Pterygium is a wing-shaped fibrovascular growth of conjunctival connective tissue over cornea resulting in cosmetic problems, decrease in visual acuity secondary to astigmatism and blockage of the optical axis. It can cause flattening of the cornea to the leading apex.
In the treatment, several different surgeries are being performed to decrease the high recurrence of bare sclera technique, such as conjunctival autografting and amniotic membrane grafting.[2–4] Recently, fibrin glue was recommended to secure the graft.
In present study, our aim was to investigate the effect of surgery type on the change in astigmatism following pterygium excision.
Materials and Methods
In this retrospective study, the data of 240 consecutive eyes that underwent pterygium excision by one surgeon (RAY) between 2003 and 2008, completed 3 months follow-up and showed no sign of recurrence were investigated. Patients with complaints of decrease in visual acuity, foreign body sensation and hyperemia due to pterygium were decided for surgery of the pterygium. History of ocular trauma, ocular surgery, and presence of corneal abnormalities such as, scarring that might affect the astigmatic value were accepted as exclusion criteria.
Institutional review board approval was obtained. All patients were informed about the alternatives in surgery available at that time, and the decision was made according to the preference of the patient together with the surgeon. Thus, patients were not randomized. Patients have signed an informed consent for surgery preoperatively.
There were 127 male and 113 female patients with a mean age of 57.5 ± 12.1 years (range 27 to 86 years). All patients underwent comprehensive ophthalmic examination. The preoperative and postoperative 3rd month data of best corrected visual acuity (BCVA) and keratometric values were noted. The BCVA values were obtained on a Snellen scale and then converted into logarithm of the minimum angle of resolution (logMar) values.
Preoperative horizontal length was measured by focusing the slit on the pterygium and using ruler of the slit incorporated in the slit-lamp from limbus to the advancing edge of pterygium (Topcon SL-7F, Topcon Co., Japan).
Keratometric values were obtained using an automated keratorefractometer (Topcon K2-8100PA, Tokyo, Japan). Only keratometric values were included in the study since in approximately half of patients, we were unable to obtain a topographic measurement.
Pterygium excision was performed as follows: Lidocaine HCL 40 mg/2 ml + epinephrine 0.025 mg/ml (Jetokain, Adeka, Turkey) was injected under the conjunctiva into the body of the pterygium. Following removal of the body, the head was bluntly lifted off the cornea. The abnormal scar tissue on the cornea was removed. A moderate amount of Tenon's capsule was removed from each patient. Either no or minimal cautery was used to the scleral bed. Following removal of the pterygium, patients underwent 5 different types of surgeries: Conjunctival autograft with sutures (CAG-s) or fibrin glue (CAG-g), conjunctival rotational flap (CRF), or amniotic membrane transplantation with either suture (AMT-s) or with glue (AMT-g).
In conjunctival autografting, an oversized graft for 1 mm of length and width relative to the scleral bed was harvested from the superotemporal limbus, with care to obtain a Tenon-free graft. The graft was subsequently moved to the nasal area. In CAG-s group, interrupted Vicryl 8-0 sutures were used to attach the graft. In the CAG-g group, fibrin glue (Tisseel VH, Baxter AG) was used to attach to the conjunctival edges and episclera. The method of application of the glue was described previously.
For CRF, a Tenon-free flap originating from the inferior bulbar conjunctiva with a hinge at the inferonasal border of the bare sclera was prepared and rotated to cover the bare sclera with interrupted 8/0 Vicryl sutures.
The amniotic membrane was prepared as described previously. For AMT, the membrane was taken out of the preservation medium and cut to the proper size to cover the defect area. The membrane was spread over the denuded area so that the epithelial/basement membrane surface would be on top, and it was sutured to the surrounding conjunctiva and episclera by using interrupted 8-0 Vicryl sutures in AMT-s group. On the other hand, in the AMT-g group, fibrin glue was used to attach the amniotic membrane as reported earlier.
The eye was covered with an eye pad after administration of topical antibiotic ointment (tobramycin). Following surgery, topical antibiotic (ofloxacin 0.3%, 4 times a day) and steroid (dexamethasone 0.1%, 4 times a day) drops were given, and were tapered over 1 month period. Sutures were removed at 2 weeks.
The data was entered into SPSS software (Statistical Package for the Social Sciences, version 13.0, SPSS Inc, Chicago, Ill, USA). The overall changes in BCVA and astigmatic degree were evaluated using Wilcoxon signed rank test. The difference in astigmatic values between groups was calculated using one way analysis of variance (ANOVA). Difference with significance of < 0.05 was accepted as statistically significant.
The most commonly performed procedure was CAG-s (N = 115). Next, the number of patients in each group was as followed: CAG-g (N = 53), CRF (N = 47), AMT-s (N = 15), and AMT-g (N = 10). The horizontal length of the pterygium changed between 2 and 7 mm (mean ± SD 3.78 ± 1.11 mm). Most of the pterygium sizes were 3 mm (N = 115), followed by 4 mm (N = 58), 5 mm (N = 30), 6 mm (N = 23), 2 mm (N = 11) and 7 mm (N = 3).
