Bi-exponential description for different forms of refractive development.

It was recently established that the axial power, the refractive power required by the eye for a sharp retinal image in an eye of a certain axial length, and the total refractive power of the eye may both be described by a bi-exponential function as a function of age (Rozema, 2023). Inspired by this result, this work explores whether these bi-exponential functions are able to simulate the various known courses of refractive development described in the literature, such as instant emmetropization, persistent hypermetropia, developing hypermetropia, myopia, instant homeostasis, modulated development, or emmetropizing hypermetropes. Moreover, the equations can be adjusted to match the refractive development of school-age myopia and pseudophakia up to the age of 20 years. All of these courses closely resemble those reported in the previous literature while simultaneously providing estimates for the underlying changes in axial and whole eye power.

Wide-field optical eye models for emmetropic and myopic eyes.

Ocular wavefront aberrations are used to describe retinal image formation in the study and modeling of foveal and peripheral visual functions and visual development. However, classical eye models generate aberration structures that generally do not resemble those of actual eyes, and simplifications such as rotationally symmetric and coaxial surfaces limit the usefulness of many modern eye models. Drawing on wide-field ocular wavefront aberrations measured previously by five laboratories, 28 emmetropic (-0.50 to +0.50 D) and 20 myopic (-1.50 to -4.50 D) individual optical eye models were reverse-engineered by optical design ray-tracing software. This involved an error function that manipulated 27 anatomical parameters, such as curvatures, asphericities, thicknesses, tilts, and translations-constrained within anatomical limits-to drive the output aberrations of each model to agree with the input (measured) aberrations. From those resultant anatomical parameters, three representative eye models were also defined: an ideal emmetropic eye with minimal aberrations (0.00 D), as well as a typical emmetropic eye (-0.02 D) and myopic eye (-2.75 D). The cohorts and individual models are presented and evaluated in terms of output aberrations and established population expectations, such as Seidel aberration theory and ocular chromatic aberrations. Presented applications of the models include the effect of dual focus contact lenses on peripheral optical quality, the comparison of ophthalmic correction modalities, and the projection of object space across the retina during accommodation.

Mechanisms of emmetropization and what might go wrong in myopia.

Studies in animal models and humans have shown that refractive state is optimized during postnatal development by a closed-loop negative feedback system that uses retinal image defocus as an error signal, a mechanism called emmetropization. The sensor to detect defocus and its sign resides in the retina itself. The retina and/or the retinal pigment epithelium (RPE) presumably releases biochemical messengers to change choroidal thickness and modulate the growth rates of the underlying sclera. A central question arises: if emmetropization operates as a closed-loop system, why does it not stop myopia development? Recent experiments in young human subjects have shown that (1) the emmetropic retina can perfectly distinguish between real positive defocus and simulated defocus, and trigger transient axial eye shortening or elongation, respectively. (2) Strikingly, the myopic retina has reduced ability to inhibit eye growth when positive defocus is imposed. (3) The bi-directional response of the emmetropic retina is elicited with low spatial frequency information below 8 cyc/deg, which makes it unlikely that optical higher-order aberrations play a role. (4) The retinal mechanism for the detection of the sign of defocus involves a comparison of defocus blur in the blue (S-cone) and red end of the spectrum (L + M-cones) but, again, the myopic retina is not responsive, at least not in short-term experiments. This suggests that it cannot fully trigger the inhibitory arm of the emmetropization feedback loop. As a result, with an open feedback loop, myopia development becomes "open-loop".

Visual outcomes comparing emmetropia vs mini-monovision after bilateral implantation of a nondiffractive extended vision intraocular lens: randomized trial.

