Horizontal relative peripheral refraction and astigmatic vector patterns in Chinese young myopic subjects

Background

The relationship between the relative peripheral refraction (RPR) of retina and the development of myopia has recently become the concerns for researchers.However, there have been few data on the RPR and the astigmatic vector patterns in myopic populations.It is needed to study the RPR and the astigmatic vector patterns in the Chinese young myopic subjects.

Objective

The RPR and astigmatic vector patterns were determined in Chinese young myopic subjects.

Methods

This prospective study comprised 301 Chinese young myopic subjects who visited ophthalmology department of Peking University People’s Hospital from June 2014 to October 2015.Horizontal peripheral refractions were measured in 5° steps out to 30° eccentricity in both the nasal and temporal visual fields using Grand Seiko WAM-5500 autorefractor.Only data from the right eyes were used for analyses.Spherical equivalent refractions (SER) at each angular position were calculated and the relative peripheral refractive errors (expressed as defocus) were determined by subtracting the peripheral SER from the central SER.The RPR was categorized based on the shapes of peripheral refractive curves and the relative positions in the nasal or temporal retinal regions.Astigmatism at each angle was decomposed into J₀ and J₄₅ vectors based on Fourier decomposition and the curve patterns for the astigmatic vectors were examined.This study adhered to the tenets of the Declaration of Helsinki and was approved by the Human Research Ethics Committee of Peking University People’s Hospital.

Results

Seven types of relative peripheral refractive curves were identified (retinal regions)∶ negative defocus, temporal positive defocus and nasal flatness, temporal positive and nasal negative defocus, temporal flatness and nasal negative defocus, flatness in both temporal and nasal retina, temporal negative defocus and nasal flatness, and positive defocus.Patterns of astigmatic vector J₀ and J₄₅ were divided into 9 categories.The rate of type Ⅰ RPR was significantly greater in the moderate and high myopia group than that in the low myopia group (χ²=26.770, P<0.05). The rate of type Ⅲ was significantly greater in the low myopia group than that in the moderate and high myopia group (χ²=12.500, P<0.05).

Conclusions

The distributions of RPR were significantly different between low myopia group and moderate and high myopia group.There were nasal-temporal asymmetries for the absolute values of astigmatism along peripheral horizontal meridian.The absolute values of astigmatism in the nasal retinal regions were increased with the increase of fixation angles (except for the value at nasal 10°).