In the present study, AL, ACD, and LT, as well as derivative LP, RLP and LRD, were measured in phakic, macula-off eyes with RRD and compared to those recorded after a successful vitrectomy and silicone oil tamponade. Results revealed that, after a mean 4.85-month duration of silicone oil tamponade, AL was approximately 0.48 mm longer than in RRD status eyes, ACD was 0.14 mm shallower, and LT was 0.09 mm thicker, causing an LP anterior move of 0.09 mm, an RLP decrease of 0.01 and an LRD increase of 0.65 mm. Therefore, a postoperative myopic shift occurs if phacovitrectomy was performed according to the preoperative data, although this effect might be neutralized by a hyperopic shift during the period of silicone oil tamponade [
18‐
20]. Previous studies have suggested that myopic shift results from underestimation of AL using A-scan ultrasonography because it measures the distance from the cornea to the inner limiting membrane as AL [
6]. IOLMaster is more accurate with less deviation in its predictive postoperative refractive error than A-scan ultrasound, as it measures from the front of cornea to the retinal pigment epithelium [
13]. However, in some macula-off RRD eyes, a similar strong interference from interfaces in the detached retina may provide a good signal-to-noise ratio measurement, even though the result is incorrect [
21], partly explaining the conflicting findings of studies measuring preoperative and postoperative AL using IOLMaster. For instance, Pongsachareonnont et al. found that underestimation of AL in macular involvement eyes with RRD was 0.59 ± 0.90 mm [
22], while Kim et al. thought this underestimation was associated with macular retinal detachment height [
7]. Furthermore, Shiraki et al. reported that AL measurement was not associated with postoperative myopic shift and considered AL to be correctly underestimated even in eyes with macula-off RRD [
1]. Using the IOLMaster 700, which provides a 44-mm scan depth, captures 2000 A-scans per second for the full-eye length tomogram acquisition and shows anatomical details of a longitudinal cut through the entire eye [
15], we observed an underestimation of AL in eyes with macula-off RRD. Furthermore, ACD of RRD eyes was also decreased by an average of 0.14 mm after vitrectomy, consistent with previous studies [
23]. Huang et al. attributed this phenomenon to abnormally low intraocular pressure prior to surgery, which results in falsely high measurements of ACD, postoperatively recovered intraocular pressure, and an operative wound, which stimulates contraction of the ciliary body muscle to induce increased lens convexity and LT [
9]. In addition, the facedown position and silicone oil tamponade may also shift the lens-iris diaphragm forward.
Theoretically, an underestimation of AL and an anterior shifting of the lens location both contribute equally to postoperative refractive error. We established the parameter LRD as AL minus LP to combine both factors. In our study, △LRD was only positively correlated with baseline AL and LRD but not preoperative ACD, LT or LP. Furthermore, underestimation of AL, rather than the thickening of LT or anterior shifting of the lens, is correlated with △LRD, suggesting that underestimating AL is the major cause of postoperative myopic shift. Kang et al. reported a postoperative myopic shift of 0.41 ± 0.67 diopters in patients with macula-sparing RRD following phacovitrectomy compared to the predicted value, considering this shift to be primarily caused by factors affecting the intraocular lens position, such as preoperative ACD and LT, rather than a change in AL [
2]. The present study confirmed a 0.09-mm anterior shift of the lens in silicone oil-filled eyes after RRD repair. According to Sun et al., a measurement error of 100 μm results in a postoperative refractive error of 0.25 diopters following the SRK formula [
8]. Thus, if phacovitrectomy was performed, according to the preoperative data, the mean 0.65-mm increase of LRD in our study leads to an approximate myopic shift of 1.63 diopters. This value is larger than that of others [
1,
2,
7] in which patients who underwent silicone oil tamponade were excluded. Interestingly, age was positively correlated with △RLP and negatively with △LRD. Since the value of △RLP is negative, while that of △LRD is positive, these data synergistically indicate that the anterior shifting of the lens after silicone oil tamponade lessens in older patients. One possible explanation might be the thicker and denser nature of the lens in older individuals.
There are also limitations to the present study. Ocular biometric measurements in these phakic eyes after silicone oil removal should be analyzed in the future. Of note, postoperative myopic shift after phacovitrectomy also occurs in patients with gas tamponade, which is caused by the buoyancy and surface tension of the gas, persisting even after the gas has disappeared 1 month postoperatively [
4]. Further studies are needed to observe the prolongation of LRD in eyes with phacovitrectomy and the final degree of myopic shift after silicone oil removal.