The mean preoperative logMar values were 0.37 ± 0.64 (range 0.00 - 3.00). Following surgery, the logMar values decreased to 0.12 ± 0.24 (range 0.00 to 2.00). This postoperative decrease was significant (P < 0.001, Wilcoxon signed rank test).
Preoperatively, the mean astigmatic value was 3.47 ± 2.50 D (range 0.00 D -12.50 D). After surgery, the mean astigmatic values decreased to 1.29 ± 1.07 D (range 0.00 D -5.50 D). The mean difference between pre- and postoperative astigmatic values was 2.18 ± 2.34 D, and this decrease was statistically significant (P < 0.001, paired t test). 162 eyes (67.5%) had a preoperative astigmatism of ≥ 2.00 D, which decreased to 51 (21.3%) postoperatively.
The distribution of pterygium sizes according to the surgery groups is shown in Fig. 1. The mean ± SD pterygium size according to the surgery type was as followed: 3.83 ± 1,16 mm in CAG-s, 3.72 ± 1.21 mm in CAG-g, 3.74 ± 1.07 mm in CRF, 3.60 ± 0.63 mm in AMT-s, and 4.00 ± 0.81 mm in AMT-g, and there was no difference between groups for pterygium sizes (P > 0.05).
The changes in astigmatism values according to the pterygium size are shown in Fig. 2. The astigmatic changes were significantly different according to the preoperative size of the pterygium (F = 3.464, P = 0.005, One way ANOVA). The Post Hoc test revealed that this difference was mainly due to differences between the pterygiae with sizes of 2 mm and 5 mm as well as 6 mm (P = 0.009 and P = 0.017, Tukey HSD). There was a positive correlation between the preoperative size of the pterygium and the change in astigmatism degree (ρ = 0.224, P < 0.001, Spearman correlation analysis). Also, the change in astigmatism was significantly correlated with preoperative astigmatic values (ρ = 0.780, P < 0.001, Spearman correlation analysis).
The postoperative astigmatism correlated positively with preoperative astigmatism (ρ = 0.351, P < 0.001, Spearman correlation analysis). On the other hand, the postoperative astigmatic values were negatively correlated with the change in astigmatism (ρ = − 0.262, P < 0.001, Spearman correlation analysis).
The changes in astigmatic values were not related to the method of surgery (P = 0.055, ANOVA) [Fig. 3]. The patient number in AMT groups was small. Thus, if we omit the groups where amniotic membrane was used from the statistical comparison, the astigmatic changes were also not statistically significant (P = 0.240, ANOVA). Also, the correlation between the surgery type and change in astigmatism was not statistically significant (ρ = −0.116, P = 0.072, Spearman correlation analysis).
In a 2nd evaluation, we omitted 56 eyes where the size of the pterygium was 5 mm or larger and performed the analysis in 184 eyes. The most commonly performed procedure was CAG-s (N = 86). Next, the number of patients in each group was as followed: CAG-g (N = 42), CRF (N = 35), AMT-s (N = 14), and AMT-g (N = 7).
The mean preoperative logMar values were 0.32 ± 0.59 (range 0.00 - 3.00). Following surgery, the logMar values decreased to 0.10 ± 0.23 (range 0.00 -2.00). This postoperative decrease was significant (P < 0.001, Wilcoxon signed rank test).
Preoperatively, the mean astigmatic value was 2.97 ± 2.28 D (range 0.00 D -12.50 D). After surgery, the astigmatic values decreased to 1.16 ± 0.91 D (range 0.00 D 4.50 D). The mean difference between pre- and postoperative astigmatic values was 1.81 ± 2.22 D, and this decrease was statistically significant (P < 0.001, paired t test).
In this group with pterygium sizes 4 mm or less, the astigmatic changes were significantly different according to the preoperative size of the pterygium (F = 3.115, P = 0.047, One way ANOVA). The Post Hoc test revealed that this difference was due to the difference between 2 mm and 4 mm pterygiae (P = 0.039, Tukey HSD). There was a positive correlation between the change in astigmatic values and change in logMar values (R = 0.344, P < 0.001, Spearman correlation analysis). The changes in astigmatic values did not correlated with the method of surgery (R = −0.141, P = 0.056, Spearman correlation analysis). Also, there was no correlation with the change in logMar values and the type of surgery (ρ = 0.042, P = 0.570, Spearman correlation analysis).
Pterygium may cause flattening of the cornea to the leading apex. An induced astigmatism was explained by several mechanisms: Pooling of the tear film at the leading edge of the pterygium, and mechanical traction exerted by the pterygium on the cornea.
As reported earlier, pterygium results in high corneal astigmatism, which decreases following an excision. Accordingly, in present study, we found that the degree of astigmatism decreased significantly following excision, and this decrease was related to the size of the pterygium. The size was affecting the change in astigmatism as well as postoperative degree of astigmatism. We also found that the change in astigmatic degree was positively correlated with the change in visual acuity. On the other hand, the type of grafting as CAG, CRF or AMT or the use of suture or glue to fixate the graft does not have a significant effect on the change in astigmatism degree.
