Corneal Optics after Reading, Microscopy and Computer Work

Effect of congenital ptosis on corneal topography and total aberrometry and comparison of these variables between ptotic and normal fellow eyes

PURPOSE

To analyze the effect of congenital ptosis on corneal topography and total aberrometry and to compare these variables between ptotic and normal fellow eyes.

METHODS

The study included 32 eyes of 16 patients with unilateral congenital blepharoptosis. A Shack-Hartmann wavefront sensor was employed to assess Zernike coefficients and root-mean-square. Computerized corneal topography, Orbscan and aberrometry were measured in the healthy and ptotic eyes. Data were analyzed using SPSS version 16. P<0.05 was considered significant.

RESULTS

The mean patient age was 21.31±6.3 years. The mean margin to light reflex distance-1 (MRD-1) was 0.6±1.44mm in the ptotic eyes. Among topography variables, surface regularity index (SRI), cylinder power, irregular astigmatism index (IAI), and flat meridian keratometry were significantly different between ptotic and non-ptotic fellow eyes (P<0.05). Some Orbscan parameters, including simulated keratometry, maximum and minimum corneal power, and astigmatism power were significantly different between ptotic and normal fellow eyes (P<0.05). There was no statistically significant difference in total aberrometry variables between paired eyes. However, in a comparison between ptotic eyes with over 1 diopter astigmatism vs. less than 1 D, high-order Zernike modes without spherical aberration at 6mm (HOW/O Z400 6mm) were significantly different between the 2 groups (P=0.02).

CONCLUSION

Unilateral congenital ptosis significantly affects corneal topography and aberrometry, especially in eyes with astigmatism≥1 D. Such differences need to be considered before keratorefractive surgery (KRS).

Prevalence of and factors associated with astigmatism in preschool children in Wuxi City, China

PURPOSE

To investigate the status of astigmatism in preschool children in Wuxi City, and explore the risk factors related to astigmatism. The risk factors related to astigmatism development as predictors can help us identify preschool children who need vision screening at an early stage to ensure good visual quality.

METHODS

The cross-sectional study was conducted in 10 kindergartens randomly selected in five districts of Wuxi City in November 2018. All preschool children were measured by objective refractometry under non-cycloplegic refraction. The basic information of preschool children was collected. The relevant factors of astigmatism in the questionnaire were completed by parents. Spss 26. 0 software was used for univariate and multivariate correlation analysis.

RESULTS

A total of 889 preschool children participated in the study, 864 were finally included in the study. The prevalence of astigmatism was 36.0%. The risk of astigmatism in premature children was higher than that in non-premature children (adjusted odds ratio = 1.841). The prevalence of astigmatism with parents' astigmatism history was higher, compared with preschool children without parents' astigmatism history (adjusted odds ratio = 2.037). When maternal age at childbirth was older (≥ 35 years old), the risk of astigmatism increased in preschool children (adjusted odds ratio = 2.181). Compared with bottle feeding, the risk of astigmatism for mixed feeding and breastfeeding reduced in preschool children. Compared with preschool children exposed to electronic screen for less than 2 h every day, preschool children exposed to electronic screen for more than 2 h had an increased risk of astigmatism (P = 0.004).

CONCLUSION

The prevalence of astigmatism among preschool children in Wuxi City was high. Some risk factors such as premature birth, parents' astigmatism history, maternal age at childbirth, feeding pattern, and electronic screen exposure time were closely related to the occurrence of astigmatism among preschool children. For preschool children with significant risk factors, their eyesight should be checked regularly to ensure their visual quality.

Changes in corneal astigmatism and near heterophoria after smartphone use while walking and sitting

Background/Aims

Smartphone use has become an indispensable part of our daily life. The handy design and powerful processor allow smartphone users to perform diversified tasks even when walking. This study aimed to investigate and compare the optical aftereffect and vergence adaptation of using a smartphone while walking and sitting.

