Comparison of Epithelial Thickness Mapping in Normal Corneas with Different Types of Astigmatism.

SIGNIFICANCE: Corneal epithelial thickness mapping has a wide range of applications including screening for keratoconus, screening for anterior basement membrane dystrophy, and assessment of dry eye. It also plays an important role in corneal laser refractive surgery. These all require an understanding of the epithelial thickness profile in a normal cornea as a reference. PURPOSE: This study aimed to compare corneal epithelial thickness along different meridians in normal eyes with different types of corneal astigmatism. METHODS: In this cross-sectional study, corneal topography and epithelial thickness mapping by anterior segment optical coherence tomography was performed for 154 normal eyes. Corneal astigmatism was classified based on the orientation of the steepest corneal meridian (with-the-rule [WTR], against-the-rule [ATR], and oblique) and the amount (low, moderate, and high). On a 9-mm epithelial thickness map, the thickness along the horizontal (180°), vertical (90°), and diagonal (45 and 135°) meridians was calculated. RESULT: With-the-rule, oblique, and ATR astigmatisms were observed in 40, 31, and 29% of the eyes, respectively. In all types of astigmatism, the mean epithelial thickness was greater along the 180° meridian and thinner along the 90° meridian. There was no statistically significant difference in mean thickness along different meridians for WTR (P = .24) and oblique (P = .46) astigmatism, whereas the difference along the 180 and 90° meridians (P = .003) for ATR astigmatism was statistically significant. Also, there was a statistically significant difference in thickness in different types of astigmatism separately for each meridian (P < .05) so that the highest and lowest thicknesses were seen for ATR and oblique astigmatisms, respectively. The epithelial thickness showed no statistical difference in various amounts of astigmatism along different meridians. CONCLUSIONS: Thicker epithelium along the horizontal meridian in ATR may point to the surface regularizing functions of the epithelium to create a regular and smooth surface, but thickness assessment along the different meridians in oblique and WTR showed no curvature-dependent changes.

Pattern visual evoked potential in hypothyroid patients.

PURPOSE: To investigate the functional integrity of visual pathway in hypothyroid patients by pattern visual evoked potential (PVEP). METHODS: We enrolled 36 female patients with history of hypothyroidism (18 overt and 18 subclinical) aged 20 to 60 years and 36 healthy women of similar age (control group). All subjects had a complete ophthalmic examination. For VEP testing, subjects were exposed to checks subtending a visual angle of 15 and 60 min of arc. RESULTS: For the 15 min of arc check size, the mean P100 latency was significantly delayed (113 milliseconds (ms)) and amplitude significantly reduced (9.2 microvolts (µv)) in the hypothyroidism group compared with controls (109.6 ms and 11.6 µv, respectively). For this 15' check size, the group differences were related to significantly increased latency and reduced amplitude of responses in the group with overt hypothyroidism compared with controls. There was no difference between the groups (hypothyroid vs control) with 60 min of arc check size. There was a significant correlation between severity of the disease and PVEP component. CONCLUSIONS: In conclusion, low levels of circulating hypothyroid hormone are associated with delay in the pattern VEP to small check sizes. This CNS involvement worsens in patients with greater severity and duration of hypothyroidism.

Comparing accommodative function between the dominant and non-dominant eye.

BACKGROUND: To compare the accommodative amplitude (AA), facility (AF), and lag between dominant and non-dominant eyes. METHODS: Seventy students [mean (SD) age: 21.2 (1.7) years, range 18-25] from Zahedan University of Medical Sciences were selected. Retinoscopy and subjective refraction was used to determine the refractive error. The hole-in-the card method was used to determine eye dominance. The accommodative amplitude (AA) was measured in the dominant and non-dominant eye using the push-up method, and accommodative facility (AF) using ±2.00 dioptre flipper lenses at 40 cm. Accommodative lag was determined using monocular estimate method (MEM) retinoscopy at 40 cm. RESULTS: The right eye was dominant in 53 subjects (75.7 %). There was no significant difference in refractive error (sphere, cylinder, and spherical equivalent) between dominant and non-dominant eyes. The mean (SD) for the AA, AF, and lag in dominant eyes was 12.48 (2.56) dioptres, 12.45 (4.83) cycles per minute, and 0.80 (0.27) dioptres respectively. The mean (SD) for the AA, AF, and lag in non-dominant eyes was 12.16 (2.37) dioptres, 12.20 (4.88) cycles per minute, and 0.83 (0.28) dioptres respectively. The mean (SD) difference in AA, AF, and lag between dominant and non dominant eyes was 0.32 (0.75) dioptres (P = 0.001), 0.25 (1.05) cycles per minute (P = 0.04), and -0.02 (0.11) dioptres (P = 0.10) respectively. The AA and AF was statistically better (P < 0.05) in the dominant eye group than in the non-dominant eye group. These data provided little evidence of any difference in the accommodative lag between dominant and non-dominant eyes (P > 0.05). CONCLUSION: The right eye was dominant in 76 % of subjects. Superior AA and AF was found in the dominant eye as determined by hole-in-the card method in young healthy adults, although these differences are perhaps not of clinical significance (<0.50 dioptres and <2 cycles per minute).

