Development of a Fast Chemiluminescent Magneto-Immunoassay for Sensitive Plasmodium falciparum Detection in Whole Blood.

The World Health Organization (WHO) estimates that over three billion people are at risk of acquiring malaria, a parasitic infection that produces more than 200 million new infections and nearly half a million deaths each year. Expanding the access to early diagnosis and treatment is one of the most effective ways to prevent disease complications, reduce patient mortality, and curb the community transmission. However, none of the diagnostic methods used currently for malaria detection, including light microscopy, polymerase chain reaction (PCR), and rapid diagnostic tests (RDTs), can provide simultaneously fast results, high sensitivity, and parasitaemia quantitation with minimal user intervention. Here, we present a magneto-immunoassay that, based on the unique combination of magnetic beads (MB), an enzymatic signal amplifier (Poly-HRP), and chemiluminescence detection, provides fast, sensitive, and quantitative malaria diagnosis with easy user manipulation. This assay quantifies Plasmodium falciparum lactate dehydrogenase (PfLDH) in lysed whole blood samples in <15 min, exhibiting a limit of detection (LOD) of 0.02 ng mL-1 and providing patient stratification consistent with the reference methods. These figures of merit surpass the performance of the magneto-immunoassays reported previously for Plasmodium detection and demonstrate for the first time that the proposed combination of MB, Poly-HRP, and chemiluminescence detection produces extremely fast, simple, and efficient assays that approach the requirements of point-of-care (POC) malaria surveillance.

Ultrastructural evidence for telocytes in equine tendon.

The three-dimensional ultrastructure of the tendon is complex. Two main cell types are classically supported: elongated tenocytes and ovoid tenoblasts. The existence of resident stem/progenitor cells in human and equine tendons has been demonstrated, but their location and relationship to tenoblasts and tenocytes remain unclear. Hence, in this work, we carried out an ultrastructural study of the equine superficial digital flexor tendon. Although the fine structure of tendons has been previously studied using electron microscopy, the presence of telocytes, a specific type of interstitial cell, has not been described thus far. We show the presence of telocytes in the equine inter-fascicular tendon matrix near blood vessels. These telocytes have characteristic telopodes, which are composed of alternating dilated portions (podoms) and thin segments (podomers). Additionally, we demonstrate the presence of the primary cilium in telocytes and its ability to release exosomes. The location of telocytes is similar to that of tendon stem cells. The telocyte-blood vessel proximity, the presence of primary immotile cilia and the release of exosomes could have special significance for tendon homeostasis.

GRINCU lens with conicoid iso-indicial surfaces: application for modeling the crystalline lens.

We introduce a new type of lens with two gradients of refractive index (GRIN) and of curvature (GRCU) of iso-indicial surfaces, i.e., GRINCU. The inner structure of the lens resembles that of an onion. Each layer is a meniscus lens with infinitesimal thickness, which coincides with an iso-indicial surface characterized by a conicoid shape and a constant refractive index. The internal distribution automatically adapts to the external geometry. Here, we consider the simplest case of a constant gradient of the curvature radius -G, which indicates a linear decrease as we move along the optical axis. The formulation of this type of lens is presented, including its generalization to nonrotationally symmetric conicoid surfaces. The formulation is then applied to model the crystalline lens; the code corresponding to the numerical computation of the 3D refractive index distribution as well as its gradient is provided as a supplementary file. Finally, we confirmed a refractive power increase of nearly 14% when G changes from 0 to 3.

Photometric and Colorimetric Evaluation of Phototherapy Instruments for Syntonic Treatment of Visual Anomalies.

