Table 1. Size of the image, prevalence of subretinal and intraretinal fluids, quality of the image, determinability of the chorio–scleral interface, choroidal thickness, and absolute value of intra-observer variability of the choroidal thickness measurement, according to the file format and the degree of compression.
| Findings |
File format and degree of image compression |
|||||
|---|---|---|---|---|---|---|
| TIFF (uncompressed) | JPEG (100% of quality) | JPEG (75% of quality) | JPEG (50% of quality) | JPEG (25% of quality) | JPEG (10% of quality) | |
| Before treatment (N=30) | ||||||
| Size of image (kb), mean±SD | 2210 | 435.8±40.9 | 109.0±16.8 | 72.6±11.7 | 46.4±7.2 | 25.8±3.1 |
| Subretinal fluid (+/−/undeterminable) | 28/2/0 | 28/2/0 | 28/2/0 | 28/2/0 | 28/2/0 | 28/2/0 |
| Intraretinal fluid (+/−/undeterminable) | 14/16/0 | 14/16/0 | 14/16/0 | 14/16/0 | 14/16/0 | 16/14/0 |
| Quality of image (A/B/C/D) | — | 30/0/0/0 | 19/11/0/0 | 3/21/6/0 | 0/13/17/0 | 0/0/30/0 |
| After three times of monthly intravitreal ranibizumab injections (N=30) | ||||||
| Size of image (kb) | 2210 | 460.5±41.3 | 120.3±17.4 | 80.7±12.3 | 51.3±7.8 | 28.0±3.7 |
| Subretinal fluid (+/−/undeterminable) | 8/22/0 | 8/22/0 | 8/22/0 | 8/22/0 | 8/22/0 | 8/21/0 |
| Intraretinal fluid (+/−/undeterminable) | 7/23/0 | 7/23/0 | 7/23/0 | 7/23/0 | 7/23/0 | 7/21/2 |
| Quality of image (A/B/C/D) | — | 30/0/0/0 | 22/8/0/0 | 2/18/10/0 | 0/15/15/0 | 0/0/30/0 |
| When relapse of the disease was noted (N=12) | ||||||
| Size of image (kb) | 2210 | 458.7±42.9 | 118.3±18.9 | 79.3±13.2 | 50.5±8.6 | 27.8±4.2 |
| Subretinal fluid (+/−/undeterminable) | 10/2/0 | 10/2/0 | 10/2/0 | 10/2/0 | 10/2/0 | 10/2/0 |
| Intraretinal fluid (+/−/undeterminable) | 6/6/0 | 6/6/0 | 6/6/0 | 6/6/0 | 6/6/0 | 6/6/0 |
| Quality of image (A/B/C/D) | 12/0/0/0 | 8/4/0/0 | 2/7/3/0 | 0/5/7/0 | 0/0/12/0 | |
| Determinability of subfoveal chorio–scleral interface and subfoveal choroidal thickness (N=30) | ||||||
| Size of image (kb), mean±SD | 2210 | 390.8±37.6 | 91.4±14.6 | 60.5±9.8 | 38.9±5.8 | 22.5±2.3 |
| Easily/hardly/undeterminable | 22/7/1 | 22/7/1 | 18/11/1 | 16/13/1 | 11/16/3 | 7/13/10 |
| Subfoveal choroidal thickness | 209.8±86.4 | 210.1±86.4 | 210.2±86.6 | 209.9±84.7 | 211.9±87.9 | 212.9±91.8 |
| ΔCT (μm), mean±SD | — | 9.5±4.7 | 9.4±7.2 | 10.6±7.4 | 16.0±11.1a | 18.2±12.3a |
Abbreviations: JPEG, Joint Photographic Experts Group; TIFF, Tag Image File Format.
The quality of the image was classified as follows: A: indistinguishable from uncompressed image; B: hardly distinguishable; C: easily distinguishable, but may not influence treatment decision; D: easily distinguishable, and improvement of quality of image will be necessary to establish the appropriate treatment decision. The determinability of subfoveal chorio–scleral interface was classified as follows: easily determinable, hardly determinable, and undeterminable. ΔCT indicates the absolute value of the difference in choroidal thickness between the TIFF and JPEG images.
Significant results when compared with intra-observer measurement variability in TIFF images.