|Year : 2012 | Volume
| Issue : 1 | Page : 18-21
Refractive change after pars plana vitrectomy
Po-Chen Tseng1, Lin-Chung Woung2, Gow-Lieng Tseng2, Ching-Yao Tsai2, Hsin-Kai Chou3, Chun-Chen Chen2, Shiow-Wen Liou2
1 Taipei City Hospital; Institute of Clinical Medicine, National Yang-Ming University, Taipei, Taiwan
2 Taipei City Hospital, Taipei, Taiwan
3 National Chung Cheng University, Chiayi, Taiwan
|Date of Web Publication||1-Mar-2012|
Department of Ophthalmology, Zhongxing Branch, Taipei City Hospital, Number 145, Zhengzhou Road, Datong District, Taipei City 103
Source of Support: None, Conflict of Interest: None
Purpose: This study investigated the changes of refractive status in both phakic and pseudophakic eyes after pars plana vitrectomy (PPV) surgery without scleral buckling or silicone oil tamponade, and examines the possible factors that may affect the refractive changes.
Methods: A retrospective case note review of 172 eyes (172 patients) undergoing PPV surgery for a variety of vitreoretinal conditions. Refractive status was measured before and after vitrectomy surgery in 60 eyes after the application of inclusion and exclusion criteria. Refractive status before and after PPV was analyzed using paired t-tests. An independent t-test and analysis of variance were subsequently conducted to analyze any significant differences in refractive change under a variety of etiological factors. Changes in refraction were also analyzed using a linear regression model.
Results: A total of 60 eyes from 60 consecutive patients were included in this study. The mean spherical equivalence (SE) before PPV was 0 diopters (D), and −1.21 D after PPV. The mean change of SE was −1.21 D (95% confidence interval −1.70 to −0.71 D, p < 0.001). The mean astigmatism (cylinder) power before PPV was −1.17 D, and was −1.23 D after PPV. The mean change of astigmatism was −0.06 D (p = 0.753). There was no significant difference in refractive change between gender, age groups, disease categories, and use of gas tamponade. There was a significant difference between the phakic and pseudophakic groups (p = 0.047). The mean change of SE in 37 phakic eyes was −1.60 D (95% confidence interval −2.35 to −0.85 D, p < 0.001), and in 23 pseudophakic eyes it was −0.59 D (95% confidence interval −0.99 to −0.18 D, p = 0.007).
Conclusions: Significant changes in refractive status were observed in patients undergoing PPV. Most of the patients experienced a myopic shift, among both phakic (−1.60 D) and pseudophakic (−0.59 D) patients. Changes in astigmatism were not significant. There are several plausible explanations; however, the true underlying etiologies of the refractive change are to be further investigated. To our knowledge, this is the first refractive study conducted after PPV among the Taiwanese population.
Keywords: astigmatism, myopia, ocular refraction, phakia/surgery, postoperative complications, pseudophakia/pathology, pseudophakia/surgery, retinal diseases/surgery, retrospective studies, vitrectomy, vitreous body
|How to cite this article:|
Tseng PC, Woung LC, Tseng GL, Tsai CY, Chou HK, Chen CC, Liou SW. Refractive change after pars plana vitrectomy. Taiwan J Ophthalmol 2012;2:18-21
|How to cite this URL:|
Tseng PC, Woung LC, Tseng GL, Tsai CY, Chou HK, Chen CC, Liou SW. Refractive change after pars plana vitrectomy. Taiwan J Ophthalmol [serial online] 2012 [cited 2021 Sep 21];2:18-21. Available from: https://www.e-tjo.org/text.asp?2012/2/1/18/203100
| 1. Introduction|| |
Because the anatomical success of pars plana vitrectomy (PPV) has improved, more attention has been drawn toward better functional outcomes and visual quality, including refractive changes. In the era of advanced refractive and cataract surgical techniques, the optimal goal is to achieve enhanced uncorrected visual acuity and better quality of life. Ophthalmologists try their best to predict and limit refractive error to within 0.5 or even 0.25 diopters (D). However, individuals with high myopia and patients who have undergone cataract surgery are at a higher risk of vitre-oretinal problems such as retinal detachment,, macular holes, and epiretinal membranes. As long as some degree of refractive change is present, it might compromise optical function, especially in the multifocal or accommodative intraocular lens (IOL).
