Age-related axial length changes in adults: a review

Characteristics of Peripheral Retinal Refraction and Its Role in Children with Different Refractive States

Introduction

Peripheral retinal refraction plays a crucial role in myopia, but the specific mechanism is not clear. We refined the retinal partitions to explore the characteristics of peripheral retinal refraction and its role in emmetropic, low, and moderate myopic children aged 6 to 12 years.

Methods

A total of 814 subjects (814 eyes) were enrolled in the study. The participants were divided into three groups according to the central spherical equivalent refraction (SER), which were emmetropia group (E), low myopia group (LM) and moderate myopia group (MM). Multispectral refractive topography (MRT) was used to measure the retinal absolute and relative refractive difference value (RDV) in different regions. The range was divided into superior, inferior, temporal, and nasal RDV (SRDV, IRDV, TRDV, and NRDV) on the basis of several concentric circles extending outward from the macular fovea (RDV15, RDV30, RDV45, RDV30-15, RDV45-30, and RDV-45). Kruskal-Wallis test was used to analyze the differences of peripheral refraction for all the regions among the three groups. Spearman rank correlation was performed to explore correlations between SER and RDV, axial length (AL) and RDV.

Results

The absolute value of RDV decreased with increasing degree of myopia in all regions (P < 0.01). Subjects with different refractive degrees had different relative value of RDV. In nasal position within 45° and temporal position within 30°, the peripheral retina exhibited significantly different relative hyperopic refractive status among Group E, Group LM, and Group MM (P < 0.05). SER was negatively correlated with NRDV within 30° (especially in the range of NRDV30-15) (r = -0.141, P < 0.01), positively correlated with TRDV within 15° (r = 0.080, P = 0.023), and not significantly correlated with SRDV and IRDV when the retina was divided into four parts. AL was positively correlated with NRDV within 30° (especially in the range of NRDV30-15) (r = 0.109, P = 0.002), negatively correlated with TRDV within 15° (r = -0.095, P = 0.007).

Conclusions

The peripheral defocus has significant implications for the genesis of myopia. The peripheral defocus of the horizontal direction, especially within the range of NRDV30, has greater effect on the development of myopia in children. Higher NRDV30 is associated with lower SER and longer AL.

Extreme myopia is more susceptible to SOX2 gene than high myopia

PURPOSE

To explore the association between two single-nucleotide polymorphisms (SNPs) in the SOX2 gene and high and extreme myopia in the Han Chinese population.

MATERIALS AND METHODS

A genetic association study using a case-control method was performed with 139 high myopia, 318 extreme myopia, and 918 healthy participants from the Chinese Han population. Two SNPs (rs4459940 and rs4575941) near SOX2 gene were selected for genotyping. We compared the allelic frequencies and haplotypes of the SNPs to assess their association with high and extreme myopia. This study was adjusted for sex and age of participants in the groups.

RESULT

The mean ages of the extreme myopia and control subjects were 47.44 ± 15.59 and 44.15 ± 14.08 years, respectively. The rs4575941 SNP of the SOX2 gene and the GG and AG genotypes showed no significant association with the risk of high myopia as opposed to the AA genotype (GG, OR = 0.94, 95% CI = 0.55-1.60, P = 0.820, Pc = NS; AG, OR = 0.91, 95% CI = 0.54-1.52, P = 0.708, Pc = NS). However, the frequency of the risk G allele of rs4575941 was significantly higher in the extreme myopia group than in the control group (OR = 1.31, 95% CI = 1.08-1.59; P = 0.007; Pc = 0.014). Furthermore, there were significant differences in the GG genotype frequency between the extreme myopia and control groups (OR = 1.77, 95% CI = 1.45-2.74, P = 0.009, Pc = 0.036). The A-G haplotype frequency was higher in the extreme group (OR = 1.27, 95% CI = 1.05-1.55, P = 0.014), while there were no significant differences found in high myopia group (OR = 1.18, 95% CI = 0.77-1.31, P = 0.979).