Methods

Twenty-nine young healthy adults (aged 19 to 24 years old) with normal binocular and accommodative functions were recruited. Participants were asked to watch a movie for 30 minutes using a smartphone while either walking on a treadmill or sitting on a chair. Corneal aberrations and near heterophoria were measured before and after smartphone use by a corneal topographer and modified Thorington heterophoria test, respectively.

Results

Using the smartphone while walking induced a change in corneal H/V astigmatism, becoming 0.11±0.03 μm less negative (two-way ANOVA repeated measures, Bonferroni post-hoc test, p = 0.001). This optical aftereffect was significantly higher than after smartphone use while sitting by 0.10±0.03 μm (paired t-test, p = 0.003). Although smartphone use did not result in a significant change in near heterophoria (Bonferroni post-hoc test, p > 0.15), the vergence adaptation showed relatively more eso- or less exo-deviation by 0.79±0.36^Δ in the walking than the sitting condition (paired t-test, p = 0.037).

Conclusions

Eyecare practitioners should be cautious of the potential optical after effect and vergence adaptation after prolonged smartphone usage.

Screen Exposure during Early Life and the Increased Risk of Astigmatism among Preschool Children: Findings from Longhua Child Cohort Study

Screen media usage has become increasingly prevalent in daily life with children being exposed to screens at an early age. This is a growing public health concern with evidence linking screen exposure to detrimental health outcomes, whereas relationship between screen exposure and the presence of astigmatism among preschoolers remains unknown, thus we aimed to resolve this issue. During the 2017 survey of the Longhua Child Cohort Study, data of 29,595 preschoolers were collected via a caregiver-reported questionnaire regarding socio-demographics, screen exposure and refraction. Cox regression models were adopted to generate adjusted prevalence ratios (APR) and 95% confidence intervals (CI) to estimate the association between early screen exposure and astigmatism. 28,029 preschoolers were included in the final analysis. After adjustment for potential confounders, screen exposure during early life was significantly associated with the increased risk of astigmatism (APR and 95% CI: 2.25, 1.76–2.88), and the greatest risk was observed in the period from birth to 1-year (APR and 95% CI: 3.10, 2.41–3.98). The risk of astigmatism increased with both the total years of exposure and the average daily duration of screen exposure. Our findings suggested that preschoolers who were exposed to screens during early life might have an increased risk of astigmatism.

Objective Verification of Physiologic Changes during Accommodation under Binocular, Monocular, and Pinhole Conditions

BACKGROUND

To objectively investigate accommodative response to various refractive stimuli in subjects with normal accommodation.

METHODS

This prospective, non-randomized clinical trial included 64 eyes of 32 subjects with a mean spherical equivalent -1.4 diopters (D). We evaluated changes in accommodative power, pupil diameter, astigmatic value, and axis when visual stimuli were applied to binocular, monocular (dominant eye, non-dominant eye, ipsilateral, and contralateral), and pinhole conditions. Visual stimuli were given at 0.25 D (4 m), 2 D (50 cm), 3 D (33 cm), and 4 D (25 cm) and accommodative response was evaluated using open view binocular autorefractor/keratometer.

RESULTS

The accommodative response to binocular stimulus was 90.9% of the actual refractive stimulus, while that of the monocular stimulus was 84.6%. The binocular stimulus induced a smaller pupil diameter than did the monocular stimulus. There was no difference in accommodative response between the dominant eye and non-dominant eye or between ipsilateral and contralateral stimuli. As the refractive stimuli became stronger, the absolute astigmatic value increased and the direction of the astigmatism axis became more horizontal. Pinhole glasses required 10%-15% less accommodative power compared with the monocular condition.

CONCLUSION

Binocular stimuli enable more precise and effective accommodation than do monocular stimuli. Accommodative response is composed of 90% true accommodation and 10% pseudo-accommodation, and the refractive stimulus in one eye affects the contralateral eye to the same extent. This should be taken into account when developing guidelines for wearing smart glasses while driving, as visual stimulation is applied to only one eye, but far distance attention is constantly needed.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT03557346.

The Influence of Environmental Factors on the Prevalence of Myopia in Poland

Purpose

In the paper, we describe and discuss the results of epidemiological studies concerning myopia carried out in Poland.