An effective hair removal algorithm for dermoscopy images.

BACKGROUND/PURPOSE: Dermoscopy is one of the major imaging modalities used in the diagnosis of pigmented skin lesions. Due to the difficulty and subjectivity of human interpretation, computerized image analysis techniques have become important tools in this research area. Hair removal from skin lesion images is one of the key problems for the precise segmentation and analysis of the skin lesions. In this study, we present a new scheme that automatically detects and removes hairs from dermoscopy images. METHODS: The proposed algorithm includes two steps: firstly, light and dark hairs and ruler marking are segmented through adaptive canny edge detector and refinement by morphological operators. Secondly, the hairs are repaired based on multi-resolution coherence transport inpainting. RESULTS: The algorithm was applied to 50 dermoscopy images. To estimate the accuracy of the proposed hair detection algorithm, quantitative analysis was performed using TDR, FPR, and DA metrics. Moreover, to evaluate the performance of the proposed hair repaired algorithm, three statistical metrics namely entropy, standard deviation, and co-occurrence matrix were used. CONCLUSION: The results demonstrate that the proposed algorithm is highly accurate and able to detect and repair the hair pixels with few errors. In addition, the segmentation veracity of the skin lesion is effectively improved after our proposed hair removal algorithm.

Corneal Biomechanical Properties in Varying Severities of Myopia.

Purpose: To investigate corneal biomechanical response parameters in varying degrees of myopia and their correlation with corneal geometrical parameters and axial length. Methods: In this prospective cross-sectional study, 172 eyes of 172 subjects, the severity degree of myopia was categorized into mild, moderate, severe, and extreme myopia. Cycloplegic refraction, corneal tomography using Pentacam HR, corneal biomechanical assessment using Corvis ST and Ocular Response Analyser (ORA), and ocular biometry using IOLMaster 700 were performed for all subjects. A general linear model was used to compare biomechanical parameters in various degrees of myopia, while central corneal thickness (CCT) and biomechanically corrected intraocular pressure (bIOP) were considered as covariates. Multiple linear regression was used to investigate the relationship between corneal biomechanical parameters with spherical equivalent (SE), axial length (AXL), bIOP, mean keratometry (Mean KR), and CCT. Results: Corneal biomechanical parameters assessed by Corvis ST that showed significant differences among the groups were second applanation length (AL2, p = 0.035), highest concavity radius (HCR, p < 0.001), deformation amplitude (DA, p < 0.001), peak distance (PD, p = 0.022), integrated inverse radius (IR, p < 0.001) and DA ratio (DAR, p = 0.004), while there were no significant differences in the means of pressure-derived parameters of ORA between groups. Multiple regression analysis showed all parameters of Corvis ST have significant relationships with level of myopia (SE, AXL, Mean KR), except AL1 and AL2. Significant biomechanical parameters showed progressive reduction in corneal stiffness with increasing myopia (either with greater negative SE or greater AXL), independent of IOP and CCT. Also, corneal hysteresis (CH) or ability to dissipate energy from the ORA decreased with increasing level of myopia. Conclusions: Dynamic corneal response assessed by Corvis ST shows evidence of biomechanical changes consistent with decreasing stiffness with increasing levels of myopia in multiple parameters. The strongest correlations were with highest concavity parameters where the sclera influence is maximal.

Pattern Visual Evoked Potentials in Dyslexic Children.

PURPOSE: This study aimed to compare pattern visual evoked potential (PVEP) components in dyslexic and normal children. METHODS: This cross-sectional analytic study recruited 72 children, including 36 dyslexic and 36 normal participants aged 8-12 years. Visual examinations included measurement of distance visual acuity, refraction, and PVEP components of amplitudes and latencies with two different check sizes of 15 and 60 minutes (min) of arc at two contrast levels of 25% and 100%. RESULTS: Our results demonstrated significant differences between dyslexic and normal children in terms of P100 latency and amplitude of PVEP at 25% contrast, with check sizes of 15 and 60 min of arc. However, there were no significant differences between the two groups regarding P100 latency and amplitude at 100% contrast with check sizes of both 15 and 60 min of arc. CONCLUSION: Dyslexic participants showed reduced amplitude and prolonged latency in most PVEP components at low-contrast levels. These findings may support the magnocellular deficit hypothesis in dyslexic participants, even though the parvocellular pathway remains intact.

