Peripheral eye length measurement techniques: a review

Structural and functional analysis of the eye according to the accommodation-age relationship

This study investigates how accommodative demand affects ocular function by examining variations in the anterior chamber depth (ACD), as well as the retinal and anterior surface curvatures of the crystalline lens across different age groups. The study included 96 right eyes from healthy individuals aged 18 to 66 years. Accommodation was assessed using an aberrometer under demands up to 5 diopters (D). Images of the anterior segment and retina were recorded and analyzed with custom software to adjust these surfaces to conic curves, providing data on changes in ACD, anterior surface curvature of the crystalline lens, and retinal shape during accommodation. The average age of participants was 35.42 ± 13.55 years. Accommodation matched the demand at low levels (up to 1D) but under-accommodated at higher demands. No significant differences were found in the anterior surface curvature of the crystalline lens with increased accommodation, though a weak trend was observed in younger individuals. ACD significantly decreased with accommodation due to the anterior displacement of the lens. Retinal curvature showed significant changes, including flattening, with increased accommodative demand. There were correlations between the anterior surface eccentricity of the crystalline lens and both ACD changes and retinal eccentricity. In conclusion, accommodation effectively responds to demands up to 1D across all ages. Our findings suggest a tendency for retinal curvature to flatten to higher demands, requiring further validation. While the central curvature of the anterior surface of the crystalline lens does not change significantly, ACD decreases with accommodation, indicating how age and presbyopia influence accommodative capacity and structural changes in the eye.

Retinal reconstruction from peripheral biometry

This study presents a method for retinal reconstruction using peripheral biometry. The incident beam is presumed to be directed toward the center of curvature of the anterior cornea, reaching the retina with minimal deviation. A significant advancement is demonstrated by extending previous approaches to three dimensions and effectively capturing the complexity of astigmatic corneal surfaces. The method was evaluated in Zemax using Navarro's eye model featuring a retina of 12 mm radius, across various levels of accommodation ranging from 0 to 8 D, and a visual field angle between 25 and 25°. The method's reliability diminishes for field angles ≥ 35°. Validation was carried out using 500 synthetically generated eyes, and the method's performance was also assessed with an ellipsoidal retina. The findings revealed that spherical equivalent differences were consistently under 0.25 D at 25° for both types of retinas. Overall, these results demonstrate the method's effectiveness, offering a promising new tool for retinal reconstruction.

Optical and retinal changes influenced by different lighting conditions

Retinal morphology, specifically in its curvature, and ocular aberrations change when the eye adapts to different lighting conditions, including photopic, scotopic, mesopic, blue light, and red light. Sixty healthy young subjects with refractive error less than ±4.00 D of sphere and 3.00 D of cylinder, not suffering from accommodative problems, ocular or systemic pathology, and not having used electronic devices half an hour before or having taken substances that alter the retina during the 2 h prior to the study were included. The subjects adapted to five lighting conditions, each for 5 min, in a controlled environment. Ocular aberrometry and Optical Coherence Tomography (OCT) were taken to capture images of the central and peripheral retina before (baseline measurements) and after adaptation to each lighting condition. The OCT images were exported and processed to analyze retinal curvature, obtaining parameters such as eccentricity, asphericity and shape factor. The results showed that the shape of the retina was hyperbolic prolate, becoming flatter in scotopic and blue light conditions, and more curved in mesopic conditions. Retinal curvature was closest to baseline under red light and photopic conditions. Aberrometric differences, particularly in the C(2,0) polynomial for defocus, showed higher values in mesopic, baseline, and scotopic conditions, and lower values in photopic, blue light, and red light. Significant differences were also observed in spherical aberrations C(4,0) and C(6,0), vertical coma C(3,-1), and trefoil C(3,-3). The spherical equivalent indicated more myopic values in mesopic, baseline, and scotopic conditions, and more hyperopic values in blue, photopic, and red light, suggesting a link between myopia and lower luminosity. This study concludes that illumination affects retinal curvature and ocular refraction, influencing myopia.

