Cone-isolation contrast sensitivity - do pupil and stimulus sizes matter?

CLINICAL RELEVANCE: Computer-based colour perception tests permit clinical assessment of cone-specific pathways, proving valuable for both identifying type and severity of hereditary colour vision deficiency and enhanced detection and monitoring of acquired colour deficiency from disease. Understanding the parameters that affect computer-based colour perception tests may enhance their veracity and clinical utility. BACKGROUND: Testing contrast sensitivity separately for the three cone systems enables a quantification of colour perception that can be clinically useful. This study evaluated the effects of pupil diameter and stimulus size on cone contrast sensitivity (CCS) assessed with the ColorDx (Konan Medical, Incorporated). METHODS: Forty subjects, aged 21-31 years, who met the inclusion criteria participated. The tested eye was randomised. Two Landolt C sizes (2.68 degrees, 6/194, "small"; 8.58 degrees, 6/619, "large") were used, with one size and three chromaticities presented per block of trials. Stimulus presentation used the adaptive screening mode, sequentially determining contrast sensitivity for long-, medium-, and short-wavelength stimuli. Subjects were tested with their natural pupil size (range 4-5 mm diameter), then while viewing through a 2.5-mm artificial pupil. Parametric statistical tests were used for comparisons of performance across pupil size and stimulus size. RESULTS: Two-way within-subjects ANOVA indicates no interaction between pupil size and stimulus size for any of the three stimulus chromaticities. The main effect of stimulus size was significant for M-cone (F = 6.506, 2-tailed P = .015) and S-cone (F = 67.728, 2-tailed P < .001) stimuli. The main effect of pupil size was significant for all three stimulus chromaticities (L-cone: F = 227.161, M-cone: F = 249.979, S-cone: F = 89.371, 2-tailed P < .001 for all). CONCLUSION: Although CCS was reduced for all three chromaticities and both stimulus sizes with lower retinal illuminance, only S-wavelength cone contrast sensitivity was significantly different for the small versus large stimuli under the 2.5-mm pupil condition in this cohort. Whether CCS in older patients with naturally small pupils changes with an enlarged stimulus or dilated pupils remains to be explored.

Impact of Pool Testing in Detection of Asymptomatic Patients with COVID-19.

OBJECTIVE: During the current pandemic, COVID-19 has been detected in patients using real-time reverse transcriptase-polymerase chain reaction (RT-PCR) that confirms the presence of SARS-CoV-2 RNA. The demand for increased testing, particularly for asymptomatic individuals required alternative approaches to single-patient RT-PCR testing, such as pooling. METHODS: This study explored the impact of dilution on the detectability of SARS-CoV-2 in asymptomatic patients using RT-PCR and demonstrated that pooling can be effective in low prevalence populations. RESULTS: The RT-PCR results for the 3:1, 5:1, and 7:1 aliquot samples showed little differences in CT values, confirming detection capability at these dilutions. CONCLUSION: Based on the results of the present study, a pooled approach with up to 5:1 sample aliquots and using the current RT-PCR methodology likely will detect SARS CoV2 RNA among asymptomatic patients.

Anisocoria assessment in subjects with dark irides - Custom-built infrared screening device vs. millimeter ruler / Evaluación de anisocoria en sujetos con iris oscuros - Dispositivo de cribado mediante infrarrojos hecho a medida vs regla milimetrada

PURPOSE: Detection of anisocoria in those with dark irides is difficult, and failure to detect anisocoria can have dire consequences. Whether infrared pupillometry and gross measurement would yield different prevalence rates for anisocoria in those with dark irides is unknown. We compared the frequency of anisocoria in healthy adults with dark irides assessed with mm ruler versus infrared pupillometry. METHODS: Pupil diameters in light (L) and dark (D) conditions were obtained to identify anisocoria in 59 human subjects with dark irides using two techniques. To avoid bias, gross measurements (S) with ruler were taken first. Pupils were imaged under infrared illumination mounted in a spectacle frame with mm tape attached. Adobe Photoshop was used to measure pupil sizes on the digital images (O). RESULTS: Proportions of anisocoria by group were SL .034, OL .130, SD 0.00, OD .135. Fisher's exact test showed that anisocoria in dim light was more frequent with the infrared photo technique. Exact binomial probability testing showed that the anisocoria in SL and SD conditions was not different from an expected proportion of 5%; whereas anisocoria in OL condition was not different from an expected proportion of 20%, and anisocoria in OD condition was not different from expected proportions of 10, 15, and 20%. CONCLUSIONS: In people with dark irides, ruler measurements of pupil size underestimate the frequency of anisoria in dim lighting conditions compared to the use of infrared pupillometry. Whether detection rates of pathologic anisocoria differ with measurement technique remain to be explored