CONCLUSION

The SOX2 rs4575941 polymorphism, in Chinese Han population, contributes to the susceptibility of extreme myopia. SOX2 may thus be implicated in extreme myopia rather than in high myopia.

Refractive development I: Biometric changes during emmetropisation

PURPOSE

Although there are many reports on ocular growth, these data are often fragmented into separate parameters or for limited age ranges. This work intends to create an overview of normal eye growth (i.e., in absence of myopisation) for the period before birth until 18 years of age.

METHODS

The data for this analysis were taken from a search of six literature databases using keywords such as "[Parameter] & [age group]", with [Parameter] the ocular parameter under study and [age group] an indication of age. This yielded 34,409 references that, after screening of title, abstract and text, left 294 references with usable data. Where possible, additional parameters were calculated, such as the Bennett crystalline lens power, whole eye power and axial power.

RESULTS

There were 3422 average values for 17 parameters, calculated over a combined total of 679,398 individually measured or calculated values. The age-related change in refractive error was best fitted by a sum of four exponentials (r²  = 0.58), while all other biometric parameters could be fitted well by a sum of two exponentials and a linear term ('bi-exponential function'; r² range: 0.64-0.99). The first exponential of the bi-exponential fits typically reached 95% of its end value before 18 months, suggesting that these reached genetically pre-programmed passive growth. The second exponentials reached this point between 4 years of age for the anterior curvature and well past adulthood for most lenticular dimensions, suggesting that this part represents the active control underlying emmetropisation. The ocular components each have different growth rates, but growth rate changes occur simultaneously at first and then act independently after birth.

CONCLUSIONS

Most biometric parameters grow according to a bi-exponential pattern associated with passive and actively modulated eye growth. This may form an interesting reference to understand myopisation.

A Study Linking Axial Length, Corneal Curvature, and Eye Axis With Demographic Characteristics in the Emmetropic Eyes of Bangladeshi People

Background Axial length (AL) and corneal curvature (CC) are one of the furthest critical parameters for optometry and oculoplastic surgery. These two variables are crucial in biometry for accurately measuring the power of the intraocular lens in cataract surgery. This research aimed to determine the association linking axial length and corneal curvature with demographic characteristics in emmetropic eyes of Bangladeshi people. Methods This descriptive cross-sectional research was carried out among 200 emmetropic eyes of Bangladeshi people attending the Department of Ophthalmology at Rajshahi Medical College, Bangladesh, with different eye conditions, between July 2017 and June 2018. Data was gathered by conducting person-to-person interviews, checking visual activity using the Snellen chart, and measuring corneal curvature using an auto-keratometer and axial eyeball length using A-scan ultrasonography. Results A total of 200 attendances were studied, 90 males and 110 females. All were emmetropic. The age range was 21-52 years, and the highest contributors were in the 21-30-year age group. The association between right axial length and right corneal curvature shows a negative relation among both sexes. It was -0.61 (β-coefficient (β-coff)), and highly significant in females at -0.89 (β-coff). Additionally, the association between left axial length and left corneal curvature shows a negative relation of -0.65 (β-coff), which was again highly significant in females at -0.87 (β-coff). Both were not significant in males. There was no significant association linking axial length and eye axis in both sexes. The multivariate regression model was used to assess the p-value, and the regression model was adjusted by age. Conclusion Optical parametric measurement is a noninvasive diagnostic and assessment tool that might help in the actual measurement of intraocular lens implantation in cataract surgery and may also provide supplementary information to the researcher domain.