PURPOSE: To compare visual outcomes and patient satisfaction after bilateral implantation of a nondiffractive extended vision intraocular lens (IOL) when targeting emmetropia vs mini-monovision. SETTING: Iladevi Cataract & IOL Research Centre, Ahmedabad, India. DESIGN: Prospective, randomized controlled trial. METHODS: Patients undergoing bilateral cataract surgery with an extended vision IOL (Vivity) randomized to group I-IOL implantation with emmetropic target in both eyes or group II-IOL implantation with mini-monovision of -0.5 diopters (D) were included in this study. Outcome measures evaluated 6 months postoperatively were unaided and corrected near visual acuity (UNVA, CNVA) at 40 cm and unaided and corrected distance (UDVA, CDVA) and intermediate (UIVA, CIVA) visual acuity at 66 cm. Mesopic contrast sensitivity, binocular defocus curve, Patient-Reported Spectacle Independence Questionnaire, and satisfaction on the McAlinden questionnaire were also assessed. RESULTS: 70 patients enrolled in this study. 34 and 33 patients in groups I and II, respectively, completed follow-up. Binocular UNVA was significantly better in group II (0.26 ± 0.05 vs 0.22 ± 0.08 logMAR, P = .03). Reading add required in group II was significantly lower. UIVA (0.09 ± 0.06 vs 0.07 ± 0.08 logMAR, P = .15) and UDVA (0.02 ± 0.04 vs 0.02 ± 0.05 logMAR, P = .78) were not significantly different between groups. Mesopic contrast sensitivity was not significantly different between the groups. Binocular defocus curve showed significantly better mean visual acuities between -2.0 D and -3.0 D in group II. Patients in both groups had high levels of spectacle independence, with no patient reporting dysphotopsia. CONCLUSIONS: Binocular UNVA was significantly better, with comparable UDVA and mesopic contrast sensitivity when targeting mini-monovision with the nondiffractive extended vision IOL as compared with targeting binocular emmetropia.

Impact of Refractive Status on Presbyopia Progression among Patients with Presbyopia.

PURPOSE: To explore the impact of refractive status on presbyopia progression among patients with presbyopia. METHODS: This retrospective observational study included patients with presbyopia who visited the Seventh Affiliated Hospital of Sun Yat-sen University and Shenzhen Polytechnic Medical College between May 2018 and August 2022. The amplitude of accommodation (AMP) and near addition power (ADD) at 6 months and 1 year were collected. RESULTS: A total of 103 patients with presbyopia were included in this study: 42 patients with myopia, 23 patients with emmetropia, and 38 patients with hyperopia. There were significant differences in ΔAMP(6-month) and ΔADD(6-month) among patients with different refractive statuses, and the values of emmetropic patients and hyperopic patients were higher than in myopic patients (all P < 0.001). The ΔAMP(1-year) and ΔADD(1-year) of hyperopic patients were significantly higher than in emmetropic patients and myopic patients (all P < 0.001). The ΔADD(1-year) of emmetropic patients was greater than in myopic patients (P = 0.045), but there were no significant differences in ΔAMP(1-year) between patients with emmetropia and myopia (P = 0.090). CONCLUSIONS: The progression of presbyopia in hyperopic patients was relatively more significant than for emmetropia, followed by myopia. The prescription of presbyopia glasses might need to be replaced more frequently in patients with hyperopia.

Corneal Biomechanical Characteristics in Myopes and Emmetropes Measured by Corvis ST: A Meta-Analysis.

PURPOSE: To comprehensively identify the corneal biomechanical differences measured by Corvis ST between different degrees of myopia and emmetropia. DESIGN: Systematic review and meta-analysis. METHODS: Electronic databases, including PubMed, Embase, and Web of Science, were systematically searched for studies comparing the corneal biomechanics among various degrees of myopes and emmetropes using Corvis ST. The weighted mean differences and 95% confidence intervals were calculated. Meta-analysis was performed in high and nonhigh myopes and in myopes and emmetropes, respectively. RESULTS: Eleven studies were included in this study. The meta-analysis among myopes and emmetropes included 1947 myopes and 621 emmetropes, and 443 high myopes and 449 nonhigh myopes were included in the meta-analysis among high and nonhigh myopia. Myopes showed the cornea with significantly longer time at the first applanation (A1t) and lower length at the second applanation (A2L) than emmetropes. High myopes showed significantly greater A1t, velocity at the second applanation (A2v), deformation amplitude at the highest concavity (HC-DA), and peak distance at the highest concavity (HC-PD) and decreased time at the second applanation (A2t) and radius of the highest concavity (HC-R). CONCLUSIONS: Corneal biomechanics is different in myopia, especially in high myopia. Compared with nonhigh myopes, the corneas of high myopes deformed slower during the first applanation, faster during the second applanation, and showed greater deformation amplitude, indicating greater elasticity and viscidity.

Visual and refractive outcomes after bilateral implantation of an enhanced monofocal intraocular lens: prospective study.

