Diversity of Peripheral Refraction Patterns—Have These Been Oversimplified?

Abstract

Purpose

To describe patterns of peripheral refraction based on spherical equivalent refraction and on tangential and sagittal refractions, and to assess the association of peripheral refraction patterns with different central refractions.

Methods

Peripheral refraction data from 737 individuals (14.7 ± 5.1 years old) were analyzed. Peripheral refraction was determined along the horizontal field at ±30° eccentricity using an open-field autorefractor in 89 hyperopes, 276 emmetropes, and 372 myopes. Values were converted into spherical equivalent refraction and into tangential and sagittal refractions. Nine different peripheral refraction patterns (A–I) were described based on spherical equivalent refraction, and 81 patterns were described based on tangential and sagittal refractions.

Results

Using spherical equivalent refraction, all nine possible peripheral refraction patterns (A–I) were represented. Type I (relative peripheral myopia in nasal and temporal retinas) was seen in 40% of hyperopes, in 32% of emmetropes, and in 8% of myopes. Type A (relative peripheral hyperopia in nasal and temporal retinas) was seen in 20% of myopes and in ≤1% of hyperopes and emmetropes. No pattern was unique to any refractive group. Using tangential and sagittal refractions, 47 out of 81 possible patterns were represented. The three refractive groups shared 19 patterns in common. Hyperopes, emmetropes, and myopes had two, six, and eleven unique patterns, respectively.

Conclusions

Many types of peripheral refraction patterns were observed, and these may provide insights into the complexities of eye growth and myopiogenesis. Tangential and sagittal refractions should be considered to understand peripheral refraction rather than spherical equivalent refraction alone.

The concept of peripheral refraction dates back to Thomas Young, who in 1801 explained how light is focused on the retina based on tangential and sagittal refractions for a schematic eye.^1,2 For the horizontal visual field, tangential and sagittal refractions correspond to refraction along the horizontal and vertical directions, respectively. When pencils of rays of light enter the eye obliquely from a point source, they are focused to mutually perpendicular foci—namely, the tangential and the sagittal foci (Fig. 1A). The differences between these foci, given as refractions, represent the astigmatism in the periphery.³

Figure 1.

(A) The pencil of rays refracted in the tangential plane focuses at the tangential image focus and the pencil of rays refracted in the sagittal plane focuses at the sagittal image focus. (B) Possible patterns of peripheral refraction based on spherical equivalent refraction, denoted as types A to I. (C) Hexagram showing the possible patterns of peripheral refraction based on spherical equivalent refraction when nasal and temporal retinas are considered. (D) Octadecagon showing possible patterns of peripheral refraction based on tangential (T) and sagittal (S) refractions. RPH, relative peripheral hyperopia; RPM, relative peripheral myopia; RPE, relative peripheral emmetropia.

Peripheral refraction was determined using various techniques in the 19th and 20th centuries.^4,5 Ferree et al.^6–8 in 1931 determined peripheral refraction out to ±60° in the horizontal meridian using a Zeiss parallax refractometer and described three patterns of peripheral refraction. Type A was a common pattern in hyperopes and emmetropes, where tangential refractions became more negative (myopic) and sagittal refractions became more positive (hyperopic) with increasing eccentricity. Type B was a common pattern in myopes in which tangential and sagittal shells became more hyperopic toward the periphery. The type C pattern had asymmetrical refraction in nasal and temporal retinal halves. Rempt et al.⁹ in 1971 described five patterns (types I, II, III, IV, and V) of peripheral refraction using retinoscopy where types I, III, and IV resembled types B, A, and C of Ferree et al.,^6–8 respectively. Mathur and Atchison¹⁰ reported a new pattern in 2013 that had characteristics of the type IV of Rempt et al.⁹ (relative hyperopia along the vertical and relative myopia along horizontal meridian) out to 40° to 50° before behaving like type I (both meridians having relative hyperopia).

