Influence of Target Parameters on Fixation Stability in Normal and Strabismic Monkeys

Purpose: The purpose of this study was to assess the effect of fixation target parameters on fixation instability in strabismic monkeys. Methods: One normal and three exotropic monkeys were presented with four differently shaped fixation targets, with three diameters, during monocular or binocular viewing. Fixation targets were white on a black background or vice versa. Binocular eye movements were recorded using the magnetic search coil technique and fixation stability quantified by calculating the bivariate contour ellipse area (BCEA). Results: Fixation instability was greater in all the strabismic monkeys compared with the normal monkey. During monocular viewing, strabismic monkeys showed significantly greater instability in the covered eye compared to the fixating eye. Multifactorial ANOVA suggested statistically significant target parameter influences, although effect sizes were small. Thus, a disk-shaped target resulted in greater instability than other target shapes in the viewing eyes of the normal monkey and two of three strabismic monkeys. A similar target-shape effect was also observed in the covered eye. Least instability was elicited with a 0.5° target in the normal monkey and a 1.0° target in the strabismic monkeys, both in the viewing and the covered eye. Target/background polarity effects were idiosyncratic. In strabismic monkeys, stability of the fixating eye during binocular viewing was not different from the stability of the same eye during monocular viewing. Conclusions: Abnormal drifts and nystagmus contribute to increased fixation instability in strabismic monkeys. Target parameters (shape and size) that influence fixation stability in a normal animal also affected fixation stability in our sample of strabismic monkeys

Fixation Stability in Monkeys with Strabismus

Purpose: To assess the effect of target parameters on fixation stability in strabismic monkeys. Methods: Eye movements were recorded in one normal and three strabismic monkeys during 72 fixation conditions (4 shapes; 3 sizes; 2 backgrounds; OD, OS or OU viewing), each repeated 5 times. Fixation stability was quantified using the Bivariate Contour Ellipse Area (BCEA). Influence of target parameters was assessed using 4-way ANOVA. Results: BCEA was greater in the strabismic monkeys compared to the normal. In strabismus, BCEA of the deviated eye was significantly greater than BCEA in the fixating eye. Target shape and size significantly influenced fixation stability in both normal and strabismic monkeys. Background effects were idiosyncratic. Conclusions: Target parameters that influence fixation stability in a normal, also affects fixation stability in disease conditions such as strabismus. Target parameter influences likely function via conjugate mechanisms since proportional effects were observed in both viewing and covered eyes.Optometry, College o

Visual outcomes and higher-order aberrations in eyes implanted with hybrid extended depth of focus intraocular lens

PURPOSE: To study the visual outcomes and higher order aberrations in eyes implanted with Hybrid EDOF IOL, particularly in Indian eyes. MATERIALS AND METHODS: This is retrospective case series where subjects aged between 40-65 years and were implanted with LUCIDIS IOL by single surgeon were included. Subjects with Pre surgery corneal astigmatism > 1.50 D, corneal guttae, IOP >22mmHg, any ocular Co morbidities, Intra or post operative complication were excluded. At 1 month follow up, uncorrected visual acuities at distance (UCDVA), intermediate (UCIVA) and near (UCNVA), refraction were recorded. Internal Higher order aberrations and strehl ratio for a fixed pupil of 4mm and 6mm were calculated using NIDEK OPD Scan. Monocular defocus curve was obtained at 4 meter logMAR chart. RESULTS: Total of 55 eyes of 35 patients with mean±SD age of 58.50±7.49 years were evaluated. 89.09% of the eyes achieved visual acuity of 6/6. 49.09% could read N10 font at intermediate distance without any correction and 85.45% of the eyes had uncorrected near visual acuity of N6. Around 67% of the eyes did not require any refractive correction whereas around 26% of the eyes required correction upto ±0.25D. The defocus curve showed that visual acuity also ranges from 0.05 logMAR to 0.2 logMAR for Plano to -3.00D respectively. Mean±SD Strehl ratio at 4 and 6 mm pupil size was 0.06±0.04 and 0.02±0.02 respectively. CONCLUSION: Hybrid EDOF IOL such as LUCIDIS provides excellent vision at all distances. This could be attributed to IOL design which is spherical aberration neutral lens

