Purpose
To assess time to stabilization and factors associated with changes in biometric parameters after scleral buckling (SB).
Design
Prospective case series.
Methods
Seventeen eyes with primary rhegmatogenous retinal detachment (RRD) that underwent SB at the Singapore National Eye Centre were enrolled. SB surgery was performed using an encircling element and segmental buckle. Axial length (AL); anterior chamber depth (ACD), defined as the distance from the corneal epithelium to the anterior lens surface; anterior/posterior corneal curvature (K); and refraction were measured preoperatively and at week 1 and months 1, 3, 6, 9, and 12 postoperatively. Stability of each parameter was defined as the earliest time point at which there is no significant difference compared to its value at month 12.
Results
AL increased (26.09 ± 1.46 to 26.51 ± 1.96, P = .01), ACD decreased (3.84 ± 0.47 to 3.32 ± 0.57, P < .001), and a myopic shift of 1.04 diopters (95% CI 0.03–2.05, P = .04) occurred at month 12. Anterior/posterior K were not significantly changed from baseline. AL stabilized at month 3 while ACD and spherical equivalent (SE) stabilized at week 1. Cryotherapy was associated with greater increase in AL ( P = .001) and myopic shift ( P = .02). More extensive segmental buckling was associated with greater increase in AL ( P = .009) and myopic shift ( P = .03).
Conclusions
Our study suggests that patients requiring cataract surgery after SB should have biometry performed no earlier than 3 months post SB surgery, and intraocular lens power calculation with a fourth-generation formula. A greater increase in AL and myopic shift was associated with cryotherapy and more extensive segmental buckling.
The use of scleral implants in the treatment of rhegmatogenous retinal detachment (RRD) dates back to 1937, when Jess reported the use of a gauze pad as the scleral implant. Schepens and associates introduced the modern scleral buckling (SB) technique in 1957, using a permanent implant such as polyethylene and, later, soft silicone rubber. This well-tolerated technique increased the anatomic success rate of SB surgery from 40% to 90%. However, the use of a scleral buckle inherently changes the anatomy of the eye. Depending on the type of buckling material used, location, and tension of scleral sutures with the circumferential tightening of the buckle, the resultant geometric changes to the globe can cause visually significant changes. These changes include alteration of the axial length (AL), anterior chamber depth (ACD, defined as the distance from the corneal epithelium to the anterior lens surface), and induced spherical or astigmatic refractive errors.
These biometric changes are important, as cataract development and/or progression happen commonly after vitreoretinal procedures. In the Scleral Buckling versus Primary Vitrectomy in RRD trial, almost half of all eyes that underwent SB developed or had progression of cataract after a mean follow-up duration of 387.6 ± 180.6 days. In another recent study by Feng and Adelman, 38% of eyes developed cataracts after SB, of which 5.7% required extraction at a mean of 11 months after surgery. Nuclear sclerosis and posterior subcapsular opacities were the most common cataracts after SB. In a meta-analysis done by Lv and associates, cataract formation post scleral buckle surgery was seen in 23.6% compared with 53.1% in eyes that have undergone trans–pars plana vitrectomy (TPPV) for primary RRD.
However, there remains considerable uncertainty regarding the optimal timing of biometric assessment and, thereafter, cataract surgery post RRD repair by SB. Some studies have shown changes in axial length and anterior chamber depth that continue beyond 12 months, while others have shown stabilization within 3 months. Moreover, various parameters may be altered differentially, which makes it difficult to predict how and in which direction the overall refractive power of a post-SB eye will change. Moreover, the effect of SB on posterior corneal astigmatism, increasingly recognized as an important contributor to the total astigmatism of the eye, is currently unknown. It is also unknown how other surgical factors, such as the use of cryotherapy, gas tamponade, and extent of buckling, may influence changes in ocular biometry.
As patients with RRD repaired by SB tend to be younger, economically active patients, accurate biometry is important to achieve good outcomes should they require cataract surgery subsequently. Thus, we conducted a prospective longitudinal study to assess the biometric changes after SB surgery and the influence of surgical factors on biometric changes.
Methods
In this prospective study, we included consecutive cases with primary RRD requiring SB surgery without vitrectomy, at the Singapore National Eye Centre, between May 2012 and March 2013. The study was performed with prospective approval from the Singhealth Institutional Review Board and in accordance with the Declaration of Helsinki. Written informed consent was obtained from all participants. All scleral buckling procedures were performed by 4 senior vitreoretinal surgeons using the same surgical technique, briefly: encirclage with silicone bands (reference number 240; MIRA Inc, Uxbridge, Massachusetts, USA) and segmental silicone tires. The encircling band was fixed 10–12 mm posterior to the limbus with a 5.0 nylon suture. External drainage of subretinal fluid was performed where possible. Retinopexy with cryotherapy intraoperatively and endotamponade with injection of air or an expansile gas were additional procedures performed at the surgeon’s discretion. Postoperatively, all patients routinely used Tobradex eye drops 4 times daily and atropine sulfate 1% 3 times daily for 2–4 weeks. The following SB surgery–related variables were collected: type and extent of segmental silicone tire, whether subretinal fluid drainage was performed, whether cryotherapy or postoperative laser retinopexy was performed, and the use of endotamponade.