SIGNIFICANCE: Ocular light exposure therapy has been used in optometric therapies to improve binocular anomalies such as accommodative or vergence dysfunctions, amblyopia therapy or to increase the visual field. Currently, syntonic phototherapy is used worldwide by behavioral optometrists, vision trainers, or occupational therapists, among others, although these treatments are supported by only a few research studies that lack consensus on the efficacy of this approach. PURPOSE: In this article, we highlight the optical characteristics of lamps without evaluating the efficacy of their use in optometric procedures. METHODS: Our work analyzes four devices often used in clinical practice in terms of spectral power distribution, illuminance levels at the corneal plane, and both theoretical photopic and melanopic contributions to the visual system. RESULTS: First, illuminance levels reaching the corneal plane depend on the characteristics of each lamp and their distance from where the eye should be positioned; for example, delta-theta filter photopic illuminance is 13.1, 93.7, 22.7, or 41.6 lux with the four evaluated devices. Second, filters or modes named the same differ in terms of their spectral power distribution. Third, substantial difference in color appearance has been found among the same configurations. CONCLUSIONS: The spectral and iluminance characteristics of syntonic systems used for vision therapy vary widely, including variations among filters with the same identifying characteristics. This provides significant sources of variability, which limit the ability to conduct evidence-based medicine clinical trials to assess the true efficacy of syntonic therapy. This study furthers our knowledge of syntonic phototherapy from a technical perspective; however, longitudinal research examining patients' evolution pre-lighting and post-lighting treatments is required to justify and understand the effects of light exposure and its impact on optometric and ocular parameters more clearly.

Choroidal Thickness and Volume Modifications Induced by Aerobic Exercise in Healthy Young Adults.

INTRODUCTION: Our aim was to evaluate the changes in choroidal thickness (CT) and volume (CV) following aerobic physical exercise in healthy young adults. METHODS: This study included 72 eyes from healthy volunteers between 22 and 37 years old. Using the International Physical Activity Questionnaire, total physical activity was computed. Measurements using an autorefractometer, ocular biometry, and spectral-domain optical coherence tomography using the Enhanced Depth Imaging protocol were taken. OCT was performed as a baseline measurement and after performing 10 min of dynamic physical exercise (3 and 10 min post-exercise). The choroidal layer was manually segmented, and the CT and CV in different areas from the Early Treatment Diabetic Retinopathy Study grid were obtained. RESULTS: In healthy adults, at 3 min post-exercise, CT was higher in the subfoveal, the 3-mm nasal, and the 6-mm superior areas. Between 3 and 10 min post-exercise, the CT was reduced in all areas, and in some areas, the values were even smaller than the baseline measurements. The CV values showed changes after exercise similar to those of thickness. The total CV recovery after exercise was related to sex and physical activity level. CONCLUSION: Individuals with higher physical activity habits had greater CV at rest than those with lower physical activity levels. During exercise, healthy young people adjust CT and CV. At 3 min post-exercise, CT and CV increase. Women and individuals with greater physical activity levels reduce their total CV more than others during recovery.

CHANGES IN TOTAL AND INNER RETINAL THICKNESSES IN TYPE 1 DIABETES WITH NO RETINOPATHY AFTER 8 YEARS OF FOLLOW-UP.

PURPOSE: To evaluate changes in retinal layer thickness in patients with Type 1 diabetes with no diabetic retinopathy after 8 years of follow-up. METHODS: Ninety Type 1 diabetes and 60 control eyes were studied. Changes in the retinal nerve fiber layer, ganglion cell layer, and inner nuclear layer thicknesses in all Early Treatment Diabetic Retinopathy Study areas were evaluated. RESULTS: The mean ages were 42.93 ± 13.62 and 41.52 ± 13.05 years in the diabetic and control group, respectively. In 2009, total retinal thickness was higher in diabetic patients; differences were statistically significant in all except the nasal areas. In both groups, the mean foveal thickness remained the same during the 8 years. Among diabetic patients, there was a significant reduction in total retinal thickness in all areas excluding the outer temporal one; controls only in the inferior areas. The thickness loss was due to the thinning of the inner retinal layers (inner nuclear layer, ganglion cell layer, and retinal nerve fiber layer). The controls showed a significant diminution in the retinal nerve fiber layer and in the ganglion cell layer areas. The inner nuclear layer showed a diminution in the diabetes mellitus group. CONCLUSION: Before the onset of diabetic retinopathy, Type 1 diabetes patients experience a diminution of their inner retinal layer thicknesses over time, supporting the hypothesis of retinal neurodegeneration.

