Diagnostic Tests for Myopia
Cycloplegic autorefraction with a threshold of ≤-0.50 diopters spherical equivalent is the gold standard diagnostic test for myopia, and should be combined with axial length measurement for comprehensive assessment. 1, 2
Primary Diagnostic Approach
The diagnosis of myopia requires objective measurement of refractive error under cycloplegia to eliminate accommodative influence, particularly critical in children and adolescents who have active accommodation 1. The consensus diagnostic threshold is a spherical equivalent refractive error of ≤-0.50 diopters, though this carries some classification bias risk 2.
Essential Diagnostic Tests
- Cycloplegic autorefraction: This is the definitive diagnostic standard, using cyclopentolate 1% to induce cycloplegia before automated refraction measurement 1, 3
- Axial length measurement: A-scan ultrasonography provides objective biometric data that correlates directly with myopic progression and helps distinguish axial myopia from refractive myopia 4, 2
- Corneal curvature radius measurement: When combined with axial length as an AL/CR ratio, this enhances diagnostic accuracy 1
Screening vs. Diagnostic Testing
Visual Acuity Screening Limitations
Uncorrected visual acuity (UCVA) alone demonstrates poor diagnostic accuracy with only 33.1% specificity when using the common 1.0 (20/20) cutoff, despite 97.7% sensitivity 1. For adolescents, a VA cutoff of 6/9.5 or worse reliably detects myopia with 97.8% sensitivity and 97.1% specificity, but this approach fails for hyperopia and astigmatism 3.
Optimal Screening Combinations
For school-based screening programs, combining UCVA with noncycloplegic refraction (NCR) achieves optimal accuracy (area under ROC curve 0.985), with age-specific cutoffs: 1
- Ages 4-6 years: UCVA <1.0 AND NCR <-0.25 D
- Ages 7-12 years: UCVA <1.0 AND NCR <-0.50 D
- Ages 13-15 years: UCVA <0.8 AND NCR <-0.75 D
The alternative combination of AL/CR ratio with NCR performs equivalently (area under ROC curve 0.987, p=0.208 for difference) 1.
Additional Diagnostic Considerations
Peripheral Refraction Assessment
Relative peripheral refractive error measured at 30 degrees in the nasal visual field provides predictive value for myopia onset, with children who become myopic showing more hyperopic peripheral refraction 2-4 years before onset 4. However, this remains primarily a research tool rather than routine clinical diagnostic test.
Critical Pitfall
Screening prevalence overestimates true myopia prevalence by 13.2% when using UCVA alone, but this reduces to only 4.7% when positive screens undergo cycloplegic refraction for confirmation 1. Always confirm screening-positive results with cycloplegic refraction before diagnosing myopia, especially in younger children where accommodation confounds noncycloplegic measurements.
Home-Based Testing Limitations
Web-based VA self-assessment tools show good agreement with clinic-based Snellen testing (mean difference 0.03 logMAR) and 94% sensitivity for detecting VA worse than 0.10 logMAR, but the refractive error algorithms overestimate myopia progression by 0.40 diopters and require recalibration for pediatric use 5.