Regional Variations in Corneal Epithelial Cell Density and Morphology Assessed Using In Vivo Confocal Microscopy.

AIM: To characterize the regional variations in corneal epithelial cell density and morphology using in vivo confocal microscopy (IVCM). METHODS: Corneal imaging (IVCM) at 10 locations was performed; corneal apex (i.e., the center), immediately anterior to the corneal nerve whorl (i.e., slightly inferior to the apex), and four quadrants (superior, nasal, inferior, and temporal) both at 1.5 mm and 4.5 mm from the corneal apex (corresponding to 3 mm central and 9 mm peripheral diameter rings). The data of 21 young adults, aged 18 to 35 years, were analyzed. Cell morphometric parameters, including cell density, area, perimeter, Feret diameter, and circularity, were measured for basal and wing cells using Image J software. RESULTS: There was a significant difference in basal cell density (BCD) ( P <0.001) and wing cell density (WCD) ( P <0.001) for different corneal locations. The BCD (mean±SD: 8,839±416 cells/mm 2 ) and WCD (mean±SD: 5,932±310 cells/mm 2 ) were highest at the corneal nerve whorl compared with all other corneal locations. There were significant differences in wing cell area ( P <0.001), perimeter ( P <0.001), Feret diameter ( P <0.001), and circularity ( P <0.001) at varying corneal locations. CONCLUSION: There are significant regional variations in corneal epithelial cell density and morphology. The BCD and WCD was highest anterior to the corneal nerve whorl.

Central and peripheral choroidal thickness and eye length changes during accommodation.

PURPOSE: Eye length increases during accommodation, both on-axis and in the periphery. The aim of this study was to determine whether the peripheral choroid thins with accommodation and to determine the relationship with eye length changes measured at the same location. METHODS: Subjects included 53 young adults in good ocular and general health, with 19 emmetropes and 34 myopes. Measurements from the right eye were made for 0 D and 6 D accommodation stimuli for ±30° horizontal visual field/retinal locations in 10° steps. Valid eye length and choroidal thickness measurements were obtained for 37 and 47 participants, respectively, and both measures were taken for 31 participants. 2.5% phenylephrine was instilled to dilate the pupils. Participants turned their eyes, without head movement, to fixate targets and to make the target 'as clear as possible' during measurements. Correction was made for the influence of lens thickness changing at different peripheral angles. Choroidal thickness was measured with a spectral-domain-Optical Coherence Tomographer. For peripheral images, the internal cross target on the capture screen was moved from the centre to 17.25° nasal/temporal positions. RESULTS: In accordance with previous literature, eye length increased with accommodation. The greatest change (mean ± SD) of 41 ± 17 µm occurred at the centre, with a mean change across the locations of 33 µm. There were no significant differences between emmetropes and myopes. Choroidal thickness decreased with accommodation, with changes being about two-thirds of those occurring for eye length. The greatest change of -30 ± 1 µm occurred at the centre, with a mean change of -21 µm. Greater choroidal thinning occurred for myopes than for emmetropes (23 ± 11 vs. 17 ± 8 µm, p = 0.02). CONCLUSIONS: With accommodation, eye length increased and the choroid thinned, at both central and peripheral positions. Choroidal thinning accounted for approximately 60% of the eye length increase across the horizontal ±30°.

Effect of multifocal spectacle lenses on accommodative errors over time: Possible implications for myopia control.

The study purpose was to improve understanding of how multifocal spectacle lenses affect accommodative errors and whether this changes over time. Fifty-two myopes aged 18 to 27 years were allocated randomly to one of two progressive addition lens (PAL) types with 1.50 D additions and different horizontal power gradients across the near-periphery boundary. Lags of accommodation were determined with a Grand Seiko WAM-5500 autorefractor and a COAS-HD aberrometer for several near distances with the distance correction and the near PAL correction. For the COAS-HD the neural sharpness (NS) metric was used. Measures were repeated at three-month intervals over 12 months. At the final visit, lags to booster addition powers of 0.25, 0.50, and 0.75 D were measured. Except at baseline, both PALs' data were combined for analysis. For the Grand Seiko autorefractor, both PALs reduced accommodative lag at baseline compared with SVLs (p < 0.05 and p < 0.01 at all distances for PAL 1 and PAL 2, respectively). For the COAS-HD, at baseline PAL 1 reduced accommodative lag at all near distances (p < 0.02), but PAL 2 only at 40 cm (p < 0.02). Lags measured with COAS-HD were greater for shorter target distances with PALs. After 12 months' wear, the PALs no longer reduced accommodative lags significantly, except at 40 cm distance, but 0.50 D and 0.75 D booster adds decreased the lags to those measured at baseline or less. In conclusion, for PALs to reduce accommodative lag effectively, addition power should be tailored to typical working distances and after the first year of wear should be boosted by at least 0.50 D to maintain efficacy.

