Effect of ethnic diversity on the saccadic reaction time among healthy Indian and Dutch adults.

Eye movement perimetry (EMP) expresses the decline in visual field (VF) responsiveness based on the deviation in saccadic reaction times (SRTs) from their expected age-similar responses (normative database). Since ethnic dissimilarities tend to affect saccade parameters, we evaluated the effect of such a factor on SRT and its interaction with age, stimulus eccentricity, and intensity. 149 healthy adults, spread into five age groups, drawn from Indian and Dutch ethnicities underwent a customized EMP protocol integrated with a saccade task from which the SRTs to 'seen' visual stimuli were computed. The EMP test had a total of 54 coordinates (five stimulus eccentricities) tested using Goldmann size III visual stimuli presented at four stimulus intensity (SI) levels against a constant background. Considering SRT as a dependent variable, a Generalized Linear Mixed Model analysis was conducted that revealed a statistically significant (p < 0.001) influence of ethnicity and interaction between the tested factors (ethnicity × age × stimulus eccentricity × intensity). However, during the post hoc analysis, out of the 100 possible pair-wise comparisons, only 6% (minor proportion) of the estimates showed statistical significance. Hence, the ethnic-specific differences need not be accounted for while implementing EMP in a diverse set of populations instead a collective database might serve the purpose.

Slowed Saccadic Reaction Times in Seemingly Normal Parts of Glaucomatous Visual Fields.

Purpose: In eye movement perimetry, peripheral stimuli are confirmed by goal-directed eye movements toward the stimulus. The saccadic reaction time (SRT) is regarded as an index of visual field responsiveness, whereas in standard automated perimetry (SAP), the visual field sensitivity is tested. We investigated the relation between visual field sensitivity and responsiveness in corresponding locations of the visual field in healthy controls and in patients with mild, moderate and advanced glaucoma. Materials and Methods: Thirty-four healthy control subjects and 42 glaucoma patients underwent a 54-point protocol in eye movement perimetry (EMP) and a 24-2 SITA standard protocol in a Humphrey Field Analyzer. The visual field points were stratified by total deviation sensitivity loss in SAP into 6 strata. A generalized linear mixed model was applied to determine the influence of the various factors. Results: The generalized linear mixed model showed that the mean SRT increased with increasing glaucoma severity, from 479 ms in the control eyes to 678 ms in the eyes of patients with advanced glaucoma (p < 0.001). Mean SRTs significantly increased with increasing SAP sensitivity loss. Even at the locations where no sensitivity loss was detected by SAP (total deviation values greater or equal than 0 dB), we found lengthened SRTs in mild, moderate and advanced glaucoma compared to healthy controls (p < 0.05) and in moderate and advanced glaucoma compared to mild glaucoma (p < 0.05). At locations with total deviation values between 0 and -3 dB, -3 and -6 dB and -6 and -12 dB, we found similar differences. Conclusions: The lengthened SRT in areas with normal retinal sensitivities in glaucomatous eyes, i.e., planning and execution of saccades to specific locations, precede altered sensory perception as assessed with SAP. Better understanding of altered sensory processing in glaucoma might allow earlier diagnosis of emerging glaucoma.

Effect of Age, Sex, Stimulus Intensity, and Eccentricity on Saccadic Reaction Time in Eye Movement Perimetry.

PURPOSE: In eye movement perimetry (EMP), the extent of the visual field is tested by assessing the saccades using an eye tracker. The aim of the present study was to determine the effects of age and sex of the subjects, the eccentricity and intensity of the peripheral stimuli on saccadic reaction time (SRT), and the interaction between these parameters in healthy participants. METHODS: Healthy participants aged between 20 to 70 years underwent a complete ophthalmic examination and an EMP test. SRT was determined from detected peripheral stimuli of four intensity levels. A multilevel mixed-model analysis was used to verify the influence of subject and stimulus characteristics on SRT within the tested visual field. RESULTS: Ninety-five subjects (mean age 43.0 [15.0] years) were included. Age, stimulus intensity, and eccentricity had a statistically significant effect on SRT, not sex. SRTs were significantly faster with increasing stimulus intensity and decreasing eccentricity (P < 0.001). At the lowest stimulus intensity of 192 cd/m2, a significant interaction was found between age and eccentricity. CONCLUSIONS: The current study demonstrated significant SRT dependence across the visual field measured up to 27°, irrespective of sex. The presented SRT values may serve as a first normative guide for EMP. TRANSLATIONAL RELEVANCE: This report of SRT interaction can aid in refining its use as a measure of visual field responsiveness.

