OCT can provide a detailed cross-sectional image of the macula and enable the non-invasive objective evaluation of the status of the MH, which is especially useful for the quantitative assessment of MH geometry. The importance of the minimum and base diameters as prognostic factors has been widely reported, where accurate or even automatic measurement of macular hole size has always been one of the research hotspots. 4,8 Whether it is GASS or the latest classification of (IVTSG),9 the measurement of macular hole has been based on horizontal scanning, which may be out of the assumption that the macular hole is a standard geometric circle, and horizontal scan through the center of the hole can truly reflect the maximum diameter of the macular hole. However, from both the infrared fundus plane image and the radial scan, it can be confirmed that the macular hole is not a standard geometric circle. As a result, the diameter of the macular hole may be underestimated, resulting in a systematic error. As finding the maximum diameter is undoubtedly one of the most important purposes of macular hole diameter measurement, more options should be considered.
In order to more accurately compare the effects of radial and horizontal scanning on the diameter of macular hole, we used 12-line radial scan and 49-line horizontal scan. It has been found that the macular hole is not a standard geometric circle, and the average values of maximum MLD and maximum BD obtained by radial scanning are larger than those obtained by horizontal scanning. A mean absolute difference of 24.03um for MLD and 28.83um for BD was observed between the radial and horizontal diameters. Among the 40 patients scanned by radiation, only 9 cases (22.5%) had the maximum MLD on the horizontal diameter, while only 12 (30%) cases had the maximum BD on the horizontal line. On the contrary, 62.5% of the maximum MLD and 72.5% of the maximum BD were distributed in the range of 0 °~ 30 °and 150 °~ 180 °.According to IVTS's macular hole grading scheme, 9 we found that 3 (7.5%) out of 40 eyes had macular hole upgrade from medium to large size, which will undoubtedly affect the homogenization comparison of different studies.
If manual measurement errors are inevitable, systematic errors need to be avoided as much as possibly. The effects of radial and horizontal scan on the measurement values cannot be neglected. This study proves that the maximum diameter of macular hole can be found easily by radial scanning rather than horizontal scanning. We observed substantial differences between the values that were derived from the two mode images for the majority of the parameters. Ophthalmologists should keep in mind that our initial intention is to find the maximum diameter of the macular hole as much as possible, but the simple horizontal scanning mode obviously cannot meet today's needs either in theory or in practice. In order to obtain the maximum macular diameter more conveniently and accurately, we suggest using radial scanning of macular hole instead of horizontal scanning, not only because the radial scan itself covers the horizontal scan, but more importantly, the maximum macular hole diameter can be found easily by a qualified radial scan. And all of this is achieved without changing your OCT equipment, without changing our measurement habits, just by changing the scanning mode.10