Megahertz multi-parametric ophthalmic OCT system for whole eye imaging

An ultrahigh-speed, wide-field OCT system for the imaging of anterior, posterior, and ocular biometers is crucial for obtaining comprehensive ocular parameters and quantifying ocular pathology size. Here, we demonstrate a multi-parametric ophthalmic OCT system with a speed of up to 1 MHz for wide-field imaging of the retina and 50 kHz for anterior chamber and ocular biometric measurement. A spectrum correction algorithm is proposed to ensure the accurate pairing of adjacent A-lines and elevate the A-scan speed from 500 kHz to 1 MHz for retinal imaging. A registration method employing position feedback signals was introduced, reducing pixel offsets between forward and reverse galvanometer scanning by 2.3 times. Experimental validation on glass sheets and the human eye confirms feasibility and efficacy. Meanwhile, we propose a revised formula to determine the "true" fundus size using all-axial length parameters from different fields of view. The efficient algorithms and compact design enhance system compatibility with clinical requirements, showing promise for widespread commercialization.

How can we better evaluate paediatric progression of myopia and associated risk factors? Lessons from the COVID-19 pandemic: A systematic review

PURPOSE

During the COVID-19 pandemic, home-based and remote learning-particularly using electronic devices-was rapidly pushed out. Increased near-work, screen time exposure and lack of outdoor time are risk factors that contribute to childhood myopia, but it is difficult to adopt recommendations from prior publications as a consistent limitation in the literature is the heterogeneity of research methodology. This review seeks to systematically evaluate how observational studies published during the pandemic have quantified and measured risk factors and myopia in school-going children and adolescents.

METHODS

Three scientific databases (PubMed, CINAHL, Scopus) were systematically searched from March 2020 to April 2022. Findings from relevant studies were descriptively summarised in relation to the PICOS-based objective of the review.

RESULTS

The final sample of 13 studies included research from six countries and comprised 1 411 908 children and adolescents. The majority of studies (N = 10; 76.9%) used spherical equivalent refraction (SER) of -0.5 dioptres or lower as a common definition of myopia. Most studies (77.8%) measuring screen time exposure found it higher during COVID-19 compared to pre-COVID, but only one study used objective measurement of screen time. The average critical appraisal score of the sample was only 66.1%, with a considerable number of studies failing to identify and adjust for potential confounders.

CONCLUSION

Future studies should consider emergent objective and validated measures of risk factors, account for potential a priori confounders and covariates and ensure more representativeness in the sociodemographic makeup of their samples.

Changes in relative peripheral refraction and optical quality in Chinese myopic patients after small incision lenticule extraction surgery

PURPOSE

To observe changes in retinal refraction difference values (RDV) and aberrations after small incision lenticule extraction (SMILE) surgery and evaluate their correlations.

METHODS

This study recruited 112 patients (112 eyes) who underwent SMILE for myopia. Participants were classified into the Low and Moderate Myopia group (LM, -0.50 to -6.0 D) and High Myopia group (HM, >-6.0 D) according to the central spherical equivalent (SE). RDVs in the five retinal eccentricities from 0° to 10°, 10° to 20°, 20° to 30°, 30° to 40°, and 40° to 53° are recorded as RDV-(0-10), RDV-(10-20), RDV-(20-30), RDV-(30-40), and RDV-(40-53), respectively; additionally, RDVs have four sectors, i.e., RDV-Superior (RDV-S), RDV-Inferior (RDV-I), RDV-Temporal (RDV-T), and RDV-Nasal (RDV-N). With a 3-month follow-up, changes in RDV (ΔRDV) and changes in aberrations [Δtrefoil, Δcoma, Δspherical aberration (SA), and Δtotal higher-order aberrations (HOA)] after surgery were recorded.

RESULTS

No significant differences were observed in total RDV (TRDV), RDV-(0-53), RDV-S, RDV-I, RDV-N, trefoil, coma, and SA between the two groups before SMILE surgery. However, after SMILE, hyperopic defocus values [TRDV, RDV-(20-53), RDV-S, RDV-T, and RDV-N] in the LM group and hyperopic defocus values [TRDV, RDV-(20-53), RDV-S, and RDV-N] in the HM group were significantly lower at 3 months postoperatively than preoperatively, and the RDV-(40-53), RDV-S, and RDV-N were lower in the HM group than in the LM group. Aberrations [trefoil (vertical), coma, and HOA] in the LM group and aberrations (trefoil, coma, SA, and HOA) in the HM group were significantly higher at 3 months postoperatively than preoperatively, and the coma, trefoil(horizontal), SA, and HOA were higher in the HM group than in the LM group. In the multivariate analysis, ΔRDV-(40-53) was significantly correlated with ΔSA, and ΔRDV-T and ΔRDV-N were significantly correlated with Δcoma (horizontal).

