Peripheral refraction of young adults with myopia: a cross-sectional study

Abstract

Objective

Peripheral refraction is associated with myopia development. Due to a varying prevalence of myopia across different ethnic groups, the aim of the present study was to investigate the peripheral refraction profile in an Arabic population.

Methods

Adults attending an optometry clinic were recruited into this cross-sectional study. Peripheral refraction of the right eyes was measured using an open field autorefractor under noncycloplegic conditions along the temporal-nasal meridians (15° and 35°) in participants with emmetropia, or low, moderate, or high myopia. Refractions were converted into power vector components, including the spherical equivalent of central refraction, J0 and J45 astigmatism. STROBE guidelines were followed for study reporting.

Results

A total of 138 adults (aged 20–29 years) were enrolled. Relative peripheral refractive error (RPRE) varied between refractive groups and increased with eccentricity. The RPRE was more hyperopic in myopia groups, with the nasal visual field being more hyperopic. A significant relationship was found between RPRE and central refraction, but not with J0 and J45 scores.

Conclusions

Participants with moderate myopia exhibited more hyperopic RPRE compared with previous findings in other ethnic groups. Hyperopic RPRE was significantly associated with myopia. Accurate RPRE measurement are essential for designing personalized lenses to slow down myopia progression. This study provides an RPRE baseline in the population investigated, which will be useful for future studies on personalized lens design, including spectacles and contact lenses.

Keywords

Peripheral refraction myopia hyperopic defocus relative peripheral refractive error young adults Saudi Arabia

Introduction

Myopia is a growing public health concern that carries substantial visual morbidity at both the individual and the population level,¹ and has been reported to carry a ﬁnancial and social burden at individual and national levels.^1–5 The prevalence of myopia has increased sharply over the past decade,⁶ with prevalence rates that are substantially higher in the East Asian population compared with the white population.^7–12 The prevalence of myopia in Saudi Arabia is comparable with that in the East Asian population.¹³ Myopia onset is increasingly occurring at a younger age and with faster progression rates,^8,11,12 which contributes to the increased prevalence and severity of myopia in the population.^7,14,15 Myopia is also linked to an increased risk of developing several ocular conditions, including glaucoma,^16,17 cataract,^18,19 macular degeneration,¹⁸ retinal detachment,²⁰ and various pathologic retinal changes.^18,21 Myopia is one of the leading causes of correctable visual impairment and blindness,^13,22–24 with a considerable amount of research conducted to investigate approaches to slow down myopic progression.²⁵

Peripheral refraction is commonly used to infer retinal shape in human eyes,^26–28 and has been investigated in animal and human studies showing the inﬂuence of peripheral retinal defocus on the development of central refraction.^29,30 Hyperopic defocus has been suggested to lead to an increased axial length in an attempt to bring the peripheral image into focus, regardless of the subsequent increase in foveal myopic shift.^30–32 Specifically, myopia greater than −2.50 D is often associated with hyperopic peripheral refraction, indicating a more prolate ocular shape.^27,30,33 Some studies in children suggest that relative peripheral hyperopia does not manifest until after the onset of myopia development.^34,35 One study reported that young adults with myopia who have myopic parents had increased hyperopic peripheral refraction versus those without a family history of myopia, indicating a potential hereditary factor.³⁶ Several studies have investigated peripheral refraction in specific ethnic groups,^37,38 while others have made comparisons between different ethnicities.^12,25

To date, peripheral refraction proﬁles of individuals from Arabic backgrounds have not been sufficiently reported. Understanding the potential differences between Arabic and other backgrounds may aid future research in investigating approaches to slow down myopic progression. Thus, the aim of the present study was to investigate peripheral refraction in participants from an Arabic background with emmetropia, or low, moderate, or high myopia in Saudi Arabia.

Patients and methods

Study population

The present prospective, cross-sectional, observational study investigated the peripheral refraction in adult participants (aged ≥18 years) of Arabian ethnicity who were randomly recruited, regardless of sex, from the Optometry OPD Clinic at King Saud University campus between September 2022 and June 2023.