Accommodation lags are higher in myopia than in emmetropia: Measurement methods and metrics matter.

PURPOSE: To determine whether accommodative errors in emmetropes and myopes are systematically different, and the effect of using different instruments and metrics. METHODS: Seventy-six adults aged 18-27 years comprising 24 emmetropes (spherical equivalent refraction of the dominant eye +0.04 ± 0.03 D) and 52 myopes (-2.73 ± 0.22 D) were included. Accommodation responses were measured with a Grand Seiko WAM-5500 and a Hartmann-Shack Complete Ophthalmic Analysis System aberrometer, using pupil plane (Zernike and Seidel refraction) and retinal image plane (neural sharpness-NS; and visual Strehl ratio for modulation transfer function-VSMTF) metrics at 40, 33 and 25 cm. Accommodation stimuli were presented to the corrected dominant eye, and responses, referenced to the corneal plane, were determined in the fellow eye. Linear mixed-effects models were used to determine influence of the refractive group, the measurement method, accommodation stimulus, age, race, parental myopia, gender and binocular measures of heterophoria, accommodative convergence/accommodation and convergence accommodation/convergence ratios. RESULTS: Lags of accommodation were affected significantly by the measurement method (p < 0.001), the refractive group (p = 0.003), near heterophoria (p = 0.002) and accommodative stimulus (p < 0.05), with significant interactions between some of these variables. Overall, emmetropes had smaller lags of accommodation than myopes with respective means ± standard errors of 0.31 ± 0.08 D and 0.61 ± 0.06 D (p = 0.003). Lags were largest for the Grand Seiko and Zernike defocus, intermediate for NS and VSMTF, and least for Seidel defocus. CONCLUSIONS: The mean lag of accommodation in emmetropes is approximately equal to the previously reported depth of focus. Myopes had larger (double) lags than emmetropes. Differences between methods and instruments could be as great as 0.50 D, and this must be considered when comparing studies and outcomes. Accommodative lag increased with the accommodation stimulus, but only for methods using a fixed small pupil diameter.

The effects of optically and digitally simulated aniseikonia on stereopsis.

PURPOSE: To simulate both lens-induced and screen-induced aniseikonia, and to assess its influence on stereopsis. Additionally, to determine if screen-based size differences could neutralise the effects of lens-induced aniseikonia. METHOD: A four-circle (4-C) paradigm was developed, where one circle appears in front or behind the others because of crossed or uncrossed disparity. This stereotest was used for three investigations: (1) Comparison with the McGill modified random dot stereogram (RDS), with anisometropia introduced with +2 D spheres and cylinders, and with aniseikonia introduced with 6% overall and 6% meridional (×180, ×90) magnifiers before the right eye; (2) Comparison of lens-induced and screen-induced 6% overall and meridional magnifications and (3) Determining if lens and screen effects neutralised, by opposing 6% lens-induced magnification to the right eye with screen-inducements of either 6% left eye magnification or 6% right eye minification. A pilot study of the effect of masking versus not masking the surround was also conducted. RESULTS: The 4-C test gave higher stereo-thresholds than the RDS test by 0.5 ± 0.2 log units across both anisometropic and aniseikonic conditions. However, variations in power, meridian and magnification affected the two tests similarly. The pilot study indicated that surround masking improved neutralisation of screen and lens effects. With masking, lens-induced and screen-induced magnifications increased stereo-thresholds similarly. With lens and screen effects opposed, for most participants stereo-thresholds returned to baseline for overall and ×180 magnifications, but not for ×90 magnification. Only three of seven participants showed good compensation for ×90 magnification. CONCLUSIONS: Effects of lens-induced aniseikonia on stereopsis cannot always be successfully simulated with a screen-based method. The ability to neutralise refractive aniseikonia using a computer-based method, which is the basis of digital clinical measurement, was reasonably successful for overall and ×180 meridional aniseikonia, but not very successful for ×90 aniseikonia.