Procedures of the posterior segment, such as scleral buckling and silicone oil tamponade, greatly alter refraction. The vitreous refractive index is identical to that of the aqueous index; hence, vitrectomy alone substituted with a balanced salt solution can induce virtually no significant change to the refractive status. However, clinically minor refractive changes between −0.5 and −0.85 D have been observed following PPV.,, Recently in our practice, some patients encountered similar refractive changes. Yet to our knowledge, there have been no related studies conducted in Taiwan. Therefore, this study investigated the effect of PPV on refractive change, and examined any possible etiology.
| 2. Methods|| |
A retrospective case chart review of 172 eyes undergoing PPV surgery for a variety of vitreoretinal conditions in Taipei City Hospital was conducted from January 2006 to December 2008. The vitrectomy procedures were conducted by different surgeons at the Zhongxing and Renai branches of the Taipei City Hospital. The surgical procedures included the standard three-port pars plana techniques; membrane peeling was carried out for epiretinal membrane, macular hole, tractional retinal detachment, proliferative diabetic retinopathy, and cystoid macular edema whenever there were tractional membranes, and internal drainage was performed in rhegmatogenous retinal detachment. Postoperatively, all patients received similar routine medication, including topical application of an antibacterial agent, and 1% prednisolone four times daily and Rinderon-A Oph Ointment before sleep. The patients were instructed to stay in a prone position postoperatively if tamponade gas was used. Refraction data were collected with auto-refractometers at the two sites separately using the same Topcon RM-8000B autorefractometer (Topcon Corporation, Itabashi-ku, Tokyo, Japan) before and after the procedure in both hospitals.
- The availability of refractive data obtained within 6 months before vitrectomy surgery
- The availability of refractive data before vitrectomy surgery, obtained at least 3 months post-cataract surgery in pseudophakic patients
- The availability of data from a refraction performed 3–4 months post-vitrectomy
- Patient is under 18 years of age
- Intraoperative IOL exchange or manipulation
- Combined vitrectomy and cataract surgery
- Scleral buckling with vitrectomy
- Silicone oil tamponade
The following data were also recorded from the notes when available: date of cataract surgery, type and power of IOL used, axial length before vitrectomy, indication for vitrectomy, time between vitrectomy and cataract extraction, vitreoretinal procedure undertaken, type of tamponade agent used, refraction before and after vitrectomy and the occurrence of any intra- or postoperative problems, and central retinal thickness by optical coherence tomography before and after vitrectomy. The study conformed to the principles of the Declaration of Helsinki.
2.2. Statistical analysis
The refraction data were converted into spherical equivalence (SE). Refractive status before and after PPV were analyzed by paired t-tests. An independent t-test and analysis of variance (ANOVA) were conducted to analyze whether a significant difference was present in the refractive change under a variety of etiological factors. Change in refraction was also analyzed via a linear regression model.
| 3. Results|| |
A total of 60 eyes from 60 consecutive patients were included. There were 26 men (43.3%) and 34 women (56.7%). More than 85% of the patients were between the ages of 51 and 80. There were 37 phakic (61.7%) and 23 pseudophakic (38.3%) eyes. An indication of PPV was for the treatment of epiretinal membrane (30%), vitreous hemorrhage (23.3%), macular hole (15%), retinal detachment (16.7%), and miscellaneous (15%). In the miscellaneous group, seven had vitreous opacity (11.7%) and two had cystoid macular edema (3.3%). Tamponade with gas (SF6 or C3F8) was used in 35 patients (58.4%) [Table 1].
The refraction error before PPV ranged from −8 to +5.5 D SE, with a mean of 0 D [standard deviation (SD) 2.57 D]. The postoperative refraction error ranged from −16.0 to +2.63 D SE, with a mean of −1.21 D (SD 2.80 D). The mean SE change was −1.21 D (95% confidence interval, −1.70 to −0.71 D). The mean astigmatism (cylinder) power before PPV was −1.17 D, and −1.23 D after PPV. The mean change of astigmatism was −0.06 D [Table 2]. Refractive change was significant for SE (p < 0.001, paired t-test), and astigmatism change was not significant (p = 0.753).
No significant difference was present in refractive changes between gender, age groups, disease types, and use of gas tamponade (independent t-test and ANOVA). Different disease types were further analyzed by Scheffe’s post-hoc test; the differences were not significant between any two of the disease subgroups. However, a significant difference was observed between the phakic and pseudophakic groups (p = 0.047) [Table 3].
We further divided the patients into phakic and pseudophakic group to assess refractive change. The mean change of SE in 37 phakic eyes was −1.60 D (95% confidence interval −2.35 to −0.85 D, p < 0.001, paired t-test), whereas the mean change of astigmatism was −0.18 D (p = 0.370, paired t-test). In pseudophakic eyes, the mean change of SE was −0.59 D (95% confidence interval −0.99 to −0.18 D, p = 0.007, paired t-test), with a mean change of astigmatism of 0.15 D (p = 0.278, paired t-test) [Table 2].
Refractive changes between gender, age groups, disease types, and use of gas tamponade were not significant within the phakic and pseudophakic subgroups (independent t-test and ANOVA) [Table 3]. [Figure 1] shows the distribution of refractive change following PPV among different groups.
3.1. Regression model
The following variables were entered into a stepwise linear regression model: disease types, age, tamponade agent, and lens status. Three of the variables were excluded from the final model, the only one remaining variable being lens status. The R2 value for the final model was 0.05, indicating that only 5.0% of the variance in Spherical Equivalent Change was due to lens status (n = 60). Standardized beta coefficients for the final model were −0.258 (p= 0.047) for lens status.
| 4. Discussion|| |
The vitreous refractive index of is 1.336, which is identical to that of the aqueous index. Removal of vitreous alone does not alter the refractive status. However, there are several possible explanations for the refractive change in PPV: (1) silicone oil tamponade; (2) changes in cornea curvature; (3) changes in anterior chamber depth (ACD); and (4) axial length change.
