Visual Activity Evoked by Infrared in Humans After Dark Adaptation

Not Applicable

Completed

Conditions: Age Related Macular Degeneration
Congenital Stationary Night Blindness
Retinitis Pigmentosa
Colorblindness

Interventions: Other: VEP
Other: Tungsten halogen light with narrow bandpass filters
Other: ERG

Registration Number: NCT02909985

Lead Sponsor: University of New Mexico

Brief Summary: This pilot study will evaluate the visual response to infrared (IR) in humans after dark adaptation. The investigators plan to determine which wavelength and intensity the human eye is most sensitive to in healthy and color-blind participants by using a broad spectrum light source and wavelength-specific IR bandpass filters.

The long-term goal of this research is to better understand the role that IR plays in visual function, and whether this can be manipulated to allow for vision in certain retinal pathologies that result from loss of photoreceptor cells. The investigators central objective is to test the electrophysiologic response to IR in the dark-adapted retinal and visual pathways. The investigator's central hypothesis is that IR evokes a visual response in humans after dark adaptation, and the characteristics of this response suggest transient receptor potential (TRP) channel involvement. The investigators rationale is that a better understanding of how IR impacts vision may allow for an alternative mechanism for vision in a number of diseases that cause blindness from the degradation or loss of function of photoreceptor cells. The investigators will test the investigator's hypothesis with the following Aims:

Aim 1:

Arm 1: To determine the optimal IR wavelength for visual perception in dark-adapted human participants. The investigators hypothesize that the healthy human eye will detect IR irradiation, with a maximum sensitivity at a specific wavelength. Using a broad-spectrum light source with wavelength-specific bandpass filters, the spectral range of visual perception to IR will be evaluated.

Arm 2: To determine the optimal IR wavelength for visual perception in dark-adapted human participants who are colorblind. The investigators hypothesize that the colorblind human eye will detect IR irradiation, with a maximum sensitivity at a specific wavelength. Using a broad-spectrum light source with wavelength-specific bandpass filters, the spectral range of visual perception to IR will be evaluated.

Detailed Description: BACKGROUND: Visual impairment affects 285 million people worldwide. The prevalence of visual impairment in the US is expected to rise from 3.3 million in 2000 to 5.5 million in 2020. This will exacerbate the current economic burden of vision loss, which is already $38.2 billion per year in direct and indirect costs. The leading cause of blindness in high-income countries is due to age-related macular degeneration (AMD), a disease that leads to gradual loss of the photoreceptor cell layer. An estimated 1.75 million people have AMD in the US and another 7.3 million are at risk. Importantly, despite the loss of photoreceptor cells in AMD, the other cellular layers in the retina remain largely intact.

The retina lines the back of the eye and is composed of structural layers. The outer nuclear layer contains photoreceptors called rods and cones. The inner nuclear layer includes bipolar, horizontal, and amacrine cells. Most anteriorly, the ganglion cell layer has axons that exit the eye as the optic nerve. Visual image formation begins when a photon of light enters the eye, passes through all retinal layers, and is absorbed by the photoreceptor cells. These cells transduce the photon of light into an electrochemical signal, which is communicated to bipolar cells, followed by the ganglion cells. Here, an action potential is generated and propagated via the optic nerve to the area of the brain where vision perception occurs. When the eye is dark-adapted, the cells in this pathway are potentially more sensitive to other types of stimuli, such as IR. The investigators believe cation channels called TRP channels in ganglion cells are activated by IR in this dark-adapted state, creating the visual response to IR. Heat is a known activator of certain subtypes of these channels elsewhere in the body. TRP channels are also responsible for IR vision in pit vipers and vampire bats.

Palczewska et al. reported that visual perception to IR occurred through a process of direct two-photon isomerization of visual pigments. However, other evidence suggests IR perception can occur through single IR photon absorption. Studies that use IR to test the functionality of implanted visual prosthesis have noted a greater response to IR in the non-implanted eye when compared to the implanted eye on both VEP tests and ERG. On ERG, a specialized response specific to IR was found called the scotopic threshold response (STR). This response occurs under dark-adapted conditions and correlates with a response at the ganglion cell layer. Direct IR activation of TRP channels on ganglion cells could initiate a visual response. Based on these findings, the investigators hypothesize the human response to IR under dark adaptation occurs at the level of the ganglion cells through heat-activated TRP channels.

RESEARCH DESIGN AIM1: To determine the optimal IR wavelength for human visual perception while dark-adapted in the healthy human eye.

Introduction for Aim 1: The objective of this aim is to determine the optimal wavelength of IR to which the human eye is sensitive. To obtain this objective, the investigators will test the working hypothesis that the healthy human eye, and those with colorblindness, will detect a range of IR wavelengths, with a preference for a specific wavelength. The investigators will test the working hypothesis using a broad-spectrum light source with wavelength-specific bandpass filters in the IR range. The investigators' rationale for this aim is that understanding the optimal IR wavelength of the human eye will aid in future investigations when testing the visual response to IR using diagnostic equipment. This is important because it could impact the way other ophthalmologic modalities use IR to diagnose and treat visual pathologies.

