ORIGINAL CLINICAL STUDY
A Prospective Study of Pterygium Excision and Conjunctival Autograft With Human Fibrin Tissue Adhesive: Effects on Vision, Refraction, and Corneal Topography Stuti Misra, MSc, BOptom, Jennifer P. Craig, PhD, MCOptom, Charles N.J. McGhee, PhD, FRCOphth, and Dipika V. Patel, PhD, MRCOphth
Purpose: This study aimed to investigate changes in visual acuity, corneal parameters, and topographic parameters after pterygium surgery. Design: A prospective observational study was conducted. Methods: Twenty eyes of 20 participants undergoing pterygium excision with conjunctival autograft secured using human fibrin tissue adhesive were included in the study. All the participants were assessed preoperatively and 1 and 3 months postoperatively. The parameters included subjective refraction, visual acuity, and pterygium size (pterygium horizontal corneal length [PHCL]) and corneal tomography by Pentacam rotating Scheimpflug tomographer (OCULUS Optikgera¨te GmbH, Wetzlar, Germany). The astigmatic changes were calculated using vector analysis. Results: The mean age of participants was 49.3 T 12.1 years. Mean PHCL was 2.68 T 0.30 mm. The mean best corrected visual acuity preoperatively was 6/7.5, improving significantly to 6/6 at 1 month (P = 0.001) with this improvement remaining stable at 3 months postoperatively (P = 0.34). There was no significant change in subjective astigmatism, however, mean topographic astigmatism decreased significantly at 1 month (4.36 diopter, P G 0.01) and remained unchanged at 3 months (P G 0.01). Greater PHCL was associated with greater changes in corneal astigmatism. Conclusions: Significant improvements and early stabilization of visual acuity and topographic astigmatism confirm the optical benefits of pterygium excision. These data also suggest a significant advantage of performing pterygium before rather than simultaneously with or after cataract surgery by enabling the most accurate biometry. Key Words: pterygium, cornea, astigmatism, topography (Asia Pac J Ophthalmol 2014;3: 202Y206)
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terygium is a fibrovascular growth of bulbar conjunctiva extending onto the cornea. The development of pterygium is strongly associated with ultraviolet B exposure.1 In particular, those people with higher-than-average ultraviolet B exposure in the first 10 years of life have a significantly increased risk of going on to develop pterygia in later years.2 Indications for surgical excision of pterygia include visual loss due to extension close to the visual axis or induced astigmatism, restriction of eye movements, ocular surface irritation,
potential future vision impairment, to enable accurate biometry before cataract surgery, or cosmetic concerns.3,4 Several studies have used computerized corneal topography systems to evaluate the corneal topography in eyes with pterygia.5Y8 These studies have demonstrated that pterygia commonly induce focal corneal flattening and ‘‘with-the-rule’’ astigmatism.8,9 In addition, pterygium dimensions have been significantly correlated with spherical power, astigmatism, surface regularity index, and surface asymmetry index.5,10 Postulated causes for the observed topographic changes include mechanical distortion of the cornea due to direct fibrovascular traction by the pterygium or indirect apparent ‘‘flattening’’ due to localized pooling of the tear film at the apex of the pterygium.9 It is well known that surgical excision of pterygium typically results in corneal topographic changes.8,10,11 Surgical excision with conjunctival autograft is widely considered to be the current criterion standard method for the surgical treatment of pterygium because of low recurrence and complication rates.12 The most commonly used method for securing the conjunctival autograft is with absorbable sutures, and studies using this technique have demonstrated improvements in spherocylinder power, astigmatism, and topographic irregularity postoperatively.6,8,13 However, human fibrin tissue adhesives have recently gained increasing popularity as an alternative to sutures as a method for securing the conjunctival autograft. Reported advantages of this technique include a significant reduction in surgical time, reduced postoperative inflammation, low risk of recurrence, and decreased postoperative pain when compared with sutured conjunctival grafts.14Y17 A recent meta-analysis concluded the superiority of fibrin glue over conventional absorbable corneal sutures in that the earlier can reduce the recurrence rate without increasing the risk of complications.18 The aims of this study were to investigate the changes in visual acuity, corneal astigmatism, and corneal topography that occur after surgical excision of pterygium with conjunctival autograft secured with human fibrin tissue adhesive and to determine the time required for these parameters to stabilize.
MATERIALS AND METHODS From the Department of Ophthalmology, New Zealand National Eye Centre, Faculty of Medical and Health Sciences, University of Auckland, Auckland, New Zealand. Received for publication May 13, 2013; accepted August 30, 2013. Supported by an unrestricted award from The Maurice and Phyllis Paykel Trust in New Zealand. The authors have no funding or conflicts of interest to declare. Reprints: Dipika Patel, PhD, MRCOphth, Department of Ophthalmology, New Zealand National Eye Centre, University of Auckland, Private Bag 92019, Auckland, New Zealand. E-mail: [email protected]. Copyright * 2014 by Asia Pacific Academy of Ophthalmology ISSN: 2162-0989 DOI: 10.1097/APO.0000000000000006
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A prospective clinical study of consecutive cases undergoing pterygium excision with conjunctival autograft secured using human fibrin tissue adhesive was conducted. All patients were recruited from the Department of Ophthalmology at Greenlane Clinical Centre by the Auckland District Health Board in New Zealand. Exclusions included eyes in which the pterygium extended into the central 3-mm pupillary region, current contact lens wearers, previous ocular surgery or trauma, and other corneal or systemic disease that may affect the cornea. Only nasal, primary pterygia were included in the study. Informed consent was obtained from all participants, and the study design adhered to the tenets of the Declaration of
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Helsinki. The study protocol was approved by the Northern X Regional Ethics Committee.
Surgical Technique All surgeries were performed by a single experienced surgeon. Two percent lignocaine gel was applied to the affected eye for 20 minutes preoperatively. The eyelids were disinfected with 5% povidone-iodine, and the eyelids and skin were covered with a sterile plastic drape. After insertion of a lid speculum, 1% subconjunctival xylocaine with adrenaline with a ratio of 1:100,000 was injected under the body of the pterygium. The body of the pterygium was then incised, and the head of the pterygium was removed by blunt dissection from the base to the apex. Tenon tissue was carefully removed from the region of the conjunctival defect and from under the surrounding conjunctiva. The dimensions of the resulting conjunctival defect were measured using a caliper. Using these measurements, a free conjunctival graft was harvested from the superotemporal conjunctiva, avoiding harvest of the perilimbal conjunctiva and taking care to leave the underlying Tenon tissue intact. A Tisseel glue concentration (Baxter Healthcare, Vienna, Austria) of 4 IU/mL was mixed according to the manufacturer’s instructions. After drying the surgical site, Tisseel glue was applied via a dual-injection system underneath the conjunctiva surrounding the defect and onto the scleral bed of the conjunctival defect. The conjunctival graft was then placed on the scleral bed, with the more limbal border of the graft positioned on the limbal side of the conjunctival defect and the whole graft was compressed gently into position. After allowing 2 minutes for the glue to set, Maxitrol ointment (0.1% dexamethasone, neomycin sulfate, and polymyxin b sulfate; Alcon Laboratories, Wellington, New Zealand) was applied, and the eye was padded for 24 hours. Postoperative treatment included Maxidex (0.1% dexamethasone alcohol; Alcon Laboratories, Wellington, New Zealand) and Chlorsig (0.5% chloramphenicol; Aspen Pharma Pty Ltd., St. Leonards, New South Wales, Australia) eye drops each for 4 times per day for 28 days. Postoperative pain was managed with 1 g of combined oral paracetamol per 16 mg of codeine phosphate every 4 hours for a maximum of 5 days postoperatively.
