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S. E. Eccles Brown, C. D. Reilly, V. A. Panday, S. Roberts; Refractive Surgery Outcomes: Corneas Thinner Than 500 µm versus Corneas Thicker Than 500 µm. Invest. Ophthalmol. Vis. Sci. 2008;49(13):2906. doi: https://doi.org/.
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To compare the refractive surgery outcomes between patients with pre-operative central corneal thickness <500 µm and those ≥500 µm. This study aims to prove the null hypothesis, stating there is no difference between the two groups. This project expands the amount of data related to refractive surgery and enables physicians to utilize a larger base of knowledge when determining the best treatment options for patients.
This long-term, retrospective, non-randomized follow-up study obtained pre-operative pachymetry readings from 5,038 patient eyes. The group was divided into those with preoperative central corneal thickness (CCT) of less than 500 microns (464 eyes) and those greater than or equal to 500 microns (4,564 eyes). Patients receiving PRK and LASEK were included in the same category. The pre-operative mean spherical equivalent (MSE), uncorrected visual acuity (UCVA) at three and six months post-operatively, and the best corrected visual acuity (BCVA) at six months post-operatively were obtained for each group. Due to variability in patient follow-up and data documentation, the number of patient eyes varies for the three and six month follow-up results. Linear regression analyses were plotted using the achieved and attempted spherical equivalent at 6 months post-operatively for both CCT groups.
Mean preoperative CCT <500 microns was 482 microns (475 microns and 482 microns for LASIK and PRK/LASEK, respectively). Mean preoperative CCT ≥500 microns was 551 microns (560 microns and 550 microns for LASIK and PRK/LASEK, respectively). None of the included eyes developed postrefractive corneal ectasia. At three month follow-up, data was obtained for two post-LASIK eyes in the CCT <500 µm group; no data was obtained for this category after this time. A slightly higher number of recorded UCVA was noted compared to BCVA at six-month follow-up, likely due to lack of documentation when the patient was seeing 20/20 or better without correction. Linear regression analyses showed similar slopes and y-intercepts for both CCT groups (0.872 and -0.323, respectively, in the group with CCT <500 µm and 0.896 and -0.295, respectively, in the group with CCT ≥500 µm).
While statistical analysis is still needed for this data, the results appear to support the null hypothesis, indicating that refractive laser surgery with LASIK, PRK, or LASEK in patients with thin corneas (<500 microns) is as safe and predictable as the use of these techniques in patients with normal thickness corneas (≥500 microns) for refractive corrections.
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