Table 4.
Visual acuity by each testing method and factors that may affect the difference in results between methods
| Factor | No. of eyes | Visual Acuity Letter Score | Mean (SD) | |
|---|---|---|---|---|
|
| ||||
| Clinical (Snellen conversion)a | Protocol (eETDRS) | Difference (Protocol - Clinical)b | ||
|
| ||||
| Hemoglobin A1c | ||||
| <7.5% | 348 | 68.1 (16.3) | 76.5 (14.4) | 8.3 (9.5) |
| ≥7.5% | 668 | 68.9 (17.5) | 76.2 (16.2) | 7.2 (9.6) |
| Age | ||||
| <60 years | 541 | 70.9 (16.8) | 77.9 (15.7) | 6.9 (9.7) |
| ≥60 years | 475 | 65.9 (17.1) | 74.5 (15.3) | 8.4 (9.4) |
| OCT Central subfield thickness (Spectralis) | ||||
| <330 μm | 344 | 78.2 (7.6) | 86.4 (6.1) | 8.2 (6.8) |
| ≥330 μm | 672 | 63.7 (18.5) | 71.1 (16.5) | 7.3 (10.7) |
| Time between protocol and clinical visit | ||||
| <6 weeks | 806 | 67.4 (17.6) | 75.0 (15.9) | 7.5 (9.9) |
| ≥6 weeks | 210 | 73.3 (14.1) | 81.3 (13.5) | 7.9 (8.0) |
| Clinical VA correction method | ||||
| Refracted | 63 | 73.9 (18.9) | 78.0 (17.5) | 3.9 (9.0) |
| Glasses or contacts | 497 | 68.5 (16.9) | 75.5 (15.2) | 6.9 (9.2) |
| Pinhole only | 117 | 66.1 (18.0) | 74.4 (16.9) | 7.9 (11.5) |
| Uncorrected | 254 | 68.6 (17.3) | 78.5 (15.1) | 9.8 (9.3) |
| Protocol VA refractive error (spherical equivalent) | ||||
| > +1.50 | 94 | 65.9 (16.7) | 74.4 (15.9) | 8.6 (8.8) |
| +1.50 to +.625 | 193 | 66.2 (18.5) | 76.0 (15.3) | 9.5 (9.7) |
| +.50 to −.50 | 371 | 70.4 (16.1) | 77.7 (15.8) | 7.3 (8.7) |
| −.625 to −1.50 | 148 | 70.1 (15.9) | 78.5 (13.9) | 8.2 (10.1) |
| <−1.50 | 210 | 67.8 (18.1) | 73.5 (16.2) | 5.5 (10.6) |
| Protocol | ||||
| AC | 419 | 57.7 (17.9) | 64.6 (15.5) | 6.8 (11.7) |
| AE | 168 | 77.2 (9.8) | 83.9 (8.2) | 6.8 (6.9) |
| W | 429 | 75.8 (12.1) | 84.7 (9.4) | 8.7 (8.0) |
| Eye enrollment | ||||
| Fellow Eye | 434 | 70.5 (16.1) | 78.8 (14.8) | 8.1 (9.4) |
| Study Eye | 582 | 67.2 (17.7) | 74.5 (16.0) | 7.2 (9.7) |
| Lens status | ||||
| IOL | 192 | 69.8 (15.5) | 76.9 (14.2) | 7.0 (8.0) |
| Phakic | 824 | 68.3 (17.4) | 76.2 (15.9) | 7.7 (9.9) |
| Diabetic retinopathy severity | ||||
| No DR to moderate NPDR (< level 47) |
121 | 63.1 (16.3) | 70.1 (14.6) | 6.9 (10.1) |
| Moderately Severe NPDR (level 47) |
225 | 72.6 (14.6) | 80.2 (14.0) | 7.7 (8.1) |
| Severe NPDR (level 53) | 117 | 63.9 (20.0) | 71.8 (18.0) | 7.8 (11.2) |
| PDR (> level 53) or prior PRP |
48 | 52.2 (19.6) | 59.0 (13.6) | 6.4 (12.5) |
a
Converted letter score = 85 + 50 × log10(Snellen fraction), rounded to the nearest letter, or = 0 for Snellen fractions <20/800.
b
VA difference outliers were truncated at the raw overall mean ± 3 SD (7.7 ± 3 × 10.3).