Association between greater residential greenness and decreased risk of preschool myopia and astigmatism.

OBJECTIVE: Rapid urbanization has led to reduced greenness in many areas, this has been linked to adverse health outcomes. The aim was to determine the association between residential greenness experienced during very early childhood with preschool myopia and astigmatism and to explore the potential mediating role of screen time on any associations. METHOD: Information regarding socio-demographic characteristics, home address, screen time during early childhood, and refraction data from vision screenings of 53,575 preschoolers from Longhua Child Cohort Study were collected via questionnaires. Residential greenness was calculated as the average of satellite-derived Normalized Difference Vegetation Index in buffers of 100, 250, and 500 m around each child's home address. Logistic and linear regression models were used to examine the relationships between residential greenness, screen time, and preschool myopia and astigmatism. RESULT: The mean (SD) age of the 53,575 preschoolers was 5.0 (0.7) years, and 24,849 (46.4%) were girls. A total of 1236 (2.3%) preschoolers had myopia and 5347 (10.0%) had astigmatism. In the adjusted model, a higher neighborhood greenness level within 100 m buffers around the home address was associated with decreased risk of myopia (adjusted odds ratios (AOR): 0.62, 95% confidence interval (CI): 0.38-0.99), and higher neighborhood greenness levels within 100, 250, and 500 m decreased the risk of astigmatism, and their AORs (95% CIs) were 0.55 (0.43-0.70) for 100 m, 0.59 (0.41-0.83) for 250 m, 0.61 (0.42-0.90) for 500 m, respectively. Greater screen time during early childhood increased the risk of myopia (AOR = 1.33) and astigmatism (AOR = 1.23). Reduction in screen time fully mediated the benefits of greater residential greenness on preschool myopia, but partially mediated that on preschool astigmatism (p < 0.05). CONCLUSION: Higher residential greenness reduces the risk of preschool myopia and astigmatism; the benefits of residential greenness were mediated through reduced daily screen time.

COVID-19: ensuring safe clinical teaching at university optometry schools.

The COVID-19 pandemic has been spreading across the globe for several months. The nature of the virus (SARS-CoV-2) with easy person-to-person transmissions and the severe clinical course observed in some people necessitated unprecedented modifications of everyday social interactions. These included the temporary suspension of considerable elements of clinical teaching at optometry schools worldwide. This article describes the challenges optometry schools were facing in early to mid 2020. The paper highlights the experiences of six universities in five countries on four continents. Strategies to minimise the risk of virus transmission, to ensure safe clinical optometric teaching and how to overcome the challenges presented by COVID-19 are described. An outlook on opportunities to further improve optometric education is provided.

Multifocal contact lens design, not addition power, affects accommodation responses in young adult myopes.

PURPOSE: Prolonged nearwork has been implicated in myopia progression. Accommodation responses of young-adult myopes wearing different multifocal contact lenses were compared. METHODS: Twenty adults, 18-25 years, with myopia (spherical equivalent refraction -0.50 to -5.50 D, mean -2.1 ± 1.6 D) wore five lens types in random order: Proclear single vision distance (SV), MiSight concentric dual-focus +2.00 D Add (MS), Biofinity aspheric centre distance +1.50 D Add (CD1) and +2.50 D Add (CD2) (all Coopervision), and NaturalVue aspheric (Visioneering Technologies) (NVue). Using a Grand-Seiko WAN-5500 autorefractor with binocular correction and viewing right eye accommodative responses were measured after a 10 min adaptation period at 4.0, 1.0, 0.5, 0.33 and 0.25 m distances. Dynamic measurements were taken for 4 s at 6 Hz. Accommodative stimuli and responses were referenced to 4 m (i.e., refraction differences between 4 m and nearer distances). Accommodation lags and refraction instabilities (standard deviations of dynamic responses) were determined. For comparison, results were obtained for an absolute presbyopic eye, where trial lenses counteracted the accommodation stimulus. RESULTS: For SV and MS, accommodation responses were similar to the stimulus values. For aspheric lenses CD1, CD2 and NVue, accommodation responses were approximately 1.0 D lower across the stimulus range than with SV and MS, and rates of change were approximately 0.84 D per 1 D stimulus change. MS produced greater refraction instabilities than other lenses. For the presbyope, changes in refraction matched the trial lenses, indicating that corrections due to measurement through the different lenses were not needed. CONCLUSION: Reductions in accommodation response occurred in young myopes wearing aspheric multifocal contact lenses independent of the labelled 'add' power. The concentric dual-focus MS lens produced minimal lags but had greater instability than the other lenses. The results indicate that the mechanism of multifocal contact lenses slowing myopia progression is unlikely to be through relaxing accommodation, at least in young adults.