The refractive components were demonstrated to stabilize at 1 month following pterygium surgery. However, in present study, we included the postoperative 3rd months' results to make sure that refraction was stabilized. The conventional keratometry evaluates the corneal refractive power from 3 or 4 data points. Hence, many authors suggested using corneal topography in evaluating the change in astigmatism following pterygium surgery. Since this was a retrospective study and we were unable to perform corneal topography in all cases, we have chosen to include only the keratometric values.
An increase in visual acuity is expected following pterygium excision. It was reported that BCVA increased from 0.53 to 0.68. Accordingly, we observed a decrease in logMar values from 0.38 to 0.13. In a similar study, the logMAR values decreased significantly from 0.41 to 0.24 in 27 eyes (P = 0.000).
Lin and Stern found a significant correlation between the size of pterygium and corneal astigmatism. It was also suggested that pterygium extending more than 45% of corneal diameter results in increasing degrees of astigmatism. Mohammad-Salih and co-workers studied the pterygium extension, width, and total area and investigated their relationship with corneal astigmatism. Among the 3, an extension had the strongest and the most significant correlation with the astigmatism (ρ = 0.462, P < 0.001, Pearson correlation analysis). The authors reported that pterygium with larger than 2.2 mm extension might contribute to corneal astigmatism >2 D. It was reported that significant astigmatism increases with an increasing size of the pterygium. Kampitak concluded that the amount of induced corneal astigmatism and timing for pterygium excision are related to the pterygium size, and reported that 2.25 mm pterygium resulted in astigmatism of 2 D, and should be considered in the limits of surgery. Accordingly, Seitz et al. concluded that with the size of pterygium from 2.5 mm, the preoperative astigmatism increases, therefore, the authors believed that the surgery should be performed before it reaches beyond this point. In present study, we compared the size of the pterygium with the change in astigmatism and found a significant correlation (P < 0.001). Main difference in change of astigmatism was between the sizes of 2 mm and 5 and 6 mm. Thus, we agree with previous reports that it is better to remove the pterygium when it measures nearly 2 mm in horizontal length.
In a prospective study, the videokeratographic changes of 55 eyes were evaluated and found that pterygium surgery significantly reduced refractive astigmatism from 3.12 to 2.51 (P = 0.05). Also, several reports showed a decrease in corneal astigmatism.[10121319–23] We also found that corneal astigmatism decreased from 3.47 D to 1.29 D. The mean difference in corneal astigmatism change was 2.18 ± 2.34 D, and this decrease was statistically significant (P < 0.001). Surgical removal of pterygium can improve the changes; however, in eyes with advanced pterygium, corneal distortion does not normalize completely and irregular changes may persist if the lesion has reached the paracentral cornea. Some other factors, like changes in corneal stroma and Bowman's layer, are suggested to be responsible for these persistent refractive changes in eyes after pterygium surgery.
We found a significant correlation between the pre- and postoperative astigmatic values (ρ = 0.351, P < 0.001). Contrary to our results, some studies show no correlation between these 2 parameters. This contradiction might be related to the larger number of patients included, and the larger horizontal pterygium sizes in present study. Similar to our results, Wu et al. found a significant correlation between the differences in refractive cylindrical power before and after surgery.
Since the primary excision with bare sclera technique has a high recurrence rate, nowadays, many surgeons prefer conjunctival autograft or amniotic membrane transplantation. Also, recently fibrin glue application is suggested as an alternative to suture placement, and its use is increasing. The results and recurrence rates of different surgical techniques is studied in several reports. However, to our knowledge, there is limited study comparing the effect of different surgical approaches on astigmatism. Frau and co-workers noticed that following surgery, corneal astigmatism exceeded more than 3 D in 7 patients and did not change dramatically in the rest of their 109 eyes with corneo-conjunctival autografting. Yilmaz et al. compared the astigmatic changes following different types of surgeries including conjunctival autografting, limbal-conjunctival autograft, bare sclera and bare sclera with mitomycin. The authors found a statistical difference between groups for mean topographical astigmatism and surgically-induced astigmatism (P = 0.033 and 0.030, respectively). In that study, the mean difference was between the bare sclera and graft techniques where postoperative astigmatism was smaller in the former. In present study, we found no difference in postoperative astigmatic changes between different surgical techniques. The main difference between the 2 studies (ours and Yilmaz et al.'s) is the measurement of astigmatism in present study via keratometry. The other difference was in surgical techniques. We did not use bare sclera technique. Also, limbal grafts were not included in this study. All 5 methods included in this study involved some type of graft or flap either secured with sutures or with fibrin glue.
In conclusion, pterygium results in high corneal astigmatism, which increases with the increase in horizontal length, and decreases to an acceptable level following excision. We found a significant correlation between the preoperative and postoperative astigmatic values as well as the changes in astigmatism with surgery. According to our study, the type of grafting as CAG, CRF or AMT or the use of suture or glue to fixate the graft does not have a significant effect on the change in astigmatism degree. Further prospective studies with topographic measurements and larger patient numbers are warranted to evaluate this topic in detail.
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Source of Support: Nil,
Conflict of Interest: None declared.