Michael J. Taravella

Incidence of intraoperative flap complications in laser in situ keratomileusis

Purpose: To evaluate the incidence of intraoperative flap complications in laser in situ keratomileusis (LASIK) and compare the incidence between eyes and between the Hansatome and Automated Corneal Shaper® (Bausch & Lomb) microkeratomes. Setting: Open‐access outpatient excimer laser surgical facility. Methods: A retrospective analysis was done of 84711 primary LASIK cases performed between November 1998 and May 2000 in 28 national open‐access laser facilities. The intraoperative flap complications were identified and categorized into type of complication, eye involved, and microkeratome type. All cases used the Automated Corneal Shaper or the Hansatome microkeratome. Results: Two hundred fifty‐six complications (0.302%) were identified: 29 failures to achieve intraocular pressure (0.034%), 84 partial flaps (0.099%), 59 buttonholes (0.070%), 74 thin or irregular flaps (0.087%), and 10 free flaps (0.012%). There were 134 right eye complications and 122 left eye complications (P = .45). No patient developed an intraoperative flap complication in both eyes. A comparison of Hansatome and Automated Corneal Shaper microkeratomes was possible for the cases performed between December 1999 and May 2000: 46 of 28 201 Hansatome procedures (0.16%) had a complication versus 21 of 329 Automated Corneal Shaper procedures (6.38%). This difference was statistically significant (P < .005). Conclusion: The incidence of intraoperative flap complications during LASIK was acceptably small. The overall complication rate was similar in both eyes. The Hansatome was associated with a lower complication rate than the Automated Corneal Shaper.

The predictability of corneal flap thickness and tissue laser ablation in laser in situ keratomileusis

OBJECTIVE To evaluate the relationship between predicted flap thickness and actual flap thickness and between predicted tissue ablation and actual tissue ablation. DESIGN Prospective, nonrandomized comparative (self-controlled) trial. PARTICIPANTS A total of 60 patients (102 eyes) who underwent laser in situ keratomileusis (LASIK). MAIN OUTCOME MEASURES Subtraction pachymetry was used to determine actual corneal flap thickness and corneal tissue ablation depth. Other measurements included flap diameter and keratometry readings. RESULTS Actual flap thickness was significantly different (P < 0.0001) from predicted flap thickness. Fifteen eyes had a predicted flap thickness of 160 micrometer and a mean actual flap of 105 micrometer (standard deviation [SD], +/-24. 3 micrometer range, 48-141 micrometer). Sixty-four had a predicted flap of 180 micrometer with an actual flap mean of 125 micrometer (SD, +/-18.5 micrometer range, 82-155 micrometer). Seventeen eyes had a predicted flap of 200 micrometer, with an actual flap mean of 144 micrometer (SD, +/-19.3 micrometer range, 108-187 micrometer). In addition, we found that significantly more tissue (P < 0.0001) was ablated than predicted. Linear regression of the observed ablation on predicted ablation yielded the following relationship: actual ablation = 14.5 + 1.5 (predicted ablation). Neither flap diameter nor flap thickness were found to increase with respect to steeper corneal curvatures. CONCLUSIONS Actual corneal flap thickness was consistently less than predicted regardless of the depth plate used; actual tissue ablation was consistently greater than predicted tissue ablation for the laser used in this study.

Modeling Passive Mechanical Interaction Between Aqueous Humor and Iris

Certain forms of glaucoma are associated with displacement of the iris from its normal contour. We present here a mathematical model of the coupled aqueous humor-iris system that accountsfor the contribution of aqueous humor flow and passive iris deformability to the iris contour. The aqueous humor is modeled as a Newtonian fluid, and the iris is modeled as a linear elastic solid. The resulting coupled equation set is solved by the finite element method with mesh motion in response to iris displacement accomplished by tracking a pseudo-solid overlying the aqueous humor. The model is used to predict the iris contour in healthy and diseased eyes. The results compare favorably with clinical observations, supporting the hypothesis that passive iris deformation can produce the iris contours observed using ultrasound biomicroscopy.

2-Octyl cyanoacrylate medical adhesive in treatment of a corneal perforation.

Purpose. To describe a case of successful treatment of a corneal perforation with 2-octyl cyanoacrylate. Methods. 2-Octyl cyanoacrylate was applied at the slit lamp with topical proparacaine anesthesia to a cornea with an inferior perforation with iris plugging the defect. Results. After application of 2-octyl cyanoacrylate, the anterior chamber was noted to deepen, and visual acuity improved to 20/200. The glue remained intact for more than 6 weeks and eventually fell out. The underlying cornea healed without scarring, vascularization, or thinning. Conclusion. We have described a case in which 2-octyl cyanoacrylate was used to treat a corneal perforation with excellent results. Further study of this adhesive will be useful in comparing the effectiveness and safety of 2-octyl cyanoacrylate with that of previously studied adhesives.