We performed a full clinical evaluation and all measurements were made pre- and postoperatively at 1 week and at 3, 6, 9, and 12 months, specifically: axial length measurements by IOLMaster (Carl Zeiss Meditec, Jena, Germany; software version 5.4), ACD in the horizontal meridian using anterior segment optical coherence tomography (ASOCT; Visante; Carl Zeiss Meditec, Jena, Germany; software version 3.0), automated refraction, automated keratometry (Topcon KR 8800 Auto-kerato-refractometer; Topcon Corporation, Tokyo, Japan), and corneal topography with the Pentacam (Oculus GmbH, Wetzlar, Germany; software version 1.17). Statistical analysis was performed using SPSS software 21.0 (SPSS Inc, Chicago, Illinois, USA). To assess stability, paired samples t test was performed comparing biometric parameters at each time point and their corresponding values at month 12, adjusting for multiple comparisons with Bonferroni correction. Stability of each parameter was defined as the earliest time point at which there was no significant difference with its value at month 12.
A linear mixed-effects model multivariate analysis was conducted to account for repeated measurements and loss of some follow-up data. Variance-covariance/correlation structures such as compound symmetry and independent and autoregressive structures were used to estimate the model fit based on Hurvich and Tsai’s criterion (AICc) and using the smaller-the-better information criterion. This model was used to analyze the multivariate relationship of biometric parameters with clock hours of scleral buckling, cryotherapy, and endotamponade, adjusting for age and sex. Significance was defined as P < .05.
Results
Table 1 shows the baseline demographics and clinical characteristics of our study cohort. The mean age was 47.0 ± 13.9 years and 62.5% of subjects were male. Most eyes were phakic with no lens opacity (64.7%) preoperatively, while none of the study eyes had proliferative vitreoretinopathy. The most commonly used segmental buckle was the 277 (13 eyes, 76.5%), followed by the 276 (3 eyes, 17.6%). The vast majority of eyes underwent drainage of subretinal fluid (94.1%). Gas tamponade was performed with either air (41.2%) or sulfur hexafluoride (47.1%). Intraoperative cryotherapy was the preferred method of sealing retinal breaks (70.6%). Primary anatomic success was achieved in 100% of patients. Three eyes with pre-existing cataract had significant progression of the cataract (17.6%), but none of these eyes underwent cataract surgery within the duration of the study.
| Age (y) | 47.0 ± 13.9 |
| Sex (male, %) | 10 (62.5) |
| Lens status | |
| Clear lens | 11 (64.7) |
| Cataract | 3 (17.6) |
| Pseudophakic | 3 (17.6) |
| Macular detachment (%) | 8 (47.1) |
| Number of detached retinal quadrants (%) | |
| 1 | 7 (41.2) |
| 2 | 7 (41.2) |
| 3 | 3 (17.6) |
| Number of retinal breaks (%) | |
| 1 | 14 (82.4) |
| 2 | 2 (11.8) |
| 3 | 1 (5.9) |
| Location of retinal breaks (%) | |
| Superior | 9 (52.9) |
| Inferior | 8 (47.1) |
| Type of buckle (%) | |
| 276 | 3 (17.6) |
| 277 | 13 (76.5) |
| 279 | 1 (5.9) |
| Clock hours of buckle (%) | |
| 3 | 4 (23.5) |
| 4 | 4 (23.5) |
| 5 | 1 (5.9) |
| 6 | 8 (47.1) |
| SRF drainage performed (%) | 16 (94.1) |
| Endotamponade (%) | |
| None | 2 (11.8) |
| Air | 7 (41.2) |
| SF6 | 8 (47.1) |
| Postoperative laser retinopexy | 5 (29.4) |
| Cryotherapy (%) | 12 (70.6) |
The mean values of biometric parameters at each time point are shown in Table 2 . SB surgery resulted in significantly longer AL (26.09 ± 1.46 mm vs 26.51 ± 1.96 mm, P = .01) and vitreous length (VL) (22.25 ± 1.66 mm vs 23.26 ± 0.28 mm, P = .001), as well as shallower ACD (3.84 ± 0.47 mm vs 3.32 ± 0.57 mm, P < .001) at 12 months after surgery, compared to preoperative values. Overall manifest astigmatism increased initially at week 1 (cylinder: −1.56 ± 1.05 diopters [D]) but decreased back to preoperative levels at month 12 (−0.81 ± 0.28 D). Both anterior and posterior cornea astigmatism increased post SB to a maximum of 2.01 ± 1.13 D (baseline 1.26 ± 0.67 D) and 0.40 ± 0.26 D (baseline 0.24 ± 0.20 D), respectively, at month 3 followed by a decrease and stabilization thereafter, but remain elevated compared to preoperative values. No statistically significant differences in anterior or posterior corneal keratometry were found between preoperative values and month 12 values.
