Findings from a recent study published in the Journal of Ophthalmology assessed the characteristics of peripheral retinal refraction and its role in emmetropic, low, and moderate myopic children.
Give me some background.
Previous studies have indicated that peripheral defocus has an important influence on the growth of eyes.
- For example: Peripheral hyperopia defocus is a high-risk factor for the occurrence and progression of myopia.
Further: Eyes with emmetropia and hyperopia have a relative peripheral myopic refractive state, while eyes with myopia have a relative peripheral hyperopic refractive state.
This study combined the partitioning methods of previous studies and measured the retinal relative difference value (RDV) in different regions to explore the effect of peripheral retinal refractive status on myopia.
How do researchers measure peripheral defocus?
Multispectral refractive topography (MRT) is a new instrument that uses fundus images to detect the refraction of each part of the retina within a range of 45° at the posterior pole of the retina.
- How: Using these calculations, a computer algorithm develops a topographic map corresponding with values of the actual refractive power for each pixel point.
Talk about the study.
Investigators included 814 participants (814 eyes), and patients were divided into three groups according to the central spherical equivalent refraction (SER):
- Emmetropia (E) group
- Low myopia (LM) group
- Moderate myopia (MM) group
A Kruskal-Wallis test was used to analyze the differences in peripheral refraction for all the regions in the three groups.
In addition, a Spearman rank correlation was performed to elucidate correlations between SER, axial length (AL), and RDV.
Break down how they measured peripheral retinal refraction.
Researchers utilized MRT to measure the retinal absolute and relative RDVs in different regions.
Fundus images were divided into four sectors of RDV (i.e., superior, inferior, etc.), and then these partitions were further divided into three concentric areas of 15° intervals from the fovea:
- Superior RDV (SRDV)
- SRDV15, SRDV30, SRDV45, SRDV30-15, SRDV45-30, SRDV45
- Inferior RDV (IRDV)
- IRDV15, IRDV30, IRDV45, IRDV30-15, IRDV45-30, IRDV45
- Temporal RDV (TRDV)
- TRDV15, TRDV30, TRDV45, TRDV30-15, TRDV45-30, TRDV45
- Nasal RDV (NRDV)
- NRDV15, NRDV30, NRDV45, NRDV30-15, NRDV45-30, NRDV45
Findings?
The absolute value of RDV decreased with increasing degree of myopia in all regions (P < 0.01).
Participants with different refractive degrees had a varying relative value of RDV.
- For example: In the nasal position within 45° and temporal position within 30°, the peripheral retina exhibited significantly different relative hyperopic refractive statuses in all three groups (P < 0.05).
What about spherical equivalent refraction?
The study authors highlighted three key findings on RDV and SER:
- SER was negatively correlated with NRDV within 30°, especially in the range of NRDV30-15 (r = -0.141, P < 0.01)
- SER was positively correlated TRDV within 15° (r = 0.080, P = 0.023)
- SER was not significantly correlated with SRDV and IRDV
And axial length?
AL was positively correlated with NRDV within 30°, especially in the range of NRDV30-15 (r = 0.109, P = 0.002), and negatively correlated with TRDV within 15° (r = -0.095, P = 0.007).
Expert opinion?
The study authors noted that autorefractometers are currently the gold standard for testing refraction of the central retina.
Plus: A previous study demonstrated that “autorefractometry and MRT show high agreement in measuring central refraction, and MRT could provide a potential objective method to assess peripheral refraction.”
Take home.
These findings suggest that peripheral defocus has significant implications for the genesis of myopia.
This study found that the peripheral defocus of the horizontal direction, especially within the range of NRDV30, had a greater effect on the development of myopia in children.
Additionally, higher NRDV30 was associated with lower SER and longer AL.
Next steps?
As a key limitation of the study was the narrow range of samples collected; further studies with larger sample sizes are required to confirm these findings.