Materials and Methods

Results from the examination of 5601 Polish school children and students (2688 boys and 2913 girls) aged 6 to 18 years were analyzed. The mean age was 11.9 ± 3.2 years. Every examined student had undergone the following examinations: distance visual acuity testing, cover test, anterior segment evaluation, and cycloplegic retinoscopy after instillation of 1% tropicamide, and a questionnaire was taken.

Results

We have found that (1) intensive near work (writing, reading, and working on a computer) leads to a higher prevalence of myopia, (2) watching television does not influence the prevalence of myopia, and (3) being outdoors decreases the prevalence of myopia.

Conclusions

The results of our study point to insufficiency of accommodation contributing to the pathogenesis of myopia.

Repeatability and reproducibility of horizontal corneal diameter and anterior corneal power measurements using the Oculus Keratograph 4

Purpose: To evaluate the repeatability and reproducibility of horizontal corneal diameter (HCD) and anterior corneal power (ACP) measurements obtained with the Oculus Keratograph 4 (OCULUS Optikgeräte GmbH).Methods: These parameters (HCD and ACP) were prospectively measured in quick succession three times in each of the right eyes of 40 healthy subjects, aged 18–28 years, with normal vision (6/6 or better visual acuity) in the first session by a single examiner. Measurements were then repeated in the second session scheduled 1 week later by the same examiner using the same instrument. Repeatability and reproducibility of HCD and ACP measurements was assessed based on the intra-session and intersession within-subject standard deviation (sw), repeatability (2.77sw), coefficient of variation (CoV) and intra-class correlation coefficient (ICC).Results: Intra-session repeatability and intersession reproducibility of all measured parameters showed a repeatability (2.77sw) of 0.35 mm or less for HCD and 0.35 D or less for ACP, a CoV of 0.30% or less and an ICC of more than 0.9.Conclusion: HCD and ACP measurements obtained using an Oculus Keratograph 4 show good repeatability and reproducibility in healthy eyes; therefore, these parameters can be used for longitudinal follow-up when measured with this device.

Myopia among school students in rural China (Yunnan)

PURPOSE

We described the prevalence and associated factors of myopia and high myopia in school children of different ethnicities in a rural community in Yunnan province, China.

METHODS

A total of 7681 (93.4%) primary and secondary school students aged 5-16 years in Mangshi participated in this study. Cycloplegic refraction was performed using an auto-refractor. Information regarding demographic factors, socioeconomic status and lifestyle-related exposures were collected using a questionnaire. Multivariate logistic regression models were fitted to estimate the risk factors for myopia and high myopia.

RESULTS

The overall prevalence of myopia and high myopia was 39.1% (95% confidence interval [CI]: 38.0, 40.2) and 0.6% (95% CI: 0.4, 0.8) in this study. Myopia prevalence increased significantly with increasing age (p for trend <0.001). Girls were more likely to have myopia compared with boys (p < 0.001). In multivariate analysis, the presence of myopia was associated with increasing height (odds ratio [OR] = 1.02; 95% CI: 1.01, 1.03), computer use (OR = 1.17; 95% CI: 1.03, 1.32), having myopic father (OR = 1.56; 95% CI: 1.24, 1.94), having myopic mother (OR = 1.33; 95% CI: 1.08, 1.63), and increasing time on reading (OR = 1.18; 95% CI: 1.09, 1.28) after adjusting for age, sex and ethnicity.

CONCLUSIONS

Nowadays myopia but not high myopia is prevalent among school children in rural China. Significant ethnic differences in myopia prevalence were not observed. A significant 'cohort effect' of myopia previously observed in urban cities had occurred in rural communities in China.

Precision (Repeatability and Reproducibility) and Agreement of Corneal Power Measurements Obtained by Topcon KR-1W and iTrace

Purpose

To evaluate the repeatability and reproducibility of corneal power measurements obtained by Topcon KR-1W and iTrace, and assess the agreement with measurements obtained by Allegro Topolyzer and IOLMaster.