Clinical Examination All subjects were examined preoperatively and at 1 and 3 months postoperatively. Uncorrected visual acuity (UCVA) was assessed using a Snellen chart at 6 m (graded to 6/4.8 and converted to logarithm of the minimum angle of resolution (logMAR) for purposes of statistical analysis). After subjective refraction, best spectacle corrected visual acuity (BSCVA) was recorded. Slit-lamp biomicroscopy was performed, and the size of the pterygium (pterygium horizontal corneal length [PHCL]) was measured from the limbus to the vascular tissue edge of the pterygium using the slit-beam as per previous studies.11,13,19 Corneal tomography was performed using the Pentacam rotating Scheimpflug tomographer (OCULUS Optikgera¨te GmbH, Wetzlar, Germany), and keratometric data were analyzed (simulated keratometry readings from the anterior corneal surface). Pentacam-derived astigmatic changes were assessed using vector analysis, such that refractive error was represented by 3 independent components; the mean spherical equivalents (MSE) were J0 and J45.20 The pterygium area was not excluded from the analysis of Pentacam parameters because the specific exclusion of areas of the cornea is not possible in Pentacam-derived maps,21 and we wished to identify any discrepancy in astigmatism between subjective refraction and computerized tomography. * 2014 Asia Pacific Academy of Ophthalmology
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Other data collected included the index of surface variance (ISV) (indicating the degree of corneal irregularity) and the index of vertical asymmetry (IVA) (indicating the degree of symmetry of corneal radii with respect to the horizontal corneal meridian as the axis of reflection). The corneal power was calculated from anterior surface measurement.
Statistical Analysis Statistical analysis was undertaken using PASW Statistics Package (version 18.0; IBM Corporation, Armonk, NY). The normality of the data was confirmed by the Kolmogorov-Smirnov test. The comparisons of outcome measures over time were performed by repeated measures analysis of variance (ANOVA). The relationship of changes to pterygium size is reported as Pearson correlation coefficients or Spearman rank correlation coefficients, for normally and not normally distributed data, respectively. In all cases, P G 0.05 was considered statistically significant.
RESULTS Twenty-three participants (23 eyes) were recruited for the study of which 20 participants returned for both 1 and 3 months of follow-up visits. Three patients were therefore excluded from further analysis. All pterygia were nasal and primary. The male-female ratio was 9:11, and the mean age was 49.3 T 12.1 years (range, 30Y70 years). Twelve right eyes and 8 left eyes were examined, and the mean PHCL was 2.68 T 0.30 mm (range, 1.0 Y 4.4 mm). The mean UCVA was 6/15 (0.37 T 0.36 logMAR) preoperatively and improved significantly at 1 month postoperatively to 6/12 (0.27 T 0.38 logMAR, P = 0.02) and 3 months postoperatively to 6/12 (0.28 T 0.38 logMAR, P = 0.04) when compared with preoperative values. There was no significant difference in UCVA between 1 and 3 months postoperatively (P = 0.24). The mean BSCVA was 6/7.5 (0.11 T 0.19 logMAR) preoperatively and improved significantly at 1 month postoperatively (6/6, 0.00 T 0.11 logMAR, P = 0.001) and 3 months postoperatively (6/6, 0.01 T 0.13 logMAR, P G 0.001) when compared with preoperative values. There was no significant difference in BSCVA between 1 and 3 months postoperatively (P = 0.34). There was no significant difference in mean subjective refractive spherical equivalent preoperatively and postoperatively (P = 0.92). However, there were significant differences in the mean topographic corneal power between preoperative and postoperative time points (P G 0.01), with postoperative ‘‘steepening’’ of the cornea by 2.2 diopter (D) at 1 month (Table 1). There was no significant difference in mean subjective refractive astigmatism preoperatively and postoperatively (P = 0.27). However, there were significant reductions in the mean topographic corneal astigmatism at 1 month (4.36 D, P G 0.01) and 3 months (4.13 D, P G 0.01) postoperatively compared with preoperative values (Fig. 1). However, there was no significant difference in topographic corneal astigmatism between 1 and 3 months postoperatively (P = 0.19). There was no significant difference in Pentacam-derived J0 (P = 0.31) or J45 (P = 0.92) between all time points. Pterygium horizontal corneal length showed positive correlation (Table 2) with subjective J0 (preoperative vs 3 months postoperative, R2 = 0.362, P = 0.005), subjective J45 (preoperative vs 3 months postoperative, R2 = 0.238, P = 0.029), Pentacamderived MSE (preoperative vs 1 month postoperative, R2 = 0.248, P = 0.018), and Pentacam-derived J45 (preoperative vs 3 months postoperative, R2 = 0.251, P = 0.024). www.apjo.org
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TABLE 1. Changes in Visual Acuity, Refraction, Corneal Topography, and Corneal Wave front Properties After Pterygium Excision With Conjunctival Autograft Secured Using Human Fibrin Tissue Adhesive Repeated Measures ANOVA Preoperatively (T SD)
Mean
1 Month Postoperatively 3 Months Postoperatively BL vs 1 BL vs 3 1 mo vs 3 (T SD) (T SD) mo mo mo
UCVA (logMAR) 0.37 T 0.36 (mean 6/15+1) 0.27 T 0.38 (mean 6/12+2) 0.28 T 0.38 (mean 6/12+1) 0.02* 0.04* BSCVA (logMAR) 0.11 T 0.19 (mean 6/7.5) T 0.11 (mean 6/6) 0.01 T 0.13 (mean 6/6) 0.001* G0.001* Subjective spherical j0.19 T 1.44 j0.19 T 1.39 j0.18 T 1.43 0.92 0.98 equivalent Subjective cylinder, D j0.24 T 0.27 j0.13 T 0.28 j0.19 T 0.25 0.27 0.27 Pentacam keratometric 42.5 T 2.2 44.7 T 2.0 44.4 T 1.9 0.02* G0.01* power, D Pentacam astigmatism, D 5.55 T 5.43 1.19 T 0.86 1.42 T 0.87 G0.01* G0.01* j0.73 T 2.97 j0.03 T 0.48 j0.08 T 0.65 0.31 0.4 Pentacam J0 0.22 T 2.04 0.17 T 0.48 0.32 T 0.45 0.92 0.82 Pentacam J45 Pentacam spherical 0.0011 T 0.0004 0.0013 T 0.0005 0.0013 T 0.0006 0.09 0.67 aberration Pentacam coma 0 j0.0005 T 0.0026 j0.0003 T 0.0008 j0.0002 T 0.0009 0.71 0.60 Pentacam coma 90 0.0002 T 0.0007 j0.0001 T 0.0007 j0.0002 T 0.0006 0.23 0.06 Pentacam trefoil 0 j0.00004 T 0.0016 j0.00002 T 0.0006 j0.0002 T 0.0006 0.97 0.73 Pentacam trefoil 30 j0.0007 T 0.0013 0.0001 T 0.0005 0.0000 T 0.0004 0.025* 0.0016*
0.24 0.34 0.98 0.55 0.58 0.19 0.77 0.32 0.35 0.72 0.49 0.45 0.80
*Probability is significant, where P G 0.05. BL, baseline (preoperative); 1 mo, 1 month postoperative; 3 mo, 3 months postoperative.