OBJETIVO: La detección de anisocoria en los sujetos con iris oscuros es difícil, y la falta de detección puede tener consecuencias nefastas. Se desconoce si la pupilometría de infrarrojos y la medición en bruto arrojarían diferentes tasas de prevalencia de anisocoria en los sujetos con iris oscuros. Comparamos la frecuencia de anisocoria en adultos sanos con iris oscuros, valorados con regla en mm versus pupilometría de infrarrojos. MÉTODOS: Se obtuvieron los diámetros de la pupila en los iris claros (L) y oscuros (D) para identificar la anisocoria en 59 sujetos con iris oscuros, utilizando dos técnicas. Para evitar sesgos, se realizaron en primer lugar las medidas brutas (S) con la regla. Las pupilas se fotografiaron mediante un sistema de iluminación de infrarrojos montado en gafas con cinta en mm anexa. Se utilizó Adobe Photoshop para medir los tamaños de las pupilas en las imágenes digitales (O). RESULTADOS: Las proporciones de anisocoria por grupo fueron SL 0,034, OL 0,130, SD 0, OD 0,135. La prueba exacta de Fisher reflejó que la anisocoria con luz tenue era más frecuente con la técnica de fotografías de infrarrojos. La prueba de probabilidad binómica exacta reflejó que la anisocoria en las situaciones de SL y SD no era diferente a la proporción prevista del 5%, mientras que la anisocoria en la situación OL no era diferente a la proporción prevista del 20%, y la anisocoria en la situación OD no era diferente a las proporciones previstas del 10, 15, y 20%. CONCLUSIONES: En las personas con iris oscuros, las mediciones del tamaño de la pupila realizadas con regla subestimaron la frecuencia de anisocoria con luz tenue, en comparación con el uso de pupilometría de infrarrojos. Queda por explorar si las tasas de detección de anisocoria patológica difieren con la técnica de medición

Anisocoria assessment in subjects with dark irides - Custom-built infrared screening device vs. millimeter ruler.

PURPOSE: Detection of anisocoria in those with dark irides is difficult, and failure to detect anisocoria can have dire consequences. Whether infrared pupillometry and gross measurement would yield different prevalence rates for anisocoria in those with dark irides is unknown. We compared the frequency of anisocoria in healthy adults with dark irides assessed with mm ruler versus infrared pupillometry. METHODS: Pupil diameters in light (L) and dark (D) conditions were obtained to identify anisocoria in 59 human subjects with dark irides using two techniques. To avoid bias, gross measurements (S) with ruler were taken first. Pupils were imaged under infrared illumination mounted in a spectacle frame with mm tape attached. Adobe Photoshop was used to measure pupil sizes on the digital images (O). RESULTS: Proportions of anisocoria by group were SL .034, OL .130, SD 0.00, OD .135. Fisher's exact test showed that anisocoria in dim light was more frequent with the infrared photo technique. Exact binomial probability testing showed that the anisocoria in SL and SD conditions was not different from an expected proportion of 5%; whereas anisocoria in OL condition was not different from an expected proportion of 20%, and anisocoria in OD condition was not different from expected proportions of 10, 15, and 20%. CONCLUSIONS: In people with dark irides, ruler measurements of pupil size underestimate the frequency of anisoria in dim lighting conditions compared to the use of infrared pupillometry. Whether detection rates of pathologic anisocoria differ with measurement technique remain to be explored.

Motion sensitivity during fixation in straight-ahead and lateral eccentric gaze.

