Accuracy of Orbscan total optical power maps in detecting refractive change after myopic laser in situ keratomileusis.

PURPOSE: To determine whether the refractive change obtained using the Orbscan-derived total optical power (TOP) map is in concordance with the manifest refractive change produced by laser in situ keratomileusis (LASIK). SETTING: LASIK Vision Canada, Vancouver, BC, Canada (an ambulatory surgical center for refractive surgery). METHODS: Twenty eyes of 10 consecutive bilateral LASIK patients were included in the study. Orbscan topographical analysis and manifest refraction were performed preoperatively and at least 1 month postoperatively. The change in manifest refraction (corrected to the corneal plane) before and after LASIK was correlated with the corneal power change averaged within the 2.0, 3.0, 4.0, and 5.0 mm diameter zones of TOP and axial power maps. RESULTS: The central 4.0 mm zone TOP map gave the best correlation between manifest refractive change and Orbscan-measured corneal power change (r2 = 0.835, P < .004). The correlation was higher with TOP maps than with anterior axial power maps. CONCLUSION: The corneal power change measured by the Orbscan TOP maps correlated highly with the changes in manifest refraction after LASIK.

Very high-frequency ultrasound corneal analysis identifies anatomic correlates of optical complications of lamellar refractive surgery: anatomic diagnosis in lamellar surgery.

OBJECTIVE: To examine the utility of very high-frequency (VHF) ultrasound scanning in determining the anatomic changes and correlates of optical complications in lamellar refractive surgery. STUDY DESIGN: Case series. PARTICIPANTS: Cases analyzed included marked asymmetric astigmatism postautomated lamellar keratoplasty (ALK), image ghosting despite normal videokeratography post-ALK, uncomplicated myopic laser in situ keratomileusis (LASIK), and hyperopic LASIK with regression. METHODS: A prototype VHF ultrasound scanner (50 MHz) was used to obtain sequences of parallel B-scans of the cornea. Digital signal processing techniques were used to measure epithelial, stromal, and flap thickness values in a grid encompassing the central 4 to 5 mm of the cornea, enabling pachymetric mapping of each layer with 2-micron precision. MAIN OUTCOME MEASURE: The appearance of the corneas in VHF ultrasound images and thickness values of individual corneal layers determined from VHF ultrasound data. RESULTS: VHF ultrasound resolved the epithelial, stromal cap, or flap and residual stromal layers 1 year after lamellar surgery. Asymmetric stromal tissue removal was differentiated from stromal cap irregularity. Epithelium acted to compensate for asymmetry of the stromal surface about the visual axis and for localized surface irregularities. Irregularities in the epithelial-stromal interface accounted for image ghosting present despite apparently normal videokeratography. Epithelial thickening was shown after uncomplicated myopic LASIK. Hyperopic LASIK demonstrated relative epithelial thickening localized to the region of ablation accounting for refractive regression. CONCLUSIONS: VHF ultrasound shows promise as a sensitive method of determining the anatomic correlates of optical complications in lamellar refractive surgery.

A modified retrobulbar block for eye surgery.

A modified retrobulbar block (MRB) using a single superomedial injection was compared with the classical retrobulbar block (RB) and peribulbar block (PB) in a randomized, prospective, surgeon-blinded study involving 150 patients undergoing cataract surgery. No serious complication occurred in any of the patients. The MRB produced higher rates of total akinesia in the orbicularis and all the extraocular muscles, which were statistically significant for the orbicularis, superior, inferior and lateral rectus and oblique muscles when compared with RB, and for the superior rectus and oblique muscles when compared with PB. MRB required less supplemental blocks, provided good operating conditions for the surgeon, and achieved high patient acceptance. It is concluded that MRB is a useful alternative method of ocular block for cataract surgery.

Corneal topography following excimer photorefractive keratectomy for myopia.

Corneal topographic analysis was performed on 97 consecutive eyes with at least one month follow-up after excimer laser photorefractive keratectomy for myopia. Centration of the ablated zone was documented in all eyes at the one month postoperative examination with the Topographic Modeling System (Computed Anatomy Inc., NY). Thirty-seven percent of eyes were within 0.25 mm of the pupillary center (PC); 48% of eyes were between 0.25 and 0.50 mm, 13% were between 0.50 and 1.00 mm, and 2% were more than 1.00 mm from the PC. The greatest amount of decentration was 1.50 mm. The mean decentration was 0.36 mm. The surface regularity index (SRI), which is a measure of the optical performance of the cornea, was significantly less at the sixth postoperative month than at the first postoperative month (P = .013). No correlation between the SRI and the amount of decentration was found. Four main patterns of ablation were noted by differential topographic analysis at the one month interval. A central uniform ablation was present in 45% of eyes; "semicircular ablations" were present in 33% of eyes, a "keyhole" ablation pattern in 12%, and a curious "central bump" ablation pattern in 10%. Corneal topographic analysis was a useful tool for documenting and quantitating results following excimer photorefractive surgery.

Acquired syphilitic uveitis.

Secondary syphilis is an overlooked cause of iritis and posterior uveitis. Three cases of acquired syphilitic uveitis were observed, two of which occurred in male homosexuals. In the first patient, a delay in diagnosis and treatment led to irreversible loss of vision and visual field. In the latter two cases, an increased index of suspicion led to earlier diagnosis and treatment, with complete recovery of vision.