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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.

SIGNIFICANCE Central motion perception, as assessed by minimum displacement detection, was reduced in highly myopic eyes. Peripheral motion detection may be influenced by myopia, particularly in the inferior-nasal retina. PURPOSE Motion discrimination is a complex visual task processed mainly via the magnocellular pathway. We investigated whether it is affected in myopia. METHODS Ninety young adults aged 18 to 28 years participated: 30 emmetropes (spherical equivalent refractions +1.00 to −0.50 diopters [D]), 30 low myopes −1.00 to −4.75 D) and 30 higher 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

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 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 co-efficients and for retinal shape estimates as functions of central spherical refraction. Linear regressions investigate 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. Conclusion: Effects of meridian and refraction on RPR and PEL 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.

Purpose: Inaccurate accommodation during nearwork and subsequent accommodative hysteresis may influence myopia development. Myopia is highly prevalent in Singapore; an untested theory is that Chinese children are prone to these accommodation characteristics. We measured the accuracy of accommodation responses during and nearwork-induced transient myopia (NITM) after periods spent reading Chinese and English texts. Methods: Refractions of 40 emmetropic and 43 myopic children were measured with a free-space autorefractor for four reading tasks of 10-minute durations: Chinese (SimSun, 10.5 points) and English (Times New Roman, 12 points) texts at 25 cm and 33 cm. Accuracy was obtained by subtracting accommodation response from accommodation demand. Nearwork-induced transient myopia was obtained by subtracting pretask distance refraction from posttask refraction, and regression was determined as the time for the posttask refraction to return to pretask levels. Results: There were significant, but small, effects of text type (Chinese, 0.97 ± 0.32 diopters [D] vs. English, 1.00 ± 0.37 D; F1,1230 = 7.24, p = 0.007) and reading distance (33 cm, 1.01 ± 0.30 D vs. 25 cm, 0.97 ± 0.39 D; F1,1230 = 7.74, p = 0.005) on accommodation accuracy across all participants. Accuracy was similar for emmetropic and myopic children across all reading tasks. Neither text type nor reading distance had significant effects on NITM or its regression. Myopes had greater NITM (by 0.07 D) (F1,81 = 5.05, p = 0.03) that took longer (by 50s) (F1,81 = 31.08, p < 0.01) to dissipate. Conclusions: Reading Chinese text caused smaller accommodative lags than reading English text, but the small differences were not clinically significant. Myopic children had significantly greater NITM and longer regression than emmetropic children for both texts. Whether differences in NITM are a cause or consequence of myopia cannot be answered from this study.

Purpose: There are some limited reports, based on questionnaire data, which suggest that outdoor activity decreases the risk of myopia in children and may offset the myopia risk associated with prolonged near work. The aim of this study was to explore the relationship between near work, indoor illumination, daily sunlight and ultraviolet (UV) exposure in emmetropic and myopic University students, given that University students perform significant amounts of near work and as a group have a high prevalence of myopia. Methods: Participants were 35 students, aged 17 to 25 years who were classified as being emmetropic (n=13), or having stable (n=12) or progressing myopia (n=10). During waking hours on three separate days participants wore a light sensor data logger (HOBO) and a polysulphone UV dosimeter; these devices measured daily illuminance and accumulative UV exposure respectively; participants also completed a daily activity log. Results: No significant between group differences were observed for average daily illuminance (p=0.732), number of hours per day spent in sunlight (p=0.266), outdoor shade (p=0.726), bright indoor/dim outdoor light (p=0.574) or dim room illumination (p=0.484). Daily UV exposure was significantly different across the groups (p=0.003); with stable myopes experiencing the greatest UV exposure (versus emmetropes p=0.002; versus progressing myopes p=0.004). Conclusions: The current literature suggests there is a link between myopia protection and spending time outdoors in children. Our data provides some evidence of this relationship in young adults and highlights the need for larger studies to further investigate this relationship longitudinally.