Methods

The right eyes of 100 normal subjects were prospectively scanned 3 times using all the 4 devices. Another observer performed additional 3 consecutive scans using the Topcon KR-1W and iTrace in the same session. About one week later, the first observer repeated the measurements using the Topcon KR-1W and iTrace. The steep keratometry (Ks), flat keratometry (Kf), mean keratometry (Km), J0 and J45 were analyzed. Repeatability and reproducibility of measurements were evaluated by the within-subject standard deviation (Sw), coefficient of variation (CoV), test-retest repeatability (2.77Sw), and intraclass correlation coefficient (ICC). Agreements between devices were assessed using Bland-Altman analysis and 95% limits of agreement (LoA).

Results

Intraobserver repeatability and interobserver and intersession reproducibility of the Ks, Kf and Km showed a CoV of no more than 0.5%, a 2.77Sw of 0.70 D or less, and an ICC of no less than 0.99. However, J0 and J45 showed poor intraobserver repeatability and interobserver and intersession reproducibility (all ICCs not greater than 0.446). Statistically significant differences existed between Topcon KR-1W and IOLMaster, Topcon KR-1W and iTrace, Topcon KR-1W and Topolyzer, iTrace and Topolyzer, iTrace and IOLMaster for Ks, Kf and Km measurements (all P < 0.05). The mean differences between Topcon KR-1W, iTrace, and the other 2 devices were small. The 95% LoA were approximately 1.0 D to 1.5 D for all measurements.

Conclusions

The Ks, Kf and Km obtained by Topcon KR-1W and iTrace showed excellent intraobserver repeatability and interobserver and intersession reproducibility in normal eyes. The agreement between Topcon KR-1W and Topolyzer, Topcon KR-1W and IOLMaster, iTrace and Topolyzer, iTrace and IOLMaster, Topcon KR-1W and iTrace were not so good, they should not be interchangeable in clinical application. Given that the intraobserver repeatability and interobserver and intersession reproducibility of corneal astigmatism measurements obtained by Topcon KR-1W and iTrace were poor, it should be cautious that Topcon KR-1W and iTrace were applied for the preparation of toric lens implantation.

Ocular aberrations and wavefront aberrometry: A review

Wavefront aberrations can be described as deviations of the wavefront exiting the eye froma reference wavefront that is aberration free and diffraction limited. Ocular aberrations canbe sub-categorised as lower and higher order aberrations. Ocular aberrations have promptedinterest amongst the ocular healthcare community owing to their influences on the visualfunctioning of patients as well as differences observed in ocular aberrations through the useof refractive surgery both pre- and post-operatively. Uncompensated refractive error remainsone of the most common reasons for which patients consult optometrists. Compensationof refractive error, or lower order aberrations, has become a routine procedure during anoptometric examination. However, there are some patients who experience visual symptomseven after their refractive errors have been compensated via spectacles or contact lenses.Higher-order aberrations may be the source of these visual disturbances. Refractive surgeryhas been found to influence and even induce various changes in higher-order aberrationspost-operatively, which in turn has led to increased interest in wavefront aberrations and howthe measurement of these aberrations can improve diagnosis and treatment within optometryand ophthalmology.

Precision and agreement of corneal power measurements obtained using a new corneal topographer OphthaTOP

Purpose

To evaluate repeatability and reproducibility of anterior corneal power measurements obtained with a new corneal topographer OphthaTOP (Hummel AG, Germany) and agreement with measurements by a rotating Scheimpflug camera (Pentacam HR, Oculus, Germany) and an automated keratometer (IOLMaster, Carl Zeiss Meditec, Germany).

Methods

The right eyes of 79 healthy subjects were prospectively measured three times with all three devices. Another examiner performed three additional scans with the OphthaTOP in the same session. Within one week, the first examiner repeated the measurements using the OphthaTOP. The flat simulated keratometry (Kf), steep K (Ks), mean K (Km), J₀, and J₄₅ were noted. Repeatability and reproducibility of measurements were assessed by within-subject standard deviation (Sw), repeatability (2.77 Sw), coefficient of variation (CoV), and intraclass correlation coefficient (ICC). Agreement between devices was assessed using 95% limits of agreement (LoA).

