Billy Randall Hammond

Macular pigments (MP; lutein, zeaxanthin, and meso-zeaxanthin) filter short-wavelength light and have been linked to reduced glare and enhanced visual performance. Whether macular pigment optical density (MPOD) is associated with contrast sensitivity (CS) under conditions of minimal MP absorption remains unclear. Fifty-two adults (mean age = 23.5 ± 8.0 years; range = 18–58 years; 85% < 25 years) participated. MPOD was measured using customized heterochromatic flicker photometry. CS was assessed monocularly in the same eye at five spatial frequencies (1.6, 3.2, 8, 16, and 24 cycles/degree), using a custom optical system with narrowband 520 nm laser stimuli. No significant correlations were found between MPOD and CS at any spatial frequency (all |r| ≤ 0.08, all p ≥ 0.59), including when individual area estimates were made for each participant’s curve (area under the logged CSF). Separate partial correlations controlling for iris lightness or habitual visual correction were also non-significant. Although MP has been shown to be related to CS when measured under glare or blue haze conditions, these findings suggest that when filtering by MP is minimized, direct effects on CS, especially on the young healthy eye, are likely minimal.

Clinical relevance: Vernier acuity (VA) is a common clinical metric used to evaluate cortical visual processing and macular health that is relatively independent of typical optical limitations (such as blurring). Background: Past studies have shown that vernier thresholds do not tend to vary according to blur, intensity and spectral content. This last variable, however, is the most inconsistent and has never been measured using relatively narrowband wavelengths. Methods: This study measured vernier thresholds (VT) as a function of wavelength (n = 15) and intensity (n = 5) in healthy young adults (mean age = 24.8 ± 2.3 years) with normal (or near-normal), corrected vision. VTs were tested using backlit apertures. Narrowband stimuli (420–660 nm) and broadband intensities were produced by a 1000 W Xenon arc lamp with interference filters. VTs, defined as the minimum detectable misalignments between two thin rectangular apertures, were recorded using a digital micrometer. Results: VTs did not vary significantly with wavelength (F (6,84) = 1.56, p = 0.17). Similarly, VTs did not vary significantly with the different broadband intensities (F (5,20) = 1.30, p =0.31). Conclusions: The stability of vernier acuity across these conditions indicates that hyperacuity performance is largely invariant to spectral composition and relatively stable across the limited photopic-to-mesopic intensity range that we tested. These findings are consistent with models proposing that vernier acuity depends primarily on post-receptoral neural mechanisms rather than optical or wavelength-dependent retinal factors.

Purpose: The contrast sensitivity function (CSF) can be used to assess even subtle changes in visual function. These changes are likely amplified in the presence of a stressor such as glare. In this study, we tested mesopic and photopic CSF in the absence/presence of an ecologically valid glare source. CSF was tested within subjects, comparing a high energy visible (HEV)-filtering contact lens against a clear comparator lens of similar material and design. Methods: This was a randomized, controlled, and double-masked study. Forty participants (19–65 years) provided photopic (n=20) or mesopic (n=20) CSF (1.6, 3.2, 8, 16, and 24 cpd) both with and without veiling glare. CSF was measured using a customized optical system. Two separate light channels were combined with a beam splitter that allowed contrast modulation using sine-wave gratings on glass. Glare was interposed between the grating and the subject's eye using an ancillary xenon-based optics channel. Results: The mean area under the CSF curve derived for both photopic and mesopic CSF (with and without glare) was significantly improved by use of the HEV-absorbing lens compared with the control. With a glare source, the least-squares mean differences (95% confidence interval) were 0.3 (0.24–0.36) and 0.14 (0.10–0.18) under photopic and mesopic conditions, respectively. In the absence of a glare source, the least-squares mean differences (95% confidence interval) were 0.26 (0.21–0.31) and 0.28 (0.20–0.37) for photopic and mesopic conditions, respectively. Conclusion: The HEV-absorbing lens significantly improved CSF when tested under mesopic and photopic conditions and both with and without veiling glare.

Wavelength influences multiple aspects of visual performance, yet its role in spatial resolution remains incompletely understood due to confounding factors such as luminance differences, chromatic aberration, and intraocular scatter. This study assessed how narrowband light of different wavelengths affects two-point separation thresholds under controlled stimulus and ocular conditions. Action spectra for fine spatial resolution were measured using an equal-energy approach. Sixty healthy young adults (mean age: 22.7 ± 3.3 years) with normal vision were tested in a two-point resolution task. Narrowband stimuli (420–660 nm) and a broadband white condition were produced by a 1,000-W Xenon arc lamp with interference filters. Participants were preselected for optimal acuity. Thresholds, defined as the minimum resolvable separation between two-point sources (two-point separation thresholds), were recorded using a digital micrometer, and converted to visual angle for analysis. Separation thresholds varied significantly with wavelength with short-wave light (420 nm) yielding poorer resolution compared to long-wave light (660 nm). Iris pigmentation (color, lightness, and a combination of color + lightness) also influenced performance with lighter irides associated with higher thresholds, and the largest group differences observed at short wavelengths. Two-point resolution shows systematic wavelength dependence under equal-energy conditions, with performance degraded in the short-wave range. These effects likely reflect the combined influence of chromatic aberration, optical scatter, and photoreceptor sampling, rather than scatter alone. Consideration of both optical and neural mechanisms is essential when interpreting wavelength-dependent changes in spatial vision.