PURPOSE: To evaluate visual and refractive outcomes, as well as patient satisfaction after bilateral implantation of an enhanced monofocal intraocular lens (IOL) with emmetropia as a target refraction. SETTING: San Carlos Hospital, Madrid, Spain. DESIGN: Prospective, monocentric, noncomparative study. METHODS: Adults 21 years or older suitable for cataract surgery and with corneal astigmatism <1.50 diopters (D) were bilaterally implanted with the RayOne EMV IOL and followed up for 3 months. Outcomes measures included refraction, monocular and binocular uncorrected distance visual acuity, corrected distance visual acuity (CDVA), uncorrected intermediate visual acuity, distance-corrected intermediate visual acuity (DCIVA), and defocus curve, aberrometry, and satisfaction. Visual symptoms were assessed using the CatQuest-9SF questionnaire. RESULTS: 50 eyes of 25 patients were included. At month 3, the mean manifest spherical equivalent was -0.39 ± 0.28 D, with all eyes within 1.00 D. Binocularly, uncorrected, at distance, 68% of patients could read ≤0.0 logMAR and 95% ≤0.2 logMAR; at intermediate 59% of patients could read ≤0.1 and 100% ≤0.2 logMAR. Mean monocular CDVA was -0.03 ± 0.06 logMAR and mean monocular DCIVA was 0.28 ± 0.07 logMAR. Binocular defocus curve demonstrated a visual acuity ≤0.2 logMAR over a 2 D range from +1.00 D to -1.25 D. Satisfaction was good in 96% of patients. CONCLUSIONS: Bilateral implantation of an enhanced monofocal IOL with emmetropia as a target provided excellent binocular CDVA and good DCIVA, with a high level of satisfaction.

Influence of Lens Thickness on Accuracy of Kane, Hill-RBF 3.0, Barrett Universal II, Emmetropia Verifying Optical, and Pearl-DGS Formulas in Eyes with Nonhigh Myopia and High Myopia.

PURPOSE: To investigate the influence of lens thickness (LT) on accuracy of Kane, Hill-RBF 3.0 Barrett Universal II (BUII), Emmetropia Verifying Optical (EVO), and Pearl-DGS formulas in eyes with different axial lengths (AL). METHODS: The prospective cohort study was conducted at Eye and ENT Hospital of Fudan University. Patients who had uneventful cataract surgery between March 2021 and July 2023 were recruited. Manifest refraction was conducted two-month post-surgery. Eyes were divided into 4 groups based on AL: short (<22mm), medium (22-24.5 mm), medium long (24.5-26mm) and very long (≥26mm). In each AL group, eyes were then divided into 3 subgroups based on the LT measured with IOLmaster700: thin (<4.5 mm), medium (4.5-5.0 mm), and thick (≥ 5 mm). The influence of LT on accuracy of Kane, Hill-RBF 3.0, BUII, EVO, and Pearl-DGS formulas were investigated in each AL group. RESULTS: A total of 327 eyes from 327 patients were analyzed, with 64, 102, 73 and 88 eyes in each AL group, respectively. In eyes with AL < 24.5 mm, myopic PE was significantly associated with greater LT using all the 5 formulas (all p < 0.05). Backward stepwise multivariate regression analyses revealed that LT was an important influencing factor for PE in all 5 formulas, particularly in eyes with AL <24.5 mm. In eyes with AL <24.5 mm and LT > 5.0 mm, PE of all 5 formulas calculated with the optional parameter LT were more myopic than those calculated without LT. CONCLUSIONS: Thicker LT was associated with more myopic PE among eyes with AL <24.5 mm when using all 5 formulas. Further optimization of current formulas is necessary, especially for eyes with short AL and thick LT.

Mean cycloplegic refractive error in emmetropic adults - The Tehran Eye Study.