Measurement method of optical properties of ex vivo biological tissues of rats in the near-infrared range.

An optical fiber-based supercontinuum setup and a custom-made spectrophotometer that can measure spectra from 1100 to 2300 nm, are used to describe attenuation properties from different ex vivo rat tissues. Our method is able to differentiate between scattering and absorption coefficients in biological tissues. Theoretical assumptions combined with experimental measurements demonstrate that, in this infrared range, tissue attenuation and absorption can be accurately measured, and scattering can be described as the difference between both magnitudes. Attenuation, absorption, and scattering spectral coefficients of heart, brain, spleen, retina, and kidney are given by applying these theoretical and experimental methods. Light through these tissues is affected by high scattering, resulting in multiple absorption events, and longer wavelengths should be used to obtain lower attenuation values. It can be observed that the absorption coefficient has a similar behavior in the samples under study, with two main zones of absorption due to the water absorption bands at 1450 and 1950 nm, and with different absolute absorption values depending on the constituents of each tissue. The scattering coefficient can be determined, showing slight differences between retina and brain samples, and among heart, spleen and kidney tissues.

Interocular Symmetry of Choroidal Thickness and Volume in Healthy Eyes on Optical Coherence Tomography.

BACKGROUND: We aimed to determine the physiological symmetry, with spectral-domain optical coherence tomography, of choroidal measurements in a healthy population in all the areas defined in the Early Treatment Diabetic Retinopathy Study (ETDRS). METHODS: One hundred and fifty-four eyes of 77 healthy young adults between the ages of 19 and 32 years were enrolled. Differences in choroidal thickness (CT) and volume (CV) between the left and right eyes were calculated. Normal ranges of absolute interocular differences were established as the 95th percentile. RESULTS: The mean ± SD subfoveal CT (SFCT) and total CV values in the right and left eyes were 342.03 ± 77.38 versus 361.64 ± 76.45 µm (correlation coefficient ρ = 0.820; p < 0.001) and 0.27 ± 0.06 versus 0.28 ± 0.06 mm3 (ρ = 0.830; p < 0.001), respectively. Differences in 5 of the 9 areas of the ETDRS map were statistically significant (p < 0.05), but with a strong interocular correlation (ρ > 0.8; p < 0.001). The 95th percentile of interocular tolerance limits for CT in the 1-, 3-, and 6-mm areas were 97, 70, and 57 µm, respectively; the 95th percentile for the volume values were 0.06, 0.51, and 1.73 mm3. CONCLUSIONS: CT and CV are highly correlated between eyes, statistically significant differences between them can be found, and absolute interocular differences may reach 97 µm in SFCT, and 1.73 mm3 in total CV.

Long time remodeling during retinal degeneration evaluated by optical coherence tomography, immunocytochemistry and fundus autofluorescence.

PURPOSE: To characterize the relationship between fundus autofluorescence (FAF), Optical Coherence Tomography (OCT) and immunohistochemistry (IHC) over the course of chronic retinal degeneration in the P23H rat. METHODS: Homozygous albino P23H rats, Sprague-Dawley (SD) rats as controls and pigmented Long Evans (LE) rats were used. A Spectralis HRA OCT system was used for scanning laser ophthalmoscopy (SLO) imaging OCT and angiography. To determine FAF, fluorescence was excited using diode laser at 488 nm. A fast retina map OCT was performed using the optic nerve as a landmark. IHC was performed to correlate with the findings of OCT and FAF changes. RESULTS: During the course of retinal degeneration, the FAF pattern evolved from some spotting at 2 months old to a mosaic of hyperfluorescent dots in rats 6 months and older. Retinal thicknesses progressively diminished over the course of the disease. At later stages of degeneration, OCT documented changes in the retinal layers, however, IHC better identified the cell loss and remodeling changes. Angiography revealed attenuation of the retinal vascular plexus with time. CONCLUSION: We provide for the first time a detailed long-term analysis of the course of retinal degeneration in P23H rats using a combination of SLO and OCT imaging, angiography, FAF and IHC. Although, the application of noninvasive methods enables longitudinal studies and will decrease the number of animals needed for a study, IHC is still an essential tool to identify retinal changes at the cellular level.

