Spectral dependency of the human pupillary light reflex. Influences of pre-adaptation and chronotype

Non-visual photoreceptors (ipRGCs) and rods both exert a strong influence on the human pupil, yet pupil models regularly use cone-derived sensitivity as their basis. This inconsistency is further exacerbated by the fact that circadian effects can modulate the wavelength sensitivity. We assessed the pupillary reaction to narrowband light stimuli in the mesopic range. Pupil size for eighty-three healthy participants with normal color vision was measured in nine experimental protocols with varying series of continuous or discontinuous light stimuli under Ganzfeld conditions, presented after 90 seconds of dark adaptation. One hundred and fifty series of stimulation were conducted across three experiments, and were analyzed for wavelength-dependency on the normalized pupillary constriction (nPC), conditional on experimental settings and individual traits. Traits were surveyed by questionnaire; color vision was tested by Ishihara plates or the Lanthony D15 test. Data were analyzed with generalized additive mixed models (GAMM). The normalized pupillary constriction response is consistent with L+M-cone derived sensitivity when the series of light stimuli is continuous, i.e., is not interrupted by periods of darkness, but not otherwise. The results also show that a mesopic illuminance weighing led to an overall best prediction of pupillary constriction compared to other types of illuminance measures. IpRGC influence on nPC is not readily apparent from the results. When we explored the interaction of chronotype and time of day on the wavelength dependency, differences consistent with ipRGC influence became apparent. The models indicate that subjects of differing chronotype show a heightened or lowered sensitivity to short wavelengths, depending on their time of preference. IpRGC influence is also seen in the post-illumination pupil reflex if the prior light-stimulus duration is one second. However, shorter wavelengths than expected become more important if the light-stimulus duration is fifteen or thirty seconds. The influence of sex on nPC was present, but showed no interaction with wavelength. Our results help to define the conditions, under which the different wavelength sensitivities in the literature hold up for narrowband light settings. The chronotype effect might signify a mechanism for strengthening the individual´s chronotype. It could also be the result of the participant’s prior exposure to light (light history). Our explorative findings for this effect demand replication in a controlled study.

Deficits in color detection in patients with Alzheimer disease

Deficits in color vision and related retinal changes hold promise as early screening biomarkers in patients with Alzheimer’s disease. This study aimed to determine a cut-off score that can screen for Alzheimer’s dementia using a novel color vision threshold test named the red, green, and blue (RGB) modified color vision plate test (RGB-vision plate). We developed the RGB-vision plate consisting of 30 plates in which the red and green hues of Ishihara Plate No.22 were sequentially adjusted. A total of 108 older people participated in the mini-mental state examination (MMSE), Ishihara plate, and RGB-vision plate. For the analyses, the participants were divided into two groups: Alzheimer’s dementia (n = 42) and healthy controls (n = 38). K-means cluster analysis and ROC curve analysis were performed to identify the most appropriate cut-off score. As a result, the cut-off screening score for Alzheimer’s dementia on the RGB-vision plate was set at 25, with an area under the curve of 0.773 (p<0.001). Moreover, there was a negative correlation between the RGB-vision plate thresholds and MMSE scores (r = -0.36, p = 0.02). In conclusion, patients with Alzheimer’s dementia had a deficit in color vision. The RGB-vision plate is a potential early biomarker that may adequately detect Alzheimer’s dementia.

Testing Color Vision in Children

It is important to screen for acquired or hereditary color vision defects as early as possible. Color vision is a critical part of the early learning experience, and children who have color deficiencies may have difficulties compared to their peers if there is color-based schoolwork. It becomes important for career interests/goals for older children as some jobs may require normal color vision. Hereditary red-green deficiencies are X-linked and therefore affect approximately 8% of males and less than 1% of females. Acquired color vision defects and blue-yellow defects are rare in the pediatric population; therefore, these conditions will be discussed minimally in this chapter. Infants are able to discern color by 2-3 months of age, but accurate color naming may not develop until 4-6 years of age. Screening tests are sensitive, fast, and easy to administer. If a deficiency is suspected through screening, further testing must be evaluated in order to determine the type and severity of the color vision defect. Color vision is typically tested starting at age 3 years and up.

Color Vision in the Gas Station Workers of Isfahan City: A Quantitative Analysis With the Farnsworth D15 Color Test

Background and Objectives: The color vision evaluation of gas station workers in Isfahan City. Methods: This cross-sectional comparative study was performed on workers at gas stations in Isfahan; all the workers were men. The participants were divided into two 40-people groups of exposure and non-exposure (the members of the fuel sales department). The participants had better vision than 8/10 and no underlying problems or eye disease. Besides, examination, including color vision was performed for all subjects. Color vision was assessed using the D15 test under high to medium light conditions. Also, the color vision test was performed monocularly. Then, the obtained data were analyzed using SPSS V. 22. Results: The two study groups significantly differed in terms of color vision impairment index (P <0.001). Also, more color vision defects were seen in the group exposed to gasoline. The color confusion index (as the indicator of color vision defects) were 1.485 and 1.129 in exposure and non-exposure to gasoline groups, respectively. Thus, color vision defects were significantly higher in the exposure to gasoline group, compared with the control group. Conclusion: The results of this study showed a difference in color vision index between the two groups. Therefore, long-term exposure to organic solvents, such as gasoline in fuel stations may cause color vision loss.

Effects of blunt trauma of eye on retinal nerve fibre layer

AIM: To study the effects of blunt trauma of eye on visual acuity and retinal nerve fiber layer (RNFL). METHODS: A prospective observational study was done on the patients of a road traffic accident (RTA) having blunt trauma injury of the eye from august 2018 to July 2019 at the Department of Ophthalmology, Hind Institute of Medical Sciences, Barabanki. Patients between the age group of 20 to 65 years undergoing RTA with ocular complaints were included in this study. Colour vision, contrast sensitivity, and best-corrected visual acuity (BCVA) were recorded, RNFL analysis was done through OCT. RESULTS: A total of 108 patients were enrolled in this study and were grouped as 54 cases and 54 controls. The mean age was 43±2.3 years with 11 (20.37%) females and 43 (79.6%) males in the case group. At initial visit after RTA, the difference between color vision, contrast sensitivity and BCVA between right and left eyes of cases and controls were significant. After a follow up of 3mo only significant difference was noted in contrast sensitivity between cases and control groups. Change in color vision and BCVA after 3mo was insignificant. Similarly, an initial significant difference was noted in mean RNFL thickness between cases and control groups, but after follow up of 3mo mean RNFL thickness difference was significant only in superior and temporal quadrants. CONCLUSION: RTA or blunt trauma of eye can lead to persistent RNFL thinning and decreased visual function.