For study inclusion, participants were required to have best corrected visual acuity (BCVA) of 20/20 with no ocular diseases. Exclusion criteria included a history of previous ocular surgery, amblyopia or strabismus, lens opacities or changes, glaucoma, and/or retinal diseases. The inclusion examinations involved evaluating general health, ophthalmic and systemic history, non-cycloplegic objective refraction, BCVA, and slit-lamp examination. BCVA was measured using the Early Treatment Diabetic Retinopathy Study (ETDRS) chart (Precision Vision, LaSalle, IL, USA).³⁹ The cutoff points for refractive powers were +2.00 D to −7.00 D for sphere and −2.00 D for cylinder. Participants were then classified with emmetropia (+1.00 D to −0.49 D), hyperopia (>+1.00 D), low myopia (−0.50 to −2.49 D), moderate myopia (−2.50 to −5.50 D) or high myopia (>−5.50 D). Only the right eyes of the participants were assessed to facilitate comparisons with previous studies that followed similar procedures and to avoid any correlation between the right and left eyes of a single participant.

The study was approved by the Ethics Committee at King Saud University (E-22-7474) and the tenets of the Declaration of Helsinki and its subsequent amendments were upheld. All participants provided written informed consent prior to study enrolment. Participant data were de-identified to ensure anonymity, and the reporting of the study conforms to STROBE guidelines.⁴⁰

Sample size calculation

The sample size was calculated using Epi Info, version 7.2.6 (Centers for Disease Control, USA; https://www.cdc.gov/epiinfo/pc.html). The input parameters included a group age of 20–35 years living in Riyadh, Saudi Arabia (a population size of 2 800 000), with an expected frequency of 50% (indicating that half have myopia),¹³ and a 95% confidence interval. The estimated required sample size was 96 participants.

The relative peripheral refractive error (RPRE)

Peripheral and central refraction were measured by open field autorefraction under normal dim light without dilation using an open-field autorefractor (Grand Seiko WV500; Grand-Seiko Co., Fukijama, Japan, also called Shin-Nippon SRW-5000), which produces valid and reliable measurements.⁴¹ The open-field autorefractor allows participants to perceive targets at various distances and angles.

Each participant viewed a board at a distance of 2 m, which had five targets aligned at the same level as their primary gaze. The first target, located at 0°, represented the central refraction. The second and third targets were positioned at 15° in both the temporal and nasal horizontal visual field. The final two targets were positioned at 35° in both the temporal and nasal horizontal visual field (Figure 1). The targets were lit red light-emitting diodes (LEDs) designed to maintain the participants’ focus. Before testing, participants were instructed to place their chin in the chin-rest and stabilized their head with a forehead strap. The median of three measurements was taken at each eccentricity of the right eye. The open-field autorefractor provided conventional sphero-cylindrical refractions. These values were then converted into power vector components: M (spherical equivalent of central refraction), J0 (with-the-rule and against-the-rule astigmatism from 90° to 180°), and J45 (oblique astigmatism from 45° to 135°) using the equations reported by Thibos et al.⁴² RPRE was calculated as the difference between the spherical equivalent of the average refraction at the fovea and the spherical equivalent of the average refractive error of the peripheral refraction at each eccentricity.

Figure 1.

Representative image displaying the detection ranges of 15° and 35° on a Goldman visual field chart.

Statistical analyses

Data were entered into Microsoft Excel and then analysed using IBM SPSS, version 21.0 (IBM Corp., Armonk, NY, USA). Data were tested for normality and non-parametric tests were applied. All outcomes are presented as median ± interquartile range (IQR). The correlations between central refraction and RPRE were examined using Spearman's rank correlation coefficient. Differences based on sex and eccentricities were analysed with Mann–Whitney U-test and Friedman test, respectively. Finally, when multiple analyses were performed between central refraction and RPRE, a P value <0.01 was considered statistically significant.