Despite motion of the entire retinal image that results from fixational eye-movements, the visual scene is perceived as stationary. One hypothesis to account for this observation is that normal motion sensitivity is limited by the variability of fixational eye velocity. The present experiments tested this hypothesis by comparing motion sensitivity and the variability of fixational eye velocity in corresponding meridians. Speed thresholds to detect horizontal, vertical, and rotary motion in a set of eight random-dot patches were measured, while normal observers monocularly viewed the stimulus with gaze either straight-ahead or deviated to the left by 45 degrees. Eye-movement recordings using the search-coil technique were used to estimate the variability of eye velocity in the horizontal, vertical, and torsional meridians during fixation. As reported previously by Murakami (2004), the averaged thresholds for horizontal and vertical motion correlated with the averaged variability of eye velocity in the horizontal and vertical meridians when observers looked straight-ahead. However, no relationship existed between the threshold for rotary motion and the variability of eye velocity in the torsional meridian. Furthermore, no relationship existed between the motion threshold and the variability of eye velocity in any meridian during fixation in lateral eccentric gaze. These results are only partly consistent with the hypothesis that fixation variability limits motion sensitivity.

The effects of interocular correlation and contrast on stereoscopic depth magnitude estimation.

PURPOSE: Decreasing the interocular correlation in random dot stereograms elevates disparity detection thresholds. Whether decorrelation also affects perceived depth from suprathreshold disparity magnitudes is unknown. The present study investigated the effects of interocular correlation and contrast on the magnitude of perceived depth in suprathreshold random dot stereograms. METHODS: Stereoscopic depth magnitude estimation as a function of percent interocular correlation of dynamic random dot stimuli was measured for five human subjects with clinically normal binocular vision. Each trial's stimulus was randomly assigned one of two magnitudes of either crossed or uncrossed relative disparity. Subjects verbally reported the direction and magnitude of perceived relative depth for each trial using a modulus-free scale. Normalized depth magnitude estimations as a function of the percent interocular correlation demonstrated the relationship between perceived depth, interocular correlation and contrast within subjects. Inter-subject variability was examined with comparisons of data across subjects. RESULTS: The depth magnitude perceived for a given magnitude of disparity declined as the percent of correlation of elements between the eyes decreased for both crossed and uncrossed directions. The effect generally was greater for uncrossed disparities and lower contrast. Some subjects demonstrated asymmetries in perceived depth for crossed vs. uncrossed disparities of the same magnitude. CONCLUSIONS: Magnitude estimation of suprathreshold stimuli provided a method of studying performance characteristics of stereoscopic depth perception across the range of functional disparities. Differences found in depth magnitude estimation as a function of the sign of disparity suggest that the neural mechanisms underlying depth perception from uncrossed disparity are more sensitive to image decorrelation, particularly at low contrast, than the mechanisms underlying depth estimation from crossed disparity. These results could occur from differences in near and far disparity-sensitive neurons, from the geometrical relationship between disparity and physical distance in normal viewing, or from the response measure independent of perception.

Stereoscopic depth magnitude estimation: effects of stimulus spatial frequency and eccentricity.

To determine the effects of stimulus spatial frequency and retinal eccentricity on the perception of depth magnitude derived from disparity cues alone, subjects were asked to estimate the magnitude of depth of a stereoscopically viewed Gabor patch presented to the central or peripheral field with either crossed or uncrossed absolute disparity. Disparity vergence responses to the same Gabor stimuli were separately estimated subjectively by determining the offset required for dichoptic nonius alignment following presentation of the stimulus. The normalized stereoscopic magnitude estimation data generally showed that crossed disparities were perceived with greater depth than uncrossed disparities of the same magnitude, whether presented to the central or peripheral field. Asymmetries in magnitude of depth perception ranged from mild differences between depth directions to complete lack of depth perception for one direction. Disparity vergence response functions varied from (1) appropriate initiation of vergence to both directions of disparity, (2) initiation of vergence to only one direction of disparity, or (3) an attenuated initiation of vergence response to either direction of disparity. Within subjects, their asymmetries in magnitude of depth perception did not correlate with their asymmetries in vergence initiation. The similarity of the asymmetric depth magnitude estimation for a given individual at both stimulus locations tested suggests that common neural mechanisms are responsible for central and peripheral depth magnitude estimation. The lack of correlation between the perceptual and motor responses to the same stimuli suggests that the neural pathways for these responses diverge shortly after the detection of disparity in primary visual cortex.