The high prevalence of myopia in Chinese children living in urban East Asian countries such as Hong Kong, Taiwan, and China has been well documented. However, it is not clear whether the prevalence of myopia would be similarly high for this group of children if they were living in a Western country. This study aims to determine the prevalence and progression of myopia in ethnic Chinese children living in Canada.Right eye refraction data of Chinese-Canadian children aged 6 to 12 years were collated from the 2003 clinical records of an optometric practice in Mississauga, Ontario, Canada. Myopia was defined as a spherical equivalent refraction (SER) equal or less than -0.50 D. The prevalence of myopia and refractive error distribution in children of different ages and the magnitude of refractive error shifts over the preceding 8 years were determined. Data were adjusted for potential biases in the clinic sample. A questionnaire was administered to 300 Chinese and 300 Caucasian children randomly selected from the clinic records to study lifestyle issues that may impact on myopia development.Optometric records of 1468 children were analyzed (729 boys and 739 girls). The clinic bias adjusted prevalence of myopia increased from 22.4% at age 6 to 64.1% at age 12 and concurrently the portion of the children that were emmetropic (refraction between -0.25 and +0.75 D) decreased (68.6% at 6 years to 27.2% at 12 years). The highest incidence of myopia for both girls ( approximately 35%) and boys ( approximately 25%) occurred at 9 and 10 years of age. The average annual refractive shift for all children was -0.52+/-0.42 D and -0.90+/-0.40 D for just myopic children. The questionnaire revealed that these Chinese-Canadian children spent a greater amount of time performing near work and less time outdoors than did Caucasian-Canadian children.Ethnic Chinese children living in Canada develop myopia comparable in prevalence and magnitude to those living in urban East Asian countries. Recent migration of the children and their families to Canada does not appear to lower their myopia risk.

PURPOSE: Accommodation errors during reading and the subsequent near work-induced transient myopia (NITM) that occurs have been implicated in the development and progression of myopia. This study investigated the effects of two letter variables, size and contrast, on accommodation accuracy during the near task and on NITM and its subsequent decay. These were varied so as to mimic what might occur when students photocopy and reduce reading materials. METHODS: Based on their refractive errors, young adult subjects (18-25 years) were classified into three groups: emmetropes (n = 19), stable myopes (n = 17), and progressing myopes (n = 17). Three print sizes (N4, N6, and N8) and two print contrasts (90% and 60%) were used to give six different reading targets. Targets were presented in random order at 25 cm (4 D demand) and the text read for comprehension for 3 minutes. For each target, accommodation accuracy and NITM and its decay were measured using the free space Shin-Nippon SRW-5000 autorefractor. RESULTS: When data for all subjects were pooled, there was a significant effect of letter size (p = 0.030) but not contrast (p = 0.898) on accommodation accuracy; however, differences were small and unlikely to be clinically relevant. NITM (p = 0.033) and its decay (p = 0.012) also varied with letter size. NITM was greater and decay longer for larger letters. We found no effect of refractive error group on accommodation accuracy. In contrast, there was a significant difference in the magnitude of NITM and its decay for emmetropic and myopic subjects (although no effect of progression status); myopes had larger NITM values and longer decay times to baseline than emmetropes (NITM myopes: 0.37 +/- 0.14D vs. emmetropes: 0.19 +/- 0.17 D, p = 0.005; decay time myopes: 15.12 +/- 6.58 seconds vs. emmetropes 7.10 +/- 4.82 seconds, p = 0.0045). The differences in NITM and its decay between the two refractive groups were of similar magnitude for all six combinations of letter size and contrast. CONCLUSIONS: Our data do not support the suggestion that common reductions in letter size or contrast of reading material (as might occur for photocopied reading materials) cause greater accommodation inaccuracy and greater near work-induced adaptation effects that would exacerbate myopia development in young adults.