Collagen shield delivery of ofloxacin to the human eye

PURPOSE To determine the ocular penetration of ofloxacin into the anterior chamber of the human eye when delivered by a presoaked collagen shield. SETTING University of Colorado School of Medicine, Denver, Colorado. METHODS This prospective randomized clinical study comprised 31 patients having cataract surgery. Patients were divided into 2 groups: the first received 3 preoperative drops of commercially available topical ofloxacin 0.3% given 10 minutes apart; the second had a collagen shield soaked in the same medication applied to the eye before surgery. Aqueous humor was extracted immediately before surgery for analysis. RESULTS Mean aqueous concentration was 287 ng/mL +/- 69 (SEM) (range 40 to 1141 ng/mL) in the drops group and 957 +/- 189 ng/mL (range 214 to 2437 ng/mL) in the shield group. The difference was statistically significant (P < .005). The minimum inhibitory concentration (MIC) for selected ocular pathogens is between 500 and 4000 ng/mL. CONCLUSIONS A collagen shield presoaked in commercially available topical ofloxacin and applied before surgery appears safe. The MICs for many common ocular pathogens were reached or exceeded. Further study is recommended to determine whether this method of infection prophylaxis is an acceptable substitute for subconjunctival injections of antibiotics.

Characterizing the learning curve in phacoemulsification

PURPOSE: To characterize how residents learn phacoemulsification and determine which steps of the procedure are most difficult to master. SETTING: University of Colorado Hospital, Aurora, Colorado, USA. DESIGN: Comparative case series. METHODS: Cataract cases were divided into 3 levels of difficulty for comparison. Residents were given a grade for each step of the procedure by the attending surgeon. Main outcome measures were total case time and a proficiency grade. Independent variables were level of resident experience and degree of difficulty. Case times of attending cases were collected for comparison. RESULTS: Nine residents were evaluated by 4 attending surgeons while performing 324 cases of phacoemulsification. Case times of 319 attending cases were used for comparison. The easiest‐to‐learn steps (highest scores versus level of experience) included intraocular lens insertion, ophthalmic viscosurgical device removal, hydrodissection, and nucleus sculpting. Wound integrity, nucleus disassembly and removal, cortex removal, and capsulorhexis had the lowest scores versus level of experience. Resident case times decreased significantly with experience, approaching average case times for attendings. CONCLUSIONS: For this study, competency was defined as the ability of the resident to perform a case in a reasonable time without intervention or complication. Using this definition, competency was achieved when case experience exceeded 75 cataract surgeries. Financial disclosure: No author has a financial or proprietary interest in any material or method mentioned.

Corneal Endothelial Deposits in Patients With Cytomegalovirus Retinitis

PURPOSE We studied six patients with human immunodeficiency virus (HIV) who had cytomegalovirus retinitis and abnormal endothelial deposits in at least one eye, to characterize their corneal endothelial deposits. METHODS The corneas of the six patients were examined by slit-lamp biomicroscopy and specular microscopy with morphometric analysis. The eyes of one patient with endothelial changes were obtained post mortem for histopathologic and ultrastructural examination. RESULTS There were multiple diffuse, fine refractile, stellate-shaped deposits on the corneal endothelium in all affected eyes. The deposits were best seen with retroillumination. Two of six patients examined with specular microscopy showed severe abnormalities, which included marked areas of polymegathism and decreased endothelial cell counts. Examination of one eye obtained post mortem disclosed chains of dendritic macrophages and fibrin adherent to the apical surface of the corneal endothelium. There was no evidence of direct infection of the corneal endothelium by cytomegalovirus. CONCLUSIONS Deposits on the corneal endothelium in patients with cytomegalovirus retinitis most likely result from an anterior uveitis. A preponderance of macrophages observed by histopathologic examination may be related to the inability of the immunodeficient patient to mount a normal T-cell response.