Purpose Atmospheric short-wave scattered light (blue haze) limits visual range by reducing the contrast of distant objects. While theoretical models and prior research suggest that filtering short wavelengths can improve visual range, significant individual differences persist in tolerance to veiling luminance, even among individuals with similar ocular health and acuity. This study examined whether a commercially available blue-light filtering (BLF) lens design could enhance visual range under simulated blue haze conditions in an older pseudophakic population. Methods Forty older pseudophakic adults (M = 71.15 ± 5.82 years) were tested using a randomized, controlled, cross-over design. Visual range was assessed via a custom two-channel optical system presenting a sinusoidal grating target veiled by adjustable blue haze (Correlated Color Temperature = 9424 K). Participants viewed the target through a clear control lens and a test BLF lens in randomized order. Visual range thresholds, defined as the maximum blue haze energy tolerated before target detection failed, were determined using the psychophysical method of limits. Results Participants tolerated significantly greater (U = 1035.00; p = 0.024) average blue haze energy with the BLF lens (3.49 log relative energy [LRE]) than with the clear control lens (3.43 LRE). On average, the BLF lens allowed participants to withstand approximately 19% more veiling luminance before target obscuration. Conclusions Consistent with theoretical predictions and prior findings in younger adults, BLF lens designs significantly enhanced visual range in older pseudophakic participants under simulated blue haze conditions. These findings suggest that BLF lenses may offer functional visual benefits in older adults, especially in populations with intraocular lens implants lacking native blue-light filtration. Future research should extend these results using field studies in outdoor environments.

Purpose: Several studies have suggested that blue‐light filtering (BLF) can enhance the perception of brightness. Evidence for this effect, however, in pseudophakic patients, particularly using natural images, is lacking. The present study tested whether a common BLF spectral profile, often used in intraocular lens (IOL) designs, would influence brightness perception of natural images in pseudophakic individuals. Methods: Forty pseudophakic participants ( M = 71.15 ± 2.27 years) with 20/40 or better best‐corrected visual acuity implanted with clear IOL implants completed a brightness matching task. Participants viewed a series of natural images through both a clear extraocular filter and a BLF test lens. The test lens was designed to approximate a typical BLF IOL transmission profile. Filter conditions were counterbalanced and randomized. Participants adjusted a short‐wave deficient comparison field until the natural scene and the comparison fields were perceived as equally bright. Matched luminance values (log relative energy, LRE) were recorded across six trials per image. Images were achromatic or short‐, mid‐, and long‐wave dominant. Results: Averaged across all images, the clear lens ( = 2.74 ± 0.14) resulted in significantly lower ( t _[78] = −2.529, p = 0.007) LRE values compared to the BLF test lens ( = 2.82 ± 0.15) indicating a modest (∼17%) increase in perceived brightness with the BLF lens. This effect was observed for four of five natural images tested and was not dependent on image contrast or chromatic content. Conclusions: The BLF produced a significant and consistent increase in perceived brightness in pseudophakic adults. These findings provide direct psychophysical evidence that clinically relevant BLF profiles can influence brightness under natural viewing conditions. Information of this type is necessary for the evaluation of BLF IOL designs and their effects on functional visual experiences following cataract surgery.

Ultraviolet (UV) induced photoluminescence is widespread in Mammalia; however, its function(s) remain unclear. Most of the research to date has focused on the surface expression of photoluminescence (e.g., pelage), described qualitatively. Here, we report a quantitative assessment of photoluminescence of white‐tailed deer ( Odocoileus virginianus , herein deer) used for marking signposts. We analyzed 146 signposts, including 109 antler rubs on trees and 37 scent‐marking scrapes. We compared the spectra of signposts to the spectra of surrounding environmental features elicited by exposure to excitation lights peaking at 365 and 395 nm. Signposts showed significant contrast when compared to environmental backgrounds ( p < 0.001), and the resulting photoluminescence would be visible to deer based on previously described deer visual capabilities. This research is the first quantitative description of the functional use of environmental photoluminescence by a mammal and gives new perspective about how white‐tailed deer perceive their environment and communicate.

Purpose: Yellow filters, including high‐energy‐visible (HEV) filtering lenses, have been thought to increase the subjective brightness of real‐world scenes, but laboratory results are mixed. This study used a brightness matching technique modified to present natural images using a broad spectrum of wavelengths: a visibly clear control contact lens was compared to a contact lens containing a HEV‐filtering additive. Methods: A total of 121 subjects were tested (mean age = 33.8 ± 13.6 years). A stratified, controlled, prospective, randomised, double‐masked, bilateral, non‐dispensing, crossover design was used. Participants attended two study visits separated by a washout period and were randomly assigned to wear a HEV‐filtering contact lens or a clear control lens binocularly, counterbalanced on the second visit. Spherical ( n = 41), multifocal ( n = 40) and toric ( n = 40) soft contact lenses were tested. Ten natural scenes were presented using a slide projector with a 550‐watt xenon light source. An adjustable comparison (broadband but short‐wave deficient), produced using parallel optics with a 1000‐watt xenon source, was varied based on the subject's judgement to match the brightness of the adjacent natural image. Three ascending/descending trials for each image were used to obtain the match. Results: The amount of energy needed to match the natural images was consistently (i.e., across all images and subject groups) higher with the contact lenses that contained the HEV‐filter. Additionally, estimated log relative energy differences between HEV‐ and non‐HEV‐filter lenses were 0.13, 0.14 and 0.17 for spherical, multifocal and toric lenses, respectively. Conclusion: The collection of images appeared ≈12% brighter (averaged across spherical, multifocal and toric lenses on a log scale) when wearing the HEV‐filtering lenses; this translates to about 40% more energy needed to match the comparison field with the adjacent images. These results illustrate that lenses filtering HEV light are capable of increasing the subjective brightness of a naturalistic scene.