Physiological disproportions between un-corrected vision and degree of myopia

School-based epidemiology study of myopia in Tianjin, China

PURPOSE

To study the epidemiology of myopia in school-aged children in Tianjin and the relationship between visual acuity-based screening and refraction-based screening.

METHOD

This school-based prospective cohort study was performed on children from 42 elementary schools and 17 middle schools in Tianjin, China. Totally 14,551 children, ages ranging from 5 to 16 years, were included in this study. Uncorrected visual acuity (UCVA) was determined by logarithmic tumbling E chart. Non-cycloplegic photorefraction was examined by the Spot (v2.1.4) photoscreener. The relationship between the UCVA and refractive error was investigated for different age groups.

RESULTS

The overall prevalence of myopia at this school based screen is 78.2%, ranged from 10% at age of 5 to 95% at age of 16. The most dramatic increase in prevalence is from age of 6 (14.8%) to age of 7 (38.5%). The overall prevalence of high myopia is 2.5%. UCVA is found corresponding to spherical equivalent refraction (SER) in a manner of normal distribution and is significantly affected by age. When using UCVA to estimate the prevalence of myopia, the overall sensitivity and specificity are 0.824 and 0.820, respectively. Age-dependent optimal cutoff points and 95% confident intervals of such estimation are reported.

CONCLUSIONS

Myopia is heavily affecting school-aged children in Tianjin, China. The refraction screening is preferable for myopia screening, whereas the UCVA screening results need to be interpreted in an age-dependent manner for myopia estimation.

Correlation of myopia severity with visual performance

PURPOSE

To describe visual performance in high myopia.

METHODS

In this cross-sectional study, 148 emmetropes [spherical equivalent (SE) - 0.50 to + 1.00 D] and 564 high myopes [SE ≤ - 6.00 D] were categorised into three groups (Group 1: SE - 6.00 to > - 8.00 D; Group 2: SE - 8.00 to > - 10.00 D; and Group 3: SE ≤ - 10.00 D). Multivariate regression analyses adjusting for age and ethnicity examined the relationship between corrected distance visual acuity (CDVA) [photopic, mesopic and super vision test-night vision goggles (SVT-NVG)] and contrast sensitivity (CS)] (mesopic and SVT-NVG) with SE and axial length (AL).

RESULTS

Mean age of subjects was 21.07 ± 1.17 years, and majority were Chinese (91.9%). Mean SE was 0.10 ± 0.23 D (emmetropes) and - 8.76 ± 2.04 D (high myopes), p < 0.001. Higher degrees of myopia were associated with reduced CDVA and CS, and increased AL (all p < 0.001). Among high myopes, Group 1 had the highest proportion of subjects with good CDVA (photopic ≤ 0.00 LogMAR, mesopic ≤ 0.00 LogMAR and NVG ≤ 0.10 LogMAR) and CS (mesopic ≥ 0.75 LogCS and NVG ≥ 0.35 LogCS) compared with Groups 2 and 3 (all p < 0.001). Among high myopes with good VA (photopic ≤ 0.00 LogMAR, mesopic ≤ 0.00 LogMAR and NVG ≤ 0.10 LogMAR), Group 1 also had the highest proportion of subjects who achieved mesopic ≥ 0.75 LogCS and NVG ≥ 0.35 LogCS (both p < 0.001). Multivariate analyses demonstrated that reduced VA and CS were associated with decreased SE and increased AL (all p < 0.001).

CONCLUSIONS

High myopia is associated with reduced VA and reduced CS.