Following the conclusion of Hoogerheide et al.¹¹ that pilots with relative peripheral hyperopia had increased risk of developing myopia, peripheral refraction has been extensively studied in humans^12–15 and animals,^16–20 with the outcomes from animal studies indicating the importance of peripheral retinal signals in regulating ocular growth. Rosén et al.²¹ determined that the claim by Hoogerheide et al.¹¹ that relative peripheral hyperopia predicts myopia development was a misconception, as their peripheral refraction measurements were probably taken at a later time point, after myopia had or had not developed. Although a few studies have reported links^22,23 between relative peripheral hyperopia and myopia development or progression, there are others that have not shown such an association.^24–26

The association between relative peripheral refraction and central refraction appears to be oversimplified in the literature, with an emphasis on spherical equivalent refraction and neglect of the tangential and sagittal refractions. When refraction along the nasal and temporal retinas is considered, there are nine theoretical combinations of peripheral refraction based on spherical equivalent refraction (Figs. 1B, 1C), and there are 81 theoretical peripheral refraction patterns based on tangential and sagittal refraction (Fig. 1D). Although several studies have reported that hyperopes and emmetropes have relative peripheral myopia and myopes have relative peripheral hyperopia based on spherical equivalent refraction,^{12–14,22,24,25,27–30} only a few studies^{8–10,23,31,32} have considered tangential and sagittal refraction. Analyzing spherical equivalent refraction alone might not be sufficient for understanding a role of peripheral refraction in myopia development. Ferree et al.⁶ (three patterns), Rempt et al.⁹ (five patterns), and Mathur and Atchison¹⁰ (six patterns) described peripheral refraction patterns based on tangential and sagittal refractions, and our study extended this work by considering 81 patterns. As a fundamental step, we aimed to determine the distribution of patterns of peripheral refraction based on spherical equivalent refraction and on off-axis tangential and sagittal refractions and to assess the association of these patterns in the nasal and temporal retinas with different central refractions.

Methods

Peripheral refraction data of 737 individuals of Indian race (49% male and 51% female) ages 5 to 33 years were analyzed to investigate the distribution of patterns of peripheral refraction based on (1) spherical equivalent refraction and (2) tangential and sagittal refractions. Figure 2 shows the methodology flowchart. Participants were patients and staff of LV Prasad Eye Institute in Hyderabad and students from school screening camps for whom peripheral refraction was determined as a part of comprehensive examinations. The spherical equivalent refraction of the participants ranged from +3.25 diopters (D) to −17.00 D. None of the participants had astigmatism (cylinder) greater than 1.75 D nor other conditions that might influence the refractive status of eyes.

Figure 2.

Methodology flowchart. M, spherical equivalent refraction.

The study adhered to the tenets of the Declaration of Helsinki. Approval from the Institutional Ethics Review Board of the LV Prasad Eye Institute was acquired before commencement. The study included participants from schools and patients from our myopia clinic. Convenience sampling was used, and retrospective data were collected from previous studies (84%) and from electronic medical records (16%) where peripheral refraction data were available. Out of 1045 participants screened, peripheral refraction data were available for 737. Informed consent was obtained from all participants or their guardians for participants < 18 years of age, as part of the specific study (approval number LEC 02-18-043), and from patients who consulted in the clinics.

Measurement of Peripheral Refraction

The central and peripheral refractions along the horizontal field meridian were determined at 30° nasal and temporal retinal eccentricities using an open-field autorefractor (NVision-K 5001; Shin-Nippon, Tokyo, Japan) for both eyes. The fixation target (Maltese cross) was placed 3 meters away on a flat wall to minimize the effect of accommodation. For 33% of participants (n = 246), central and peripheral refractions were determined 30 minutes after the administration of 1% tropicamide (two drops, 5 minutes apart). The open-field autorefractor permits power resolutions of 0.12 D and 0.25 D for both sphere and cylinder adjustments. For this study, a 0.25-D increment was employed, consistent with previous research.³³ Participants were instructed to keep their heads fixed on the headrest and rotate their eyes to fixate the center of the target. This method was adopted because no differences in measurements were reported previously between eye rotation and head rotation while measuring peripheral refraction.³⁴ The instrument was aligned with the participant's eye, and the mires were focused at the geometric center of the pupil. Three readings were taken at each position, and the manufacturer's representative value was used. The representative value and an average are usually similar.³⁵