Results

A total of 138 participants (106 male and 32 female; aged 20–29 years [median, 23 ± 4 years]) were included in the study. All participants had normal visual acuity of 0.00 ± 0.00 LogMAR (20/20). The central distance refraction was similar between male (–1.00 ± 1.50 D, range +2.25 D to −8.00 D) and female (–1.12 ± 1.25 D, range 0.25 to −5.75 D) participants (Mann–Whitney U = 876, P = 0.07). The central J0 and J45 were similar between male and female participants (00 ± 0.50 for both categories). The central distance refraction in male and female participants for the different refractive groups is summarized in Table 1. Overall, 31 participants were categorized with emmetropia, seven with hyperopia, 80 with low myopia, 15 with moderate myopia, and five with high myopia. The M, RPRE, J0 and J45 values at temporal-nasal eccentricities are reported in Table 2.

Table 1.

Central distance refraction in 138 adults of Arabian ethnicity categorized according to different refractive groups.

Refraction classification	Subgroup		Overall
Refraction classification	Male(n = 106)	Female(n = 32)	Overall
Emmetropia, D	−0.12 ± 0.25	−0.25 ± 0.3	−0.25 ± 0.25
Low myopia, D	−1.25 ± 1.00	−1.25 ± 0.80	−1.25 ± 1.00
Moderate myopia, D	−3.00 ± 1.75	−5.25 ± −1.25	−3.00 ± 1.5
High myopia, D	−6.25 ± 1.25	–	−6.25 ± 1.25
Hyperopia, D	+1.80 ± 1.00	–	+1.80 ± 1.00

Data presented as median ± interquartile range.

Table 2.

Refraction characteristics at peripheral eccentricities in 100 adults with myopia of Arabian ethnicity.

Refraction characteristic	Visual field
	Temporal		Nasal
	–15°	–35°	15°	35°
M	−1.00 ± 1.25	−1.25 ± 1.75	−0.75 ± 1.50	−1.00 ± 1.75
RPRE	00 ± 1.00	−0.25 ± 1.50	00 ± 1.50	−0.25 ± 1.75
J₀	00 ± 0.50	00 ± 0.50	00 ± 0.50	00 ± 0.50
J₄₅	00 ± 0.75	00 ± 0.50	00 ± 0.50	00 ± 0.75

Data presented as median ± interquartile range.

M, spherical equivalent; RPRE, relative peripheral refractive errors; J0, 90° to 180° astigmatism; J45, 45° to 135° astigmatism.

The RPRE varied across the refractive groups (Figure 2). Of note, participants with emmetropia displayed a myopic RPRE. In participants with low myopia, the RPRE was relatively hyperopic, while participants with moderate myopia exhibited more hyperopic peripheral refraction, with the nasal visual filed being more hyperopic. In participants with high myopia, the RPRE was more comparable to those with low myopia. Lastly, participants with hyperopia exhibited a myopic RPRE in both the nasal and temporal visual fields (>−0.50 D).

Figure 2.

The median relative peripheral refractive error (RPRE) at temporal (−15° and −35°) and nasal (15° and 35°) visual field in 138 adults of Arabian ethnicity categorized according to different refractive groups.

The differences found at the four eccentricities were statistically significant (Friedman test, X² = 14.8, P = 0.001), but this asymmetry was not observed in J0 and J45 outcomes (Friedman test, X² = 0.50, P = 0.40, and X² = 0.43, P = 0.50, respectively). Asymmetry between temporal and nasal eccentricities was also observed in spherical equivalent (Friedman test, X² = 15, P = 0.001). When RPRE was compared within different refractive groups, it was also found to be statistically significant (Friedman test, X² = 435, P = 0.001).

A correlation of moderate strength was found between RPRE at the temporal-nasal eccentricities and central refraction (Table 3). Finally, no statistically significant relationship was found between central refraction and J0 and J45 value at temporal-nasal eccentricities (P > 0.05).