Results

Intraobserver repeatability and interobserver and intersession reproducibility of all measured parameters showed a 2.77 Sw of 0.29 diopter or less, a CoV of less than 0.24%, and an ICC of more than 0.906. Statistically significant differences (P<0.001) were found between the parameters analyzed by the three devices, except J₀ and J₄₅. The mean differences between OphthaTOP and the other two devices were small, and the 95% LoA was narrow for all results.

Conclusions

The OphthaTOP showed excellent intraobserver repeatability and interobserver and intersession reproducibility of corneal power measurements. Good agreements with the other two devices in these parameters were found in healthy eyes.

Binocular saccades in myopes and emmetropes

PURPOSE

To compare saccadic eye movements in groups of myopes and emmetropes, as eye movements could have an influence on refractive error development. Individual saccadic eye movement parameters were also compared with subjective refraction and axial length data.

METHODS

Horizontal eye movements of 28 participants (14 myopes and 14 emmetropes; mean age [SD], 27.0 [4.7] years) were recorded using a head-mounted eye tracker. To reduce the influence of head movements, a chin rest was used. Two fixation stimuli lying symmetrically at ±10 degrees on either side of the median line were presented on a computer monitor and were alternately displayed for durations of 2 seconds each. The participants alternated their fixation between the target positions immediately after they became aware that the target had changed. Only right eye data were considered for analysis.

RESULTS

Durations, amplitudes, and peak velocities of the main saccades and the numbers of overshoots, undershoots, and exact fixations were analyzed. For all analyzed parameters, no significant differences were found between myopes and emmetropes. When analyzing the whole study population or the emmetropic group alone, none of the saccadic eye movement parameters were correlated with axial length or refractive error. In myopes, only the peak velocity showed a weak correlation with refractive error and axial length, but this failed to reach statistical significance when allowance was made for multiple testing.

CONCLUSIONS

Because saccadic eye movements seem to be similar in myopes and emmetropes, there is no evidence that saccadic eye movements are involved in myopia development.

Anterior segment changes following short-term reading and its correlation with corneal biomechanical characteristics

PURPOSE

To investigate the changes in anterior segment following short-term reading and evaluate the correlation of such changes with corneal biomechanical characteristics (CBC).

METHODS

Thirty-six right eyes of 36 healthy subjects were examined. Anterior segment parameters were measured using the Pentacam before and after 30 min of reading. Ocular Response Analyzer was used to record CBC after reading. The following were recorded: central corneal thickness (CCT), central corneal power (CCP), superior corneal power (SCP), inferior corneal power (ICP), anterior chamber depth (ACD), anterior chamber volume (ACV), anterior chamber angle (ACA), corneal hysteresis (CH) and corneal resistance factor (CRF). Statistical analysis was performed with the paired student t-test and Pearson correlation test in SPSS 16.

RESULTS

There were statistically significant decreases in CCP, SCP, ACD and ACV values following reading (p < 0.05). Our results showed a statistically significant negative correlation between CH and changes in ICP (r = 0.36, p = 0.02). Significant negative correlations were also found between CRF and changes in ICP (r = 0.41, p = 0.01) and SCP (r = 0.34, p = 0.04). On the other hand, statistical analysis indicated no correlation between CBC and other studied parameters (p > 0.05).

CONCLUSION

This study demonstrated significant changes in some anterior segment parameters after reading. Being knowledgeable about these changes may have important implications in high accuracy examinations such as pre-operative assessment of corneal refractive surgery candidates. This could also help researchers have a better understanding of the factors that may influence near work related development of refractive errors.

A comprehensive assessment of the precision and agreement of anterior corneal power measurements obtained using 8 different devices

Purpose

To comprehensively assess the precision and agreement of anterior corneal power measurements using 8 different devices.