PURPOSE: In children under 20 years, refractive development targets a cycloplegic refractive error of +0.5 to +1.5D, while presbyopes over 40 years generally have non-cycloplegic errors of ≥ +1D. Some papers suggest these periods are separated by a period of myopic refractive error (i.e., ≤ -0.50D), but this remains unclear. Hence, this work investigates the mean cycloplegic refractive error in adults aged between 20 - 40 years. METHODS: In 2002 a cross-sectional study with stratified cluster sampling was performed on the population of Tehran, providing cycloplegic and non-cycloplegic refractive error data for the right eyes of 3,576 participants, aged 30.6±18.6 years (range: 1-86 years). After grouping these data into age groups of 5 years, the refractive error histogram of each group was fitted to a Bigaussian function. The mean of the central, emmetropized peak was used to estimate the mean refractive error without the influence of myopia. RESULTS: The mean cycloplegic refractive error at the emmetropized peak decreased from +1.10±0.11D (95 % confidence interval) to +0.50±0.04D before 20 years and remains stable at that value until the age of 50 years. The non-cycloplegic refractive error also sees a stable phase at 0.00±0.04D between 15 - 45 years. After 45 - 50 years both cycloplegic and non-cycloplegic refractive error become more hypermetropic over time, +1.14±0.12D at 75 years. CONCLUSIONS: The cycloplegic refractive error in adults is about +0.50D between 20 - 50 years, disproving the existence of the myopic period at those ages.

Longitudinal changes in crystalline lens thickness and power in children aged 6-12 years old.

OBJECTIVES: To determine the three-year changes in crystalline lens power (LP) and thickness (LT) in children and their associated factors. METHODS: Schoolchildren aged 6-12 years living in Shahroud, northeast Iran were examined in 2015 and 2018. The Bennett formula was used to calculate LP. Multiple generalized estimating equations (GEE) analysis was used for data analysis. RESULTS: Among the 8089 examined eyes, the mean LP in Phase 1 and 2, and the three-year change were 21.61 ± 1.47D, 21.00 ± 1.42D, and -0.61 ± 0.52D, respectively. The GEE model showed that negative shifts in LP were less pronounced with increasing age (ß = 0.176; p < 0.001), and were also less noticeable in hyperopes compared to emmetropes (ß = 0.120; p < 0.001). The changes in LP decreased when outdoor activity increased among urban residents (ß = 0.013; p = 0.039), while it increased in rural area (ß = -0.020; p = 0.047). Mean three-year change in LT was 0.002 ± 0.13 mm. Female sex and aging by one year increased the LT by 0.022 mm (P < 0.001). However, LT decreased in 6-8-year-olds, while it increased in 10-12-year-old children, both in a linear fashion. The change in LT was less in myopes than in emmetropes (ß = -0.018, P-value = 0.010). CONCLUSION: LP decreases after three years in 6 to 12-year-old children. LT increases slightly after three years in 6 to 12-year-old children. The changes in LP and LT were associated with the refractive errors, place of residence, age and gender and outdoor activity time.

Ablation of mpeg+ Macrophages Exacerbates mfrp-Related Hyperopia.

Purpose: Proper refractive development of the eye, termed emmetropization, is critical for focused vision and is impacted by both genetic determinants and several visual environment factors. Improper emmetropization caused by genetic variants can lead to congenital hyperopia, which is characterized by small eyes and relatively short ocular axial length. To date, variants in only four genes have been firmly associated with human hyperopia, one of which is MFRP. Zebrafish mfrp mutants also have hyperopia and, similar to reports in mice, exhibit increased macrophage recruitment to the retina. The goal of this research was to examine the effects of macrophage ablation on emmetropization and mfrp-related hyperopia. Methods: We utilized a chemically inducible, cell-specific ablation system to deplete macrophages in both wild-type and mfrp mutant zebrafish. Spectral-domain optical coherence tomography was then used to measure components of the eye and determine relative refractive state. Histology, immunohistochemistry, and transmission electron microscopy were used to further study the eyes. Results: Although macrophage ablation does not cause significant changes to the relative refractive state of wild-type zebrafish, macrophage ablation in mfrp mutants significantly exacerbates their hyperopic phenotype, resulting in a relative refractive error 1.3 times higher than that of non-ablated mfrp siblings. Conclusions: Genetic inactivation of mfrp leads to hyperopia, as well as abnormal accumulation of macrophages in the retina. Ablation of the mpeg1-positive macrophage population exacerbates the hyperopia, suggesting that macrophages may be recruited in an effort help preserve emmetropization and ameliorate hyperopia.

The Role of Dopamine in Emmetropization Modulated by Wavelength and Temporal Frequency in Guinea Pigs.

