Preoperative Scheimpflug Analysis of Refractive Surgery Patients With Posterior Embryotoxon
Narrative Responses:
Purpose
To identify the atypical tomography of patients presenting for refractive surgery with posterior embryotoxon and the differentiating features from forme fruste keratoconus.
Methods
Retrospective analysis of 1015 consecutive refractive surgery patient records wherein all atypical examination findings and topography/tomograms were monitored as part of a quality improvement process. Eighteen (18) patients were found to have posterior embryotoxon on clinical examination in one or both eyes. Nine (9) of these patients met the inclusion criteria of available preoperative Scheimpflug testing.
Results
The mean preoperative manifest refraction spherical equivalent was -4.01 (-1.125 to -7.325), the mean pachymetry at the thinnest point was 556.72 (504 to 630), the mean Back Surface Elevation (BSE) was 17.56 (8-35), while the mean BSE in clinically affected eyes was 19.85. The Corneal Thickness Spatial Profile (CTSP) was steeper in 16/18 eyes (89%). The I-S ratio mean was 0.76 (0 – 1.5). No patients showed significant anterior surface elevation (mean =3.722, range 0 to +10) or significant corneal thinning compared to the pupil centered pachymetry suggestive of a keratoconus suspect (mean = 1.722, range of 0 to 5 microns).
Conclusion
Patients whose cornea tomography shows greater than normal BSE and steeper CTSP should be evaluated for posterior embryotoxon. Analysis of the I-S ratio, pachymetry change from the pupil to the thinnest point, and front surface elevation is helpful in differentiating these patients from keratoconus suspects.