Methods

Thirty-five eyes from 35 healthy subjects were included in the prospective study. In the first session, a single examiner performed on each subject randomly measurements with the RC-5000 (Tomey Corp., Japan), KR-8000 (Topcon, Japan), IOLMaster (Carl Zeiss Meditec, Germany), E300 (Medmont International, Australia), Allegro Topolyzer (Wavelight AG, Germany), Vista (EyeSys, TX), Pentacam (Oculus, Germany) and Sirius (CSO, Italy). Measurements were repeated in the second session (1 to 2 weeks later). Repeatability and reproducibility of corneal power measurements were assessed based on the intrasession and intersession within-subject standard deviation (Sw), repeatability (2.77Sw), coefficient of variation (COV), and intraclass correlation coefficient (ICC). Agreement was evaluated by 95% limits of agreement (LoA).

Results

All devices demonstrated high repeatability and reproducibility of the keratometric values (2.77Sw<0.36D, COV<0.3%, ICC>0.98). Repeated-measures analysis of variance with Bonferroni post test showed statistically significant differences (P<0.01) among mean keratometric values of most instruments; the largest differences were observed between the EyeSys Vista and Medmont E300. Good agreement (i.e., 95%LoA within ±0.5D) was found between most instruments for flat, steep and mean keratometry, except for EyeSys and Medmont. Repeatability and reproducibility of vectors J₀ and J₄₅ was good, as the ICCs were higher than 0.9, except J₄₅ of Medmont and Pentacam. For the 95% LoAs of J₀ and J₄₅, they were all ≤ ±0.31 among any two paired devices.

Conclusions

The 8 devices showed excellent repeatability and reproducibility. The results obtained using the RC-5000, KR-8000, IOLMaster, Allegro Topolyzer, Pentacam and Sirius were comparable, suggesting that they could be used interchangeably in most clinical settings. Caution is warranted with the measurements of the EyeSys Vista and Medmont E300, which should not be used interchangeably with other devices due to lower agreement.

Trial Registration

ClinicalTrials.gov NCT01587287

Dose-dependent and synergistic effects of proteoglycan 4 on boundary lubrication at a human cornea-polydimethylsiloxane biointerface

OBJECTIVES

Proteoglycan 4 (PRG4), also known as lubricin, is a boundary lubricating mucin-like glycoprotein present on several tissue surfaces in the body. The objectives of this study were to (1) implement and characterize an in vitro boundary lubrication test at a human cornea-polydimethylsiloxane (PDMS) biointerface and (2) determine the dose-dependent and synergistic effects of PRG4, with hyaluronan (HA), on ocular surface boundary lubrication using this test.

METHODS

Human corneas and model PDMS material were articulated against each other, at effective sliding velocities v(eff) between 0.3 and 30 mm/sec under physiologic loads of approximately 8 to 25 kPa. Samples were tested serially in (1) saline, PRG4 at 30, 100, 300 μg/mL resuspended in saline, then saline again or (2) saline, AQuify Comfort Eye Drops (containing 0.1% HA), 300 μg/mL PRG4 in saline, 300 μg/mL PRG4 in AQuify, then saline again. Both static and kinetic friction coefficients were calculated.

RESULTS

PRG4 effectively lowered friction at the cornea-PDMS biointerface, both alone in a dose-dependent manner and in combination with HA. PRG4 reduced kinetic friction coefficients, <μ(kinetic, Neq)>, from approximately 0.30 in saline, to approximately 0.30, 0.24, and 0.17 in 30, 100, and 300 μg/mL PRG4, respectively. Values of <μ(kinetic, Neq)> in AQuify, approximately 0.32, were similar to those in saline; however, when combined with 300 μg/mL PRG4, values of <μ(kinetic, Neq)> were reduced to approximately 0.15.

CONCLUSIONS

PRG4 functions as an effective ocular surface boundary lubricant, both alone in a dose-dependent manner and in combination with HA.