Purpose: Wavelength and temporal frequency have been found to influence refractive development. This study investigated whether retinal dopamine (DA) plays a role in these processes. Methods: Guinea pigs were randomly divided into nine groups that received different lighting conditions for 4 weeks, as follows: white, green, or blue light at 0, 0.5, or 20.0 Hz. Refractions and axial lengths were measured using streak retinoscopy and A-scan ultrasound imaging. DA and its metabolites were measured by high-pressure liquid chromatography-electrochemical detection. Results: At 0 Hz, green and blue light produced myopic and hyperopic shifts compared with that of white light. At 0.5 Hz, no significant changes were observed compared with those of green or blue light at 0 Hz, whereas white light at 0.5 Hz induced a myopic shift compared with white light at 0 or 20 Hz. At 20 Hz, green and blue light acted like white light. Among all levels of DA and its metabolites, only vitreous 3, 4-dihydroxyphenylacetic acid (DOPAC) levels and retinal DOPAC/DA ratios were dependent on wavelength, frequency, and their interaction. Specifically, retinal DOPAC/DA ratios were positively correlated with refractions in white and green light conditions. However, blue light (0, 0.5, and 20.0 Hz) produced hyperopic shifts but decreased vitreous DOPAC levels and retinal DOPAC/DA ratios. Conclusions: The retinal DOPAC/DA ratio, indicating the metabolic efficiency of DA, is correlated with ocular growth. It may underlie myopic shifts from light exposure with a long wavelength and low temporal frequency. However, different biochemical pathways may contribute to the hyperopic shifts from short wavelength light.

Meridional Anisotropy of Foveal and Peripheral Resolution Acuity in Adults With Emmetropia, Myopia, and Astigmatism.

Purpose: To quantify astigmatism-related meridional anisotropy in visual resolution at central, nasal, and inferior visual fields. Methods: Three groups of young adults (range, 18-30 years) with corrected-to-normal visual acuity (logMAR 0) were recruited: (1) myopic astigmats (MA): spherical-equivalent error (SE) < -0.75D, with-the-rule astigmatism ≥ 2.00D, n = 19; (2) simple myopes (SM): SE < -0.75D, astigmatism ≤ 0.50D, n = 20; and (3) emmetropes (EM): SE ± 0.50D, astigmatism ≤ 0.50D, n = 14. Resolution acuity was measured for the horizontal and vertical gratings at central and peripheral visual fields (eccentricity: 15°) using a 3-down 1-up staircase paradigm. On- and off-axis refractive errors were corrected by ophthalmic lenses. Results: The MA group exhibited meridional anisotropy preferring vertical gratings. At the central field, the MA group had better resolution acuity for vertical than horizontal gratings, and their resolution acuity for horizontal gratings was significantly worse than the SM and EM groups. At peripheral visual fields, both the SM and EM groups showed better resolution acuity for the radial (i.e., nasal field: horizontal gratings; inferior field: vertical gratings) than tangential orientation. However, the MA group tended to have better resolution acuity for the tangential orientation (i.e., vertical gratings), and their resolution acuity for horizontal gratings was significantly lower than the SM and EM groups at the nasal field. No significant differences were found in the inferior field among the three groups. Conclusions: This study provided evidence of astigmatism-related meridional anisotropy at the fovea and nasal visual fields, underscoring the significant impact of astigmatism on orientation-dependent visual functions.

The Role of Retinal Connexins Cx36 and Horizontal Cell Coupling in Emmetropization in Guinea Pigs.

Purpose: The purpose of this study was to determine whether retinal gap junctions (GJs) via connexin 36 (Cx36, mediating coupling of many retinal cell types) and horizontal cell (HC-HC) coupling, are involved in emmetropization. Methods: Guinea pigs (3 weeks old) were monocularly form deprived (FD) or raised without FD (in normal visual [NV] environment) for 2 days or 4 weeks; alternatively, they wore a -4 D lens (hyperopic defocus [HD]) or 0 D lens for 2 days or 1 week. FD and NV eyes received daily subconjunctival injections of a nonspecific GJ-uncoupling agent, 18-ß-Glycyrrhetinic Acid (18-ß-GA). The amounts of total Cx36 and of phosphorylated Cx36 (P-Cx36; activated state that increases cell-cell coupling), in the inner and outer plexiform layers (IPLs and OPLs), were evaluated by quantitative immunofluorescence (IF), and HC-HC coupling was evaluated by cut-loading with neurobiotin. Results: FD per se (excluding effect of light-attenuation) increased HC-HC coupling in OPL, whereas HD did not affect it. HD for 2 days or 1 week had no significant effect on retinal content of Cx36 or P-Cx36. FD for 4 weeks decreased the total amounts of Cx36 and P-Cx36, and the P-Cx36/Cx36 ratio, in the IPL. Subconjunctival 18-ß-GA induced myopia in NV eyes and increased the myopic shifts in FD eyes, while reducing the amounts of Cx36 and P-Cx36 in both the IPL and OPL. Conclusions: These results suggest that cell-cell coupling via GJs containing Cx36 (particularly those in the IPL) plays a role in emmetropization and form deprivation myopia (FDM) in mammals. Although both FD and 18-ß-GA induced myopia, they had opposite effects on HC-HC coupling. These findings suggest that HC-HC coupling in the OPL might not play a significant role in emmetropization and myopia development.

