Clinical evaluation of the intraoperative refraction technique for intraocular lens power calculation.
OBJECTIVE
To evaluate clinically the intraoperative refraction technique for intraocular lens (IOL) power calculation using 2 existing formulas proposed by Ianchulev and Leccisotti and to derive alternative formulas for this technique.


METHODS
Comparative case series.


METHODS
One hundred eighty-two eyes from 182 patients with cataract.


METHODS
Recruited patients were separated into a normal cornea group and a special group that included eyes with surgically altered corneas. Phacoemulsification was carried out for all cases. Intraoperative aphakic autorefraction using a portable autorefractor was performed. An IOL with power calculated before surgery then was implanted. In each eye, postoperative refraction was obtained. The IOL power that would have achieved emmetropia was calculated retrospectively. Aphakic autorefraction readings obtained during surgery were used to calculate the aphakic spherical equivalent (SE). The 2 formulas incorporating aphakic SE were applied to calculate the target IOL power. Comparison then was made to determine the accuracy of the formulas.


METHODS
A difference (referred to as IOL difference) was calculated by subtracting the adjusted emmetropic IOL power determined by postoperative refraction from the emmetropic IOL power calculated by the 2 formulas using intraoperative aphakic SE.


RESULTS
One hundred forty-four patients were in the normal cornea group and 18 were in the special group. In the normal group, the Ianchulev formula showed a relatively accurate prediction for IOL power to achieve emmetropia over almost the full range of axial length except in extremely long eyes. The Leccisotti formula tended to overestimate IOL power and worked particularly poorly in short eyes. It worked best in long eyes. In the special group, neither of the 2 formulas was able to show superiority universally. Using data from the normal group, alternative formulas for IOL power calculation were derived. These new formulas then were validated on the special group that showed good estimation.


CONCLUSIONS
The Ianchulev formula could be applied to most eyes, with the exception of those in highly myopic subjects. The Leccisotti formula showed good performance in myopic patients. For eyes falling into the special group, an alternative formula, correction factor, or both, may be required. The new formulas reported herein may be an option.


BACKGROUND
The author(s) have no proprietary or commercial interest in any materials discussed in this article.
Wong
Albert Chak Ming
AC
Department of Ophthalmology, Caritas Medical Centre, Kowloon, Hong Kong, People's Republic of China.
Mak
Shiu Ting
ST
Tse
Raymond Kwok Kay
RK
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001036:Aphakia, Postcataract / Q000503:physiopathology*; D003315:Cornea / Q000503:physiopathology; D003941:Diagnostic Techniques, Ophthalmological; D005260:Female; D006801:Humans; D006956:Hyperopia / Q000503:physiopathology; D007432:Intraoperative Period; D019654:Lens Implantation, Intraocular; D007910:Lenses, Intraocular; D008297:Male; D008875:Middle Aged; D009216:Myopia / Q000503:physiopathology; D055095:Optics and Photonics; D018918:Phacoemulsification; D012029:Refraction, Ocular / Q000502:physiology*; D015203:Reproducibility of Results