The effectiveness of home-based pencil push-up therapy versus office-based therapy for the treatment of symptomatic convergence insufficiency in young adults.

PURPOSE: To compare the effectiveness of pencil push-up therapy (PPT) versus office-based vision therapy in patients with convergence insufficiency. MATERIALS AND METHODS: In this study, 60 students from Zahedan University of Medical Sciences with convergence insufficiency were selected. After determining their refractive error (with a retinoscope), near point of convergence (by millimeter ruler), near heterophoria (by alternate prism cover test), and positive fusional vergence at near (by prism bar), subjects were divided into two groups to receive PPT (at least three times a day for 5 minutes each time) or office-based therapy (two times each week for 60 minutes each visit) without home reinforcement. Subjects were re-examined 4 and 8 weeks after initiation of treatment. Statistical analysis was performed with the independent samples t-test and the analysis of variance (ANOVA). Statistical significance was indicated by P < 0.05. RESULTS: The near point of convergence, phoria, and positive fusional vergence were not statistically different between the two groups before treatment (P > 0.05). After 4 and 8 weeks of therapy, only the positive fusional vergence was statistically significantly different between groups (P = 0.001). Results from ANOVA indicated a considerable difference between the two groups in general but the observed difference was related only to positive fusional vergence. CONCLUSION: PPT and office-based vision therapy are comparable for treatment of convergence insufficiency. While we do not deny the more efficacious nature of office-based therapy, it is not always practical, may be too expensive, and may not be locally available. A home-based therapy offers a cost-effective reasonable alternative.

Refractive Outcomes, Contrast Sensitivity, HOAs, and Patient Satisfaction in Moderate Myopia: Wavefront-Optimized Versus Tissue-Saving PRK.

PURPOSE: To compare refractive outcomes, contrast sensitivity, higher-order aberrations (HOAs), and patient satisfaction after photorefractive keratectomy for correction of moderate myopia with two methods: tissue saving versus wavefront optimized. METHODS: In this prospective, comparative study, 152 eyes (80 patients) with moderate myopia with and without astigmatism were randomly divided into two groups: the tissue-saving group (Technolas 217z Zyoptix laser; Bausch & Lomb, Rochester, NY) (76 eyes of 39 patients) or the wavefront-optimized group (WaveLight Allegretto Wave Eye-Q laser; Alcon Laboratories, Inc., Fort Worth, TX) (76 eyes of 41 patients). Preoperative and 3-month postoperative refractive outcomes, contrast sensitivity, HOAs, and patient satisfaction were compared between the two groups. RESULTS: The mean spherical equivalent was -4.50 ± 1.02 diopters. No statistically significant differences were detected between the groups in terms of uncorrected and corrected distance visual acuity and spherical equivalent preoperatively and 3 months postoperatively. No statistically significant differences were seen in the amount of preoperative to postoperative contrast sensitivity changes between the two groups in photopic and mesopic conditions. HOAs and Q factor increased in both groups postoperatively (P = .001), with the tissue-saving method causing more increases in HOAs (P = .007) and Q factor (P = .039). Patient satisfaction was comparable between both groups. CONCLUSIONS: Both platforms were effective in correcting moderate myopia with or without astigmatism. No difference in refractive outcome, contrast sensitivity changes, and patient satisfaction between the groups was observed. Postoperatively, the tissue-saving method caused a higher increase in HOAs and Q factor compared to the wavefront-optimized method, which could be due to larger optical zone sizes in the tissue-saving group.

Pattern Visual Evoked Potentials in Dyslexic versus Normal Children.

PURPOSE: Presence of neurophysiological abnormalities in dyslexia has been a conflicting issue. This study was performed to evaluate the role of sensory visual deficits in the pathogenesis of dyslexia. METHODS: Pattern visual evoked potentials (PVEP) were recorded in 72 children including 36 children with dyslexia and 36 children without dyslexia (controls) who were matched for age, sex and intelligence. Two check sizes of 15 and 60 min of arc were used with temporal frequencies of 1.5 Hz for transient and 6 Hz for steady-state methods. RESULTS: Mean latency and amplitude values for 15 min arc and 60 min arc check sizes using steady state and transient methods showed no significant difference between the two study groups (P values: 0.139/0.481/0.356/0.062). Furthermore, no significant difference was observed between two methods of PVEPs in dyslexic and normal children using 60 min arc with high contrast (P values: 0.116, 0.402, 0.343 and 0.106). CONCLUSION: The sensitivity of PVEP has high validity to detect visual deficits in children with dyslexic problem. However, no significant difference was found between dyslexia and normal children using high contrast stimuli.

Effect of target distance on accommodative amplitude measured using the minus lens technique.