Eyes grow towards mild hyperopia rather than emmetropia in Chinese preschool children.

PURPOSE: To document one-year changes in refraction and refractive components in preschool children. METHODS: Children, 3-5 years old, in the Jiading District, Shanghai, were followed for one year. At each visit, axial length (AL), refraction under cycloplegia (1% cyclopentolate), spherical dioptres (DS), cylinder dioptres (DC), spherical equivalent refraction (SER) and corneal curvature radius (CR) were measured. RESULTS: The study included 458 right eyes of 458 children. The mean changes in DS, DC and SER were 0.02 ± 0.35 D, -0.02 ± 0.33 D and 0.01 ± 0.37 D, while the mean changes in AL, CR and lens power (LP) were 0.27 ± 0.10 mm, 0.00 ± 0.04 mm and - 0.93 ± 0.49 D. The change in the SER was linearly correlated with the baseline SER (coefficient = -0.147, p < 0.001). When the baseline SER was at 1.05 D (95% CI = 0.21 to 2.16), the change in SER was 0 D. The baseline SER was also linearly associated with the change in LP (coefficient = 0.104, p = 0.013), but not with the change in AL (p = 0.957) or with the change in CR (p = 0.263). CONCLUSION: In eyes with a baseline SER less than +1.00 D, LP loss was higher compared to axial elongation, leading to hyperopic shifts in refraction, whereas for those with baseline SER over this range, loss of LP compared to axial elongation was reduced, leading to myopic shifts. This model indicated the homeostasis of human refraction and explained how refractive development leads to a preferred state of mild hyperopia.

Spectral composition of artificial illuminants and their effect on eye growth in chicks.

In broadband light, longitudinal chromatic aberration (LCA) provides emmetropization signals from both wavelength defocus and the resulting chromatic cues. Indoor illuminants vary in their spectral output, potentially limiting the signals from LCA. Our aim is to investigate the effect that artificial illuminants with different spectral outputs have on chick emmetropization with and without low temporal frequency modulation. In Experiment 1, two-week-old chicks were exposed to 0.2 Hz, square-wave luminance modulation for 3 days. There were 4 spectral conditions: LED strips that simulated General Electric (GE) LED "Soft" (n = 13), GE LED "Daylight" (n = 12), a novel "Equal" condition (n = 12), and a novel "High S" condition (n = 10). These conditions were all tested at a mean level of 985 lux. In Experiment 2, the effect of intensity on the "Equal" condition was tested at two other light levels (70 lux: n = 10; 680 lux: n = 7). In Experiment 3, the effect of temporal modulation on the "Equal" condition was tested by comparing the 0.2 Hz condition with 0 Hz (steady). Significant differences were found in axial growth across lighting conditions. At 985 lux, birds exposed to the "Equal" condition showed a greater reduction in axial growth (both p < 0.01) and a greater hyperopic shift compared to "Soft" and "Daylight" (both p < 0.01). The "High S" birds experienced more axial growth compared to "Equal" (p < 0.01) but less than in "Soft" and "Daylight" (p < 0.01). Axial changes in "Equal" were only observed at 985 lux with 0.2 Hz temporal modulation, and not with lower light levels or steady light. We conclude that axial growth and refraction were dependent on the lighting condition in a manner predicted by wavelength defocus signals arising from LCA.

Tree shrews do not maintain emmetropia in initially-focused narrow-band cyan light.