Associations between the menstrual cycle, lifestyle factors and clinical assessment of the ocular surface: a prospective observational study.

BACKGROUND: Little is known about the ocular surface changes over the menstrual cycle in young women and the interactions with lifestyle factors. Therefore, the purpose of this study was to explore the associations between modifiable lifestyle factors and menstrual cycle phases on the ocular signs and symptoms of dry eye in young healthy women. METHODS: This was a prospective 1-month observational study. Thirty young healthy women with regular, 24 to 32-day menstrual cycles were recruited. Participants attended three visits at day 7, 14, and 21 (± 1) of their menstrual cycle. At baseline, general health questionnaire was conducted. At each visit, symptomology was quantified using Ocular Surface Disease Index (OSDI) and overall ocular comfort (OOC, visual analogue scale). Ocular signs were assessed using Efron scales, tear break-up time (TBUT) and phenol red thread (PRT). Pearson's correlation was used to determine associations between variables at each visit. RESULTS: A total of 26 participants (mean age = 22.3 ± 3.7 years) with an average menstrual cycle of 28.3 ± 1.3 days completed the 3 visits. The interaction between signs/symptoms and lifestyle factors changed over the cycle. At the follicular phase (day 7), lifestyle factors such diet and levels of stress were correlated with PRT and OSDI, (r = - 0.4, p = 0.022; r = 0.4, p = 0.045 respectively). At the ovulation phase (day 14), the general health score was correlated with OOC scores (r = 0.4, p = 0.047). At day 14, exercise frequency correlated with PRT (r = - 0.4, p = 0.028) and caffeine intake was positively correlate with both; TBUT (r = 0.5, p = 0.020) and PRT (r = 0.5, p = 0.014). At the luteal phase (day 21), we found no correlations between lifestyle factors and dry eye signs or symptoms. CONCLUSIONS: The associations between lifestyle factors and objective and subjective ocular surface assessment appeared to be more pronounced during the ovulation phase of the menstrual cycle compared to the follicular and luteal phases. Misalignment of these factors with the ocular health during the luteal phase could be attributed to central sensitization and changes in levels of luteinising hormone. Natural hormonal changes during menstrual cycle should be considered for diagnosis and treatment of dry eye in young healthy women.

Effects of simulated anisometropia and aniseikonia on stereopsis.

PURPOSE: Stereopsis depends on horizontally disparate retinal images but otherwise concordance between eyes. Here we investigate the effect of spherical and meridional simulated anisometropia and aniseikonia on stereopsis thresholds. The aims were to determine effects of meridian, magnitude and the relative effects of the two conditions. METHODS: Ten participants with normal binocular vision viewed McGill modified random dot stereograms through synchronised shutter glasses. Stereoacuities were determined using a four-alternative forced-choice procedure. To induce anisometropia, trial lenses of varying power and axes were placed in front of right eyes. Seventeen combinations were used: zero (no lens) and both positive and negative, 1 and 2 D powers, at 45, 90 and 180 axes; spherical lenses were also tested. To induce aniseikonia 17 magnification power and axis combinations were used. This included zero (no lens), and 3%, 6%, 9% and 12% at axes 45, 90 and 180; overall magnifications were also tested. RESULTS: For induced anisometropia, stereopsis loss increased as cylindrical axis rotated from 180° to 90°, at which the loss was similar to that for spherical blur. For example, for 2 D meridional anisometropia threshold increased from 1.53 log sec arc (i.e. 34 sec arc) for x 180 to 1.89 log sec arc (78 sec arc) for x 90. Anisometropia induced with either positive or negative lenses had similar detrimental effects on stereopsis. Unlike anisometropia, the stereopsis loss with induced meridional aniseikonia was not affected by axis and was about 64% of that for overall aniseikonia of the same amount. Approximately, each 1 D of induced anisometropia had the same effect on threshold as did each 6% of induced aniseikonia. CONCLUSION: The axes of meridional anisometropia but not aniseikonia affected stereopsis. This suggests differences in the way that monocular blur (anisometropia) and interocular shape differences (aniseikonia) are processed during the production of stereopsis.

