Radial keratotomy clear zone diameter errors.

PURPOSE: To examine the variability of achieved clear zone diameters following radial keratotomy and to determine if refractive outcomes are correlated to clear zone diameter errors. METHODS: Twenty-six patients with radial keratotomy (51 eyes) were studied retrospectively. The central clear zone diameter for each radial incision meridian was measured using a slit-lamp and a photograph. The achieved clear zone diameters were statistically compared to the intended clear zone sizes and to the refractive outcomes. RESULTS: Twenty-nine of the 51 eyes met various exclusion criteria. Ninety individual slit-lamp clear zone measurements were obtained for the remaining 22 eyes. Sixty-two of 90 (69%) achieved clear zone diameters were more than 0.25 mm different than the intended clear zone size. A maximum difference of +/- 0.80 mm from the intended clear zone marker size was observed. The average clear zone diameter error did not statistically differ between the three refractive outcome groups (undercorrection, emmetropia, and overcorrection). CONCLUSIONS: In selected cases of centripetal radial keratotomy, the achieved clear zone diameter can vary widely from the intended clear zone size despite extensive surgeon experience.

The call of the sirens: ethically navigating the sea of nonvalidated therapies.

Medical research and innovation are vital to the advancement of medicine and, ultimately, benefit society and individual patients. However, the ethical principles of beneficence, respect for persons, and justice must guide the development and implementation of new practices. Ethical codes governing clinical practice and research already warn practitioners to avoid the use of nonvalidated practices outside of controlled clinical trials. Nonetheless, lack of compliance with these codes places many patients at risk for harm. Ophthalmologists, as well as all physicians, must recommit themselves to these ethical principles and codes and establish more vigorous peer-review methods to protect patients from nonvalidated practices that are implemented without a scientific basis.

Measurement of radial keratotomy clear zone diameters.

BACKGROUND: To compare the accuracy of photographic measurements to slit-lamp measurements of radial keratotomy clear zone diameters in order to develop an independent, objective, unbiased, and reproducible method of verifying clinical observations. METHODS: Twenty-five patients (48 eyes) following radial keratotomy had matched slit-lamp and photographic measurements of the diameter of the central clear cornea between the ends of opposite radial incision pairs. Matched slit-beam, photographic, and pathologic observations were compared statistically. RESULTS: Two hundred fifty-four slit-lamp clear zone diameter measurements were obtained. In twenty instances (8%), the radial incision end-point could not be identified on the photograph. For the remaining 234 measurements, the mean slit-lamp clear zone diameter was statistically smaller than the photographic measurement by 0.03 mm (t-test, p = 2.2 x 10(-5)). The slit-lamp and photographic clear zone measurements were strongly positively correlated (Pearson r = 0.99, p < 1.0 x 10(-15)). Matched slit-lamp, photographic, and pathologic clear zone measurements (N=8) in one excised corneal button were not statistically different. CONCLUSIONS: For radial keratotomy clear zone diameters, slit-beam measurements and photographic caliper measurements yield indistinguishable results that are highly concordant over a wide range of diameters. Both slit-beam and photographic measurements yield accurate and reliable results that reflect the true pathologic achieved clear zone diameter following radial keratotomy surgery.

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.

Superior rectus muscle overaction after cataract extraction.

Four patients with an ipsilateral hypertropia after cataract extraction consistent with superior rectus muscle overaction were identified between March 1990 and April 1992. Operative trauma was the most likely causative factor, as other likely conditions were excluded. The proposed pathogenesis for all cases is similar to that of botulinum type-A toxin therapy: a transient postoperative weakness of the ipsilateral inferior rectur muscle leads to a contracture or strengthening of the ipsilateral antagonist (the superior rectus muscle). Possible mechanisms of injury that would result in a transient inferior rectus muscle palsy would include anesthetic myotoxicity or direct trauma to the muscle and related structures from the retrobulbar injection (or subconjunctival injection). Surgical intervention consisting of an ipsilateral superior rectus muscle recession and posterior fixation sutures (when the vertical incomitance was large) yielded excellent results in restoring single binocular vision. Possible preventive measures would include using a minimal volume of anesthetic along with careful needle placement.