The mean ISV was 90.7 T 54.9 preoperatively and improved significantly at 1 month postoperatively (28.2 T 15.8, P G 0.01) and 3 months postoperatively (29.0 T 17.6, P = G0.01). There was no significant difference in ISV index between 1 and 3 months postoperatively (P = 0.66). The mean IVA was 0.77 T 0.53 preoperatively and improved significantly at 1 month postoperatively (0.24 T 0.12, P = G0.01) and 3 months postoperatively (0.25 T 0.17, P = G0.01). There was no significant difference in the IVA index at 1 and 3 months postoperatively (P = 0.98). Repeated measures ANOVA highlighted no significant presurgery and postsurgery differences in spherical aberration (P = 0.202), coma 0 (P = 0.725), or trefoil 0 (P = 0.876). However, there were significant increases in trefoil 30 after
surgery (P = 0.005). These increases were significant between baseline and 1 month (P = 0.025) and baseline and 3 months, (P = 0.016) but not between 1 and 3 months postsurgery. No complications occurred during the follow-up period.
DISCUSSION Although several studies have previously investigated alterations in visual, refractive, and corneal parameters after surgical excision of pterygium with conjunctival autograft, all have used absorbable corneal sutures to secure the conjunctival graft.7,11,22,23 To our knowledge, the current study is the first to investigate alterations in the aforementioned parameters when the conjunctival graft is secured with human fibrin tissue adhesive.
FIGURE 1. Pentacam-derived sagittal curvature maps taken preoperatively and 3 months after pterygium excision and conjunctival autograft with human fibrin tissue adhesive. Although there was a large change in topographic astigmatism, there was little change in the patient’s subjective refractive astigmatism (+0.25/j0.50 10 preoperatively and +0.25/j1.00 118 postoperatively in 3 months).
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TABLE 2. Correlations (Pearson or Spearman Rank, as Appropriate) for Pterygium Horizontal Corneal Length With Changes in Subjective and Pentacam-Derived Mean Spherical Equivalent and J0 and J45 (Astigmatism) Subjective Difference in MSE BL vs 1 mo BL vs 3 mo 1 mo vs 3 mo Difference in J0 BL vs 1 mo BL vs 3 mo 1 mo vs 3 mo Difference in J45 BL vs 1 mo BL vs 3 mo 1 mo vs 3 mo Pentacam Difference in MSE BL vs 1 mo BL vs 3 mo 1 mo vs 3 mo Difference in J0 BL vs 1 mo BL vs 3 mo 1 mo vs 3 mo Difference in J45 BL vs 1 mo BL vs 3 mo 1 mo vs 3 mo
R2
P
G0.0001 0.048 0.049
0.924 0.339 0.346
0.173 0.362 0.048
0.068 0.005* 0.352
0.166 0.238 0.048
0.075 0.029* 0.352
0.248 0.178 0.159
0.018* 0.057 0.082
0.002 0.002 0.002
0.860 0.865 0.845
0.228 0.251 0.005
0.033* 0.024* 0.774
BL, baseline (preoperative); 1 mo, 1 month postoperative; 3 mo, 3 months postoperative. *Correlation is significant, where P G 0.05 (2 tailed).
Although other studies have reported improved visual acuity after pterygium excision, this parameter has typically only been tested at a single postoperative time point.7,22,24,25 In the current study, both unaided and BSCVA improved significantly at 1 month postoperatively, and our data demonstrate that this level was maintained 3 months postoperatively. These results suggest that visual acuity stabilizes by 1 month after surgery. This study also demonstrated large, significant improvements in both surface regularity (reduced ISV) and degree of symmetry of corneal radii with respect to the horizontal corneal meridian as the axis of reflection (reduced IVA). These are in agreement with previous studies, which reported improvements in surface regularity and asymmetry indices as assessed by computerized videokeratography.24,25 As observed with visual acuity, both ISV and IVA remained stable after 1 month postoperatively. The reduction in corneal irregularity postsurgery likely results in enhancement of the optical quality, which is reflected in improved visual acuity.26 Previous studies have reported reductions in subjective refractive corneal astigmatism ranging from 0.61 D7 to 2.4 D22 compared with the current study, which observed a more modest and not statistically significant reduction of 0.11 D in subjective refractive corneal astigmatism at 1 month. However, conventional statistical methods suitable for nondirectional data are inappropriate for analyzing directional data such as refractive * 2014 Asia Pacific Academy of Ophthalmology
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astigmatism. In the current study, to perform conventional statistics without obtaining misleading results, astigmatism has been geometrically represented, in rectangular vector form, with independent power at 0 degree (J0) and at 45 degrees (J45). The Pentacam-derived astigmatism in the current study showed a significant decrease in absolute topographic corneal astigmatism of 4.36 D at 1 month postoperatively, conversely, there were no significant changes in Pentacam-derived J0 or J45 postoperatively. Mean topographic astigmatism, as measured by Pentacam or videokeratography, has previously been reported to reduce postoperatively.11,26 One theory is that the pterygium compresses, distorts, and flattens the cornea, such that, after pterygium surgery, there is an apparent steepening of the cornea9,27; however, we postulate that the tear meniscus at the apex of the pterygium may also produce an artifactual flattening on corneal tomography. The decrease in absolute topographic corneal astigmatism in this study is greater than what was reported in other studies, which reported decreases in topographic corneal astigmatism of between 0.95 D6 and 4.01 D.24 This difference may relate to differences in the PHCL, a parameter that was not reported in relation to corneal topographic changes in most studies. Indeed, in agreement with previous reports,19 this study confirms that the greater the encroachment of the pterygium onto