Comparison of blur and magnification effects on stereopsis: overall and meridional, monocularly- and binocularly-induced.

PURPOSE: To determine whether monocularly- and binocularly-induced spherical and meridional blur and aniseikonia had similar effects on stereopsis thresholds. METHODS: Twelve participants with normal binocular vision viewed McGill modified random dot stereograms to determine stereoacuities in a four-alternative forced-choice procedure. Astigmatism was induced by placing trial lenses in front of the eyes. Twenty-three conditions were used, consisting of zero (no lens), +1 D and +2 D spheres and cylinders at axes 180, 45 and 90 in front of the right eye, and the following binocular combinations of both lens powers: R × 180/L × 180, R × 45/L × 45, R × 90/L × 90, R sphere/L sphere, R × 180/L × 90, R × 45/L × 135, R × 90/L × 180. Aniseikonia was induced by placing magnifying lenses in front of the eyes. Twenty-three conditions were used, consisting of zero, 6% and 12% overall magnification and both magnifications at axes 180, 45 and 90 in front of the right eye only, and the following binocular combinations using 3% and 6% lenses: R × 90/L × 90, R × 45/L × 45, R × 180/L × 180, R overall/L overall, R × 90/L × 180, R × 45/L × 135, and R × 180/L × 90. RESULTS: Stereopsis losses for binocular blur effects with parallel axes (non-anisometropic) were the same as for monocular blur effects of the same axes, and these were strongly dependent on axis (spherical blur and ×90 had the greatest effects). Binocular blur effects with orthogonal axes had greater effects than with parallel axes, with the axis combination of the former having no effect (e.g. R × 90/L × 180 was similar to R × 45/L × 135). For induced aniseikonia, splitting the magnifications between the eyes improved stereopsis slightly, and the effects were not dependent on axis. CONCLUSION: Binocular blur affects stereopsis similarly to monocular meridional blur if axes in the two eyes are parallel, whereas the effect is greater if the axes are orthogonal. In meridional aniseikonia, splitting magnification between the right and left lenses produces a small improvement in stereopsis that is independent of axis direction and right/left combination.

Zone of Clear Single Binocular Vision in Myopic Orthokeratology.

PURPOSE: To examine the zone of clear single binocular vision (ZCSBV) in myopic children and young adults after 12 months of orthokeratology (OK) wear, in comparison with single-vision soft contact lens (SCL) wear. METHODS: Twelve children (8-16 years) and 8 adults (18-29 years) were assessed with a series of near-point binocular vision tests when myopia was corrected using single-vision SCLs and again after 1 and 12 months of OK wear, and axial length was measured. The ZCSBV was constructed for baseline SCL wear and after 12 months of OK wear. RESULTS: After 1 month of OK wear, increased accommodative responses were noted in children (C) and adults (A) as increased binocular amplitude (C:P=0.03, A:P=0.04) and reduced accommodative lag (C:P=0.01, A:P=0.01). Divergence reserves improved after 1 month in both groups (P<0.04), and a near exophoric shift was evident at 12 months (C:P=0.01, A:P=0.04). All changes at 1 month maintained stability at 12 months. An increase in accommodation and vergence responses without reduction in range resulted in an expansion of the ZCSBV in both age groups. Axial length did not significantly change in either children (P=0.25) or adults (P=0.72). CONCLUSION: In both pediatric and young adult myopes, the ZCSBV expands toward a more divergent, increased accommodation response in OK compared with SCL wear. This occurs without a corresponding loss of convergence or accommodation deactivation, indicating improved depth of focus. These findings are relevant to visual acceptance and possible mechanisms of OK's efficacy for myopia control.

Experimental Study of Refraction Effects of Nominally Plano Ophthalmic Prisms and Magnifying Lenses.