CHOROIDAL THICKNESS AND VOLUME IN A HEALTHY PEDIATRIC POPULATION AND ITS RELATIONSHIP WITH AGE, AXIAL LENGTH, AMETROPIA, AND SEX.

PURPOSE: To evaluate choroidal thickness (CT) and volume in healthy pediatric individuals using enhanced depth imaging spectral domain optical coherence tomography (SD-OCT), as well as its association with age, sex, axial length (AL), and refractive error. METHODS: Ninety-three eyes from 93 healthy pediatric individuals were examined. An Early Treatment Diabetic Retinopathy Study grid was applied to analyze CT and volume map in each of its nine sectors. RESULTS: The mean subfoveal CT and volume were 314.22 ± 55.48 µm and 0.25 ± 0.04 mm, respectively. The nasal CT and volume of both the inner and the outer rings were significantly lower than the temporal area of the same ring and lower than the subfoveal choroidal thickness. A significant negative correlation between the subfoveal CT and AL (r = -0.250, P = 0.015) and a significant positive correlation between the subfoveal CT and refractive error (r = 0.238, P = 0.006) were found. The estimation of the variation in the subfoveal CT in relationship to the AL was -13.55 µm per millimeter. The variation in the subfoveal CT with refractive error was 7.52 µm per diopter. The estimation of the variation in the total choroidal volume related to the AL and ametropia was, respectively, -0.2354 mm per millimeter and 0.1412 mm per diopter. CONCLUSION: Healthy pediatric subjects exhibit choroidal differences in refractive error and AL. In the study population, CT and volume show an increase with age after adjusting for AL.

Structure-Function Relationship between Frequency-Doubling Technology Perimetry and Optical Coherence Tomography in Glaucoma.

Purpose: To assess the relationship between the retinal nerve fibre layer (RNFL) thickness and the frequency-doubling technology perimetry (FDT) outcome. Methods: Sixty-two healthy individuals and 72 glaucoma patients were prospectively selected. All participants underwent a reliable FDT and optical coherence tomography (OCT). Pearson correlations were calculated between the unlogged threshold values of FDT and RNFL thicknesses measured by OCT. Results: Mild to moderate correlations were found between a few points from FDT and RNFL thicknesses in the vertical axis. The nasal superior area of FDT and the RNFL thickness at the 7-o'clock position had the strongest correlation (0.434, p < 0.001). Conclusions: The poor agreement between FDT and OCT parameters suggests that both instruments assess different characteristics of glaucomatous optic neuropathy. The map obtained validates previously reported clinical findings and contributes to a better understanding of the structure-function relationship in glaucoma. © 2014 S. Karger AG, Basel.

Comparison of two visual-verbal tests of ocular motility using an eye-tracker.

PURPOSE: This study aims to compare eye movements monitored with an eye tracker during two visuo-verbal tests for assessing ocular motility. The study explores the potential of digital assessment and eye tracking technology in enhancing the understanding of ocular motility during these tests. METHODS: 47 healthy participants were included (20 males, 27 females), with a mean age of 21.34±1.77 years. The participants underwent optometric examinations to ensure visual health and exclude any dysfunctions or pathologies. The experimental protocol involved the digitized versions of the DEM and King-Devick tests, monitored with an eye tracker. RESULTS: The vertical subtests of DEM test showed fewer saccades, longer fixation durations, smaller saccade amplitudes, and slower saccade speeds compared to the horizontal subtest. The King-Devick test exhibited comparable fixation and saccade numbers, while fixation duration slightly increased with test difficulty. Statistically significant differences were found between the tests, but a positive correlation was observed. CONCLUSIONS: Statistically significant differences were observed between the DEM and King-Devick tests, indicating that they measure similar aspects but are not interchangeable. The DEM test offers more comprehensive information with vertical saccade assessment. Test duration correlates positively with saccade and fixation count, fixation duration, and saccade speed.