the cornea, the greater the reduction of corneal astigmatism achieved after excision of the pterygium. To our knowledge, only 1 other study analyzed vectorial change of corneal astigmatism after pterygium excision.8 Although Ozdemir et al8 reported no significant difference in vectorial change at the 2-week period compared with the 3-week postoperative period, there was no comment about the significance of the preoperative vs postoperative changes. In addition, the specific method of vector analysis was not referred to, and the values for J0 and J45 were not provided thus the results are not comparable with those from the current study. This prospective study highlights a poor agreement between subjective refractive and topographic astigmatism, an observation that has been previously noted,19 with higher degrees of corneal astigmatism apparent on topography compared with subjective refraction. This difference has been primarily attributed to the hemi-astigmatic nature of the induced change. Subjective refraction demands patients’ attention to 2 images, that is, 1 from the more spherical temporal cornea and the other from the astigmatic nasal cornea. The more spherical image is generally better tolerated in comparison with the second astigmatic image that could cause visual complaints.19 Furthermore, the refractive differential across the irregular cornea caused by pterygium can be suppressed subjectively but are noted in objective tomography.11,19 We also postulate that the tear meniscus at the apex of the pterygium may be erroneously measured by topographic systems as an area of greater flattening (induced astigmatism). The lack of agreement between overall subjective and objective refraction for astigmatic errors has been previously reported.28,29 To the best of our knowledge, this is the first study to investigate alterations in visual, refractive, and corneal parameters after surgical excision of pterygium with conjunctival autograft secured with human fibrin tissue adhesive. The significant improvements in vision and corneal astigmatism confirm the advantage of pterygium excision to maximize BSCVA and to enable accurate biometry before performing cataract surgery. It is also the first study to investigate the aforementioned parameters at multiple postoperative time points, demonstrating stabilization of vision, absolute topographic corneal astigmatism, ISV, and IVA by 1 month. These results indicate that www.apjo.org
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accurate biometry may be obtained as early as 1 month after pterygium excision. REFERENCES 1. Saw SM, Tan D. Pterygium: prevalence, demography and risk factors. Ophthalmic Epidemiol. 1999;6:219Y228.
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15. Ratnalingam V, Eu AL, Ng GL, et al. Fibrin adhesive is better than sutures in pterygium surgery. Cornea. 2010;29:485Y489. 16. Nieuwendaal CP, van der Meulen IJ, Mourits M, et al. Long-term follow-up of pterygium surgery using a conjunctival autograft and Tissucol. Cornea. 2011;30:34Y36.
2. Mackenzie FD, Hirst LW, Battistutta D, et al. Risk analysis in the development of pterygia. Ophthalmology. 1992;99:1056Y1061.
17. Koranyi G, Seregard S, Kopp ED. Cut and paste: a no suture, small incision approach to pterygium surgery. Br J Ophthalmol. 2004;88:911Y914.
3. Starck T, Kenyon KR, Serrano F. Conjunctival autograft for primary and recurrent pterygia: surgical technique and problem management. Cornea. 1991;10:196Y202.
18. Pan HW, Zhong JX, Jing CX. Comparison of fibrin glue versus suture for conjunctival autografting in pterygium surgery: a meta-analysis. Ophthalmology. 2011;118:1049Y1054.
4. Hirst LW. The treatment of pterygium. Surv Ophthalmol. 2003;48:145Y180.
19. Lin A, Stern G. Correlation between pterygium size and induced corneal astigmatism. Cornea. 1998;17:28Y30.
5. Tomidokoro A, Miyata K, Sakaguchi Y, et al. Effects of pterygium on corneal spherical power and astigmatism. Ophthalmology. 2000;107:1568Y1571.
20. Thibos LN, Horner D. Power vector analysis of the optical outcome of refractive surgery. J Cataract Refract Surg. 2001;27:80Y85.
6. Wu PL, Kuo CN, Hsu HL, et al. Effect of pterygium surgery on refractive spherocylinder power and corneal topography. Ophthalmic Surg Lasers Imaging. 2009;40:32Y37.
21. Swartz T, Marten L, Wang M. Measuring the cornea: the latest developments in corneal topography. Curr Opin Ophthalmol. 2007;18:325Y333.
7. Bahar I, Loya N, Weinberger D, et al. Effect of pterygium surgery on corneal topography: a prospective study. Cornea. 2004;23:113Y117.
22. Maheshwari S. Effect of pterygium excision on pterygium induced astigmatism. Indian J Ophthalmol. 2003;51:187Y188.
8. Ozdemir M, Cinal A. Early and late effects of pterygium surgery on corneal topography. Ophthalmic Surg Lasers Imaging. 2005;36:451Y456.
23. Maheshwari S. Pterygium-induced corneal refractive changes. Indian J Ophthalmol. 2007;55:383Y386.
9. Oldenburg JB, Garbus J, McDonnell JM, et al. Conjunctival pterygia. Mechanism of corneal topographic changes. Cornea. 1990;9:200Y204. 10. Errais K, Bouden J, Mili-Boussen I, et al. Effect of pterygium surgery on corneal topography. Eur J Ophthalmol. 2008;18:177Y181. 11. Yilmaz S, Yuksel T, Maden A. Corneal topographic changes after four types of pterygium surgery. J Refract Surg. 2008;24:160Y165. 12. Tan DT, Chee SP, Dear KB, et al. Effect of pterygium morphology on pterygium recurrence in a controlled trial comparing conjunctival autografting with bare sclera excision. Arch Ophthalmol. 1997;115:1235Y1240. 13. Mohammad-Salih PA, Sharif AF. Analysis of pterygium size and induced corneal astigmatism. Cornea. 2008;27:434Y438. 14. Srinivasan S, Dollin M, McAllum P, et al. Fibrin glue versus sutures for attaching the conjunctival autograft in pterygium surgery: a prospective observer masked clinical trial. Br J Ophthalmol. 2009;93:215Y218.