BACKGROUND: The aim was to investigate the effect on the measured amplitude of accommodation and repeatability of using the minus lens technique with the target at distance or near. METHODS: Forty-three students (average age: 21.17 ± 1.50 years, 35 female) had their amplitude of accommodation measured with minus lenses on top of their distance correction in a trial frame with the target at far (6.0 m) or near (0.4 m). The minus lens power was gradually added with steps of 0.25 D. Measurements were taken on two occasions at each distance, which were separated by a time interval of at least 24 hours. RESULTS: The measured amplitude at six metres was significantly lower than that with the target at 40 cm, by 1.56 ± 1.17 D (p < 0.001) and this varied between individuals (r = 0.716, intraclass correlation coefficient = 0.439). With either target distance, repeated measurement was highly correlated (r > 0.9) but the agreement was better at 6.0 m (±0.74 D) than at 40 cm (± 0.92 D). CONCLUSION: The measurements of the amplitude of accommodation with the minus lens technique using targets at far or near are not comparable and the difference between the target distances may provide clinically relevant information.

Prevalence of Refractive Errors in Students with and without Color Vision Deficiency.

PURPOSE: To evaluate refractive errors in school age children with color vision deficiency (CVD) and those with normal color vision (NCV) in order to make a better understanding of the emmetropization process. METHODS: A total of 4,400 primary school students aged 7-12 years were screened for color vision using Ishihara pseudoisochromatic color vision plate sets. Of these, 160 (3.6%) students had CVD. A total of 400 age- and sex-matched students with NCV were selected as controls. Refractive status was evaluated using objective cyclorefraction. RESULTS: The CVD group included 136 male (85%) and 24 female (15%) subjects with mean age of 10.1 ± 1.8 years. The NCV group comprised of 336 male (84%) and 64 female (16%) subjects with mean age of 10.5 ± 1.2 years. The prevalence of myopia (7.7% vs. 13.9%, P < 0.001) and hyperopia (41% vs. 57.4%, P = 0.03) was significantly lower in the CVD group. Furthermore, subjects with CVD subjects demonstrated a lower magnitude of refractive errors as compared to the CVD group (mean refractive error: +0.54 ± 0.19 D versus + 0.74 ± 1.12 D, P < 0.001). CONCLUSION: Although the lower prevalence of myopia in subjects with CVD group supports the role of longitudinal chromatic aberration in the development of refractive errors; the lower prevalence of hyperopia in this group is an opposing finding. Myopia is a multifactorial disorder and longitudinal chromatic aberration is not the only factor influencing the emmetropization process.

Correlation between Worth Four Dot Test Results and Fusional Control in Intermittent Exotropia.

PURPOSE: To compare the results of Worth 4-dot test (WFDT) performed in dark and light, and at different distances, with fusional control in patients with intermittent exotropia (IXT). METHODS: Dark and light WFDT was performed for new IXT subjects at different distances and the results were compared with level of office-based fusional control. RESULTS: Fifty IXT patients including 17 male and 33 female subjects participated in the study. A significant difference (P<0.05) was observed between levels of home and office-based fusional control (P<0.05). A weak correlation was present between the results of WFDT and level of office-based fusional control; the highest agreement (Kappa=0.088) was observed with dark WFDT performed at a distance of 4m. CONCLUSION: Evaluation of fusional state by far WFDT, especially in a dark room, shows modest correlation with office-based fusional control in IXT patients and can be used as an adjunct to more complex tests such as far stereoacuity.

Effect of cataract type and severity on visual acuity and contrast sensitivity.

PURPOSE: To determine the effect of cataract type and severity in eyes with pure types of age-related lens opacities on visual acuity (VA) and contrast sensitivity in the presence and absence of glare conditions. METHODS: Sixty patients with senile cataracts aged 40 years or older with no other ocular pathologies were evaluated for VA and contrast sensitivity with and without glare. Lens opacities were classified according to the Lens Opacities Classification System (LOCS) III. VA was measured using the Snellen chart. Contrast sensitivity was measured with the Vector Vision CSV-1000E chart in the presence and absence of glare by calculating the area under log contrast sensitivity (log CS) function (AULCSF). RESULTS: Cataracts were posterior subcapsular in 26 eyes, cortical in 19 eyes and nuclear in 15 eyes. VA significantly decreased with increasing cataract severity and there was significant loss of contrast sensitivity at all spatial frequencies with increasing cataract severity. AULCSF significantly decreased with increasing cataract severity in the presence and absence of glare conditions. Contrast sensitivity was significantly reduced at high spatial frequency (18 cpd) in cortical cataracts in the presence of glare in day light and at low spatial frequency (3 cpd) in night light. CONCLUSION: Increased cataract severity is strongly associated with a decrease in both VA and AULCSF. Contrast sensitivity scores may offer additional information over standard VA tests in patients with early age-related cataracts.