Background: Young chicks can adjust their eye growth to compensate for both imposed hyperopia and myopia (using negative and positive spectacle lenses); the rate of eye elongation increases in the former and slows in the latter case. This emmetropizing behavior implies that the eye can distinguish the sign and magnitude of defocus, although the identity of the cue(s) involved is unknown. As the spectacle lenses used in these studies generally introduce significant retinal image size differences that are in opposite directions for negative and positive lenses (minification vs. magnification), we asked whether retinal image size might provide the required sign information. Methods. This question was addressed by manipulating retinal image size while keeping lens power constant. We also investigated the effect of eliminating other potential cues, accommodation and chromatic aberration, under these conditions. Three negative 'size' lenses of approximately -11 D optical power were used, with 2 of the lenses producing magnification rather than minification as typical of negative lenses (i.e. +1.9% and +6.9% compared to -2.9%). The lenses were fitted monocularly to 7-day-old chicks, which were subsequently measured at 9 and 11 days of age (refractive error and axial dimensions). The same lens-wearing schedule was applied to two other groups of chicks that had monocular ciliary nerve section surgery to prevent accommodation 2 days posthatching; one of these groups was reared under monochromatic yellow light instead of white light. Results. Near- perfect refractive compensation was seen by the end of the treatment period with all three lenses, for all three treatment groups, and there was also little difference in the rate of compensation among the various groups. In all cases, the typical responses of axial (mainly vitreous chamber) elongation and myopia were observed. Conclusions. That manipulations to retinal image size, which either decrease or reverse the usual effects of negative lenses, did not disrupt compensation to the imposed hyperopic defocus, even in the absence of accommodation and chromatic aberration cues, argues against imposed retinal image size changes being the directional cue to defocus in experimental emmetropization.Young chicks can adjust their eye growth to compensate for both imposed hyperopia and myopia; the rate of eye elongation increases in the former ad slows in the latter case. This emmetropizing behavior implies that the eye can distinguish the sign and magnitude of defocus. As the spectacle lenses generally introduce significant retial image size differences that are in opposite directions for negative and positive lenses. The ability of the retinal image size to provide the required sign formation is analyzed. This addressed by manipulating retinal image size while keeping lens power. The effect of eliminating other potential cues, accommodation and chromatic aberration, under these conditions is investigated.

This study compared the compensatory response to hyperopic defocus imposed on chicks in two different ways: (1) with-10 D spectacle lenses, and (2) with plano hard contact lens. The hyperopia seen with the contact lenses in situ was a consequence of their flat profile relative to the chick cornea, resulting in a negative fluid lens of approximately 16 D at day 2 and 9 D by day 10. This decrease with age reflects the corneal flattening that accompanies normal eye growth. By optically neutralizing the cornea, the contact lenses also had two other important effects: (1) a reduction in refractive astigmatism to almost negligible levels, and (2) a reduction in accommodative gain. The latter effect reflects the loss of the corneal component of the chick's accommodation and was estimated to be of the order of 40 to 57%, based on measurements made using topically applied nicotine to stimulate accommodation. Thus any estimate of the imposed hyperopic defocus based on accommodative effort required to overcome such errors will be too large. Chicks wearing either lens type on a continuous basis from hatching to 10 days only partially compensated for the imposed hyperopia through an increase in vitreous chamber growth. However, the effects were smaller in the spectacle lens group (e.g., a mean myopic shift of -4.1 +/- 2.3 D compared to -6.3 +/- 2.4 D for the contact lens group at day 10), although both groups experienced similar amounts of hyperopic defocus around day 10 (effective power of -10 D spectacle lens: -9.4 D). The changes seen in the spectacle lens group thus represent poorer compensation, i.e., 44 vs. 71% of the imposed error. However, overcompensation is the predicted effect, if any, of the accommodative deficit imposed on the contact lens group, and this was not seen. That compensation, albeit incomplete, occurred with the contact lens as well as the spectacle lens, suggests that neither accommodation nor astigmatism are fundamental cues for emmetropization as modeled here.