Conductive keratoplasty and the coupling phenomenon.
OBJECTIVE
To determine whether changes in corneal astigmatism with astigmatic conductive keratoplasty (CK) treatment obey Gaussian coupling (i.e., the steepening of the flat axis associated with the flattening of the steep axis) and to measure the coupling ratio and the coupling constant to determine the effect of astigmatic CK treatment on spherical equivalent.


METHODS
Retrospective review of 33 eyes in 24 patients who had undergone CK for hyperopia and who were treated intraoperatively for induced astigmatism. Induced astigmatism was determined by comparison of keratometric readings before and after CK.


RESULTS
The coupling ratio was calculated according to two equations: clinical coupling ratio (1.61 +/- 0.81 diopters) and coupling ratio of the surgically induced refractive change (1.57 +/- 1.16 diopters). Values of the coupling ratio between 0.72 and 1.88 indicate coupling.


CONCLUSIONS
The cornea does not behave according to Gauss's law of elastic domes. The targeted flat axis and steep axis 90 degrees away are affected by CK in opposite but not equal amounts. Therefore, when correcting surgically induced astigmatism with CK, the overall spherical equivalent of the patient will change because the coupling ratio is not equal to 1.
Sokol
Jason A
JA
Mount Sinai School of Medicine, New York, NY 10029-6574, USA.
Tammaro
Yolanda R
YR
Haji
Shamim A
SA
Brodie
Scott E
SE
Asbell
Penny A
PA
D001251:Astigmatism / Q000209:etiology / Q000601:surgery*; D003319:Corneal Stroma / Q000601:surgery*; D004564:Electrocoagulation / Q000379:methods*; D005260:Female; D006801:Humans; D006956:Hyperopia / Q000601:surgery*; D007431:Intraoperative Complications; D008297:Male; D012189:Retrospective Studies