Table 3.

Correlation between relative peripheral refractive errors and central refraction at different eccentricities in 138 adults of Arabian ethnicity.

	Visual field
	Temporal		Nasal
	–15°	–35°	15°	35°
r	−0.54	−0.50	−0.42	−0.49
Statistical significance	P < 0.0001	P < 0.0001	P < 0.0001	P < 0.0001

Statistically significant at P < 0.01 (Spearman’s rank correlation coefficient).

Discussion

The present study investigated peripheral refraction in adult participants of Arabic ethnicity. Myopia and its progression is a serious ocular condition that requires proactive interventions.¹ By 2050, without effective interventions, visual impairment due to myopic macular degeneration is estimated to potentially affect 55.7 million people.²⁴ In a 2-year prospective study predicting myopia onset, subjects who developed myopia had hyperopic RPRE, while those who did not remained relatively myopic or emmetropic.³⁵ Other studies have also found that hyperopic RPRE does not manifest until the onset of myopia,^43,44 however, the hypothesis that hyperopic RPRE is causative for axial myopia, or that it may predict future myopia development, remains insufficiently proven.^32,45 Nonetheless, there is ample evidence in the literature suggesting that the focus state in the peripheral retina is linked to foveal refraction. Optical correction of peripheral refraction has shown clear clinical benefits, indicating a link to other aspects of peripheral visual image quality that may drive myopia.^32,45 Therefore, further investigation into the link between peripheral refraction and the development of axial myopia is needed.³² Understanding this link would enable the development of various types of optical correction that may help reduce its effect.

To the best of our knowledge, the present study is the first in Saudi Arabia to investigate the above issue. Adults were recruited into the study because myopia can continue to increase during adulthood,⁴⁶ and understanding myopia progression and the hyperopic defocus in myopia is crucial. Peripheral refraction was measured horizontally at 15° and 35° eccentricities, based on previous reports suggesting that peripheral refraction at these horizontal eccentricities is closely related to refractive development and eye growth.^25,38 The vertical meridian was not assessed, as previous studies have shown that individuals with either emmetropia or myopia displayed no hyperopic relative peripheral refraction, with both exhibiting relative peripheral myopia.^33,47

In agreement with previous studies, the present study showed that participants with myopia tend to have relative peripheral hyperopia, particularly in the nasal visual field.^26,30,48 The variability in RPRE from the median in the present population (Table 2) was similar to that reported in previous studies,^44,49 however, the variability of RPRE in the recruited participants was unexpected. Tabernero et al.³¹ who found similar results, discussed this in detail and suggested several interpretations that require validation in long-term studies.

The current participants with myopia showed increased eccentricity as relative hyperopic defocus increased, in agreement with previous reports.^26,36,46,50 Furthermore, the present results indicated that participants with hyperopia show peripheral relative myopic defocus, also in agreement with previous studies.⁴⁶ Additionally, a significant relationship was found between RPRE and central refraction, consistent with previous studies that found significant correlations between RPRE beyond 20° and myopia.^25,38 Finally, temporal–nasal asymmetry in RPRE was noted. Previous studies have suggested that changes in RPRE are more pronounced in the nasal visual ﬁeld than in the temporal visual ﬁeld.^30,51

Although the J0 and J45 results appeared to vary in the present study, and changed according to eccentricities, these changes were not statistically significant, consistent with previously published findings.⁴⁸ This result also aligns with the J45 scores from another study, but contrast with their findings on J0.⁵² Furthermore, no significant relationship was found in the present study population between peripheral J0 and J45 values and foveal refraction. The study by Ehsaei et al.⁵² did not explore this relationship, but the study by Radhakrishnan et al.⁴⁸ found a correlation only between J45 on the nasal side at 20° and myopia (Pearson’s correlation coefﬁcient = –0.27; P = 0.004). This reported correlation was of weak strength, explaining only 7% of the variation between the two variables. The changes in J0 and J45 across different eccentricities may be attributed to the high variability in peripheral refraction and ocular shape,^53,54 which is common in human eyes.

