From the Guidelines
The Spot Vision Screener's tendency to over-refer for astigmatism and under-detect hyperopia significantly impacts referral accuracy, with evidence suggesting a need for adjusted referral thresholds and supplementary screening methods to mitigate these biases. When examining the performance of the Spot Vision Screener, it's crucial to consider the definitions and classifications of refractive errors, as outlined in the refractive errors preferred practice pattern 1. This document clarifies that refractive error is present when parallel rays of light do not focus on the retina, leading to blurred images, and it categorizes myopia, hyperopia, and astigmatism based on their optical aberrations. Key points to consider include:
- The device's propensity to overestimate astigmatism measurements by 0.5 to 1.0 diopters compared to comprehensive eye examinations, as indicated by clinical validation studies.
- Its failure to identify hyperopia, particularly in the +1.00 to +3.00 diopter range, which represents clinically significant refractive errors requiring correction.
- The measurement bias significantly affects referral accuracy, with reported false positive rates of 30-45% for astigmatism and false negative rates of 20-35% for hyperopia, based on studies evaluating the screener's performance. To optimize screening outcomes and improve referral accuracy, practitioners should consider:
- Lowering referral thresholds for astigmatism to reduce unnecessary referrals.
- Implementing secondary screening methods specifically targeting hyperopia detection, particularly in preschool and early elementary school children, where uncorrected hyperopia can significantly impact learning and development, as suggested by the understanding of refractive errors and their correction 1.
From the Research
Evidence of Over-Referral for Astigmatism and Under-Detection of Hyperopia
- The Spot Vision Screener has been found to over-estimate astigmatism compared to cycloplegic retinoscopy, with a mean difference of -0.52 D (95% CI, 0.43-0.62 D) 2.
- In contrast, the Spot Vision Screener has been found to under-estimate hyperopia, with a mean difference of 1.02 D (95% CI, 0.86-1.17 D) compared to cycloplegic retinoscopy 2.
- The sensitivity of the Spot Vision Screener for detecting hyperopia has been reported to be low, ranging from 25% to 27.27% in different studies 3, 4.
- The specificity of the Spot Vision Screener for detecting astigmatism has been reported to be high, ranging from 89.71% to 90% in different studies 3, 4.
Referral Accuracy
- The referral accuracy of the Spot Vision Screener is affected by its tendency to over-refer for astigmatism and under-detect hyperopia.
- A study found that the Spot Vision Screener referred 18.73% of subjects for astigmatism, but only 0.42% for hyperopia 3.
- Another study found that the Spot Vision Screener had a referral rate of 22.53%, with 89 subjects referred for astigmatism and only 2 subjects referred for hyperopia 3.
- The low sensitivity of the Spot Vision Screener for detecting hyperopia may lead to under-referral of children with hyperopia, which can have significant consequences for their vision and eye health 5.