SIGNIFICANCE: Nominally plano ophthalmic prisms give autorefraction results similar to those predicted on the basis of how effective powers change with pantoscopic tilt, and magnifying lenses give autorefraction results similar to those predicted on the basis of vergence changes. Without appreciation of the optics involved, these effects might wrongly be considered artifacts. PURPOSE: The purpose of this study was to investigate the interactions of autorefractors with lenses and prisms. METHODS: There were 15 adult participants across three experiments, with a range of ages and refractions. In experiments 1 and 2, participants wore frames containing base-up and base-down nominally plano prisms. In experiment 3, participants wore a lens that produced either 6.3% magnification or 5.9% minification, depending on which surface faced the eye. Autorefracting instruments with different operating principles were used: Shin-Nippon SRW5000 autorefractor, Grand Seiko 5100K autorefractor, Hoya AR-530 autorefractor, a Complete Ophthalmic Analysis System-High Definition wavefront sensor, and Tomey FC-800 autorefractor. A theory on the likely effects of magnifying lenses was presented. RESULTS: For ophthalmic prisms, refractions showed results similar to those predicted on the basis of how effective prism powers change with pantoscopic tilt. As tilt increased, base-up prism gave more positive mean refractions and more negative horizontal/vertical astigmatism and vice versa for base-down prisms. In the presence of 10° tilt, 8Δ base-up prisms and 8Δ base-down prisms had different effects by a mean of 0.36 diopters. Magnifying lenses affected refractions similar to those predicted on the basis of vergence changes, with 6% magnification and minification producing mean changes of -11 and +8%, respectively, in absolute mean refraction. There was no strong evidence that different instruments had different effects. CONCLUSIONS: The results have implications for studies in which prisms and lenses are placed in the front eyes, such as accommodation studies using thick lenses close to the eyes to stimulate accommodation rather than by changing object distance.

The Effect of Vertically Yoked Prisms on Binocular Vision and Accommodation.

SIGNIFICANCE: Vertically yoked prisms have been used in treatment of binocular vision dysfunction despite minimal supporting evidence. In people with normal binocular vision, the impact on phorias has been assessed but not the impact on accommodation, accommodation vergence interactions, or the horopter. We found that vertically yoked prisms have minor effects during short-term wear in young adults. PURPOSE: The purpose of this study was to determine effects of vertically yoked prisms on accommodative response and several binocular vision tasks. METHODS: There were 45 participants aged 18 to 24 years. The 23 myopes wore distance-corrected soft contact lenses. In a random arrangement, each person wore spectacles containing planopower lenses with either 8 Δ base-up, 4 Δ base-up, zero, 4 Δ base-down, and 8 Δ base-down prisms. Before spectacle wear, baseline measurements of near heterophoria, accommodation response, negative and positive relative accommodations, fusional vergence, and Nonius-horopter spatial perception were taken. Measurements were repeated after a 40-minute wear, spectacles were removed, and tests were performed 20 minutes later. On a 22-participant subset, on a separate occasion, measurements of heterophoria, accommodation response, and relative accommodation were made immediately after spectacles were fitted. RESULTS: Most changes relative to baseline were not significant. Where effects occurred, these were nearly all associated with prism presence rather than adaptation. There were significant effects on accommodation response, but these seem to be refraction effects produced by pantoscopic tilt-induced power changes rather than perceptual effects altering accommodation. There were statistically significant effects on negative relative accommodation (P < .01), with zero prism giving more negative relative accommodation than 8 Δ base-down prisms. Tendencies were noted for prisms to move horopter limits toward the observer. Effects were small and likely not of clinical relevance. CONCLUSIONS: Vertically yoked prisms have minor effects on accommodation and binocular vision, at least during short-term wear in young adults with normal binocular vision.

Effects of eye rotation and contact lens decentration on horizontal peripheral refraction.

