1. Evaluation of Corneal Tomography in Primary Pterygium Sahil Goel, MD (Presenting Author), Murugesan Vanathi MD *The authors have no financial interests to disclosure

2. A) B) INTRODUCTION  Correlations between the magnitude of refractive cylinder & topographic cylinder are not good. This can be due to the hemi-astigmatic nature of the induced changes  Existing studies have evaluated corneal astigmatism in pterygium using keratometry, VKG. Corneal topography changes have been studied using VKG, aberrometry PURPOSE To study the effect of pterygium on  corneal tomography & corneal wavefront aberrations at the anterior & posterior corneal surface using Scheimpflug imaging with Pentacam  To correlate this with the dimensional parameters of pterygium (Length, Height, Area)

3. A) B) METHOD Prospective observational study of clinical data 55 patients Inclusion Criteria : Unilateral primary pterygium, > 18 years of age Exclusion Criteria: Recurrent pterygium, double headed pterygium, any previous ocular surgery, pterygium with central corneal encroachment, any associated ocular surface / lid / corneal pathology Parameters: -Scheimpflug imaging using Pentacam -Clinical photographic imaging using zeiss slit lamp mounted camera and dimensions (length, height, corneal area encroached) measured using NIH image J software

4. A) Statistical Analysis: Spearman correlation analysis was performed to evaluate the effect of pterygium on corneal tomography and wavefront aberrations Unpaired t test and Mann-Whitney test was used for comparison between the two groups for parametric and non parametric tests respectively. Length (L) Height (H) Area (A)

5. A) B) Mean Values Pterygium Eyes (n= 55) Control Eyes (n= 37) Pterygium Length (mm)2.23 - Pterygium Height (mm)4.85 - Pterygium Area (mm 2 )8.078 + 5.9 - Visual acuity (S.D.)0.2141 (0.21)0.12 (0.5) Ka1 (D)41.094543.1279 Ka2 (D)44.332743.9811 Anterior corneal astigmatism (D)3.23820.8514 Kp1 (D)6.146.1297 Kp2 (D)6.526.4649 Posterior corneal astigmatism (D)0.38870.3352 RESULTS Pterygium Eyes: mean age 43.4 + 11.5, male: female ratio = 30:26

6. A) B) RESULTS Mean Values Pterygium Eyes (n= 55) Control Eyes (n= 37) Anterior corneal elevation (microns) - 8.5 + 18.9 -3.4 + 15. 9 Posterior corneal elevation (microns) - 6.6 + 24.1 - 14.0 + 21.7 Kmax (D)50.2 + 9.7 47.4 + 5.6 Q value (A / P)- 0.23 + 0.4/ - 0.36 + 1.7- 0.27 + 0.2 / - 0.12 + 0.7 Corneal Aberrations (A / P)1.5 + 1.2/ 0.3 + 0.10.7 + 0.4 / 0.3 + 0.3 Anterior LOA / HOA1.4 + 1.1 / 0.4 + 0.30.7 + 0.4 / 0.2 + 0.2 Posterior LOA / HOA0.2 + 0.1 / 0.09 + 0.10.2 + 0.3 / 0.09 + 0.1 Total corneal aberrations1.5 + 1.30.7 + 0.6 Spherical equivalent 0.6 + 1.0 0.1 + 1.2 Corneal thickness (microns) 536.8 + 39.6 530.1 + 33.1

7. A) B) RESULTS  Significant correlation of corneal astigmatism (flattening of horizontal axis) with dimensions of pterygium (rho=0.469 for height, rho=0.465 for area and rho=0.357 for length of pterygium, p<0.0005) was noted  At the posterior corneal surface against the rule astigmatism was noted; at the anterior corneal surface with the rule astigmatism was noted  Significantly higher corneal wavefront aberrations were noted in eyes with pterygia (both lower and higher order at anterior surface and only higher order at posterior surface) with Spearman’s correlation coefficient being highest with corneal area encroached by pterygium (rho=0.540 for LOA and 0.553 for HOA) & distance from pupillary centre (rho=0.531 for LOA and 0.564 for HOA)

8. A) B) RESULTS  Strongest correlation was seen between fraction of corneal area encroached by pterygium with induced astigmatism, rho= 0.738, p<0.0005 Fig2: Scatter plot with 95% confidence interval showing correlation between induced astigmatism vs. fraction of total corneal area covered by pterygium across all grades of pterygia

9. A) B) RESULTS  Bland-Altman plots comparing astigmatism reading from Pentacam with that from Keratometer and Videokeratography in eyes with pterygium and fellow normal eyes, showing very poor agreement in eyes with pterygium as compared to normal eyes

10. A) B) CONCLUSION  Pterygium leads to deterioration of visual performance not only by causing refractive and topographic changes but also by causing a significant increase in corneal wavefront aberrations (both lower order and higher order)  This may explain why the patients have significant visual symptoms despite visual axis sparing and appreciated visual correction  Unlike normal, in eyes with pterygium there is poor correlation between Scheimpflug device and keratometer and videokeratograph

11. A) B) References 1. Gumus K, Erkilic K, Topaktas D, Colin J.Effect of pterygia on refractive indices, corneal topography, and ocular aberrations. Cornea. 2011 Jan;30(1):24-9. 2. Mohammad-Salih PA, Sharif AF. Analysis of pterygium size and induced corneal astigmatism. Cornea. 2008 May;27(4):434-8. 3. Zare M, Zarei-Ghanavati S, Ansari-Astaneh MR, Baradaran- Rafiee A, Einolahi B. Effects of pterygium on ocular aberrations. Cornea. 2010 Nov;29(11):1232-5. 4. Maheshwari S. Pterygium-induced corneal refractive changes.Indian J Ophthalmol. 2007 Sep-Oct; 55(5):383-6.