A total of 213 eyes of 213 RRD patients were included in this study. The mean ΔAL after PPV was 0.37 ± 0.62 mm, and the ΔAL was closely and positively correlated with preoperative hypotony and extreme myopia.
PPV combined with phacoemulsification has been widely used in the treatment of RRD, but the refractive results are not always optimal.[6, 7] Accurate AL measurements are essential for the IOL power calculation. Both A-scan ultrasonography and assessment using the IOLMaster have been used in clinical practice. The IOLMaster measures the distance from the front of the cornea to the retinal pigment epithelium,[17] while A-scan ultrasonography measures the distance from the cornea to the internal limiting membrane, which has led to AL underestimation in previous studies.[3] In addition, changes in the refractive medium can also lead to inaccurate A-scan ultrasonography measurements.[18] The IOLMaster uses a technique based on partial coherence interferometry and is considered to be more accurate.[19] The new non-contact, swept-source-based IOLMaster 700, which provides a deeper scan depth and faster scan speed,[20] shows great repeatability and reliability for AL measurement,[21] and thus was used to study ΔAL in this study.
Previous studies have found ΔAL to be between 0.1 and 0.63 mm postoperatively [9–11, 22]; a ΔAL of 0.37 mm was reported in the current study, which is within this range. Analysis found that this change in AL was significant. Previously, Mukhtar et al.[10] and Liu et al.[9] reported a significant increase in AL after PPV for RRD, while Huang et al.[11] and Kang et al.[6] found no significant ΔAL. After close inspection of the data, it was noticed that Huang et al.[11] in fact reported a ΔAL of 0.63 mm postoperatively (preoperative AL 24.15 mm and 6-month postoperative AL 24.78 mm); however, they defined a P-value less than 0.005 as statistically significant. Kang et al.[6] only recruited macular-on RRD patients with BCVA ≥ 0.7, while patients with longer AL (AL ≥ 28 mm) were not recruited. However, myopia has a high prevalence in Asian populations,[23] and a large study in Taiwan showed that 10.51% of RRD patients were highly myopic (> −6.0 D).[24] In contrast, nearly half of the RRD patients were macular-off.[25] In the current study, 46 eyes were extremely myopic, one-third (76/213) were hypotonic, and half of the eyes (134/213) were macular-off, which may explain the variation among studies. When considering the 106 eyes that had neither hypotony nor extreme myopia preoperatively, the change of AL was also non-significant (pre: 24.76 ± 1.45 mm; post: 24.83 ± 1.53 mm; P = 0.034), which is in line with the results of Kang et al.[6]
It has been reported that a difference of 0.30 mm is correlated to a clinically significant 0.75-D error in the IOL power calculation,[26] and thus, 0.30 mm was used as the standard to separate the ΔAL in our study. Multivariate logistic regression analysis revealed that hypotony and extreme myopia were closely and positively correlated with increased ΔAL (Table 2). Zhang et al.[27] and Cho et al.[28] also reported that the change in IOP was related to increases in AL. In their studies, a 1.7–2-mmHg increases in postoperative IOP resulted in a 0.36–0.43-D myopic shift.[27, 28] Similarly, in our study, a mean increase of 5 mmHg of IOP was correlated with a 0.27-mm increase in AL (approximately 0.65-D myopic shift).[26, 28] RRD is often accompanied by a reduction in IOP.[29] It was reported that eyes with uncomplicated unilateral retinal detachments have a mean IOP 1.3–3.5 mmHg lower than the fellow eyes,[30–33] and our study showed that 207 unilateral RRD eyes have a mean IOP 2.34 mmHg lower than the fellow eyes (P < 0.001) (Supplementary Figure 1). Therefore, in hypotonic eyes, AL may be more likely to be underestimated preoperatively.
Another important factor associated with ΔAL was extreme myopia. Previously, Jee et al.[34] found that the ΔAL was significant in highly myopic eyes (0.46 ± 0.28 mm; P = 0.043) and non-significant in non-high myopic eyes (0.11 ± 0.34 mm; P = 0.135). Jeoung et al.[8] reported that in eyes with an AL of > 26 mm preoperatively, postoperative AL increased significantly (0.25 ± 0.23 mm; P < 0.05). Several factors may contribute to the change in AL in highly myopic eyes, such as the thickness of the sclera. Globe wall stress [35] can be calculated by IOP*(r/2t), in which “r” is AL/2, and “t” is the wall thickness, which shows that stress is positively related with AL, and negatively with eye wall thickness. As a result, the same IOP change may lead to more stress changes in highly myopic eyes, which have a higher AL and thinner eye wall; this may explain the increased changes in AL.
Patients with RRD and cataracts can be treated with combined PPV and phacoemulsification, and the IOL may be implanted during the same procedure, or later. Our results suggest that for patients with hypotony or extreme myopia, it is better to re-measure the AL after the retina is reattached. This will result in a more accurate IOL calculation. The present study was limited by its single-center design, limited number of patients, and inclusion of only Chinese patients who received SO tamponade. Thus, the results require further verification.