Vascular endothelial growth factor from retinal pigment epithelium is essential in choriocapillaris and axial length maintenance

Myopia, which prevalence is rapidly increasing, causes visual impairment; however, the onset mechanism of pathological axial length (AL) elongation remains unclear. A highly vascularized choroid between the retinal pigment epithelium (RPE) and sclera not only maintains physiological activities, but also contributes to ocular development and growth regulation. Vascular endothelial growth factor (VEGF) secreted from the RPE to the choroid is essential for retinal function and maintenance of the choriocapillaris. Herein, we demonstrated that the loss of VEGF secreted from the RPE caused abnormal choriocapillaris development and AL elongation, with features similar to those of the lens-induced myopia (LIM) mouse model, whereas VEGF overexpression by knocking-out von Hippel-Lindau (VHL) specific to the RPE expands the choriocapillaris and shortens the AL. Additionally, LDL Receptor Related Protein 2 (LRP2) deletion in the RPE downregulated VEGF expression and leads to pathological AL elongation. Furthermore, high-myopia patients without choriocapillaris demonstrated longer ALs than did those with preserved choriocapillaris. These results suggest that physiological secretion of VEGF from the RPE is required for proper AL development by maintaining the choriocapillaris. The pinpoint application of VEGF to the choriocapillaris may become a potential intervention for the prevention and treatment of axial myopia progression.

Evaluation of ocular biometry in the Japanese population using a multicenter approach: Prospective observational study

This prospective observational study aimed to evaluate the ocular biometry of Japanese people through a multicenter approach. The uncorrected and corrected distance visual acuity (UDVA and CDVA, respectively) in the log minimum angle of resolution (logMAR), subjective and objective spherical equivalent values (SE) of ocular refraction, anterior and posterior corneal curvature (ACC and PCC, respectively), anterior and posterior corneal asphericity (ACA and PCA, respectively), central corneal thickness (CCT), anterior chamber depth (ACD), and ocular axial length (AL) were measured in the eyes of 250 participants (mean age = 46.5 ± 18.0 years, range: 20–90 years) across five institutions in Japan. The mean UDVA, CDVA, subjective SE, objective SE, ACC, PCC, ACA, PCA, CCT, ACD, and AL were 0.68, −0.08, −2.42 D, −2.66 D, 7.77 mm, 6.33 mm, −0.31, −0.39, 0.55 mm, 2.92 mm, and 24.78 mm, respectively. Age-related changes and sex-based differences were noted in the visual acuity, refraction, corneal shape, ACD, and AL. Our results serve as basis for future studies aiming to develop refractive correction methods and various vision-related fields.

Masticatory Muscle Thickness and Activity Correlates to Eyeball Length, Intraocular Pressure, Retinal and Choroidal Thickness in Healthy Women versus Women with Myopia

This study aims to examine the correlations between masticatory and neck muscle thickness and activity versus eyeball length, retinal thickness, choroidal thickness, and intraocular pressure in healthy women versus women with myopia. The study group consisted of 21 women aged 24 years and a control group of 19 women (mean age 23 years). For bioelectrical activity analysis within the temporalis anterior, the superficial part of the masseter muscle, the middle part of the sternocleidomastoid muscle, and the anterior belly of the digastric muscle, an eight-channel BioEMG III electromyograph were used. An M-Turbo ultrasound machine was used to analyze masticatory and neck muscle thickness. The eyeball length was examined by IOL Master 500; choroidal and retinal thickness by Optovue Angiovue; and intraocular pressure by Tono-Pen XL. Refractive errors are related to differences in muscle thickness and electromyographic activity. Bioelectrical activity within the temporalis anterior seems to be associated with ocular length, retinal thickness, and choroidal thickness in women with myopia.

Mutations of CX46/CX50 and Cataract Development

Cataract is a common disease in the aging population. Gap junction has been considered a central component in maintaining homeostasis for preventing cataract formation. Gap junction channels consist of connexin proteins with more than 20 members. Three genes including GJA1, GJA3, and GJA8, that encode protein Cx43 (connexin43), Cx46 (connexin46), and Cx50 (connexin50), respectively, have been identified in human and rodent lens. Cx46 together with Cx50 have been detected in lens fiber cells with high expression, whereas Cx43 is mainly expressed in lens epithelial cells. Disrupted expression of the two connexin proteins Cx46 and Cx50 is directly related to the development of severe cataract in human and mice. In this review article, we describe the main role of Cx46 and Cx50 connexin proteins in the lens and the relationship between mutations of Cx46 or Cx50 and hereditary cataracts. Furthermore, the latest progress in the fundamental research of lens connexin and the mechanism of cataract formation caused by lens connexin dysfunction are summarized. Overall, targeting connexin could be a novel approach for the treatment of cataract.