Analysis of head position used by myopes and emmetropes when performing a near-vision reading task

The aim of the study was to compare head posture in young, adult emmetropes and corrected myopes during a reading task. Thirty-two (32) myopes (mean spherical equivalent: -3.46±2.35 D) and 22 emmetropes (mean spherical equivalent: -0.03±0.36 D) participated in the study. Of the myopes, 16 were progressing (rate of progression ⩾-0.5D over the previous 2 years), 12 were stable (changes of -0.25 D or less over 2 years) and four could not be classified. Seated subjects were asked to read a text binocularly in their habitual posture. To measure head posture, two simultaneous images were recorded from different directions. In a separate study with the same subjects and conditions, a motion monitor was used to track head posture for 1 min. The habitual reading distance was measured in both studies, together with the stereoscopic acuity and fixation disparity for each subject. The results of the photographic study showed no significant differences in head posture or reading distance between the myopic and emmetropic groups (p>0.05) but there was some evidence that downward pitch angles were greater in progressing myopes than in non-progressing myopes (p=0.03). No correlations were observed between the binocular parameters and head posture. Reading distances were systematically shorter with the helmet-mounted eye tracker and it was concluded that posture was affected by the weight of the equipment. With this reservation, it appeared that the rate of change of downward pitch angle over the 1-min recording session increased with the subject's rate of myopia progression (correlation between myopia progression and slope of pitch: r(2)=-0.69, p=0.001), implying a greater reliance on head movements when reading down a page. Overall, while no differences in mean head posture were found between myopes and emmetropes, there was some evidence that head posture and movement during reading may differ in progressing myopes.

Measurement of ocular aberrations in downward gaze using a modified clinical aberrometer

Changes in corneal optics have been measured after downward gaze. However, ocular aberrations during downward gaze have not been previously measured. A commercial Shack-Hartmann aberrometer (COAS-HD) was modified by adding a relay lens system and a rotatable beam splitter to allow on-axis aberration measurements in primary gaze and downward gaze with binocular fixation. Measurements with the modified aberrometer (COAS-HD relay system) in primary and downward gaze were validated against a conventional aberrometer. In human eyes, there were significant changes (p<0.05) in defocus C(2,0), primary astigmatism C(2,2) and vertical coma C(3,-1) in downward gaze (25 degrees) compared to primary gaze, indicating the potential influence of biomechanical forces on the optics of the eye in downward gaze. To demonstrate a further clinical application of this modified aberrometer, we measured ocular aberrations when wearing a progressive addition lens (PAL) in primary gaze (0 degree), 15 degrees downward gaze and 25 degrees downward gaze.

Effects of confined space and near vision stimulation on refractive status and vitreous chamber depth in adolescent rhesus monkeys

This study aimed to investigate the effects of sustained near vision stimulation, on the refractive development and elongation of the vitreous chamber in adolescent rhesus monkeys. A total of 12 adolescent rhesus monkeys (1.5-2.0 years old) were randomly assigned to 3 groups. In groups A (n=4) and B (n=4), monkeys were reared in close-vision cages for 8 and 4 h d(-1), respectively; tiny granules were added on the cage floor to avoid visual deprivation and to encourage near gaze. In group C (n=4), monkeys were reared in open-vision cages, with non-granule food as a control. Vitreous chamber depth, refractive status, and corneal refractive power were assessed over 18 months. Paired t-test was used to compare the differences and a P-value<0.05 was considered to be statistically significant. In group A, vitreous chamber depth and optical axis elongated significantly, and refractive error shifted towards myopia during the observation period. In group B, vitreous chambers and optical axis elongated but the refractive power did not show significant changes. In group C, there was no significant elongation in vitreous chambers and optical axis, and the refractive power changed slightly towards hypermetropia. There were no significant changes in corneal refractive power in each group. Sustained near vision can promote vitreous chamber growth and induce myopic shifts in refractive power in adolescent monkeys. Our results demonstrate the potential for a primate model of near-work-related myopia.

Ocular findings among young men: a 12-year prevalence study of military service in Poland

PURPOSE

To determine the prevalence of ocular diseases among young men and to assess the main ocular causes reflecting discharge from military service in Poland.

METHODS

A retrospective review of the medical records of 105 017 men undergoing a preliminary examination for military service during the period 1993-2004. Sample size for the study was calculated with 99% confidence within an error margin of 5%. All of the study participants were White men of European origin, most of whom live or lived in Poland. Data regarding the vision status were assessed in 1938 eyes of 969 participants. Two groups were distinguished based on the age of the participants: group I aged 18-24 years, and group II aged 25-34 years.