Respirable particles in the excimer laser plume

Purpose: To determine whether respirable‐size particles are present in the excimer laser plume following ablation of the corneal stroma. Setting: Outpatient laser vision correction facility. Methods: In this experimental study, an excimer laser was used to ablate 2 eye‐bank corneas. Material from the plume was collected with filter paper that was coupled to a smoke evacuator. The filter paper was examined and photographed with an electron microscope. The particle size was measured with a computer program using digitized images of the photographs. As a control, room air was sampled using a smoke evacuator connected to a holder containing filter paper prior to the tissue ablation. Results: Ninety‐eight particles were measured. The mean diameter was 0.22 &mgr;m ± 0.056 (SD). No particles were seen on the control filter paper. Conclusions: The plume created during excimer laser ablation of the cornea contained respirable‐size particles. It is not known whether inhalation of these particles poses a significant health hazard. However, we recommend that a mask be worn by the surgeon and technical personnel assisting in excimer laser surgery. The plume should also be evacuated.

Incidence of Nd:YAG Capsulotomy After Implantation of AcrySof Multifocal and Monofocal Intraocular Lenses: A Case Controlled Study

PURPOSE To compare the frequency of posterior capsulotomies in patients receiving a multifocal or monofocal intraocular lens (IOL) of a similar design following cataract extraction. METHODS Four hundred seventeen eyes underwent cataract extraction and IOL implantation; 275 eyes received the AcrySof SN6OWF (Alcon Laboratories Inc) one-piece monofocal lens (monofocal group) and 142 eyes received the RESTOR multifocal lens (SN60D3 or SA60D3, Alcon Laboratories Inc) (multifocal group). Surgery was performed by two surgeons at one site. Primary outcome measures were incidence, time of onset, and preoperative corrected distance visual acuity (CDVA) for those patients receiving posterior capsulotomies. RESULTS After average 22-month postoperative follow-up (range: 2 to 41 months), 22 (15.49%) eyes in the multifocal group underwent posterior capsulotomies compared with 16 (5.82%) eyes in the monofocal group (P = .0014). The main indication for Nd:YAG laser capsulotomy in the multifocal group was complaint of poor quality of vision rather than decreased CDVA. The multifocal group underwent capsulotomies after a mean of 8.8 months (range: 1.7 to 29.2 months), whereas the monofocal group required capsulotomies after a mean of 10.4 months (range: 0.8 to 28.6 months) (P = .559). Mean logMAR CDVA before capsulotomy was 0.113 (range: 0 to 0.6) for the multifocal group and 0.244 (range: 0 to 0.48) for the monofocal group (P = .073). CONCLUSIONS Use of the RESTOR multifocal IOL in clinical practice may result in more frequent Nd:YAG laser capsulotomies. Reasons for this may include increased visual demands of patients receiving presbyopic-correcting IOLs or complex visual phenomena associated with the interaction of multifocal optics and posterior capsule opacification.

Hyperopic laser in situ keratomileusis to treat overcorrected myopic LASIK

Purpose: To evaluate the safety and efficacy of hyperopic laser in situ keratomileusis (LASIK) in treating hyperopia caused by overcorrected myopic LASIK and to evaluate a new technique to place the hyperopic treatment after lifting the initial myopic flap. Setting: Open‐access outpatient excimer laser surgical facility. Methods: A retrospective analysis was performed of 54 eyes in 47 patients who had spherical hyperopic LASIK by 21 surgeons for the treatment of significant hyperopia after overcorrected LASIK for myopia. In 42 eyes, the initial LASIK flaps were lifted and in 12 eyes, new flaps were cut. The mean age of the 25 men (53%) and 22 women (47%) was 48.2 years ± 8.4 (SD). Outcome measures included refractive error, uncorrected visual acuity (UCVA), best spectacle‐corrected visual acuity (BSCVA), and complications. The mean follow‐up was 2.97 months. Results: In eyes in which postoperative emmetropia was attempted (n = 45), the mean spherical equivalent improved from +1.21 ± 0.49 diopters (D) preoperatively to –0.38 ± 0.50 D postoperatively (P < .001). The mean UCVA improved from 20/38.6 ± 16.3 to 20/27.4 ± 9.4 (P < .001). At the last follow‐up, 69% of eyes were within ±0.5 D and 96% were within ±1.0 D of emmetropia; 42% had a UCVA of 20/20 and 96% had a UCVA of 20/40 or better. No eyes lost 2 or more lines of BSCVA. No vision‐threatening complications occurred. Results in patients who had initial flaps lifted and those who had new flaps cut were statistically indistinguishable. On average, achieved hyperopic corrections were 18% greater than intended. Conclusion: Hyperopic LASIK was safe, predictable, and effective in the treatment of hyperopia caused by overcorrected myopic LASIK. Results were similar whether the original flap was lifted or a new one was cut.