Biometry of the human cornea and globe: An evaluation by age, gender and population

The purpose of this study was to examine the effects of age, gender and population origin on human globe and corneal dimensions and to explore the relationships between the dimensions. Human post-mortem eyes were obtained in Hyderabad (n = 223; range, 0-85 years) and Miami (n = 486; range, 6-103 years). The eyes were freed of extraneous tissues and globe antero-posterior length (GAPL), mean globe diameter (MGD) (average of horizontal and vertical), and corneal horizontal (HCD) and vertical (VCD) diameters were measured using digital calipers. The relationships of age, gender and population origin with globe and corneal dimensions and the relationships between the dimensions were assessed by bivalent and multiple regression analyses. Globe and cornea dimensions increase asymptotically with age until around the late teens but do not change thereafter. Bivariate and multivariate regression analysis of the >20-year-old eyes showed that population was significantly correlated with GAPL, MGD. HCD and VCD. Male globes and corneas were larger than those from females, but the difference did not appear to be statistically significant. All Hyderabad dimensions were significantly larger than those from the Miami. Neither GAPL nor MGD were correlated with the corneal dimensions. GAPL was significantly correlated with MGD as was HCD with VCD.

Relationship between axial length and spherical equivalent refraction in Chinese children

Purpose

To evaluate the relationship between axial length (AL) and spherical equivalent refraction (SER) in Chinese children.

Methods

This hospital-based cross-sectional study included 1208 eyes (from 617 Chinese boys and 591 Chinese girls), ranging between 2 and 12 years. All subjects were divided into subgroups according to the spherical equivalent refraction (SER) (hyperopia, emmetropia, and myopia) and age (2-6 years, 7-9 years, and 10-12 years). Comparisons were made between age, sex, and SER groups. Multiple linear regression analysis was used to evaluate the correlation of AL and SER for all groups.

Results

The mean AL and SER were significantly different among the three age groups: 2-6 years group (AL: 22.24 ​± ​1.59 ​mm; SER: 0.73 ​± ​2.67 D); 7-9 years group (AL: 23.49 ​± ​1.10 ​mm; SE: -0.68 ​± ​1.97 D) and 10-12 years group (AL: 24.33 ​± ​1.02 ​mm; SER: -1.72 ​± ​1.86 D). Boys showed longer AL compared with the girls (23.66 ​± ​1.51 ​mm vs 23.05 ​± ​1.32 ​mm). However, as for SER, the girls (-0.70 ​± ​2.17 D) showed smaller SER (more myopia) compared with the boys (-0.4 ​± ​2.48 D). After adjusting for age and sex, the SER tended to decrease (became more myopic) 1.23 D (95% CI: 1.15-1.30D) with a 1 ​mm increase of AL. Among the different SER groups, the SER tended to become more myopic per mm of AL by 1.09 D (95% CI: 0.97-1.21D) for the myopia group, 1.38 D (95% CI: 1.23-1.54 D) for the hyperopia group, and 0.05 D (95% CI: 0.02-0.08 D) for the emmetropic group. In addition, an increase of 1 ​mm elongation of AL showed a decrease of SER by 1.05 D (95% CI: 0.90-1.20 D) among 2 - 6-year-olds, by 1.40 D (95% CI: 1.30-1.51 D) among 7 - 9-year-olds, and by 1.37 D (95% CI: 1.21-1.52 D) among 10-12-year-olds. As for sexual differences, the girls 1.68 D, (95% CI: 1.57-1.79 D) showed a more significant myopic shift of SER with a 1 ​mm increase of AL compared with the boys (0.94 D, 95% CI: 0.84-1.04 D).

Conclusions

Our results indicated a strong linear relationship between SER and AL and an early-rising trend of myopia in Chinese children.