Accuracy of corneal astigmatism estimation by neglecting the posterior corneal surface measurement.
OBJECTIVE
To evaluate the accuracy of corneal astigmatism estimation by neglecting the posterior corneal surface measurement.


METHODS
Prospective, observational study.


METHODS
The right eyes of 493 subjects were measured with a rotating Scheimpflug camera (Pentacam; Oculus, Wetzlar, Germany). The keratometric corneal astigmatism (KA) was obtained by using the anterior corneal surface measurement and the keratometric index (1.3375) while neglecting the posterior corneal surface measurement. The Pentacam-derived total corneal astigmatism (PA) was derived by doubled-angle vector analysis of the astigmatisms on both corneal surfaces.


RESULTS
The mean arithmetic and absolute estimation errors of the KA magnitude for the PA magnitude were -0.06 +/- 0.28 diopters (D) (range, -0.59 to 0.91 D) and 0.24 +/- 0.16 D (range, 0 to 0.91 D), respectively. The mean arithmetic and absolute estimation errors of the KA angle for the PA angle were -0.6 degrees +/- 12.7 degrees (range, -69.9 degrees to 83.4 degrees) and 7.4 degrees +/- 10.3 degrees (range, 0 degrees to 83.4 degrees), respectively. Among all eyes, 142 eyes (28.8%) had either a KA magnitude that differed by > 0.50 D from the PA magnitude or a KA angle that differed by > 10 degrees from the PA angle. For the 282 eyes with a KA magnitude exceeding 1.0 D (that are candidates for intraoperative correction of a preexisting astigmatism during cataract surgery), 29 eyes (10.3%) had either a KA magnitude that differed by > 0.50 D from the PA magnitude or a KA angle that differed by > 10 degrees from the PA angle.


CONCLUSIONS
Neglecting the posterior corneal surface measurement may lead to significant deviation in the corneal astigmatism estimation in a proportion of eyes.
Ho
Jau-Der
JD
Department of Ophthalmology, Taipei Medical University Hospital, Taipei, Taiwan.
Tsai
Ching-Yao
CY
Liou
Shiow-Wen
SW
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001251:Astigmatism / Q000175:diagnosis*; D002648:Child; D003315:Cornea / Q000473:pathology*; D003941:Diagnostic Techniques, Ophthalmological / Q000295:instrumentation; D005260:Female; D006801:Humans; D008297:Male; D008433:Mathematics; D008875:Middle Aged; D010781:Photography / Q000379:methods; D011446:Prospective Studies; D015203:Reproducibility of Results; D055815:Young Adult