The central and peripheral refraction readings along the horizontal visual field in the right eye, obtained as sphere Sp, cylinder C, and axis θ, were converted into spherical equivalent refraction M, tangential refraction T, and sagittal refraction S, as described by Atchison and Smith³:

$$M=Sp+C/2$$

$$T=Sp+C\mathrm{si}{\mathrm{n}}^2\theta$$

$$S=Sp+C\mathrm{co}{\mathrm{s}}^2\theta$$

As mentioned earlier, for refraction in the horizontal visual field, tangential and sagittal meridians correspond to the horizontal and vertical meridians in the pupil, respectively. For example (Fig. 3), for −3.00 DS/−1.00 DC × 180°, the tangential refraction is −3.00 D and the sagittal refraction is −4.00 D.

Figure 3.

(A) Illustration of the focus of light rays for the example of −3.00 DS/−1.00 DC × 180° for a horizontal visual field location. (B) The solid dark blue line shows the tangential (T) refraction, and the dashed red line shows the sagittal (S) refraction. The dotted line represents the retina (R).

Participants were classified into refractive groups based on baseline central spherical equivalent values. Participants with central spherical equivalent refraction ≥ +0.50 D were grouped as hyperopes, those with spherical equivalent refraction between −0.50 D and +0.50 D as emmetropes, and those with spherical equivalent refraction ≤ −0.50 D as myopes.

Relative peripheral refraction was determined by deducting the central values from peripheral values. Positive values ≥ 0.50 D indicated relative peripheral hyperopia, and negative values ≤ −0.50 D indicated relative peripheral myopia. Values within −0.50 D and +0.50 D were considered as relative peripheral emmetropia. Based on our previous report,³³ the repeatability for peripheral refraction using an open-field autorefractor was found to be 0.16 D (95% confidence interval [CI], 0.08–0.24). Therefore, we choose a 0.50-D cutoff for relative peripheral refraction considering the repeatability of the instrument.

Patterns of peripheral refraction were based on spherical equivalent refraction and tangential and sagittal refractions. For each region (i.e., nasal and temporal) we have three possible peripheral refraction profiles: relative peripheral hyperopia, relative peripheral myopia, and relative peripheral emmetropia. The number of possible patterns based on spherical equivalent refraction is 3 (nasal) × 3 (temporal) = 9 patterns (types A–I) (Figs. 1A–1C). The number of possible patterns based on tangential and sagittal refractions is 9 (tangential refraction) × 9 (sagittal refraction) = 81 patterns (types 1–81) (Fig. 1D). A common pattern was defined as one that was shared by at least two participants in each refractive group. Unique patterns were defined as patterns that were specific to only one refractive group.

Statistical Analysis

Statistical analysis was performed using SPSS Statistics 26 (IBM Corporation, Chicago, IL, USA) and Excel 2021 (Microsoft, Redmond, WA, USA). Descriptive analysis was conducted for age and refraction. The Shapiro–Wilk test indicated that spherical equivalent refraction and age were not normally distributed; therefore, non-parametric tests were employed for the analysis. The Kruskal–Wallis test was used to compare the refractive groups. The Wilcoxon signed-rank test was used to compare the peripheral refraction between the nasal and temporal retina. Statistical significance was considered as P < 0.05. No statistical analysis was done to compare the patterns based on spherical equivalent and tangential and sagittal refractions.

Results

Participant ages, spherical equivalent refractions, and relative peripheral refractions were significantly different among hyperopes, emmetropes, and myopes (P < 0.01) (Table). Based on spherical equivalent refraction, relative peripheral myopia in both nasal and temporal retinas occurred in the hyperope group (median [Q1, Q3]: nasal, −0.62 D [−1.00 D, −0.25 D]; temporal, −0.62 D [−1.00 D, 0.00 D]; P = 0.18) and in the emmetrope group (nasal, −0.50 D [−0.75 D, −0.12 D]; temporal: −0.50 D [−1.00 D, 0.00 D]; P = 0.11). Relative peripheral emmetropia in both nasal and temporal retinas occurred in the myope group (nasal, 0.00 D [−0.62 D, 0.50 D]; temporal, 0.37 D [−0.25 D, 1.00 D]; P < 0.001).