The present outcomes align with a previous study of Chinese children,³⁸ in which RPRE was shown to increase with eccentricities. However, the previous study did not specify the nasal-temporal visual field,³⁸ and the present results indicated a higher hyperopic defocus in moderate myopia. Regarding high myopia, the hyperopic defocus was lower than in moderate myopia in both the present and previously published study,³⁸ which might suggest that refractive status is more stable at this stage. In another study, peripheral refraction was investigated in white and East Asian adult participants.²⁵ East Asian participants with moderate myopia were reported to exhibit a greater degree of RPRE hyperopia than white participants. The present results were comparable to the previously reported data that showed increasing RPRE with eccentricities,²⁵ although the present findings in moderate myopia were higher than the published study in the nasal visual field of East Asian participants. Based on the current findings, which showed larger hyperopic defocus than in white and East Asian individuals, it is possible that the present population may be at a comparable or higher risk of myopia than East Asian populations.

Some customized lenses that induce uniform peripheral defocus have been designed to slow myopic progression, using power based on average data rather than individual values.^55,56 Some of these lenses have shown effectiveness in reducing myopia progression;^57–59 however, to precisely correct peripheral refraction and induce the appropriate amount of peripheral defocus, lens deign should be based on accurate individual peripheral refraction data, which may vary significantly between individuals. The high variability in peripheral refraction across all refractive groups may be attributed to individual differences in retinal contour or shape.⁵³ This variation may limit the effectiveness of a uniform lens design in slowing myopic progression, highlighting the need for individual correction and lens designs.^31,46 A major limitation of this intervention, as well as other myopia interventions, is the shortage of long-term follow-up studies.¹ These scientific debates underscore the importance and contribution of this work for future studies.

Limitations

The results of the present study may be limited by the cross-sectional study design, which restricts its ability to determine whether peripheral hyperopic defocus is a cause of myopia. In addition, the findings only demonstrate that RPRE at eccentricities between 15° and 35° are associated with myopia. As cycloplegic refraction was not used, participants may have accommodated (up to 0.50 D) while viewing distant targets at 2 meters. Finally, the difference in sample sizes between male and female groups may have influenced the accuracy of the conclusions.

Conclusion

The findings of this study suggest that adults with myopia of Arabian ethnicity exhibited increasing peripheral hyperopic defocus, which was greater than that reported for individuals from other ethnic groups. There was more hyperopic defocus at 35° in both the nasal and temporal regions of the retina in young adults with myopia than at 15° eccentricities. These findings may be helpful for future designs of personalized lenses, including spectacles and contact lenses. Future studies are also needed to explore RPRE in children to develop a full profile of RPRE across all age groups. Further studies may also investigate the efficacy of personalized lenses for myopia control.

Footnotes

Author contributions

Ali Alsaqr: conceptualization; formal analysis; visualization; writing – original draft, review & editing; funding acquisition.

Manal Alharbi: supervision; formal analysis; writing – review & editing.

Noura Aldossary: supervision; formal analysis; writing – review & editing.

Abdulaziz Alruwished: methodology; investigation; data collection; review & editing.

Mohammed Alharbi: methodology; investigation; data collection; review & editing.

Khalid Alghaib: methodology; investigation; data collection; review & editing.

Abeer Alabdulkarim: methodology; investigation; data collection; review & editing.

Alhamdan Shatha: methodology; investigation; data collection; review & editing.

Ali Abusharha: supervision; formal analysis; writing – review & editing.

Data availability statement

All the relevant data have been provided in the manuscript. Supplementary datasets used and/or analysed during the current study are available from the corresponding author upon reasonable request.

Declaration of conflicting interest

The authors declare that there are no conflicts of interest.

Funding

The project was funded by the Researchers supporting project number (RSPD2024R854), King Saud University, Riyadh, Saudi Arabia.

ORCID iD

Ali Alsaqr

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