The Influence of Accommodative Demand on Ocular Aberrations: A Study of Zernike Coefficients Repeatability and Variability.

PURPOSE: To evaluate the repeatability of the Zernike coefficients in healthy eyes when monocular accommodation was stimulated at different vergences demands. METHODS: A total of 36 right eyes from healthy volunteers were prospectively and consecutively recruited for this study. Wavefront aberrometry was conducted to objectively characterize the ocular optical quality during accommodation, from the individual's far point to a 5 D accommodation demand in steps of 0.5 D. The repeatability of Zernike coefficients up to the fourth order was assessed by calculating the within-eye repeatability (Sw), the coefficient of repeatability (CR), the coefficient of variation (CV), and the intraclass correlation coefficient (ICC) as an indicator of measurement reliability. RESULTS: Correlation among repeated measurements showed high reliability (ICC > 0.513) for all parameters measured except some fourth-order Zernike coefficients, C(4, -4) (ICC < 0.766), C(4, -2) (ICC < 0.875), C(4, 2) (ICC < 0.778) and C(4, 4) (ICC < 0.811). Greater repeatability and less variability were obtained for high-order Zernike coefficients (CR < 0.154), although an increase in CR in the coefficients analyzed was observed with increasing accommodative demand. No clear trend was evident in CV; however, it was observed that the low-order Zernike coefficients exhibit lower CV (CV < 1.93) compared to the high-order Zernike coefficients (CV > 0). CONCLUSIONS: The reliability of Zernike coefficients up to the fourth order in healthy young individuals demonstrated a strong consistency in measuring terms up to the fourth order, with more variability observed for high-order terms. The Zernike coefficients up to the third order exhibited the highest level of repeatability.

Anterior Chamber and Retinal Morphological Changes During Accommodation in Different Age Ranges.

PURPOSE: Accommodation mainly affects the lens, a structure of the eyeball that degrades with age. The aim of this work was to study the morphological changes of different ocular structures during accommodation, both in the anterior pole and the posterior pole, which may also be involved in the accommodation process. METHODS: The study will be carried out by stimulating accommodation through lenses of -1.00, -3.00 and -5.00 D starting from the spherical equivalent (M) of each participant in different age groups, from 18 to 66 years. To obtain the M value, aberrometry was achieved, and retinal optical coherence tomography and anterior pole tomography were performed to evaluate the possible structural modifications (central and peripheral), while accommodation was progressively stimulated. RESULTS: It showed that as the accommodative demand increased, morphological changes were produced in retinal thickness, both in the central and peripheral retina, in all age groups. A thinning of the retina was observed in the central 3 mm, while significant progressive thickening was observed closer to the periphery (up to 6 mm from the fovea) as the required accommodative power increased. A decrease in the anterior chamber depth (ACD) and anterior chamber volume (ACV) was observed with increasing lens power. CONCLUSION: Structural changes were observed in the central and peripheral retina, as well as in the ACD and ACV, while progressively greater accommodation was stimulated, showing that these structures were modified in the accommodation process even in advanced presbyopes.

Reproducibility and repeatability of Cirrus and Spectralis Fourier-domain optical coherence tomography of healthy and epiretinal membrane eyes.

PURPOSE: To evaluate the accuracy and reproducibility of retinal thickness measurements in healthy and epiretinal membranes (ERM) eyes by Cirrus and Spectralis Fourier-domain optical coherence tomography devices. METHODS: Eighty-seven ERM and 122 healthy subjects underwent 3 macular scans using both optical coherence tomography instruments. Mean thickness measurements in the nine Early Treatment Diabetic Retinopathy Study areas were compared, evaluating the repeatability and the relationship between devices. RESULTS: Macular thickness increase was detected in ERM eyes for all optical coherence tomography parameters (P < 0.001). Mean foveal thickness was 423.5 ± 81.4 and 438.0 ± 54.2 µm for ERM eyes and 267.1 ± 20.2 and 277.5 ± 18.9 µm for healthy eyes using Cirrus and Spectralis, respectively. Macular average thickness in ERM eyes as determined by both optical coherence tomography was correlated (r = 0.812; P < 0.001) but significantly different (P = 0.044). In ERM eyes, measurements showed a mean of the coefficients of variation of 2.95%, 2.2%, and 1.01% using Cirrus, Spectralis, and Spectralis progression feature, respectively. Intraclass correlation coefficients were higher than 0.919 in all cases. CONCLUSION: Reproducibility of both Cirrus and Spectralis optical coherence tomography was high in healthy and ERM eyes. However, considerable differences were found between macular thickness measurements obtained by both devices despite the high correlation between them.