RESULTS

Presented visual impairment [visual acuity (VA)<20/40)] followed by colour vision defects were the most common ocular disorders, accounting for 13.2%. There were statistically significant differences in uncorrected VA as well as in the rates of particular refractive errors in between the age groups (p<0.05). The prevalence of glaucoma and ocular hypertension was significantly higher in older participants. Six hundred and sixty-seven (68.8%) participants examined medically in the study period were accepted for military service. However, 302 (31.2%) failed their examination and were temporarily or permanently discharged from duty. Fifty-two of them (17.2%) were discharged because of various ocular disorders. The most common causes were high refractive errors, which accounted for 38.5% of all the ocular discharges, followed by chronic and recurrent diseases of the posterior segment of the eye, which accounted for 19.2%.

CONCLUSION

The prevalence of ocular disorders among young men in an unselected military population was closer to the results obtained in other population-based studies comprising both men and women in the same age group. High refractive errors followed by chronic and recurrent diseases of the posterior segment of the eye are important causes of medical discharges from military service in Poland.

Nearwork-Induced Changes in Topography, Aberrations, and Thickness of the Human Cornea After Interrupted Reading

PURPOSE

Recent experiments have suggested transient changes in corneal optics after short durations of reading. This study investigated an interrupted 1-hour period of reading on corneal topography in a sample of young myopic and emmetropic adults.

METHODS

Ten myopic and 9 emmetropic young adult subjects were recruited for the study. They read adult-level text binocularly at 40 cm with approximately 30 degree downward gaze for 1 hour, with distance correction in place. Orbscan II corneal topography was performed at baseline and 5, 15, 30, and 60 minutes after reading during 1 test session to assess for changes in corneal power, aberrations, and thickness.

RESULTS

Myopes exhibited greater corneal power and spherical aberration than emmetropes both before and after reading. Increased corneal higher-order aberrations (at baseline only) and thickness (superior position only) were observed in myopes versus emmetropes.

CONCLUSIONS

Several corneal parameters differed in the myopes after reading as compared with emmetropes. Differences in corneal parameters were smaller in this study than found in earlier studies, perhaps because of the interrupted nature of the task in the former versus the continuous nature in the latter.

A review of astigmatism and its possible genesis

Astigmatism is a refractive condition encountered commonly in clinical practice. This review presents an overview of research that has been carried out examining various aspects of this refractive error. We examine the components of astigmatism and the research into the prevalence and natural course of astigmatic refractive errors throughout life. The prevalence of astigmatism in various ethnic groups and diseases and syndromes is also discussed. We highlight the extensive investigations that have been conducted into the possible aetiology of astigmatism, however, no single model or theory of the development of astigmatism has been proven conclusively. Theories of the development of astigmatism based on genetics, extraocular muscle tension, visual feedback and eyelid pressure are considered. Observations and evidence from the literature supporting and contradicting these hypotheses are presented. Recent advances in technology such as wavefront sensors and videokeratoscopes have led to an increased understanding of ocular astigmatism and with continued improvements in technology, our knowledge of astigmatism and its genesis should continue to grow.

Factors Influencing Lid Pressure on the Cornea

PURPOSE

To investigate the effects of eyelid pressure on corneal topography in different angles of gaze and under different eye movement conditions.

METHODS

Ten young subjects with healthy eyes were recruited for the study. Corneal topography of the right eye was measured with a videokeratoscope before and after four 15-minute visual tasks (downward gaze of 25 degrees or 45 degrees , both with no eye movements or 1 Hz eye movements). The four tasks were conducted on four separate mornings. RESULTS.: All subjects showed significant regions of topographic change after each of the four tasks. In general, eye movements were found to cause greater topographic changes than tasks without eye movements, and the larger angle of downward gaze led to greater changes in topography. The topographic changes were located close to the lid margin position during each task.

CONCLUSIONS

The pressure exerted by the eyelid is capable of altering corneal topography. These changes are enhanced when the eye looks downward and when the eye moves laterally.