24. Stern GA, Lin A. Effect of pterygium excision on induced corneal topographic abnormalities. Cornea. 1998;17:23Y27. 25. Yagmur M, Ozcan AA, Sari Set al. Visual acuity and corneal topographic changes related with pterygium surgery. J Refract Surg. 2005;21:166Y170. 26. Oltulu R, Demirel S, Sarac O, et al. Evaluation of corneal and anterior chamber changes following pterygium surgery using a Pentacam Scheimplug system: a prospective study. Semin Ophthalmol. 2013;28:206Y209. 27. Budak K, Khater TT, Friedman NJ, et al. Corneal topographic changes induced by excision of perilimbal lesions. Ophthalmic Surg Lasers. 1999;30:458Y464. 28. Pesudovs K, Weisinger HS. A comparison of autorefractor performance. Optom Vis Sci. 2004;81:554Y558. 29. Goss DA, Grosvenor T. Reliability of refractionVa literature review. J Am Optom Assoc. 1996;67:619Y630.
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A Prospective Study of Pterygium Excision and Conjunctival Autograft With Human Fibrin Tissue Adhesive: Effects on Vision, Refraction, and Corneal Topography Stuti Misra, MSc, BOptom, Jennifer P. Craig, PhD, MCOptom, Charles N.J. McGhee, PhD, FRCOphth, and Dipika V. Patel, PhD, MRCOphth
Purpose: This study aimed to investigate changes in visual acuity, corneal parameters, and topographic parameters after pterygium surgery. Design: A prospective observational study was conducted. Methods: Twenty eyes of 20 participants undergoing pterygium excision with conjunctival autograft secured using human fibrin tissue adhesive were included in the study. All the participants were assessed preoperatively and 1 and 3 months postoperatively. The parameters included subjective refraction, visual acuity, and pterygium size (pterygium horizontal corneal length [PHCL]) and corneal tomography by Pentacam rotating Scheimpflug tomographer (OCULUS Optikgera¨te GmbH, Wetzlar, Germany). The astigmatic changes were calculated using vector analysis. Results: The mean age of participants was 49.3 T 12.1 years. Mean PHCL was 2.68 T 0.30 mm. The mean best corrected visual acuity preoperatively was 6/7.5, improving significantly to 6/6 at 1 month (P = 0.001) with this improvement remaining stable at 3 months postoperatively (P = 0.34). There was no significant change in subjective astigmatism, however, mean topographic astigmatism decreased significantly at 1 month (4.36 diopter, P G 0.01) and remained unchanged at 3 months (P G 0.01). Greater PHCL was associated with greater changes in corneal astigmatism. Conclusions: Significant improvements and early stabilization of visual acuity and topographic astigmatism confirm the optical benefits of pterygium excision. These data also suggest a significant advantage of performing pterygium before rather than simultaneously with or after cataract surgery by enabling the most accurate biometry. Key Words: pterygium, cornea, astigmatism, topography (Asia Pac J Ophthalmol 2014;3: 202Y206)
P
terygium is a fibrovascular growth of bulbar conjunctiva extending onto the cornea. The development of pterygium is strongly associated with ultraviolet B exposure.1 In particular, those people with higher-than-average ultraviolet B exposure in the first 10 years of life have a significantly increased risk of going on to develop pterygia in later years.2 Indications for surgical excision of pterygia include visual loss due to extension close to the visual axis or induced astigmatism, restriction of eye movements, ocular surface irritation,
potential future vision impairment, to enable accurate biometry before cataract surgery, or cosmetic concerns.3,4 Several studies have used computerized corneal topography systems to evaluate the corneal topography in eyes with pterygia.5Y8 These studies have demonstrated that pterygia commonly induce focal corneal flattening and ‘‘with-the-rule’’ astigmatism.8,9 In addition, pterygium dimensions have been significantly correlated with spherical power, astigmatism, surface regularity index, and surface asymmetry index.5,10 Postulated causes for the observed topographic changes include mechanical distortion of the cornea due to direct fibrovascular traction by the pterygium or indirect apparent ‘‘flattening’’ due to localized pooling of the tear film at the apex of the pterygium.9 It is well known that surgical excision of pterygium typically results in corneal topographic changes.8,10,11 Surgical excision with conjunctival autograft is widely considered to be the current criterion standard method for the surgical treatment of pterygium because of low recurrence and complication rates.12 The most commonly used method for securing the conjunctival autograft is with absorbable sutures, and studies using this technique have demonstrated improvements in spherocylinder power, astigmatism, and topographic irregularity postoperatively.6,8,13 However, human fibrin tissue adhesives have recently gained increasing popularity as an alternative to sutures as a method for securing the conjunctival autograft. Reported advantages of this technique include a significant reduction in surgical time, reduced postoperative inflammation, low risk of recurrence, and decreased postoperative pain when compared with sutured conjunctival grafts.14Y17 A recent meta-analysis concluded the superiority of fibrin glue over conventional absorbable corneal sutures in that the earlier can reduce the recurrence rate without increasing the risk of complications.18 The aims of this study were to investigate the changes in visual acuity, corneal astigmatism, and corneal topography that occur after surgical excision of pterygium with conjunctival autograft secured with human fibrin tissue adhesive and to determine the time required for these parameters to stabilize.
MATERIALS AND METHODS From the Department of Ophthalmology, New Zealand National Eye Centre, Faculty of Medical and Health Sciences, University of Auckland, Auckland, New Zealand. Received for publication May 13, 2013; accepted August 30, 2013. Supported by an unrestricted award from The Maurice and Phyllis Paykel Trust in New Zealand. The authors have no funding or conflicts of interest to declare. Reprints: Dipika Patel, PhD, MRCOphth, Department of Ophthalmology, New Zealand National Eye Centre, University of Auckland, Private Bag 92019, Auckland, New Zealand. E-mail: [email protected]. Copyright * 2014 by Asia Pacific Academy of Ophthalmology ISSN: 2162-0989 DOI: 10.1097/APO.0000000000000006
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A prospective clinical study of consecutive cases undergoing pterygium excision with conjunctival autograft secured using human fibrin tissue adhesive was conducted. All patients were recruited from the Department of Ophthalmology at Greenlane Clinical Centre by the Auckland District Health Board in New Zealand. Exclusions included eyes in which the pterygium extended into the central 3-mm pupillary region, current contact lens wearers, previous ocular surgery or trauma, and other corneal or systemic disease that may affect the cornea. Only nasal, primary pterygia were included in the study. Informed consent was obtained from all participants, and the study design adhered to the tenets of the Declaration of
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Helsinki. The study protocol was approved by the Northern X Regional Ethics Committee.
