Corneal Astigmatism Alteration after Combined Silicone Oil Removal and Cataract Surgery with Intraocular Lens Implantation

Purpose To explore short-term changes in corneal astigmatism after combined silicone oil removal and cataract (SORC) surgery. Methods We enrolled 89 patients (43 men and 46 women). Zeiss IOLMaster was used to measure corneal astigmatism status and axial length on the day before and after the SORC surgery. Best-corrected visual acuity (BCVA) and intraocular pressure (IOP) were recorded. The results were compared to the outcomes at 3 days, 1 week, and 1 month postoperatively. Results Compared to baseline, K1 decreased significantly at 3 days postoperatively (P = 0.016), 1 week (P = 0.009), and 1 month (P = 0.035), while K2 increased significantly at 3 days postoperatively (P = 0.002), 1 week (P < 0.001), and 1 month (P = 0.001), as well as corneal astigmatism (all P < 0.001). Compared to that at the baseline, BCVA significantly improved at 3 days, 1 week, and 1 month postoperatively (all P < 0.001). Meanwhile, IOP decreased significantly at 3 days postoperatively (P < 0.001), 1 week (P = 0.005), and 1 month (P = 0.007). Similarly, axial length decreased at all follow-up time points (all P < 0.001). Conclusion Corneal astigmatism increased in the short term after the SORC operation but gradually decreased at 1 month postoperatively. BCVA improved steadily, and SORC was widely used in the clinic.


Introduction
Pars plana vitrectomy (PPV) has been highly developed for various vitreoretinal diseases [1], and transconjunctival 23G PPV has become a standard procedure [2][3][4]. As an important temporal vitreous tamponade during eye surgery, silicone oil has been extensively applied in the clinic for diseases such as retinal detachment and diabetic retinopathy because of its nontoxicity, good optical permeability, and large surface tension [5,6].
Long-term silicone oil tamponade causes a series of complications, including cataracts, glaucoma, and corneal degeneration; therefore, silicone oil should be removed 3-6 months postoperatively [7][8][9]. Since cataract has the highest incidence among complications [10,11], combined silicone oil removal and cataract (SORC) surgery with intraocular lens implantation is routinely considered in phakic eyes when silicone oil should be removed [12][13][14]. During SORC surgery, doctors can check the fundus more clearly and easily compared to simple silicone oil removal (SOR) surgery. Moreover, SORC surgery can improve postoperative visual acuity and reduce costs by avoiding secondary surgery. Terefore, a combination of SORC surgery with intraocular lens implantation is widely used.
As a common refractive error, astigmatism can cause blurred vision and visual fatigue, which directly infuence quality of life. Surgically induced astigmatism (SIA), an important component of astigmatism, afects visual quality and visual rehabilitation postoperatively [15,16]. However, previous studies have mainly focused on changes in corneal astigmatism after cataract surgery, and there are few relevant studies on SORC surgery with intraocular lens implantation.
Tis study aimed to explore the short-term changes in corneal astigmatism after SORC surgery to reduce postoperative astigmatism in future clinical work.

Patients.
Eighty-nine patients (43 men and 46 women) were enrolled in the Department of Ophthalmology at Renmin Hospital of Wuhan University. Patients with rhegmatogenous retinal detachment and proliferative diabetic retinopathy who underwent SORC surgery between November 2021 and June 2022 were included in this study. Only one eye was enrolled for every indivious condition. Te study conformed to the Declaration of Helsinki, and ethical approval was obtained from the Medical Ethics Committee of the Renmin Hospital of Wuhan University. All patients signed informed consent forms after being informed of the purposes, contents, and potential risks.

Inclusion and Exclusion
Criteria. Te inclusion criteria were eyes with rhegmatogenous retinal detachment and proliferative diabetic retinopathy undergoing SORC surgery by an experienced surgeon with no history of any ocular surgery, phakic eyes, and capable of IOLMaster examination. We excluded eyes with other retinal detachments, such as exudative retinal detachment; vitreous hemorrhage caused by other reasons, such as retinal hole, retinal vein occlusion, wet age-related macular degeneration; or any other eye diseases, keratopathy, uveitis, glaucoma, orbital tumors, eye trauma, or any history of ocular surgery. Patients who did not follow scheduled visits postoperatively were excluded.

Surgical Technique.
All surgeries were performed under retrobulbar anesthesia by the same professional surgeon (Tao He) [17]. SORC surgery was performed approximately 3 months after PPV. All patients were treated with retrobulbar anesthesia. Te 23G scleral trocars were made 3.5 mm from the corneal limbus, and the perfusion tube was inserted into the subtemporal trocar. Te trocars were closed. A 3.2 mm incision and a two-point corneal auxiliary incision were made, and viscoelastic agent was injected into the anterior chamber. Continuous annular capsulorhexis was performed using the capsulorhexis forceps. Te lens was aspirated by phacoemulsifcation, and a foldable intraocular lens was inserted into the capsular bag. Te anterior chamber was restored by injecting balanced salt solution, and a clear corneal incision was closed. Te perfusion tube was opened and the silicone oil in the vitreous cavity was removed from the scleral trocar. Te scleral trocar port was then sutured with 7-0 absorbable sutures. Conjunctival sutures were removed 1 week postoperatively.