PURPOSE: Peripheral refraction is important in design of myopia control therapies. The aim was to investigate the influence of contact lens decentration associated with eye rotation on peripheral refraction in the horizontal visual field. METHODS: Participants were 10 emmetropes and 10 myopes in good general and ocular health. Right eyes underwent cycloplegic peripheral refraction, using a Grand-Seiko WAM-5500 Autorefractor, in 5° steps to ±35° eccentricities along the horizontal visual field. Targets were fixated using eye rotation only or head rotation only. Refractions were measured without correction and with three types of contact lenses: single vision, a multifocal centre-distance aspheric with +2.50 D add and NaturalVue aspheric. Photographs of eyes during lens wear were taken for each eye rotation. Effects of visual field angle, lens type and test method (head or eye rotation) on vector components of relative peripheral refraction were evaluated using repeated measures anovas. Test method for each visual field angle/lens combination were compared via paired t-tests. RESULTS: Horizontal decentration ranges across the visual field were 1.2 ± 0.6 mm for single vision and 1.2 ± 0.4 mm for multifocal lenses but smaller at 0.7 ± 0.4 mm for NaturalVue lenses. There were only two significant effects of test method across the visual field angle/lens type combinations (single vision: for emmetropes horizontal/vertical astigmatism component at 35° nasal with mean difference -0.38 D and for myopes spherical equivalent refraction at 20° temporal with mean difference +0.24 D). CONCLUSION: Upon eye rotation the contact lenses decentred on the eye, but not enough to affect peripheral refraction. For the types assessed and for the horizontal visual field out to ±35° when measurements were performed with the Grand-Seiko WAM-5500 autorefractor, it is valid to use eye rotations to investigate peripheral refraction.

Effect of Accommodation on Peripheral Eye Lengths of Emmetropes and Myopes.

PURPOSE: To investigate the effect of accommodation on central and peripheral axial lengths in young adult emmetropes and myopes. METHODS: On-axis and peripheral axial lengths were measured with the Haag-Streit Lenstar in 83 young adult participants for 0D and 6D accommodation demands. A Badal system was used to both correct refractive errors and induce accommodation. Participants were emmetropes (n = 29, mean spherical equivalent refraction +0.35 ± 0.35D), low myopes (32, -1.38 ± 0.73D), and higher myopes (22, -4.30 ± 0.73D). Ages were similar for all groups (22 ± 2 years). Pupils were dilated with 2.5% phenylephrine to allow a large field of measurement while maintaining active accommodation. Axial lengths were measured in 5° steps to ±30° across the horizontal visual field. RESULTS: With accommodation, axial length increased for all refractive groups at all positions, but with lessening effect away from fixation. Axial length changes were greater for higher myopes than for emmetropes on-axis (higher myopes 41 ± 14 µm, emmetropes 30 ± 12 µm, P = .005), for higher myopes than for low myopes at 30° nasal (P = .03), and for the higher myopes than for the other groups at 20° nasal (P < .05). There were significant correlations between myopia and changes in axial length at all positions, with the highest correlation on-axis (R = 0.30, P < .001). CONCLUSIONS: During accommodation, eye length increased out to at least ±30° visual angle in young adult myopes and emmetropes. The increase was significantly greater for higher myopes than for the other groups at some positions. At all positions, there were significant correlations between myopia and accommodation-induced changes in axial length.

Differences in retinal shape between East Asian and Caucasian eyes.

PURPOSE: To investigate whether retinal shape is different between East Asians and Caucasians. METHODS: There were 36 East Asian and 40 Caucasian young adults, with refractions between +0.75D and -5.50D. Peripheral eye lengths were obtained after pupil dilation using the Lenstar partial coherence interferometer. Measurements were obtained along the horizontal and vertical meridians of the visual field out to ±35° and ±30°, respectively, in 5° steps. Retinal co-ordinates were estimated using a validated method from the peripheral eye length measurements and ray-tracing through a modified Le Grand full theoretical eye. Rays were directed normally towards the anterior cornea. Retinal shapes were described in terms of vertex radius of curvature (Rv ), asphericity (Q) and equivalent radius of curvature (REq ) along both horizontal and vertical meridians. RESULTS: Rv was smaller in East Asian than in Caucasians (mean difference ± 95% CI -0.7 ± 0.5 mm), along the horizontal meridian than the vertical meridian (-1.2 ± 0.6 mm), and in myopia than in emmetropia (-1.0 ± 0.6 mm). Rv along the horizontal meridian, but not along the vertical meridian, became smaller as myopia increased. Q did not vary significantly with meridian, refraction group or race. The same pattern of results occurred for REq as for Rv . The percentage differences of heights under the estimated retinal surfaces showed steeper retinas in East Asians than in Caucasians; the differences between East Asian and Caucasian emmetropes were 2.5% and <1% along horizontal and vertical meridians, respectively, and corresponding differences for myopes were 4.6% and 1.8%. CONCLUSION: East Asians had steeper retinas than Caucasians. The horizontal meridian had steeper retinas than the vertical meridian. Myopes had steeper retinas than emmetropes. Racial differences in retinal shape in both emmetropes and myopes, combined with the high prevalence of myopia in East Asia, suggest that retinal shape may play a role in myopia development.