Table.

Participant Ages, Spherical Equivalent Refractions, and Relative Peripheral Refractions in Different Refractive Groups and Myopic Subgroups (Mild, Moderate, and High Myopes)

Refractive Group	Age (Y), Median (Min–Max)	SER (D), Median (Q1, Q3)	RPSER (D), N30 Median (Q1, Q3)	RPSER (D), T30 Median (Q1, Q3)	RPTR (D), N30 Median (Q1, Q3)	RPTR (D), T30 Median (Q1, Q3)	RPSR (D), N30 Median (Q1, Q3)	RPSR (D), T30 Median (Q1, Q3)
Hyperopes	17 (10–32)	0.75 (0.50, 1.12)	−0.62 (−1.00, −0.25)	−0.62 (−1.00, 0.00)	−1.23 (−1.66, −0.74)	−1.28 (−1.98, −0.90)	−0.04 (−0.53, 0.42)	0.40 (−0.29, −0.97)
Emmetropes	14 (10–33)	0.00 (−0.12, 0.25)	−0.50 (−0.75, −0.12)	−0.50 (−1.00, 0.00)	−0.92 (−1.33, −0.46)	−1.25 (−1.95, −0.72)	−0.02 (−0.28, 0.35)	0.24 (−0.14, 0.71)
Myopes	13 (5–33)	−3.37 (−5.12, −2.00)	0.00 (−0.62, 0.50)	0.37 (−0.25, 1.00)	−0.64 (−1.43, 0.06)	−0.50 (−1.25, 0.13)	0.62 (−0.05, 1.22)	1.34 (0.75, 1.99)
P	<0.001	<0.001	<0.001	<0.001	<0.001	<0.001	<0.001	<0.001
Mild myopes	14 (6–33)	−1.87 (−2.37, −1.25)	−0.12 (−0.50, 0.37)	0.25 (−0.37, 0.75)	−0.64 (−1.13, 0.01)	−0.58 (−1.22, −0.03)	0.50 (−0.04, 0.89)	0.99 (0.45, 1.60)
Moderate myopes	13 (5–29)	−4.25 (−5.00, −3.50)	0.12 (−0.62, 0.75)	0.50 (−0.12, 1.12)	−0.50 (−1.46, 0.24)	−0.44 (−1.29, 0.19)	0.75 (0.00, 1.38)	1.45 (0.92, 2.13)
High myopes	12 (5–29)	−7.25 (−8.75, −6.37)	−0.18 (−1.00, 0.75)	0.56 (−0.12, 1.75)	−0.83 (−1.88, 0.18)	−0.35 (−1.36, 0.87)	0.60 (−0.50, 1.54)	1.78 (1.07, 2.83)
P	0.01	<0.001	<0.20	<0.001	0.11	0.20	0.08	<0.001

N30, nasal 30°; RPSER, relative peripheral spherical equivalent refraction; RPSR, relative peripheral sagittal refraction; RPTR, relative peripheral tangential refraction; SER, spherical equivalent refraction; T30, temporal 30°.

Peripheral Refraction Patterns Based on Spherical Equivalent Refraction

For a more comprehensive analysis, nine possible combinations of peripheral refraction patterns were considered and denoted as types A to I (Fig. 1B). These patterns were arranged from type A, indicating maximum relative hyperopia, to type I, indicating maximum relative myopia. The distributions of peripheral refraction patterns are shown in Figure 4 with the patterns arranged based on descending order of their occurrence in myopes. Among the nine possible peripheral refraction patterns, all refractive groups exhibited all nine patterns, and there was no unique pattern specific to any refractive group. The type I pattern (i.e., relative peripheral myopia in both nasal and temporal retinas) occurred in 40% of the hyperopes, 32% of the emmetropes and 8% of the myopes. Among all myopes, type A (i.e., relative peripheral hyperopia along both meridians) was seen in 20%, followed by type C (i.e., relative peripheral emmetropia in the nasal retina and relative peripheral hyperopia in the temporal retina, 17%) and by type D (i.e., relative peripheral emmetropia in both nasal and temporal retinas, 15%). The subgroup analysis of myopes revealed that 20% of mild myopes showed the type D pattern, whereas 26% of moderate myopes and 20% of high myopes showed the type A pattern.