| Baseline | Week 1 | Month 1 | Month 3 | Month 6 | Month 9 | Month 12 | P a | |
|---|---|---|---|---|---|---|---|---|
| AL (mm) | 26.09 ± 1.46 | 25.84 ± 1.70 | 26.29 ± 1.82 | 26.19 ± 1.93 | 26.34 ± 1.77 | 26.58 ± 1.85 | 26.51 ± 1.96 | .01 |
| ACD (mm) | 3.84 ± 0.47 | 3.46 ± 0.69 | 3.39 ± 0.50 | 3.25 ± 0.57 | 3.50 ± 0.70 | 3.26 ± 0.49 | 3.32 ± 0.57 | <.001 |
| VL (mm) | 22.25 ± 1.66 | 22.52 ± 1.73 | 22.97 ± 1.82 | 22.90 ± 1.74 | 22.83 ± 1.71 | 23.32 ± 1.63 | 23.26 ± 0.28 | .001 |
| Sphere (D) | −3.49 ± 2.16 | −3.68 ± 4.14 | −4.39 ± 3.54 | −5.00 ± 3.73 | −5.00 ± 3.61 | −5.20 ± 3.35 | −4.85 ± 3.25 | .05 |
| Cylinder (D) | −0.81 ± 0.51 | −1.56 ± 1.05 | −1.32 ± 0.85 | −1.12 ± 0.78 | −1.05 ± 0.47 | −0.98 ± 0.52 | −0.81 ± 0.28 | .85 |
| SE (D) | −3.89 ± 2.34 | −4.54 ± 4.02 | −5.06 ± 3.36 | −5.56 ± 3.69 | −5.51 ± 3.67 | −5.68 ± 3.43 | −5.25 ± 3.32 | .05 |
| Anterior cornea astigmatism (D) | 1.26 ± 0.67 | 1.92 ± 1.02 | 2.00 ± 1.10 | 2.01 ± 1.13 | 1.64 ± 1.46 | 1.68 ± 1.19 | 1.66 ± 1.19 | .50 |
| Posterior cornea astigmatism (D) | 0.24 ± 0.20 | 0.40 ± 0.26 | 0.40 ± 0.26 | 0.40 ± 0.26 | 0.36 ± 0.25 | 0.35 ± 0.21 | 0.33 ± 0.26 | .25 |
| Anterior K (D) | 42.82 ± 1.20 | 42.74 ± 1.52 | 43.25 ± 1.37 | 43.09 ± 1.14 | 43.09 ± 1.31 | 43.10 ± 1.29 | 43.04 ± 1.30 | .94 |
| Posterior K (D) | −6.19 ± 0.38 | −6.09 ± 0.32 | −6.16 ± 0.23 | −6.19 ± 0.28 | −6.18 ± 0.32 | −6.18 ± 0.30 | −6.21 ± 0.35 | .79 |
a Paired t test comparing value at baseline with value at month 12.
Table 3 shows the mean difference between values of AL, ACD, and spherical equivalent (SE) at each time point and their corresponding values at month 12. Comparing preoperative values with the corresponding values at month 12, there was a mean increase in AL of 0.58 mm (95% confidence interval [CI] 0.32–0.83, P < .001), a mean decrease in ACD of 0.48 mm (95% CI 0.23–0.74, P < .001), and a mean myopic shift of 1.04 D (95% CI 0.03–2.05, P = .04). AL continued to increase until month 3 ( P = .49) before stabilization. ACD decreased initially during the first week ( P = .07) and thereafter stabilized. The myopic shift in SE was observed to stabilize after the first week ( P = 1.00). Anterior and posterior astigmatism/keratometry values did not differ significantly from month 12 values at any time point (all P = 1.00).
| Axial Length | Anterior Chamber Depth | Spherical Equivalent | |||||||
|---|---|---|---|---|---|---|---|---|---|
| Mean Difference a | 95% CI of Difference | P b | Mean Difference a | 95% CI of Difference | P b | Mean Difference a | 95% CI of Difference | P b | |
| Preop | 0.58 | 0.32 to 0.83 | <.001 | −0.48 | −0.74 to −0.23 | <.001 | −1.04 | −2.05 to −0.03 | .04 |
| Week 1 | 0.48 | 0.22 to 0.73 | <.001 | −0.26 | −0.52 to 0.01 | .07 | −0.41 | −1.33 to 0.52 | 1.00 |
| Month 1 | 0.30 | 0.06 to 0.55 | .008 | −0.08 | −0.33 to 0.16 | 1.00 | −0.06 | −0.86 to 0.73 | 1.00 |
| Month 3 | 0.17 | −0.09 to 0.44 | .49 | 0.08 | −0.18 to 0.33 | 1.00 | 0.02 | −0.83 to 0.87 | 1.00 |
| Month 6 | 0.09 | −0.16 to 0.34 | 1.00 | −0.11 | −0.35 to 0.13 | 1.00 | 0.03 | −0.49 to 1.10 | 1.00 |
| Month 9 | 0.02 | −0.23 to 0.26 | 1.00 | 0.12 | −0.11 to 0.35 | .94 | 0.27 | −0.52 to 1.06 | 1.00 |
a Mean difference is given by subtracting the mean at each specified time point from the mean at month 12.
b Paired t test adjusted for multiple comparisons with Bonferroni correction.
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