Jornal de Oftalmologia Clínica e Experimental
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Assessment of the Corneal Aberration and Elevation Changes after Pterygium Surgery

Ismail Ahmed Nagib Omar, Heba Radi Attaallah

Aim: To assess the changes in corneal higher order aberrations and changes in the elevation of the front and back corneal surfaces using the Oculus Pentacam.
Study design: It was a prospective study that included 63 eyes of fifty patients with primary pterygium.
Place and duration of the study: It was done between December 2012 and November 2013 in Elminya university hospital.
Methodology: All patients had pterygial excision with conjunctival autograft and intraoperative application of Mitomicin C 0.5%. Patients were examined with Oculus Pentacam to assess the corneal aberrations and elevation induced by pterygium preoperatively and six months after its excision.
Results: Eight eyes were in female patients (12.7%) and fifty five in male patients (87.3%). The mean age was 47.2 ± 5.3 ranging from 38 to 56 years. The preoperative mean front corneal cylinder was 3.9 ± 2.7 (0.8 to 10.6) and that of the posterior surface was 0.2 ± 0.15 (0 to 0.6) and changed postoperatively to 1.45 ± 1.1 (0.2 to 4) (p=0.001) and 0.19 ± 0.1 (0 to 0.5) (p=0.03) respectively and both are statistically significant. The mean keratometric power of the anterior surface increased significantly from 42.7 ± 2.11 D (39.9 to 48.7) preoperatively to 44.7 ± 1.9 D (42.7 to 48.9) postoperatively (p=0.001).
The root mean square (RMS) of total and higher order aberrations decreased postoperatively except for the spherical aberration (0.26 ± 0.2μm preoperatively versus 0.43 ± 0.17 μm postoperatively, p=0.001). The RMS of postoperative coma and trefoil decreased significantly (-0.01 ± 0.2 μm versus 0.006 ± 0.4 μm, p=0.03 for coma) and (-0.07 ± 0.6 μm versus -0.15 ± 0.3 μm, p=0.04 for trefoil). Regarding the corneal asphericity (Q-value), there was increased prolation of the anterior surface (-0.40 ± 0.2 vs -0.38 ± 0.8 p=0.8), but for the posterior surface there was mild oblation (-0.39 ± 0.12 vs-0.41 ± 0.16 p=0.4).
Analysis of the corneal elevation revealed that the front and back elevations decreased significantly six months postoperatively at the 7 mm zone (-68.1 ± 25.1mm versus -44.8 ± 46.6 mm p=0.001 for the front), and (-198.43 ± 66.5 mm versus-157.07 ± 117.8 mm p=0.017 for the back).
Conclusion: Pterygium affects the corneal surface and induces elevation changes and aberrations that is why it should be removed to improve the visual performance of the patients. We should consider pterygial excision before any refractive surgery or lens surgery planned for those patients.