Figure 4.

(A, B) Donut plots illustrating the distribution of peripheral refraction patterns based on spherical equivalent in hyperopes, emmetropes, and myopes (A) and in myopic subgroups (B). Each ring corresponds to one of the three refractive groups or subgroups. N, nasal; T, temporal. *Values ≤ 3%.

Peripheral Refraction Patterns Based on Tangential and Sagittal Refractions

Based on median values of peripheral tangential refraction, relative peripheral myopia in both nasal and temporal retinas was observed in the three refractive groups. Based on peripheral sagittal refraction, relative peripheral emmetropia occurred in the hyperope and in the emmetrope groups, whereas relative peripheral hyperopia was observed in the myope group.

Sagittal refraction in the temporal retina was relatively more hyperopic than tangential refraction in all refractive groups and myopic subgroups. The relative peripheral sagittal hyperopia in the temporal retina was higher in myopes than in non-myopes, and it increased with the severity of myopia.

Pattern details and the distribution for all 81 patterns across refractive groups are shown in Supplementary Table S1. Forty-seven patterns occurred, with 47% (22/47) occurring in the hyperope group, 70% (33/47) occurring in the emmetrope group, and 82% (39/47) occurring in the myope group. Figure 5A shows the overall distributions of patterns in the refraction groups. Visual representation of the unique patterns observed in refractive groups is presented in a Venn diagram (Figs. 5B, 5C). Two, six, and 11 patterns were specific to the hyperope group, emmetrope group, and myope group, respectively. In the myopic subgroups, the mild, moderate, and high myope groups displayed five, three, and one unique patterns, respectively. Figure 6 shows the common and top five occurring patterns in the different refractive groups and myopic subgroups. The three refractive groups and myopic subgroups had 40% (19/47) of patterns in common. Type I, where both tangential and sagittal refractions became myopic towards the periphery, occurred in 11% of the hyperope group followed by 4% of the emmetrope group and 1% of the myope group. Type XI, where both tangential and sagittal refractions showed relative peripheral hyperopia, occurred in only 4% of the myope group. Hyperopes and emmetropes did not exhibit this pattern.

Figure 5.

(A) Sparklines indicating the distribution of patterns of peripheral refraction in hyperopes, emmetropes, and myopes. (B, C) Venn diagram representing patterns in the refractive groups (B) and myopic subgroups (C). Fifteen patterns were common among the refractive groups.

Figure 6.

(A, B) Common patterns and top five patterns observed in hyperopes, emmetropes, and myopes (A) and in myopic subgroups (B). The solid dark blue lines indicate tangential refraction, and the dashed red lines indicate sagittal refraction.

Out of the 19 patterns commonly observed among the refractive groups, for tangential refraction eight patterns had nasotemporal relative peripheral myopia, 11 patterns had nasotemporal asymmetry and none had nasotemporal relative peripheral hyperopia. For these 19 patterns and sagittal refraction, one pattern had nasotemporal relative peripheral myopia, four patterns had nasotemporal relative peripheral hyperopia, and 14 patterns had nasotemporal asymmetry.

Out of the 19 commonly observed patterns among the myopic subgroups, for tangential refraction, five patterns had nasotemporal relative peripheral myopia, one pattern had nasotemporal relative peripheral hyperopia and 13 patterns had nasotemporal asymmetry. For these 19 patterns and sagittal refraction, eight patterns had relative peripheral hyperopia, 11 patterns had nasotemporal asymmetry, and none had relative peripheral myopia.

Discussion

Peripheral refraction patterns were described for 737 participants along the horizontal meridian at ±30° eccentricity. Based on spherical equivalent refraction, all groups exhibited all nine patterns. Based on tangential and sagittal refractions, 47 of the 81 patterns occurred in individuals with 19 patterns shared among the refractive groups. Hyperopes showed 22 of 47 patterns, emmetropes showed 33 of 47 patterns, and myopes showed 39 of 47 patterns. Although a number of patterns occurred across these groups, there was no dominant pattern.