Silicone oil has a refraction index of 1.405, compared to that of vitreous, which is 1.336. Refraction error can be expected to change by 5e9 D, and occasionally, by as much as 14 D. Silicone oil tamponade causes a hyperopic shift by an average of +5.5 to +7.6 D in phakic eyes,, and a mean of +5.69 D in pseudophakic eyes, whereas it causes a myopic shift of −6 to −7 D in aphakic eyes., Because of the magnificent refractive change in silicone oil tamponade, patients with intraoperative silicone oil use were excluded from our study.
Central corneal steepening was noted in the immediate postoperative period. However, Weinberger et al showed that cornea curvature changes returned to preoperative curvature after 3 months. Hence, we did not collect refraction information before 3 months. Although our study was weakened by the absence of keratometric and topographic data, our results showed that there phakic and pseudophakic patients.
The phacoemulsification procedure is more difficult in vitrectomized eyes than in non-vitrectomized eyes because of problems such as a deep or fluctuating anterior chamber (93%), which is caused by zonular damage, increased mobility of the lens-iris diaphragm, or lack of vitreous gel support. Therefore, it is reasonable to expect a change in ACD following PPV and use of gas tamponade. However, Byrne et al noticed that no significant change was present in ACD after vitrectomy, and no significant difference was found in patients with refractive change with or without gas tamponade. Unfortunately, we did not measure the pre- and postoperative ACD in most of our patients because it is not routinely examined in vitreoretinal patients. However, our study revealed that using tamponade gas showed no significant difference.
A possible explanation for myopic shift is that false autorefraction is measured when macular thickening, subretinal fluid at the macular area, pre-retinal hemorrhages, tractional membranes, or any changes in the morphology of macula are present. Once the macula morphology returns to normal after vitrectomy with or without membrane peeling, it could theoretically result in a myopic shift. Since the changes of −0.59 D could be achieved by only about 200 μm change in the axial length, any change in the macula or macular surface could have caused this refraction change. It should be noted, though, that we did not have the complete measurement of the pre- and postoperative central retinal thickness with optical coherence tomography–which is not routinely carried out in many surgical vitreoretinal diseases. However, after analysis using ANOVA and Scheffe’s post-hoc test, our series showed that there was no significant difference in refractive change between any two of the disease subgroups in both phakic or pseudophakic eyes, especially between epiretinal membrane and macular hole, while macula hole was considered to induce the least false autorefraction. Nevertheless, it is also possible that we did not have enough case numbers to reveal the significant difference between the disease groups.
Brazitikos et al found that there was a small but significant increase in axial length (0.1 mm) after vitrectomy, which could produce the refractive changes we observed. Jeoung et al postulated that this may be a true increase in axial length associated with scleral stretching and thinning. Sutureless sclerotomies may have been similar to scleral expansion surgery in that they increased the axial length. Unfortunately, we did not measure the pre- and postoperative axial length in most of our patients. It would be a difficult task to access the precise axial length in most patients with vitreoretinal disease.
A number of studies reported mild myopic shifts of between −0.5 and −0.85 D after pseudophakic vitrectomy,,, whereas Kumagai et al found that there was only a temporary −0.3 refraction following vitrectomy. In our study, significant refractive changes (−1.21 D) were observed in patients who underwent PPV. The mean refractive change was a myopic shift in both phakic (−1.60 D) and pseudophkic patients (−0.59 D). This study was limited by its retrospective nature, lack of sufficient case numbers, and the large number of factors that may affect refractive status; however, the findings were compatible with those of previous research. Sclerotic changes and cataract formation might cause more myopic shifts in the phakic group. The incidence of cataract after vitrectomy is up to 100% within a 2-year follow-up period, and post-vitrectomy cataracts in older patients are more likely to be nuclear sclerotic. Apparently, cataract formation and lens opacities could induce more refraction changes in phakic eyes than in pseudophakic eyes. The exact etiologies of myopic shifts following PPV are yet to be investigated more thoroughly. A prospective randomized study with measurement of axial length, keratometry, and ACD pre- and postoperatively in larger case numbers of patients undergoing conventionally sutured 20-gauge surgery and narrow gauge sutureless vitrectomy surgery with a longer time of follow-up (6 months or more) will be needed. This study presents our clinical data for Taiwan; therefore, we can expect to see a slight refractive change after PPV, and can offer our patients better advice in advance.
| 5. Conclusion|| |
Significant changes in refractive status were observed in patients undergoing PPV. Most patients experienced a myopic shift, among both phakic (−1.60 D) and pseudophakic (−0.59 D) patients. Changes in astigmatism were not significant. There are several plausible explanations; however, the true underlying etiologies of the refractive change are to be further investigated. To our knowledge, this is the first study on refraction following PPV among the Taiwanese population.
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[Table 1], [Table 2], [Table 3]