Is a pillow a risk factor for glaucoma?

PURPOSE: To study whether a clinically significant increase in intraocular pressure (IOP) occurs during simulated sleep conditions with the subject's head turned comfortably into a pillow (the simulated sleep position) and the effect of protective glasses on any such IOP rise. METHODS: A specially developed electronic epipalpebral pressure (EPP) sensor was attached to an eyelid of the right eye of all participants: 11 patients with primary open-angle glaucoma and 11 healthy volunteers. During calibration, mechanical pressure was applied to the EPP sensor taped to the lower eyelid and the IOP was measured simultaneously at the slit lamp by Goldmann applanation tonometry. The EPP was increased in a stepwise fashion to assess the relationship between EPP and IOP for each individual eye. Thereafter, EPP (with the sensor now taped to the upper eyelid) measurements were performed in the simulated sleep position, both with and without protective glasses. The EPP was determined in each individual eye, and the estimated IOP was then inferred from the established EPP/IOP relationship. RESULTS: In the simulated sleep position, the mean IOP increased by an estimated 19.6 mmHg (SD: 7.5; range 11.6-32.8; p < 0.0001) in the patient group and 28.0 mmHg (SD: 9.6; range 12.3-41.1); p < 0.0001) in the control group. When the subjects wore protective glasses, the mean estimated IOP decreased again by 16.3 mmHg (SD: 5.6; range 9.8-28.1; p < 0.0001) in the patient group and 25.1 mmHg (SD: 8.2; range 11.7-38.3; p = <0.0001) in the control group. CONCLUSION: Turning the head into a pillow gave a large and clinically significant increase in the estimated IOP in the simulated sleep position. With protective glasses, however, the increase in estimated IOP was almost absent. Therefore, protective shielding of the eyes during sleep may be a treatment option in glaucoma.

Attenuation Coefficients From SD-OCT Data: Structural Information Beyond Morphology on RNFL Integrity in Glaucoma.

PURPOSE: The purpose of this study is to explore the attenuation coefficient (AC) of the retinal nerve fiber layer (RNFL) in spectral domain optical coherence tomography (OCT) images, in healthy eyes and eyes affected by glaucoma. To assess the relation between RNLF AC, disease severity, RNFL thickness, visual field sensitivity threshold, spatial location and age. PATIENTS AND METHODS: We analyzed peripapillary circle scans of a clinical OCT device (Spectralis OCT, Heidelberg Engineering, Heidelberg, Germany) in 102 glaucoma patients and 90 healthy controls. The images were fully automatically converted into depth-resolved AC images. Next, the median AC within the RNFL was calculated based on the Spectralis segmentation. We compared the RNFL AC between healthy, mild, moderate and advanced glaucomatous eyes and assessed the correlation with patient characteristics such as age and visual field sensitivity threshold (HFA, Carl Zeiss Meditec, Dublin, CA) in a generalized estimating equations (GEE) model. Finally, we explored the ability to discriminate between glaucomatous and healthy eyes by RNFL AC. RESULTS: Median RNFL AC decreased with increasing disease severity up to moderate glaucoma (P<0.001) in all 4 sectors around the optic nerve head. The largest relative decrease occurred in the nasal sector. The RNFL AC (AUC, 0.834±0.028) effectively discriminated healthy from glaucomatous eyes, although RNFL thickness (AUC, 0.975±0.013) performed even better (P<0.001). Prediction of visual field sensitivity improved significantly when RNFL thickness was augmented with RNFL AC as covariates (P<0.001). CONCLUSIONS: This study demonstrated that RNFL AC provides complementary information on the RNFL's health compared with RNFL thickness measurements alone.