Research Design for Aim 1: A total of healthy 21 participants (15 with normal vision and 6 with colorblindness) aged 18 and older will be recruited using the University of New Mexico (UNM) Clinical and Translational Science Center (CTSC) Clinical Research Volunteer Registry HRRC-06412. Informed consent, participant demographics, past medial and visual history, and a general eye exam will be obtained using the CTSC research coordinator. Each participant will be placed in a dark room for an hour to allow for optimal dark adaptation of the eye. The investigators will use a broad-spectrum light source with wavelength-specific bandpass filters of different IR wavelengths. A total of 12 filters will be used ranging from 850 nm to 1400nm. Intensity curves will be built for each wavelength, by slowly turning up the power until the participant indicates a visual response to the stimulus.

Data Analysis for Aim 1: Data will be analyzed by the investigators. Descriptive statistics will be used to evaluate demographics, general and visual health information, and reported optimal wavelengths. The investigators' analysis will compare differences among responses for each wavelength. To the investigators' knowledge, there have been no studies evaluating which IR wavelength is optimal for human visual perception, thus the investigators assume a low effect size of 10%, which would produce an 82% chance of at least two out of 30 healthy participants giving a preferred response to a specific wavelength. The investigators will describe the estimated effect sizes in response to the findings.

Expected Outcomes for Aim 1: The investigators expect the human eye to perceive a range of IR wavelengths, but have a specific wavelength optimal in terms of brightness.

Potential Problems \& Alternative Strategies for Aim 1: To prevent sampling bias, the investigators plan to obtain a representative sample from New Mexico; however, participants may be younger and more educated than the general population. The confounding bias of light pollution may occur, which would prevent dark adaptation and decrease the IR sensitivity. A photometer will assess the room for background photons.

Recruitment & Eligibility

Status: COMPLETED

Sex: All

Target Recruitment: 21

Inclusion Criteria

Normal Vision
Colorblindness
Age related macular degeneration
Congenital Stationary Night Blindness

Exclusion Criteria

Diabetes
Heart disease
History of eye injury
History of eye trauma
History of eye disease except for those specified in the inclusion criteria
Pregnant women will also be excluded from Aim 2 and 3
Persons with allergies to adhesives will be excluded from Aim 2 and 3
Contact dermatitis
Documented adverse reaction to dilating drops
Documented adverse reaction to topical anesthetics
Vulnerable populations

Study & Design

Study Type: INTERVENTIONAL

Study Design: PARALLEL

Arm && Interventions

Group	Intervention	Description
Visual Evoke Potential Test	VEP	1. 5 healthy participants will undergo an VEP with standard baseline tests followed by similar tests using IR, with standard baseline tests followed by similar tests using IR 2. A total of 15 participants, or five per retinal disease, will be recruited . Retinal diseases include retinitis pigmentosa, age related macular degeneration, congenital stationary night blindness, cataracts. Participants will undergo an VEP with standard baseline tests followed by similar tests using IR, with standard baseline tests followed by similar tests using IR
Visual response to IR	Tungsten halogen light with narrow bandpass filters	1. 15 healthy participants will describe IR light passing through narrow bandpass filters over a broad spectrum light source 2. 10 colorblind participants will describe IR light passing through narrow bandpass filters over a broad spectrum light source For both groups, as intensity in increased from 0 to 12 V, participants will say if/when they see a visual response to infrared light from a broad band Tungsten halogen light with narrow bandpass filters ranging from 850 nm to 1400 nm. At the end of three trials per filter, the intensity will be turned up to 12 V, and participants will describe the color they see.
Electroretinography	ERG	1. 5 healthy participants will undergo an ERG with standard baseline tests followed by similar tests using IR, with standard baseline tests followed by similar tests using IR 2. A total of 15 participants, or five per retinal disease, will be recruited . Retinal diseases include retinitis pigmentosa, age related macular degeneration, congenital stationary night blindness, cataracts. Participants will undergo an ERG with standard baseline tests followed by similar tests using IR, with standard baseline tests followed by similar tests using IR

Primary Outcome Measures

Name	Time	Method
Visual Perception to Infrared: Mean Minimal Intensity (uW) at Which Participants Could See IR Between 900 - 1400 nm.	after 30 minutes of dark adaptation, up to 2 hours	We measured the minimum threshold intensities (uW) via subjective perception of near IR light (900 - 1400 nm) in 50 nm intervals. After 30 minutes of dark adaptation and over three trials, participants verbalized by saying 'yes' to the minimal intensity they could see the IR stimulus as the power source for the light was slowly increased from 0V to 12 V. The voltage was averaged for the three trials at each wavelength. Analysis of variance was used to evaluate the effect of the wavelength on the threshold intensity. This was done for two groups/arms, one with normal color vision and one with colorblind vision.

Secondary Outcome Measures

Name	Time	Method
Description of Color	after 30 minutes of dark adaptation, up to 2 hours	A subjective description of color was given by each participant for each wavelength between 850 - 1400nm while at 12V.