Purpose: To estimate the minimum number of cells required to obtain reliable data in a specular microscope, which could possibly represent the real clinical condition of the corneal endothelium. Methods: A cross-sectional study of 122 eyes of 61 individuals submitted to noncontact specular microscope was conducted. Data generated by the manufacturer's software were uploaded to specific statistical software for sampling relative error calculation. When relative error was above 5%, new images were acquired and more cells counted until the desired relative error was reached. Data analyzed in this study for the desired relative error were number of cells marked by the examiner for each eye (marked cells), number of cells used for data analysis (analyzed cells), endothelial area used for analysis, sampling error, and absolute number of images used for each eye. Results: The average number of marked cells required to obtain a relative sampling error of less than 5% was 425.2 ± 102.2 cells. The average number of analyzed cells used by the specular microscope to generate the data was 247.4 ± 51.6 cells. The average endothelial area of the analyzed cells was 0.43 ± 0.08 mm2. The mean sampling error was 3.7% ± 0.6%, and an average of 2.95 ± 0.74 images was needed to obtain a relative sampling error of less than 5%. Conclusions: We conclude that, theoretically, a minimum of 425.2 cells from 2.95 images must be marked to obtain reliable results, which could possibly represent the real endothelial clinical condition of the whole cornea.
Intrastromal corneal ring segments (ICRS) improve corneal topographic symmetry and reduce corneal aberrations through regularization of the corneal surface, thereby functioning as a viable surgical intervention for patients with keratoconus. This study aims to evaluate changes in lower- (LOAs) and higher-order aberrations (HOAs) amongst varying pupil sizes pre- and post- ICRS implantation in keratoconus patients. We specifically investigate the impact of pupil size on total corneal HOAs up to the 6th order. Twenty-one eyes that underwent ICRS implantation were included in this prospective interventional study. LOAs and HOAs measurements at the 6 mm, 4 mm, and 2 mm pupil diameters were collected preoperatively and at 6 months postoperatively using the Zernicke analysis function on a Scheimpflug device. ICRS implantation demonstrated a statistically significant effect in vertical coma with a −0.23 reduction (p = 0.015) for a 4 mm pupil size and a −1.384 reduction (p < 0.001) for 6 mm, with no significant effect at 2 mm. Horizontal coma, astigmatism 0°, astigmatism 45°, trefoil 5th order 30°, and RMS HOA demonstrated significant reductions at 4 mm or 6 mm pupil sizes but not at 2 mm. Our analysis demonstrates a favorable effect of ICRS implantation on larger pupil sizes, suggesting the importance of pupil size as it correlates with HOAs reduction.
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