the fovea (15.5 dB) than in paracentral regions (18.2 dB). We noted a significant straylight increase with age. Although, in our study population, it was only a slight,-0.18 dB decline per decade of the average IR-sensitivity. The retinal-pathology group demonstrated impaired sensitivity to IR light. Conclusions: We showed that IR-light sensitivity does not significantly decrease with age despite a straylight increase. A reference level for the IR threshold was proposed. The application of IR-light microperimetry can be extended to the assessment of retinal pathology.

Infrared- and white-light retinal sensitivity in glaucomatous neuropathy

“…Figure 2 contains a schematic drawing of the setup. It employs a femtosecond laser, the HighQ-2 laser (Spectra-Physics, CA, USA), to project IR-light stimuli through ultrashort pulses with 63 MHz of the pulse-repetition frequency and 250-fs pulse width 17 , 18 . The monochromatic IR light has a wavelength of 1045 nm and a full width at half maximum of 8 nm.…”

“…

Figure 2 Block diagram of the the optical setup for infrared-light retinal-sensitivity measurements. λ = wavelenght; F = repetition frequency; = pulse width; SM = single mode; NDF = neutral density filter; PM = power meter; PH = pinhole; LD = laser diode; APD = avalanche photodiode; SLO = scanning laser ophthalmoscopy, PC = personal computer 18 .

…”

“…A recently introduced two-photon excitation technique provides a new parameter of retinal function 15 – 19 . In contrast to standard (single-photon) vision 20 , the two-photon absorption by photoreceptor cells is a non-linear process that yields color perception while exposing the eye to infrared (IR) light 15 – 18 . For instance, a 1045-nm beam of light can be seen as green with the wavelength corresponding approximately to half of the stimulation beam (i.e., 522.5 nm) 15 , 18 .…”

“…In contrast to standard (single-photon) vision 20 , the two-photon absorption by photoreceptor cells is a non-linear process that yields color perception while exposing the eye to infrared (IR) light 15 – 18 . For instance, a 1045-nm beam of light can be seen as green with the wavelength corresponding approximately to half of the stimulation beam (i.e., 522.5 nm) 15 , 18 . In laboratory studies, the two-photon excitation approach demonstrated a higher precision than visible-light technology in testing retinal function and resistance to lenticular opacification 16 , 21 .…”

“…In laboratory studies, the two-photon excitation approach demonstrated a higher precision than visible-light technology in testing retinal function and resistance to lenticular opacification 16 , 21 . This novel approach has recently been applied in the studies of IR vision in the healthy population and patients with diabetic retinopathy 17 , 18 . However, the impact of glaucoma on IR-light sensitivity has not yet been evaluated.…”