Surgical Technique All surgeries were performed by a single experienced surgeon. Two percent lignocaine gel was applied to the affected eye for 20 minutes preoperatively. The eyelids were disinfected with 5% povidone-iodine, and the eyelids and skin were covered with a sterile plastic drape. After insertion of a lid speculum, 1% subconjunctival xylocaine with adrenaline with a ratio of 1:100,000 was injected under the body of the pterygium. The body of the pterygium was then incised, and the head of the pterygium was removed by blunt dissection from the base to the apex. Tenon tissue was carefully removed from the region of the conjunctival defect and from under the surrounding conjunctiva. The dimensions of the resulting conjunctival defect were measured using a caliper. Using these measurements, a free conjunctival graft was harvested from the superotemporal conjunctiva, avoiding harvest of the perilimbal conjunctiva and taking care to leave the underlying Tenon tissue intact. A Tisseel glue concentration (Baxter Healthcare, Vienna, Austria) of 4 IU/mL was mixed according to the manufacturer’s instructions. After drying the surgical site, Tisseel glue was applied via a dual-injection system underneath the conjunctiva surrounding the defect and onto the scleral bed of the conjunctival defect. The conjunctival graft was then placed on the scleral bed, with the more limbal border of the graft positioned on the limbal side of the conjunctival defect and the whole graft was compressed gently into position. After allowing 2 minutes for the glue to set, Maxitrol ointment (0.1% dexamethasone, neomycin sulfate, and polymyxin b sulfate; Alcon Laboratories, Wellington, New Zealand) was applied, and the eye was padded for 24 hours. Postoperative treatment included Maxidex (0.1% dexamethasone alcohol; Alcon Laboratories, Wellington, New Zealand) and Chlorsig (0.5% chloramphenicol; Aspen Pharma Pty Ltd., St. Leonards, New South Wales, Australia) eye drops each for 4 times per day for 28 days. Postoperative pain was managed with 1 g of combined oral paracetamol per 16 mg of codeine phosphate every 4 hours for a maximum of 5 days postoperatively.
Clinical Examination All subjects were examined preoperatively and at 1 and 3 months postoperatively. Uncorrected visual acuity (UCVA) was assessed using a Snellen chart at 6 m (graded to 6/4.8 and converted to logarithm of the minimum angle of resolution (logMAR) for purposes of statistical analysis). After subjective refraction, best spectacle corrected visual acuity (BSCVA) was recorded. Slit-lamp biomicroscopy was performed, and the size of the pterygium (pterygium horizontal corneal length [PHCL]) was measured from the limbus to the vascular tissue edge of the pterygium using the slit-beam as per previous studies.11,13,19 Corneal tomography was performed using the Pentacam rotating Scheimpflug tomographer (OCULUS Optikgera¨te GmbH, Wetzlar, Germany), and keratometric data were analyzed (simulated keratometry readings from the anterior corneal surface). Pentacam-derived astigmatic changes were assessed using vector analysis, such that refractive error was represented by 3 independent components; the mean spherical equivalents (MSE) were J0 and J45.20 The pterygium area was not excluded from the analysis of Pentacam parameters because the specific exclusion of areas of the cornea is not possible in Pentacam-derived maps,21 and we wished to identify any discrepancy in astigmatism between subjective refraction and computerized tomography. * 2014 Asia Pacific Academy of Ophthalmology
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Other data collected included the index of surface variance (ISV) (indicating the degree of corneal irregularity) and the index of vertical asymmetry (IVA) (indicating the degree of symmetry of corneal radii with respect to the horizontal corneal meridian as the axis of reflection). The corneal power was calculated from anterior surface measurement.
Statistical Analysis Statistical analysis was undertaken using PASW Statistics Package (version 18.0; IBM Corporation, Armonk, NY). The normality of the data was confirmed by the Kolmogorov-Smirnov test. The comparisons of outcome measures over time were performed by repeated measures analysis of variance (ANOVA). The relationship of changes to pterygium size is reported as Pearson correlation coefficients or Spearman rank correlation coefficients, for normally and not normally distributed data, respectively. In all cases, P G 0.05 was considered statistically significant.
RESULTS Twenty-three participants (23 eyes) were recruited for the study of which 20 participants returned for both 1 and 3 months of follow-up visits. Three patients were therefore excluded from further analysis. All pterygia were nasal and primary. The male-female ratio was 9:11, and the mean age was 49.3 T 12.1 years (range, 30Y70 years). Twelve right eyes and 8 left eyes were examined, and the mean PHCL was 2.68 T 0.30 mm (range, 1.0 Y 4.4 mm). The mean UCVA was 6/15 (0.37 T 0.36 logMAR) preoperatively and improved significantly at 1 month postoperatively to 6/12 (0.27 T 0.38 logMAR, P = 0.02) and 3 months postoperatively to 6/12 (0.28 T 0.38 logMAR, P = 0.04) when compared with preoperative values. There was no significant difference in UCVA between 1 and 3 months postoperatively (P = 0.24). The mean BSCVA was 6/7.5 (0.11 T 0.19 logMAR) preoperatively and improved significantly at 1 month postoperatively (6/6, 0.00 T 0.11 logMAR, P = 0.001) and 3 months postoperatively (6/6, 0.01 T 0.13 logMAR, P G 0.001) when compared with preoperative values. There was no significant difference in BSCVA between 1 and 3 months postoperatively (P = 0.34). There was no significant difference in mean subjective