The current study has resemblances to certain patterns in the study by Rempt et al.⁹ Type II (relative peripheral myopia in tangential refraction and relative peripheral hyperopia in sagittal refraction), occurred in 3% of hyperopes, 2% of emmetropes, and 7% of myopes. This pattern resembles the type IV pattern described by Rempt et al.⁹ that occurred in 72% of hyperopes, 62% of emmetropes, and 20% of myopes. Type I (relative peripheral myopia in both tangential and sagittal refractions) occurred in 11% of hyperopes, 4% of emmetropes, and 1% of myopes. This resembles the type V pattern of Rempt et al.,⁹ which occurred in 20% of hyperopes, 7% of emmetropes, and 0.7% of myopes. Type XI (relative peripheral hyperopia in both tangential and sagittal refractions) occurred in 4% of myopes. It resembles the type I pattern of Rempt et al.⁹ that occurred in 2% of hyperopes, 6% of emmetropes, and 64% of myopes.

Despite the similarities in the patterns, the current study shows lower percentages for types II and XI than the types IV and I of Rempt et al.,⁹ respectively. Variations in optical properties of the eye, including the gradient refractive index of the lens,³⁶ corneal curvature, anterior chamber depth,³⁷ and retinal shape,³⁸ will contribute to the range of patterns. The foveal pit is approximately 5° to the temporal side of the optical axis; this has to be a major contributor to asymmetry of patterns. Our findings are in accordance with previous literature that reported asymmetric peripheral refraction profiles³⁰ in an Indian population and asymmetric eye shapes in other ethnicity.³⁹ The presence of these patterns challenges the simplified links often made between peripheral refraction and central refraction. Based on tangential and sagittal refraction, 61% and 52% of all participants, respectively, exhibited nasotemporal symmetrical patterns. It is possible that specific combinations of peripheral refraction contribute to myopia progression.

As well as the 0.50-D cutoff for defining relative peripheral patterns, we considered what would happen with a 0.25-D cutoff. Based on the spherical equivalent refraction criteria, both myopes and emmetropes exhibited all nine patterns, and hyperopes exhibited eight patterns (see Supplementary Fig. S2). Using the tangential and sagittal refractions, 51 of the 81 patterns occurred in individuals, with 15 patterns shared between the refractive groups (see Supplementary Figs. S3, S4).

After Hoogerheide et al.¹¹ reported a possible link between peripheral refraction and myopiogenesis, there have been studies that support and studies that do not support this idea. Mutti et al.¹² reported that Asian children (6–14 years old) who developed myopia had relative peripheral hyperopia in the temporal retina before the onset of myopia. For white children (6–7 and 12–13 years old), Leighton et al.²² found that relative peripheral hyperopia in the nasal retina had an increased risk of myopia progression after 1 year. For adolescent myopes (14–22 years), Radhakrishnan et al.¹³ found an increase in relative peripheral hyperopia in the nasal retina after 2 years, but peripheral refraction did not predict myopia progression into the future. Faria-Ribeiro et al.²³ found that the relative peripheral tangential and sagittal refraction in progressive myopes had greater magnitudes of relative peripheral hyperopia when compared with non-progressors. Although Lin et al.⁴⁰ indicated that relative peripheral myopia at 10° superior retina in emmetropic Chinese children (8–15 years old) could serve as a predictor for myopia development, Zheng et al.,⁴¹ using two-dimensional multispectral refraction topography out to 45° in Chinese adults, found that retinal regions between 20° and 45° may be related to myopia development.

Other studies do not support the pattern of peripheral refraction influencing the development of myopia. Mutti et al.,²⁵ for 2043 children of various ethnicities, reported that relative peripheral hyperopia had minimal influence on myopia onset and progression. Other longitudinal studies^24,42,43 conducted in children have reported that baseline relative peripheral refraction did not correlate with myopia progression at follow-up visits. Lin et al.⁴⁴ observed no significant changes in the peripheral refraction patterns in Chinese children (9–16 years old) over a period of 2 years.