Peripheral Refraction, Peripheral Eye Length, and Retinal Shape in Myopia.

PURPOSE: To investigate how peripheral refraction and peripheral eye length are related to retinal shape. METHODS: Relative peripheral refraction (RPR) and relative peripheral eye length (RPEL) were determined in 36 young adults (M +0.75D to -5.25D) along horizontal and vertical visual field meridians out to ±35° and ±30°, respectively. Retinal shape was determined in terms of vertex radius of curvature Rv, asphericity Q, and equivalent radius of curvature REq using a partial coherence interferometry method involving peripheral eye lengths and model eye raytracing. Second-order polynomial fits were applied to RPR and RPEL as functions of visual field position. Linear regressions were determined for the fits' second order coefficients and for retinal shape estimates as functions of central spherical refraction. Linear regressions investigated relationships of RPR and RPEL with retinal shape estimates. RESULTS: Peripheral refraction, peripheral eye lengths, and retinal shapes were significantly affected by meridian and refraction. More positive (hyperopic) relative peripheral refraction, more negative RPELs, and steeper retinas were found along the horizontal than along the vertical meridian and in myopes than in emmetropes. RPR and RPEL, as represented by their second-order fit coefficients, correlated significantly with retinal shape represented by REq. CONCLUSIONS: Effects of meridian and refraction on RPR and RPEL patterns are consistent with effects on retinal shape. Patterns derived from one of these predict the others: more positive (hyperopic) RPR predicts more negative RPEL and steeper retinas, more negative RPEL predicts more positive relative peripheral refraction and steeper retinas, and steeper retinas derived from peripheral eye lengths predict more positive RPR.

GABAAα1 and GABAAρ1 subunits are expressed in cultured human RPE cells and GABAA receptor agents modify the intracellular calcium concentration.

PURPOSE: Gamma-aminobutyric acid A (GABAA) receptors (GABAARs), which are ionotropic receptors involving chloride channels, have been identified in various neural (e.g., mouse retinal ganglion cells) and nonneural cells (e.g., mouse lens epithelial cells) regulating the intracellular calcium concentration ([Ca(2+)]i). GABAAR ß-subunit protein has been isolated in the cultured human and rat RPE, and GABAAα1 and GABAAρ1 mRNAs and proteins are present in the chick RPE. The purpose of this study was to investigate the expression of GABAAα1 and GABAAρ1, two important subunits in forming functional GABAARs, in the cultured human RPE, and further to explore whether altering receptor activation modifies [Ca(2+)]i. METHODS: Human RPE cells were separately cultured from five donor eye cups. Real-time PCR, western blots, and immunofluorescence were used to test for GABAAα1 and GABAAρ1 mRNAs and proteins. The effects of the GABAAR agonist muscimol, antagonist picrotoxin, or the specific GABAAρ antagonist 1,2,5,6-tetrahydropyridin-4-yl) methylphosphinic acid (TPMPA) on [Ca(2+)]i in cultured human RPE were demonstrated using Fluo3-AM. RESULTS: Both GABAAα1 and GABAAρ1 mRNAs and proteins were identified in cultured human RPE cells; antibody staining was mainly localized to the cell membrane and was also present in the cytoplasm but not in the nucleus. Muscimol (100 µM) caused a transient increase of the [Ca(2+)]i in RPE cells regardless of whether Ca(2+) was added to the buffer. Muscimol-induced increases in the [Ca(2+)]i were inhibited by pretreatment with picrotoxin (300 µM) or TPMPA (500 µM). CONCLUSIONS: GABAAα1 and GABAAρ1 are expressed in cultured human RPE cells, and GABAA agents can modify [Ca(2+)]i.