refractive spherical equivalent preoperatively and postoperatively (P = 0.92). However, there were significant differences in the mean topographic corneal power between preoperative and postoperative time points (P G 0.01), with postoperative ‘‘steepening’’ of the cornea by 2.2 diopter (D) at 1 month (Table 1). There was no significant difference in mean subjective refractive astigmatism preoperatively and postoperatively (P = 0.27). However, there were significant reductions in the mean topographic corneal astigmatism at 1 month (4.36 D, P G 0.01) and 3 months (4.13 D, P G 0.01) postoperatively compared with preoperative values (Fig. 1). However, there was no significant difference in topographic corneal astigmatism between 1 and 3 months postoperatively (P = 0.19). There was no significant difference in Pentacam-derived J0 (P = 0.31) or J45 (P = 0.92) between all time points. Pterygium horizontal corneal length showed positive correlation (Table 2) with subjective J0 (preoperative vs 3 months postoperative, R2 = 0.362, P = 0.005), subjective J45 (preoperative vs 3 months postoperative, R2 = 0.238, P = 0.029), Pentacamderived MSE (preoperative vs 1 month postoperative, R2 = 0.248, P = 0.018), and Pentacam-derived J45 (preoperative vs 3 months postoperative, R2 = 0.251, P = 0.024). www.apjo.org
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TABLE 1. Changes in Visual Acuity, Refraction, Corneal Topography, and Corneal Wave front Properties After Pterygium Excision With Conjunctival Autograft Secured Using Human Fibrin Tissue Adhesive Repeated Measures ANOVA Preoperatively (T SD)
Mean
1 Month Postoperatively 3 Months Postoperatively BL vs 1 BL vs 3 1 mo vs 3 (T SD) (T SD) mo mo mo
UCVA (logMAR) 0.37 T 0.36 (mean 6/15+1) 0.27 T 0.38 (mean 6/12+2) 0.28 T 0.38 (mean 6/12+1) 0.02* 0.04* BSCVA (logMAR) 0.11 T 0.19 (mean 6/7.5) T 0.11 (mean 6/6) 0.01 T 0.13 (mean 6/6) 0.001* G0.001* Subjective spherical j0.19 T 1.44 j0.19 T 1.39 j0.18 T 1.43 0.92 0.98 equivalent Subjective cylinder, D j0.24 T 0.27 j0.13 T 0.28 j0.19 T 0.25 0.27 0.27 Pentacam keratometric 42.5 T 2.2 44.7 T 2.0 44.4 T 1.9 0.02* G0.01* power, D Pentacam astigmatism, D 5.55 T 5.43 1.19 T 0.86 1.42 T 0.87 G0.01* G0.01* j0.73 T 2.97 j0.03 T 0.48 j0.08 T 0.65 0.31 0.4 Pentacam J0 0.22 T 2.04 0.17 T 0.48 0.32 T 0.45 0.92 0.82 Pentacam J45 Pentacam spherical 0.0011 T 0.0004 0.0013 T 0.0005 0.0013 T 0.0006 0.09 0.67 aberration Pentacam coma 0 j0.0005 T 0.0026 j0.0003 T 0.0008 j0.0002 T 0.0009 0.71 0.60 Pentacam coma 90 0.0002 T 0.0007 j0.0001 T 0.0007 j0.0002 T 0.0006 0.23 0.06 Pentacam trefoil 0 j0.00004 T 0.0016 j0.00002 T 0.0006 j0.0002 T 0.0006 0.97 0.73 Pentacam trefoil 30 j0.0007 T 0.0013 0.0001 T 0.0005 0.0000 T 0.0004 0.025* 0.0016*
0.24 0.34 0.98 0.55 0.58 0.19 0.77 0.32 0.35 0.72 0.49 0.45 0.80
*Probability is significant, where P G 0.05. BL, baseline (preoperative); 1 mo, 1 month postoperative; 3 mo, 3 months postoperative.
The mean ISV was 90.7 T 54.9 preoperatively and improved significantly at 1 month postoperatively (28.2 T 15.8, P G 0.01) and 3 months postoperatively (29.0 T 17.6, P = G0.01). There was no significant difference in ISV index between 1 and 3 months postoperatively (P = 0.66). The mean IVA was 0.77 T 0.53 preoperatively and improved significantly at 1 month postoperatively (0.24 T 0.12, P = G0.01) and 3 months postoperatively (0.25 T 0.17, P = G0.01). There was no significant difference in the IVA index at 1 and 3 months postoperatively (P = 0.98). Repeated measures ANOVA highlighted no significant presurgery and postsurgery differences in spherical aberration (P = 0.202), coma 0 (P = 0.725), or trefoil 0 (P = 0.876). However, there were significant increases in trefoil 30 after
surgery (P = 0.005). These increases were significant between baseline and 1 month (P = 0.025) and baseline and 3 months, (P = 0.016) but not between 1 and 3 months postsurgery. No complications occurred during the follow-up period.
DISCUSSION Although several studies have previously investigated alterations in visual, refractive, and corneal parameters after surgical excision of pterygium with conjunctival autograft, all have used absorbable corneal sutures to secure the conjunctival graft.7,11,22,23 To our knowledge, the current study is the first to investigate alterations in the aforementioned parameters when the conjunctival graft is secured with human fibrin tissue adhesive.
FIGURE 1. Pentacam-derived sagittal curvature maps taken preoperatively and 3 months after pterygium excision and conjunctival autograft with human fibrin tissue adhesive. Although there was a large change in topographic astigmatism, there was little change in the patient’s subjective refractive astigmatism (+0.25/j0.50 10 preoperatively and +0.25/j1.00 118 postoperatively in 3 months).
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TABLE 2. Correlations (Pearson or Spearman Rank, as Appropriate) for Pterygium Horizontal Corneal Length With Changes in Subjective and Pentacam-Derived Mean Spherical Equivalent and J0 and J45 (Astigmatism) Subjective Difference in MSE BL vs 1 mo BL vs 3 mo 1 mo vs 3 mo Difference in J0 BL vs 1 mo BL vs 3 mo 1 mo vs 3 mo Difference in J45 BL vs 1 mo BL vs 3 mo 1 mo vs 3 mo Pentacam Difference in MSE BL vs 1 mo BL vs 3 mo 1 mo vs 3 mo Difference in J0 BL vs 1 mo BL vs 3 mo 1 mo vs 3 mo Difference in J45 BL vs 1 mo BL vs 3 mo 1 mo vs 3 mo
R2
P
G0.0001 0.048 0.049
0.924 0.339 0.346
0.173 0.362 0.048
0.068 0.005* 0.352
0.166 0.238 0.048
0.075 0.029* 0.352
0.248 0.178 0.159
0.018* 0.057 0.082
0.002 0.002 0.002
0.860 0.865 0.845
0.228 0.251 0.005
0.033* 0.024* 0.774
BL, baseline (preoperative); 1 mo, 1 month postoperative; 3 mo, 3 months postoperative. *Correlation is significant, where P G 0.05 (2 tailed).