We asked if emmetropia, achieved in broadband colony lighting, is maintained in narrow-band cyan light that is well focused in the emmetropic eye, but does not allow for guidance from longitudinal chromatic aberrations (LCA) and offers minimal perceptual color cues. In addition, we examined the response to a -5 D lens in this lighting. Seven tree shrews from different litters were initially housed in broad-spectrum colony lighting. At 24 ± 1 days after eye opening (Days of Visual Experience, DVE) they were housed for 11 days in ambient narrow-band cyan light (peak wavelength 505 ± 17 nm) selected because it is in focus in an emmetropic eye. Perceptually, monochromatic light at 505 nm cannot be distinguished from white by tree shrews. While in cyan light, each animal wore a monocular -5 D lens (Cyan -5 D eyes). The fellow eye was the Cyan no-lens eye. Daily awake non-cycloplegic measures were taken with an autorefractor (refractive state) and with optical low-coherence optical interferometry (axial component dimensions). These measures were compared with the values of animals raised in standard colony fluorescent lighting: an untreated group (n = 7), groups with monocular form deprivation (n = 7) or monocular -5 D lens treatment (n = 5), or that experienced 10 days in total darkness (n = 5). Refractive state at the onset of cyan light treatment was low hyperopia, (mean ± SEM) 1.4 ± 0.4 diopters. During treatment, the Cyan no-lens eyes became myopic (-2.9 ± 0.3 D) whereas colony lighting animals remained slightly hyperopic (1.0 ± 0.2 D). Initially, refractions of the Cyan -5 D eyes paralleled the Cyan no-lens eyes. After six days, they gradually became more myopic than the Cyan no-lens eyes; at the end of treatment, the refractions were -5.4 ± 0.3 D, a difference of -2.5 D from the Cyan no-lens eyes. When returned to colony lighting at 35 ± 1 DVE, the no-lens eye refractions rapidly recovered towards emmetropia but, as expected, the refraction of the -5 D eyes remained near -5 D. Vitreous chamber depth in both eyes was consistent with the refractive changes. In narrow-band cyan lighting the emmetropization mechanism did not maintain emmetropia even though the light initially was well focused. We suggest that, as the eyes diverged from emmetropia, there were insufficient LCA cues for the emmetropization mechanism to utilize the developing myopic refractive error in order to guide the eyes back to emmetropia. However, the increased myopia in the Cyan -5 D eyes in the narrow-band light indicates that the emmetropization mechanism nonetheless detected the presence of the lens-induced refractive error and responded with increased axial elongation that partly compensated for the negative-power lens. These data support the conclusion that the emmetropization mechanism cannot maintain emmetropia in narrow-band lighting. The additional myopia produced in eyes with the -5 D lens shows that the emmetropization mechanism responds to multiple defocus-related cues, even under conditions where it is unable to use them to maintain emmetropia.

Emmetropic, But Not Myopic Human Eyes Distinguish Positive Defocus From Calculated Blur.

Purpose: Defocus blur imposed by positive lenses can induce hyperopia, whereas blur imposed by diffusers induces deprivation myopia. It is unclear whether the retina can distinguish between both conditions when the magnitude of blur is matched. Methods: Ten emmetropic (average 0.0 ± 0.3 diopters [D]) and 10 subjects with myopia (-2.7 ± 0.9 D; 24 ± 4 years) watched a movie on a large screen (65 inches at 2 meters (m) distance. The movie was presented either unfiltered ("control"), with calculated low-pass filtering equivalent to a defocus of 2.5 D, or with binocular real optical defocus of +2.5 D. Spatial filtering was done in real-time by software written in Visual C++. Axial length was followed with the Lenstar LS-900 with autopositioning system. Results: Watching unfiltered movies ("control") caused no changes in axial length. In emmetropes, watching movies with calculated defocus caused axial eye elongation (+9.8 ± 7.6 µm) while watching movies with real positive defocus caused shorter eyes (-8.8 ± 9.2 µm; difference between both P < 0.0001). In addition, in myopes, calculated defocus caused longer eyes (+8.4 ± 9.0 µm, P = 0.001). Strikingly, myopic eyes became also longer with positive defocus (+9.1 ± 11.2 µm, P = 0.02). The difference between emmetropic and myopic eyes was highly significant (-8.8 ± 9.2 µm vs. +9.1 ± 11.2 µm, respectively, P = 0.001). Conclusions: (1) In emmetropic human subjects, the retina is able to distinguish between real positive defocus and calculated defocus even when the modulation transfer function was matched, (2) in myopic eyes, the retina no longer distinguishes between both conditions because the eyes became longer in both cases. Results suggest that the retina in a myopic eye has reduced ability to detect positive defocus.