CONCLUSIONS

Our findings suggest that SMILE reduces retinal peripheral hyperopic defocus but introduces some higher-order aberrations, especially in people with high myopia refractive errors.

Optical beam scanner with reconfigurable non-mechanical control of beam position, angle, and focus for low-cost whole-eye OCT imaging

Whole-eye optical coherence tomography (OCT) imaging is a promising tool in ocular biometry for cataract surgery planning, glaucoma diagnostics and myopia progression studies. However, conventional OCT systems are set up to perform either anterior or posterior eye segment scans and cannot easily switch between the two scan configurations without adding or exchanging optical components to account for the refraction of the eye's optics. Even in state-of-the-art whole-eye OCT systems, the scan configurations are pre-selected and cannot be dynamically reconfigured. In this work, we present the design, optimization and experimental validation of a reconfigurable and low-cost optical beam scanner based on three electro-tunable lenses, capable of non-mechanically controlling the beam position, angle and focus. We derive the analytical theory behind its control. We demonstrate its use in performing alternate anterior and posterior segment imaging by seamlessly switching between a telecentric focused beam scan to an angular collimated beam scan. We characterize the corresponding beam profiles and record whole-eye OCT images in a model eye and in an ex vivo rabbit eye, observing features comparable to those obtained with conventional anterior and posterior OCT scanners. The proposed beam scanner reduces the complexity and cost of other whole-eye scanners and is well suited for 2-D ocular biometry. Additionally, with the added versatility of seamless scan reconfiguration, its use can be easily expanded to other ophthalmic applications and beyond.

A Quantitative Comparison of Multispectral Refraction Topography and Autorefractometer in Young Adults

Purpose: Purpose of this study is to evaluate the measuring consistency of central refraction between multispectral refraction topography (MRT) and autorefractometry.

Methods: This was a descriptive cross-sectional study including subjects in Sun Yat-sen Memorial Hospital from September 1, 2020, to December 31, 2020, ages 20 to 35 years with a best corrected visual acuity of 20/20 or better. All patients underwent cycloplegia, and the refractive status was estimated with autorefractometer, experienced optometrist and MRT. We analyzed the central refraction of the autorefractometer and MRT. The repeatability and reproducibility of values measured using both devices were evaluated using intraclass correlation coefficients (ICCs).

Results: A total of 145 subjects ages 20 to 35 (290 eyes) were enrolled. The mean central refraction of the autorefractometer was −4.69 ± 2.64 diopters (D) (range −9.50 to +4.75 D), while the mean central refraction of MRT was −4.49 ± 2.61 diopters (D) (range −8.79 to +5.02 D). Pearson correlation analysis revealed a high correlation between the two devices. The intraclass correlation coefficient (ICC) also showed high agreement. The intrarater and interrater ICC values of central refraction were more than 0.90 in both devices and conditions. At the same time, the mean central refraction of experienced optometrist was −4.74 ± 2.66 diopters (D) (range −9.50 to +4.75D). The intra-class correlation coefficient of central refraction measured by MRT and subjective refraction was 0.939.

Conclusions: Results revealed that autorefractometry, experienced optometrist and MRT show high agreement in measuring central refraction. MRT could provide a potential objective method to assess peripheral refraction.

Ocular biometry in children and adolescents from 4 to 17 years: a cross-sectional study in central Germany

PURPOSE

To evaluate ocular biometry in a large paediatric population as a function of age and sex in children of European descent.

METHODS

Children were examined as part of the LIFE Child Study (Leipzig Research Centre for Civilization Disease), a population-based study in Leipzig, Germany. Altogether, 1907 children, aged from 4 to 17 years, were examined with the Lenstar LS 900. Data from the right eye was analysed for axial length, central corneal thickness, flat and steep corneal radii, aqueous depth, lens thickness and vitreous depth. Wavefront-based autorefraction was employed for analysis.

