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.

DESIGN

Comparative case series.

PARTICIPANTS

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.

MAIN OUTCOME MEASURES

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.

FINANCIAL DISCLOSURE(S)

The author(s) have no proprietary or commercial interest in any materials discussed in this article.

Complications of small clear-zone radial keratotomy

PURPOSE

To review the postoperative outcome of patients with radial keratotomy who have clear-zone diameters below 2.75 mm.

METHODS

A retrospective review was performed of all patients with radial keratotomy who have clear-zone diameters less than 2.75 mm presenting for consultation from August 1993-September 1995. Preoperative records and surgical reports were reviewed, and a thorough ophthalmic examination was performed.

RESULTS

A total of 37 eyes had a clear-zone size below 2.25 mm. Six eyes were excluded from subsequent analysis due to keratoconus. The remaining 31 eyes had an average clear-zone size of 1.5 mm (standard deviation, 0.4 mm; range, 0.9-2.2 mm). Postoperative morbidity included severe disabling glare in 31 (100%) of 31 eyes, contact lens intolerance in 19 (100%) of the 19 eyes fitted, Snellen visual acuity loss (> 2 lines) in 25 (81%) of 31 eyes, inability to drive at night in 11 (69%) of 16 patients, moderate to severe diurnal visual fluctuation in 21 (68%) of 31 eyes, refractive undercorrection by greater than 1 diopter in 16 (52%) of 31 eyes, loss of employment in 4 (25%) of 16 patients, polyopia in 5 (16%) of 31 eyes, refractive overcorrection by greater than 1 diopter in 3 (10%) of 31 eyes, and a retinal detachment attributable to pilocarpine use in 1 (3%) of 31 eyes.

CONCLUSIONS

Using radial keratotomy clear-zone diameters smaller than 2.25 mm has a high complication rate and is unsafe. Small clear-zone radial keratotomy should be abandoned. Although this study was limited to clear zones less than 2.25 mm, the authors endorse current recommendations that the clear zone should be at least 3.0 mm in diameter.

Dynamic shifts in corneal topography after radial and transverse keratotomy

PURPOSE

The authors aimed to quantitate the dynamic patterns of change in corneal topography after multistaged radial and transverse keratotomy using digitized video-keratography.

METHODS

Single and paired radial and transverse keratotomies, with videokeratoscopy between each stage and at the end of the procedure, were performed on fresh animal cadaver eyes using an artificial orbit system.

RESULTS

All incisions led to central flattening. A single radial keratotomy caused flattening adjacent to the incision, and steepening 180 degrees away. A paired radial keratotomy caused increased flattening in the meridian of the incisions, and less flattening 90 degrees away. A single transverse incision caused steepening adjacent to the incision and diffuse flattening elsewhere. A paired transverse incision caused flattening near the optical center along the meridian bisecting the incisions and steepening 90 degrees away.

CONCLUSION

The authors have demonstrated that computerized videokeratography can be used successfully to systematically quantitate dioptric shifts in multiple hemimeridians and measurement zone diameters after refractive surgery.