Associations between visual function and magnitude of refractive error for emmetropic to moderately hyperopic 4- and 5-year-old children in the Vision in Preschoolers - Hyperopia in Preschoolers Study.

PURPOSE: To evaluate associations between visual function and the level of uncorrected hyperopia in 4- and 5-year-old children without strabismus or amblyopia. METHODS: Children with spherical equivalent (SE) cycloplegic refractive error of -0.75 to +6.00 on eligibility testing for the Vision in Preschoolers-Hyperopia in Preschoolers (VIP-HIP) study were included. Children were grouped as emmetropic (<1D SE myopia or hyperopia), low hyperopic (+1 to <+3D SE) or moderate hyperopic (+3 to +6D SE). Children with anisometropia or astigmatism (≥1D), amblyopia or strabismus were excluded. Visual functions assessed were monocular distance visual acuity (VA) and binocular near VA with crowded HOTV charts, accommodative lag using the Monocular Estimation Method and near stereoacuity by 'Preschool Assessment of Stereopsis with a Smile'. Visual functions were compared as continuous measures among refractive error groups. RESULTS: 554 children (mean age 58 months) were included in the analysis. Mean SE (SD) {N} for emmetropia, low and moderate hyperopia were +0.52D (0.49) {N = 270}, +2.18D (0.57) {N = 171} and +3.95D (0.78) {N = 113}, respectively. There was a consistent trend of poorer visual function with increasing hyperopia (p < 0.001). Although all children had age-normal distance VA, logMAR (Snellen) VA of 0.00 (6/6) or better was achieved (distance, near) among more emmetropic (52%, 26%) and low hyperopic (47%, 15%) children than moderate hyperopes (25%, 9%). Mean (SD) distance logMAR VA declined from emmetropic 0.05 (0.10), to low hyperopic 0.06 (0.10) to moderately hyperopic children 0.12 (0.11) (p < 0.001); A mild progressive decrease in near VA also was observed from the emmetropic 0.13 (0.11) to low hyperopic 0.15 (0.10) to moderate hyperopic 0.19 (0.11) groups, (p < 0.001). Accommodative responses showed an increased lag with increasing hyperopia (ρ = 0.50, p < 0.001). Median near stereoacuity for emmetropes, low and moderate hyperopes was 40, 60 and 120 sec arc, respectively. The percentage of these groups with no reduced near visual functions was 83%, 61%, and 34%, respectively. CONCLUSIONS: Decreasing visual function was associated with increasing hyperopia in 4- and 5-year-olds without strabismus or amblyopia. As hyperopia with reduced visual function has been associated with early literacy deficits, near visual function should be evaluated in these children.

Myopia, corneal endothelial cell density and morphology in a Japanese population-based cross-sectional study: the JPHC-NEXT Eye Study.

This population-based cross-sectional study was performed to determine the mean corneal endothelial cell density (ECD), coefficient of variation (CV), and hexagonality (HEX), and their associations with myopia in Japanese adults living in Chikusei city. Of 7109 participants with available data, 5713 (2331 male and 3382 female) participants were eligible for analysis. After assessing the relationship between participant characteristics and spherical equivalent refraction (SER), the association of SER with the abnormal value of ECD (< 2000 cells/mm), CV (≥ 0.40), and HEX (≤ 50%) were determined using the logistic regression models adjusting for potential confounders (age, intraocular pressure, keratometric power, height, and antihypertensive drug use). In male participants, there was no statistically significant relationships between SER and endothelial parameters. In female participants, compared to emmetropia, SER ≤ - 6 D had significantly higher odds ratio (OR) of having the abnormal value of CV (OR = 2.07, 95% confidence interval [CI] 1.39-3.10) and HEX (OR = 2.04, 95% CI 1.29-3.23), adjusted for potential confounders, indicating that the high myopia was associated with the abnormal values of CV and HEX. Further adjustment for contact lenses wear partly attenuated these associations. Association between the SER and ECD was not detected.