Visual Quality, Motility Behavior, and Retinal Changes Associated with Reading Tasks Performed on Electronic Devices.

BACKGROUND: The purpose of this study was to objectively evaluate visual discomfort using an eye tracker and aberrometer after a 21-min reading session on an iPad and an Ebook. Additionally, retinal changes were analyzed using optical coherence tomography (OCT). METHODS: A total of 31 young subjects (24 ± 4 years) participated in this study. They read for 21 min on an Ebook and for another 21 min on an iPad under controlled lighting conditions while their eye movements were monitored using an eye tracker. Aberrometry and retinal OCT measurements were taken before and after each reading session. Parameters such as pupil diameter, fixations, saccades, blinks, total aberration, high-order aberration, low-order aberration, and central and peripheral retinal thickness in the nine early treatment diabetic retinopathy study (ETDRS) areas were measured for each reading situation. Statistical analysis was performed on the collected data. RESULTS: No statistically significant differences (p > 0.05) between the two devices were observed in terms of the different types of eye movements or the changes in retinal thickness. However, the aberrometric analysis showed variations in post-reading situations depending on the device used. CONCLUSION: Reading speed and visual discomfort resulting from electronic device usage can be objectively assessed using an eye tracker and aberrometer. Additionally, changes found in central and peripheral retinal thickness between the two devices and the baseline measurements were not significant and remained relatively stable.

Ocular Motility Patterns in Intellectual Disability: Insights from the Developmental Eye Movement Test.

PURPOSE: To measure the ocular motility parameters of the Developmental Eye Movement (DEM) test objectively, with an eye tracker in subjects with intellectual disability (ID). METHODS: The DEM test was performed on 45 subjects with ID, while their eye movements were recorded with an eye tracker. Some objective parameters of ocular motility were obtained through each subtest (A, B, and C) of the full DEM test. RESULTS: There was a significant positive correlation between the saccadic speed (cc: 0.537; p = 0.001) and length (cc: 0.368; p = 0.030) of both eyes for the same subject. People with a higher percentage of ID exhibited a greater number of fixations, saccades, and errors, and took longer to perform the DEM test than those with a lower ID percentage, who had greater numbers of these parameters than subjects without ID. Subjects without ID exhibited faster saccades, with a higher amplitude, than subjects with ID. CONCLUSIONS: The eye tracker quantifies ocular motility parameters involved in the DEM test in subjects with ID. Both eyes' movements in subjects with ID were conjugated, exhibiting saccades of the same length and speed. All parameters were different in subjects with ID compared to those in subjects without ID, so normative tables specifically for subjects with ID are necessary.

Optical and motor changes associated with lighting and near vision tasks in electronic devices.

Purpose: To assess optical and motor changes associated with near vision reading under different controlled lighting conditions performed with two different types of electronic screens. Methods: Twenty-four healthy subjects with a mean age of 22.9±2.3 years (18- 33) participated in this study. An iPad and an e-ink reader were chosen to present calibrated text, and each task lasted 5 minutes evaluating both ambient illuminance level and luminance of the screens. Results: Eye-tracker data revealed a higher number of saccadic eye movements under minimum luminance than under maximum luminance. The results showed statistically significant differences between the iPad (p=0.016) and the e-ink reader (p=0.002). The length of saccades was also higher for the minimum luminance level for both devices: 6.2±2.8 mm and 8.2±4.2 mm (e-ink max vs min), 6.8±2.9 mm and 7.6±3.6 mm (iPad max vs min), and blinking rate increased significantly for lower lighting conditions. Conclusions: Performing reading tasks on electronic devices is highly influenced by both the configuration of the screens and the ambient lighting, meanwhile, low differences in visual quality that are transient in healthy young people, were found.