Refractive Analysis.
Te refractive status was determined using IOLMaster (ZEISS, Germany) preoperatively and at 3 days, 1 week, and 1 month postoperatively. All examinations were performed three times by a blinded observer. Te following data were compiled postoperatively: best-corrected visual acuity (BCVA), refraction, intraocular pressure (IOP), retinal and macular status, and complications over a minimum 1month follow-up period.

Statistical Analysis.
Statistical analyses were performed using SPSS 26.0 (IBM SPSS Statistics, USA). Quantitative data are presented as mean ± standard deviation. Te differences at every follow-up time point were analyzed using one-way analysis of variance with Dunnett's multiple comparison two-sided test. P < 0.05 was considered statistically signifcant.

Demographics and Characteristic Data.
We enrolled 89 eyes of 89 patients, including 41 right and 48 left eyes; 43 patients were men while 46 were women. Te average age was 59.31 ± 7.57 years (range: 41-75). Te primary diseases included rhegmatogenous retinal detachment and proliferative diabetic retinopathy (Table 1).
To investigate the alterations in K1, K2, and corneal astigmatism postoperatively, we further compared each follow-up time point at 3 days postoperatively. Both K1 and K2 showed signifcant diferences at 1 month postoperatively  Table 3).  (Table 5). Te BCVA showed signifcant diferences at both 1 week and 1 month postoperatively when compared with 3 days (all P < 0.001), as well as the IOP (P � 0.005 and 0.006, respectively). However, the axial length showed no statistical diferences at either 1 week or 1 month postoperatively when compared with 3 days (P � 0.653 and 0.765, respectively).

Discussion
Many studies have reported on corneal astigmatism after cataract surgery. However, studies on corneal astigmatism after SORC surgery are lacking, especially in the short term. To our knowledge, this study is the frst to explore shortterm changes in astigmatism after SORC surgery, which has clinical signifcance for guiding surgical operations.
Our study found that corneal astigmatism increased signifcantly in the short-term postoperatively. Corneal astigmatism increased signifcantly 3 days postoperatively, which lasted until 1 week postoperatively, and gradually decreased 1 month postoperatively, approaching the preoperative level. Some studies on cataract surgery showed that corneal astigmatism increased signifcantly at one week and two weeks postoperatively, while corneal astigmatism gradually decreased at 4 weeks postoperatively, which was close to the preoperative state [18,19]. Tis trend is consistent with the results of this study. Te increased corneal astigmatism in the short-term postoperative period may be related to the phacoemulsifcation technique. With the development of phacoemulsifcation technology and the clinical application of folded lenses, the length of the clear corneal incision for cataract phacoemulsifcation technology was mostly 3.2 mm. Te thermal damage of phacoemulsifcation and repeated warping of the inner and outer lamellae during the operation causes slight displacement of the incision [20]. Meanwhile, the radial tissue at the surgical incision is relaxed and the curvature is reduced, resulting in SIA [21,22]. Conversely, short-term corneal edema postoperatively may cause increased corneal astigmatism. Corneal edema after cataract surgery can lead to varying degrees of curvature of the corneal surface, resulting in increased astigmatism. In this study, the degree of corneal astigmatism was the highest at 3 days postoperatively and gradually decreased at 1 week and 1 month postoperatively, which may be related to the gradual improvement of corneal edema [23].
In addition, there was some controversy regarding whether scleral tunnel incision could cause corneal SIA. Some studies suggested that simple PPV surgery will not lead to changes in corneal astigmatism [24,25]. However, some studies also found that the steepest meridian of the cornea changed in the early postoperative 25G PPV, and the difference was statistically signifcant [26]. A study on vitrectomy combined with cataract surgery found that corneal astigmatism was the largest at 1 week postoperatively, and corneal astigmatism gradually recovered to preoperative levels 1 and 3 months postoperatively. In addition, the suture of the early scleral tunnel incision would cause eye discomfort and foreign body sensation, which would afect the stability of the patient's tear flm and lead to poor patient cooperation during the examination. Tese factors may increase measured corneal astigmatism.
Some studies have suggested that the length of the eye axis changes after the removal of silicone oil. Some researchers believe that there is no statistically signifcant diference in axial length pre-and postoperatively [27][28][29]. Other researchers reported that the axial length of the eye      Journal of Ophthalmology was reduced compared with the silicone oil-flled state, which may be related to the reduction in ocular contents and intraocular pressure [30]. Elbendary and Elwan found that the refractive index shifted to hyperopia after SORC surgery [31]. In the long-term postoperative period, intraocular pressure gradually increased, resulting in an increase in axial length compared with the early stage of SOR. Tere was a reduction in the refractive error of hyperopia, but it still drifted towards hyperopia. In terms of visual acuity, although the corneal astigmatism of the patients increased at 3 days and 1 week postoperatively, the postoperative visual acuity improved compared with that preoperatively. In addition, the corneal astigmatism in the two groups of patients was signifcantly diferent at 1 week and 1 month postoperatively, and the diference in visual acuity was not obvious. Visual acuity was mostly afected by the diopter reserved and condition of the fundus.
Our study had some limitations. First, we were unable to observe any longer after the SORC surgery. Meanwhile, the patient population was small, and a larger sample size should be considered in further investigations.

Conclusion
In general, SORC surgery is a safe and efective method for improving BCVA. Te corneal astigmatism gradually decreases postoperatively.

Data Availability
Te data used to support the fndings of this study are available from the corresponding author upon request.

Conflicts of Interest
Te authors declare that there are no conficts of interest.