Evaluation of Corneal Changes following Pterygium Surgery Using Pentacam Ahmad Kheirkhah MD, Hasan Hashemi MD Rahman Nazari MD, Hamid Safi Farabi Eye Hospital, Tehran, Iran The authors have no financial interest in the subject matter of this poster.

Introduction Pterygium Pterygium surgery Definition: Encroachment of a fibrovascular tissue from the bulbar conjunctiva onto the cornea. Causes regular or irregular astigmatism 1 Produces significant alterations in corneal shape and curvature Pterygium surgery Improves the visual acuity Reduces the corneal astigmatism and irregularity Changes corneal topographic indices

Introduction Corneal topographical changes with decreased corneal astigmatism after pterygium surgery have been documented. 2,3 But, Few studies have calculated the surgically-induced correction of the astigmatism. 4,5 Corneal elevation changes after surgery has not been studied yet. No study has used Pentacam (Oculus, Wetzlar, Germany) for investigating the effects of pterygium and its excision on cornea. Purpose: To use Pentacam for evaluation of corneal changes in patients undergoing pterygium surgery.

Materials & Methods Study population: 80 eyes of 80 consecutive patients with primary pterygium at Farabi Eye Hospital, Tehran, Iran from August 2008 to January 2009. Surgical technique: Excision of pterygium, mitomycin C application, free conjunctival autograft or amniotic membrane transplantation. Pentacam examination was performed preoperatively and at 1, 3, and 6 months after surgery. Measured corneal indices: mean keratometry, best fit sphere (BFS) and central corneal elevation(CCE).

Materials & Methods Surgically induced astigmatsm (SIA) was calculated from the topographical keratometric and astigmatic values by vectoral analysis using Holladay’s method. Statistical analysis was performed by SPSS software and statisical significance was tested using ANOVA and Paired t-test.

RESULTs Value are expressed as mean ± standard deviation Preop 1 month 3 months 6 months SIA 3.72 3.60 3.57 Keratometry(front) 42.88 ± 1.91 44.30 ± 1.78 44.13 ± 1.72 44.02 ± 1.67 Keratomery (back) -6.35 ± 0.33 -6.29 ± 0.28 -6.30 ± 0.27 -6.31 ± 0.29 BFS (front) 8.02 ± 0.32 7.76 ± 0.28 7.75 ± 0.48 7.77 ± 0.56 BFS (back) 6.44 ± 0.25 6.54 ± 0.25 6.54 ± 0.22 6.54 ± 0.26 CCE (front) 5.21 ± 4.55 4.70 ± 5.60 4.24 ± 4.04 4.93 ± 6.54 CCE (back) 4.66 ± 5.59 6.23 ± 4.63 5.24 ± 7.04 6.34 ± 5.72 Value are expressed as mean ± standard deviation SIA: Surgically-induced astigmatism BFS: Best fit sphere CCE: Central corneal elevation

Results SIA showed steepening of the cornea in the horizontal meridian. After surgery, the mean front keratometry increased (P<0.001) while mean back keratometry decreased (P=0.11). Decreases in front BFS and increases in back BFS were statistically significant (P<0.001). Decreases in front CCE and increase in back central elevation were not statistically significant.

Discussion & Conclusion Pterygium surgery improves pterygium-induced with the rule astigmatism. Cornea becomes steeper after surgery. Pterygium surgery causes non-significant alteration in central corneal elevation. Further studies are needed to evaluate the factors influencing surgically-induced astigmatism.

References 1. Oldenburg JB, Garbus J, McDonnell JM, McDonnell PJ. Conjunctival pterygia. Mechanism of corneal topographic changes. Cornea. 1990 Jul;9(3):200-4. 2. Bahar I, Loya N, Weinberger D, Avisar R. Effect of pterygium surgery on corneal topography: a prospective study. Cornea. 2004 Mar;23(2):113-7. 3. Wu PL, Kuo CN, Hsu HL, Lai CH. Effect of pterygium surgery on refractive spherocylinder power and corneal topography. Ophthalmic Surg Lasers Imaging. 2009;40(1):32-7. 4. Ozdemir M, Cinal A..Early and late effects of pterygium surgery on corneal topography. Ophthalmic Surg Lasers Imaging. 2005;36(6):451-6. 5. Fong KS, Balakrishnan V, Chee SP, Tan DT. Refractive change following pterygium surgery. CLAO J. 1998 Apr;24(2):115-7.