Adaptive Illuminance Effects on Retinal Morphology and Refraction: A Comprehensive Study of Night Myopia.

BACKGROUND: We aimed to study the optical and retinal modifications that occur after adapting to different lighting conditions including photopic, mesopic, scotopic, blue light and red light conditions. METHODS: Thirty young healthy subjects with a mean age of 23.57 ± 3.45 years were involved in the study (both eyes included). They underwent aberrometry and optical coherence tomography at both the central and peripheral retina with the 3 × 3 mm2 macular cube protocol before starting adaptation to the illuminations (baseline) and after remaining for 5 min under the five different lighting conditions inside a controlled lighting cabinet. RESULTS: Significant myopization (p = 0.002) was observed under scotopic and mesopic lighting conditions, while hypermetropization occurred under the influence of blue LED light. In the central retina, a significant thickening of the inner temporal (p = 0.025) and outer inferior (p = 0.021) areas was observed in the scotopic area, and the thickening increased even more under blue and red light. The mean central thickness decreased significantly under photopic lighting conditions (p = 0.038). There was an increase in the mean volume of the central retinal area with red light and a reduction in the volume under photopic lighting (p = 0.039). In the peripheral retina, no significant thickness changes were observed after adapting to any of the lighting conditions (p > 0.05). Regarding morphological changes, a significant increase in retinal eccentricity (p = 0.045) and the shape factor (p = 0.036) was found. In addition, a significant correlation was found only between the eccentricity and volume of the central retina in scotopic conditions (r = -0.265; p = 0.041), meaning that a higher volume was associated with lower retinal eccentricity. CONCLUSIONS: When exposed to different lighting conditions, the retina changes in shape, and ocular refraction is modified to adapt to each condition, revealing the phenomenon of night myopia when transitioning from photopic to scotopic regimes.

Hess Lancaster Screen Test with Eye Tracker: An Objective Method for the Measurement of Binocular Gaze Direction.

BACKGROUND: To objectively measure with an eye tracker both eye movement conjugacy and gaze direction in different positions when performing the Hess Lancaster Screen Test (HLST) in a sample of control subjects without binocular dysfunction and compare the results with those of the traditional subjective HLST performance. METHODS: The sample was selected avoiding subjects who suffered from suppression of one of the two eyes, visual acuity less than 20/25 on the Snellen chart in each eye, strabismus, or any symptom of binocular dysfunction that could alter the results. While performing the HLST, the examiner wrote down each of the points on a template in a traditional way while the eye tracker (Tobii Pro Fusion, Tobii AB, Danderyd, Sweden), placed in front of the subject, took objective measurements of the position of both eyes at each point. Of the 29 subjects recruited in this study, 13 subjects between 18 and 27 years old underwent the complete optometric examination and the HLST wearing anaglyph glasses; meanwhile, 16 people were excluded because of binocular or accommodative dysfunctions or because they didn't give reliable eye-tracking results. Additionally, a specific program called Etracker Parse Video (University of Zaragoza, Zaragoza, Spain) was developed to analyse the prismatic deviation between both eyes at each evaluated point. RESULTS: Similar horizontal prismatic deviations of visual axes were obtained in the different gaze positions with the Maddox rod, the manually annotated HLST, and the eye-tracker measurement. Variations were found in the magnitude of the deviation between methods but not in the direction. On the other hand, vertical deviations were more difficult for the examiner to detect and quantify, especially those with small magnitudes; more exact values were obtained when measuring objectively with the eye tracker. CONCLUSION: The HLST is very useful and allows the amount of heterophoria or heterotropia to be recorded in the patient's medical record in all the main gaze positions. This test is complementary; by itself, it is not diagnostic and does not replace a complete examination of binocular vision. The eye tracker is an objective method with which we can evaluate the HLST in patients with no binocular problems, obtaining more accurate results than when it is performed in the traditional manner.