Loosely coupled level sets for simultaneous 3D retinal layer segmentation in optical coherence tomography.

Optical coherence tomography (OCT) yields high-resolution, three-dimensional images of the retina. Reliable segmentation of the retinal layers is necessary for the extraction of clinically useful information. We present a novel segmentation method that operates on attenuation coefficients and incorporates anatomical knowledge about the retina. The attenuation coefficients are derived from in-vivo human retinal OCT data and represent an optical property of the tissue. Then, the layers in the retina are simultaneously segmented via a new flexible coupling approach that exploits the predefined order of the layers. The accuracy of the method was evaluated on 20 peripapillary scans of healthy subjects. Ten of those subjects were imaged again to evaluate the reproducibility. An additional evaluation was performed to examine the robustness of the method on a variety of data: scans of glaucoma patients, macular scans and scans by a two different OCT imaging devices. A very good agreement on all data was found between the manual segmentation performed by a medical doctor and the segmentation obtained by the automatic method. The mean absolute deviation for all interfaces in all data types varied between 1.9 and 8.5 µm (0.5-2.2 pixels). The reproducibility of the automatic method was similar to the reproducibility of the manual segmentation.

Validity and Repeatability of Saccadic Response Times Across the Visual Field in Eye Movement Perimetry.

PURPOSE: To assess the validity and repeatability of saccadic reaction times (SRT) across the visual field up to 30° using eye movement perimetry (EMP). METHODS: Eighteen subjects (36 eyes) were shown a central stimulus on a flat monitor screen. Next, peripheral stimuli were shown using an overlap paradigm. Subjects were instructed to look at detected peripheral stimuli and then refixate the central stimulus again. In three repetitive measurement series, a total of 288 visual stimuli (3 series × 24 locations × 4 contrast levels) were presented. Levene's test for equality of variances was applied to test the effect of stimulus location and measurement series on SRT variance. A Wilcoxon signed ranks test was used to compare SRTs between measurement series. RESULTS: A total of 26 eyes were included in the study (72%). On average, 90.5% of the peripheral stimuli were labeled as 'seen' based on eye movement responses. Between the series, the mean SD of SRT differences was approximately 100 ms. Significantly faster SRTs were only found at contrast level 0.8 in series III compared with series II. In series I, SRT variance was independent in 75% of all locations. Across the three series, SRT variance was independent in 87.5% of all locations. CONCLUSIONS: The present study demonstrates low variability of SRT across the visual field up to 30° eccentricity and across measurement series. TRANSLATIONAL RELEVANCE: SRT as a measure for visual field responsiveness may be a potential marker to detect risk areas in specific parts of the visual field.

Is Hyperopia an Important Risk Factor for PACG in the Dutch Population?-A Case Control Study.

Objectives. To determine if hyperopia is a risk factor for primary angle-closure glaucoma (PACG) in the Dutch population and to identify other biometrical parameters as risk factors for PACG including axial length (AL), anterior chamber depth (ACD), and k values. Methods. The study population consisted of PACG patients that had undergone a laser peripheral iridotomy (LPI). The control group consisted of age- and gender-matched cataract patients. The main outcome was hyperopia (spherical equivalent ≥+0.5 dioptres) measured with IOL Master or autorefractor. Refractive error, ACD, AL, and k values were tested with a Mann-Whitney U test and by logistic regression. Results. 117 PACG patients and 234 controls were included (mean age = 80 years ± 3.6). The prevalence of hyperopia in patients and controls was 69.6% and 61.1%, respectively (Fisher's test P = 0.076). Mann-Whitney U test showed no statistically significant relation with refractive error (P = 0.068) or k values (P = 0.607). In contrast, ACD and AL were statistically significant (P < 0.001). Tested with logistic regression, only ACD was a significant predictor of PACG (P < 0.001). Conclusion. There was no statistically significant correlation between refractive error and PACG. ACD was strongly correlated, though, with PACG, whereas AL turned out to be a less significant risk factor.