Although there is a debate on a potential role of peripheral refraction in ocular growth, clinical trials on humans with peripheral defocus spectacles, multifocal contact lenses, and orthokeratology that induce relative peripheral myopia indicate good efficacy of these treatments.^45–54 However, there were non-responders or slow responders (15%–20%) who showed minimum efficacy to these treatment modalities. In addition, for one particular spectacle lens type (defocus incorporated multiple segments), there is a reported finding that children with baseline relative peripheral myopia show statistically significant greater axial elongation and myopia progression over 2 years than children with baseline relative peripheral hyperopia (0.34 ± 0.24 mm vs. 0.19 ± 0.20 mm; −0.72 ± 0.64 D vs. −0.31 ± 0.48 D).⁵⁵ Some studies have found poor correlation between relative peripheral refraction and relative peripheral multifocal electroretinogram signals.^56,57

The use of peripheral refraction by the visual system to control myopia progression is not understood. The diverse peripheral refraction patterns and the mixed evidence regarding the role of peripheral refraction in myopia development raise questions: Are any specific meridians, eccentricities, or magnitudes of defocus important in myopia management? Is there a need to consider tangential and sagittal refractions? In addition to peripheral defocus, are there other factors and mechanisms governing axial elongation, such as that high contrast between adjacent cones inducing axial elongation (contrast theory)?⁵⁸ The findings of this study show that there was relative tangential peripheral myopia in both nasal and temporal retinas in the three refractive groups, relative sagittal peripheral emmetropia in the non-myopic groups, and relative sagittal peripheral hyperopia in the myope group, based on the median values, with large variation seen through the wider interquartile range, demonstrating the complexity of peripheral refraction patterns. The diverse patterns observed in tangential and sagittal peripheral refraction show the inadequacy of considering only the simplified measure of spherical equivalent refraction in peripheral refraction. Our findings show considerable variability in relative peripheral refraction, with no specific refractive errors having unique patterns.

Ganglion cells in the retina have radially extended receptive fields⁵¹ that are orientation sensitive⁵² and may be used to compare the positions of tangential and sagittal foci to identify the defocus sign in regulating ocular growth.^59,60 There could be a particular region in the peripheral retina particularly sensitive or responsive to tangential or sagittal foci locations and different magnitudes of defocus signals. Experiments conducted by Smith et al.⁶¹ indicated that, in cases of mixed astigmatism (tangential foci located anterior and sagittal foci located posterior to retina), ocular growth occurs to reposition the retina toward the posteriorly located focus, but in compound astigmatism (tangential and sagittal foci located posterior to retina) the ocular growth acts to reposition retina toward the less posterior foci.

The strengths of the study lie in the heterogeneity of data and the inclusion of both spherical equivalent refraction and tangential and sagittal refraction, which provided an extended approach to peripheral refraction patterns. The study has a few limitations. The vertical field was not investigated, and measurement was taken at only ±30° horizontal field eccentricities, so that patterns are specific to these locations. Due to the cross-sectional nature of this study, it was not possible to identify any specific pattern of peripheral refraction linked with myopia progression. We did not analyze how peripheral refraction patterns varied with age due to the uneven age distribution across the different refractive groups. Further research is warranted to explore how peripheral refraction patterns based on tangential and sagittal refractions vary with age. In addition, we lacked information to help determine how different the biometries were in the participants having different peripheral refraction patterns. Considering that the fixation targets were positioned at a distance of 3 meters and peripheral refraction was not measured under cycloplegia for all participants, existing studies^62–66 indicate that accommodation has minimal or no influence on relative peripheral refraction. As is usual, the refractions were determined without spectacle or contact lens correction. If corrections had been used, there would have been some change to the patterns; for example, spectacle correction for myopia usually shifts relative peripheral refraction in the negative (hyperopic) direction.⁶⁷

In conclusion, this study revealed the diverse and complex nature of peripheral refraction, thus providing further insights into the complexities of eye growth and myopiogenesis. Although there is some evidence from animal studies highlighting the importance of peripheral retina on ocular growth, the inference that “relative peripheral hyperopia” based on spherical equivalent refraction triggers axial elongation in humans appears oversimplified. In addition to spherical equivalent refraction, tangential and sagittal refractions need be taken into account in order to comprehend peripheral refraction.