RESULTS

Axial length increased in girls from 21.6 mm (4 years) up to 23.4 mm (17 years); this increase (0.174 mm per year) was statistically significant up to age 14 (23.3 mm). Axial length increased in boys from 22.2 mm (4 years) up to 23.9 mm (17 years); this increase (0.178 mm per year) was statistically significant up to age 10 (23.3 mm). No change was observed for central corneal thickness (average: girls 550 µm; boys 554 µm). Corneal curvature in girls was somewhat flatter at age 4 (7.70 mm) compared to age 10 (7.78 mm), whereas it was constant in boys (7.89 mm). Aqueous depth at age 4 was 2.73 mm for girls and 2.86 mm for boys, with the same rate of increase per year (girls: 0.046 mm; boys: 0.047 mm) from age 4 to 10. At age 17, aqueous depth was 3.06 mm in girls and 3.20 mm in boys. Lens thickness was reduced from age 4 (3.75 mm) to age 10 (3.47 mm) in girls and from age 4 (3.73 mm) to age 10 (3.44 mm) in boys, with the same rate of decrease per year of 0.046 and 0.047 mm, respectively. At age 17, lens thickness was 3.52 mm in girls and 3.50 mm in boys. Vitreous depth at age 4 was 14.51 mm for girls and 15.08 mm for boys; with 0.156 mm (girls) or 0.140 mm (boys) increase per year until age 14 (girls: 16.08 mm; boys: 16.48 mm). At age 17, vitreous depth was 16.29 mm in girls and 16.62 mm in boys.

CONCLUSIONS

Eye growth (axial length) in girls showed a lag of about four years compared to boys. Aqueous depth increase matches the lens thickness decrease from ages 4 to 10 years in girls and boys. Lens thickness minimum is reached at 11 years in girls and at 12 years in boys. All dimensions of the optical ocular components are closely correlated with axial length. These data may serve as normative values for the assessment of eye growth in central European children and will provide a basis for monitoring refractive error development.

Feasibility and repeatability of ocular biometry measured with Lenstar LS 900 in a large group of children and adolescents

PURPOSE

To evaluate the feasibility and repeatability of Lenstar LS 900 biometry measurements in a paediatric population.

METHODS

Children were examined as part of the LIFE Child Study (Leipzig Research Centre for Civilization Diseases), a population-based study in Leipzig, Germany. Altogether, 1917 children, aged from 3.5 to 17.5 years, were assessed with the Haag Streit Lenstar LS 900. Three consecutive measurements of the right eye were analysed for axial length, central corneal thickness, anterior chamber depth, aqueous depth, lens thickness and flat and steep corneal radii. The number of successful measurements and repeatability were evaluated for each parameter and three age bands (3.5 to 6.5 years, 6.5 to 10.5 years and 10.5 to 17.5 years).

RESULTS

Best measurement feasibility was found for axial length and central corneal thickness (91% to 100%), followed by flat and steep corneal radii (86% to 100%), anterior chamber and aqueous depth (76% to 92%) and lens thickness (50% to 81%), with higher numbers for older children. Repeatability values (in mm) were: axial length 0.025 to 0.035; central corneal thickness 0.003 to 0.027; aqueous depth 0.024 to 0.058; anterior chamber 0.024 to 0.054; lens thickness 0.034 to 0.067. An overall trend showed better repeatability for older children, especially for central corneal thickness, aqueous depth and lens thickness.

CONCLUSIONS

For ocular biometry in the paediatric population, axial length, central corneal thickness, flat and steep corneal radii can be measured very reliably even in children from 4 years old onward using the Lenstar LS 900. Lens thickness can be quantified in a limited number of younger children. Repeatability was high for all variables investigated. Repeatability improved with age, reaching adult values in the adolescent age band. Established repeatability limits can be applied in future studies as a quality parameter.

Myopia induces meridional growth asymmetry of the retina: a pilot study using wide-field swept-source OCT

Myopic axial eye growth has mechanical implications on ocular structures, such as the retinal and foveal shape integrity or choroidal thickness. The current study investigated myopia-related changes of retinal radius of curvature, foveal width, depth, slope and choroidal thickness. Wide-field swept-source OCT line and volume scans were performed on 40 young adult participants in horizontal and vertical directions. OCT scans were corrected for their scan display distortions before automated extraction of retinal and foveal shape parameters. All findings were correlated to refractive error and axial length. The horizontal retinal radius of curvature and the directional ratio between horizontal and vertical retinal shape correlated significantly with axial length ([Formula: see text] and [Formula: see text]). Vertical retinal shape and foveal pit parameters neither showed any significant correlations with axial length nor refractive error (all [Formula: see text] 0.05). Choroidal thickness correlated significantly with refractive error in all analyzed regions ([Formula: see text]), but less with axial length ([Formula: see text] to - 0.37). Horizontal retinal shape and choroidal thickness, but not foveal pit morphology, were altered by myopic eye growth. Asymmetries in horizontal versus vertical retinal shape with increasing myopia were detected. These parameters could act as promising biomarkers for myopia and its associated complications.