Corneal biomechanical properties in normal, forme fruste keratoconus, and manifest keratoconus after statistical correction for potentially confounding factors.

PURPOSE: To evaluate the difference in corneal biomechanical properties, after controlling for potentially confounding factors, along the spectrum of keratoconic disease as measured by the keratoconus severity score. METHODS: The corneal biomechanical properties of 73 keratoconic (KCN) eyes of 54 patients, 42 forme fruste keratoconic (FFKCN) eyes of 32 patients, and 115 healthy eyes of 115 age- and sex-matched patients were reviewed retrospectively. The main outcome measures were corneal hysteresis (CH) and corneal resistance factor (CRF). RESULTS: In the normal group, the mean CH was 11.0 ± 1.4 mm Hg and mean CRF was 11.1 ± 1.6 mm Hg. The FFKCN mean CH was 8.8 ± 1.4 mm Hg and mean CRF was 8.6 ± 1.3 mm Hg. The KCN mean CH was 7.9 ± 1.3 mm Hg and mean CRF was 7.3 ± 1.4 mm Hg. There were statistically significant differences in the mean CH and CRF in the normal group compared with the FFKCN and the KCN groups (P < 0.001) after statistically controlling for differences in central corneal thickness, age, and sex. CONCLUSIONS: There is a significant difference in the mean CH and CRF between normal and FFKCN corneas after controlling for differences in age, sex, and central corneal thickness. However, there is a significant overlap in the distribution of CH and CRF values among all groups. The biomechanical parameters CH and CRF cannot be used alone but may be a useful clinical adjunct to other diagnostic tools, such as corneal tomography, in distinguishing normal from subclinical keratoconic corneas.

Corneal ectasia after laser in situ keratomileusis after laser thermal keratoplasty.

PURPOSE: To report a case of corneal ectasia following hyperopic laser in situ keratomileusis in a patient who had previous laser thermal keratoplasty. METHODS: Case report. RESULTS: We report a case of a 66-year-old emmetropic man initially presented with complaint of difficulty reading without correction. Laser thermal keratoplasty (LTK) was performed on the non-dominant right eye, resulting in successful monovision. Three years later, the patient presented with decreased unaided near vision caused by hyperopic regression of the LTK. Conventional hyperopic laser in situ keratomileusis (LASIK) was performed, again resulting in successful monovision. More than three years later, the patient returned with worsening near vision. A focal corneal ectasia was noted in the same location as the 6 o'clock LTK leukoma. CONCLUSIONS: To our knowledge, this is the first report of ectasia occuring after LASIK following LTK. Consideration should be given to performing photorefractive keratectomy (PRK) instead of LASIK following thermal keratoplasty.