Although other studies have reported improved visual acuity after pterygium excision, this parameter has typically only been tested at a single postoperative time point.7,22,24,25 In the current study, both unaided and BSCVA improved significantly at 1 month postoperatively, and our data demonstrate that this level was maintained 3 months postoperatively. These results suggest that visual acuity stabilizes by 1 month after surgery. This study also demonstrated large, significant improvements in both surface regularity (reduced ISV) and degree of symmetry of corneal radii with respect to the horizontal corneal meridian as the axis of reflection (reduced IVA). These are in agreement with previous studies, which reported improvements in surface regularity and asymmetry indices as assessed by computerized videokeratography.24,25 As observed with visual acuity, both ISV and IVA remained stable after 1 month postoperatively. The reduction in corneal irregularity postsurgery likely results in enhancement of the optical quality, which is reflected in improved visual acuity.26 Previous studies have reported reductions in subjective refractive corneal astigmatism ranging from 0.61 D7 to 2.4 D22 compared with the current study, which observed a more modest and not statistically significant reduction of 0.11 D in subjective refractive corneal astigmatism at 1 month. However, conventional statistical methods suitable for nondirectional data are inappropriate for analyzing directional data such as refractive * 2014 Asia Pacific Academy of Ophthalmology
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astigmatism. In the current study, to perform conventional statistics without obtaining misleading results, astigmatism has been geometrically represented, in rectangular vector form, with independent power at 0 degree (J0) and at 45 degrees (J45). The Pentacam-derived astigmatism in the current study showed a significant decrease in absolute topographic corneal astigmatism of 4.36 D at 1 month postoperatively, conversely, there were no significant changes in Pentacam-derived J0 or J45 postoperatively. Mean topographic astigmatism, as measured by Pentacam or videokeratography, has previously been reported to reduce postoperatively.11,26 One theory is that the pterygium compresses, distorts, and flattens the cornea, such that, after pterygium surgery, there is an apparent steepening of the cornea9,27; however, we postulate that the tear meniscus at the apex of the pterygium may also produce an artifactual flattening on corneal tomography. The decrease in absolute topographic corneal astigmatism in this study is greater than what was reported in other studies, which reported decreases in topographic corneal astigmatism of between 0.95 D6 and 4.01 D.24 This difference may relate to differences in the PHCL, a parameter that was not reported in relation to corneal topographic changes in most studies. Indeed, in agreement with previous reports,19 this study confirms that the greater the encroachment of the pterygium onto the cornea, the greater the reduction of corneal astigmatism achieved after excision of the pterygium. To our knowledge, only 1 other study analyzed vectorial change of corneal astigmatism after pterygium excision.8 Although Ozdemir et al8 reported no significant difference in vectorial change at the 2-week period compared with the 3-week postoperative period, there was no comment about the significance of the preoperative vs postoperative changes. In addition, the specific method of vector analysis was not referred to, and the values for J0 and J45 were not provided thus the results are not comparable with those from the current study. This prospective study highlights a poor agreement between subjective refractive and topographic astigmatism, an observation that has been previously noted,19 with higher degrees of corneal astigmatism apparent on topography compared with subjective refraction. This difference has been primarily attributed to the hemi-astigmatic nature of the induced change. Subjective refraction demands patients’ attention to 2 images, that is, 1 from the more spherical temporal cornea and the other from the astigmatic nasal cornea. The more spherical image is generally better tolerated in comparison with the second astigmatic image that could cause visual complaints.19 Furthermore, the refractive differential across the irregular cornea caused by pterygium can be suppressed subjectively but are noted in objective tomography.11,19 We also postulate that the tear meniscus at the apex of the pterygium may be erroneously measured by topographic systems as an area of greater flattening (induced astigmatism). The lack of agreement between overall subjective and objective refraction for astigmatic errors has been previously reported.28,29 To the best of our knowledge, this is the first study to investigate alterations in visual, refractive, and corneal parameters after surgical excision of pterygium with conjunctival autograft secured with human fibrin tissue adhesive. The significant improvements in vision and corneal astigmatism confirm the advantage of pterygium excision to maximize BSCVA and to enable accurate biometry before performing cataract surgery. It is also the first study to investigate the aforementioned parameters at multiple postoperative time points, demonstrating stabilization of vision, absolute topographic corneal astigmatism, ISV, and IVA by 1 month. These results indicate that www.apjo.org
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accurate biometry may be obtained as early as 1 month after pterygium excision. REFERENCES 1. Saw SM, Tan D. Pterygium: prevalence, demography and risk factors. Ophthalmic Epidemiol. 1999;6:219Y228.
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15. Ratnalingam V, Eu AL, Ng GL, et al. Fibrin adhesive is better than sutures in pterygium surgery. Cornea. 2010;29:485Y489. 16. Nieuwendaal CP, van der Meulen IJ, Mourits M, et al. Long-term follow-up of pterygium surgery using a conjunctival autograft and Tissucol. Cornea. 2011;30:34Y36.
2. Mackenzie FD, Hirst LW, Battistutta D, et al. Risk analysis in the development of pterygia. Ophthalmology. 1992;99:1056Y1061.
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3. Starck T, Kenyon KR, Serrano F. Conjunctival autograft for primary and recurrent pterygia: surgical technique and problem management. Cornea. 1991;10:196Y202.
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19. Lin A, Stern G. Correlation between pterygium size and induced corneal astigmatism. Cornea. 1998;17:28Y30.
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6. Wu PL, Kuo CN, Hsu HL, et al. Effect of pterygium surgery on refractive spherocylinder power and corneal topography. Ophthalmic Surg Lasers Imaging. 2009;40:32Y37.
21. Swartz T, Marten L, Wang M. Measuring the cornea: the latest developments in corneal topography. Curr Opin Ophthalmol. 2007;18:325Y333.
7. Bahar I, Loya N, Weinberger D, et al. Effect of pterygium surgery on corneal topography: a prospective study. Cornea. 2004;23:113Y117.
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8. Ozdemir M, Cinal A. Early and late effects of pterygium surgery on corneal topography. Ophthalmic Surg Lasers Imaging. 2005;36:451Y456.
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9. Oldenburg JB, Garbus J, McDonnell JM, et al. Conjunctival pterygia. Mechanism of corneal topographic changes. Cornea. 1990;9:200Y204. 10. Errais K, Bouden J, Mili-Boussen I, et al. Effect of pterygium surgery on corneal topography. Eur J Ophthalmol. 2008;18:177Y181. 11. Yilmaz S, Yuksel T, Maden A. Corneal topographic changes after four types of pterygium surgery. J Refract Surg. 2008;24:160Y165. 12. Tan DT, Chee SP, Dear KB, et al. Effect of pterygium morphology on pterygium recurrence in a controlled trial comparing conjunctival autografting with bare sclera excision. Arch Ophthalmol. 1997;115:1235Y1240. 13. Mohammad-Salih PA, Sharif AF. Analysis of pterygium size and induced corneal astigmatism. Cornea. 2008;27:434Y438. 14. Srinivasan S, Dollin M, McAllum P, et al. Fibrin glue versus sutures for attaching the conjunctival autograft in pterygium surgery: a prospective observer masked clinical trial. Br J Ophthalmol. 2009;93:215Y218.
24. Stern GA, Lin A. Effect of pterygium excision on induced corneal topographic abnormalities. Cornea. 1998;17:23Y27. 25. Yagmur M, Ozcan AA, Sari Set al. Visual acuity and corneal topographic changes related with pterygium surgery. J Refract Surg. 2005;21:166Y170. 26. Oltulu R, Demirel S, Sarac O, et al. Evaluation of corneal and anterior chamber changes following pterygium surgery using a Pentacam Scheimplug system: a prospective study. Semin Ophthalmol. 2013;28:206Y209. 27. Budak K, Khater TT, Friedman NJ, et al. Corneal topographic changes induced by excision of perilimbal lesions. Ophthalmic Surg Lasers. 1999;30:458Y464. 28. Pesudovs K, Weisinger HS. A comparison of autorefractor performance. Optom Vis Sci. 2004;81:554Y558. 29. Goss DA, Grosvenor T. Reliability of refractionVa literature review. J Am Optom Assoc. 1996;67:619Y630.
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