Age-related variations in corneal stress-strain index in the Indian population

Purpose: To report age-related variations in corneal stress–strain index (SSI) in healthy Indians. Methods: It was a retrospective study where healthy Indian individuals aged between 11 and 70 years who had undergone corneal biomechanics assessment using Corvis ST between January 2017 and December 2021 were enrolled. Composite corneal biomechanical parameters and corneal SSI were abstracted from Corvis ST and compared across different age groups using one-way analysis of variance (ANOVA). Also, Pearson's correlation was used to evaluate the association between age and SSI. Results: Nine hundred and thirty-six eyes of 936 patients with ages between 11 and 77 years with mean ± SD intraocular pressure (IOP) and pachymetry of 16.52 ± 2.10 mmHg and 541.13 ± 26.39 μs, respectively. Composite corneal biomechanical parameters such as deformation amplitude ratio max at 1 mm (P < 0.001) and 2 mm (P < 0.001), biomechanically corrected IOP (P = 0.004), stiffness parameter at A1 (P < 0.001, Corvis biomechanical index (P < 0.018), and SSI (P < 0.001) were found to be significantly different as a function of age group. We noted a statistically significant positive association of SSI with age (P < 0.001), spherical equivalent refractive error (P < 0.001), and IOP (P < 0.001) and a significant negative association with anterior corneal astigmatism (P < 0.001) and Anterior chamber depth (ACD) (P < 0.001). Also, SSI was positively associated with SPA1 and bIOP, whereas negatively associated with integrated radius, max inverse radius, and Max Deformation amplitude (DA) ratio at 1 mm and 2 mm. Conclusion: We noted a positive association of corneal SSI with age in normal healthy Indian eyes. This information could be helpful for future corneal biomechanical research

Association between anterior corneal astigmatism and posterior corneal astigmatism across age groups: a cross-sectional analysis

AIM: To assess the anterior corneal astigmatism(ACA)and posterior corneal astigmatism(PCA)patterns across various age groups. We also evaluated the association between magnitudes and axes of the ACA and PCA across these age groups. METHODS: The present study was a cross-sectional analysis of clinical data of 381 eyes. We converted the clinical astigmatic notation to vector notation for analysis of ACA and PCA. We estimated the correlation between magnitude and axes of the ACA and PCA in the whole population and in four age groups(5-19, 20-39, 40-59, and ≥ 60y). We used random effects linear regression models for estimating the association between the magnitudes of ACA and PCA.RESULTS: The mean of the magnitude of the ACA(3.59D)and the PCA(0.50D)was highest in children(5 to 9y). Overall, the magnitude of the ACA ranged from 0D to 10.0 Diopters(D)and the magnitude of the PCA ranged from 0 to 3.5 D. There was a significant correlation between the ACA and the PCA in the younger age group(r=0.85, PP=0.03)with each unit increase in the ACA, the increase was the smallest in this age group.CONCLUSION: It will be prudent to measure the both the magnitude and axis of the PCA, particularly in those above 60y rather than rely on rule-of-thumb calculations based on ACA parameters for IOL power calculation

Unusual fractured dexamethasone implant in the vitreous cavity

Ozurdex is an approved drug for managing vitritis. Raised intraocular pressure and cataract formation are known complications of Ozurdex implant; however, a fractured Ozurdex implant after injection is a rare entity. Here, we report a case of a 19-year-old male patient who received an intravitreal Ozurdex implant for vitritis, which was found to be broken into three pieces at a 1-week follow-up. Usually, the breakage of Ozurdex in the vitreous cavity does not alter its efficacy or result in any complications and, thus, does not require any intervention. However, frequent and careful monitoring is required to rule out any unexpected complications