Kerry K. Assil

Regression and its mechanisms after laser in situ keratomileusis in moderate and high myopia

OBJECTIVE The purpose of the study was to evaluate the degree and mechanism of regression after laser in situ keratomileusis (LASIK) on moderate to highly myopic eyes during the first postoperative year. DESIGN A prospective, single-center, clinical trial. PARTICIPANTS A total of 52 eyes of 38 patients were entered in the study; 47 eyes had complete data available at each postoperative visit. INTERVENTION The intervention was LASIK using the microkeratome to create an 8.5- to 9.0-mm diameter, 130- to 160-micron-thick flap. A spherical midstromal multizone ablation (inner zone, 4.5 mm; outer zone, 5.5-6.0) was then performed using the Summit OmniMed excimer laser (Summit Technology, Inc, Waltham, MA). The mean preoperative refraction was -14.02 diopters (D). Retreatment for undercorrection and regression was performed between postoperative months 3 and 6 on 13 eyes. MAIN OUTCOME MEASURES Manifest spherical equivalent, mean central corneal power, and central corneal thickness were the parameters measured. RESULTS At 3 months, follow-up data were available on 47 eyes. The mean refractive regression was -1.07 D (7.6%) from the first week to the third month. During the first postoperative year, the mean regression of manifest spherical equivalent (MSE), increase in corneal power, and increase in corneal thickness were symmetric in magnitude and time course for the 34 eyes that did not require retreatment (-0.96 D, +1.03 D, and 15 microns, respectively). CONCLUSION Early regression of refractive effect after LASIK appears to be a consequence of an increase in corneal thickness associated with central corneal steepening. No evidence of progressive corneal ectasia was observed during the first year of follow-up. Longer follow-up is required to confirm these trends.

Two-year outcomes of intrastromal corneal ring segments for the correction of myopia ☆

OBJECTIVE To evaluate the safety and efficacy of Intrastromal Corneal Ring Segments (ICRS) for the correction of myopia. DESIGN Nonrandomized, comparative trial. PARTICIPANTS Patients enrolled in the United States Food and Drug Administration phase II and phase III clinical trials of the ICRS had best spectacle-corrected visual acuity (BSCVA) of 20/20 or better, myopia of -1.00 to -3.50 diopters (D), and a cylindrical correction of 1.00 D or less as measured by manifest refraction. INTERVENTION Surgical correction of myopia with an ICRS. MAIN OUTCOME MEASURES Efficacy was assessed by predictability of refractive outcome (deviation from predicted cycloplegic refraction spherical equivalent), stability of refractive effect, and postoperative uncorrected visual acuity. Safety was assessed by adverse events, maintenance or loss of preoperative BSCVA, and induced manifest refraction cylinder. RESULTS Four hundred fifty-two patients were enrolled at 11 investigational sites in both studies. Of the 454 surgical attempts, 449 received an ICRS in one eye (0.25, 0.30, and 0.35 mm in 148, 151, and 150 eyes, respectively). First surgeries were attempted in 452 patients. An ICRS was successfully implanted in 447 initial eyes, and 5 surgeries were discontinued. Of the five discontinued surgeries, three patients subsequently exited from the study, and two patients went on to have the ICRS implanted in the second eye, bringing the total number of successful implants to 449 patient eyes. Month 24 postoperative follow-up was completed on 358 patients (80%). At month 24, 328 of 354 eyes (93%) were within +/-1.00 D of predicted refractive outcome. Refraction changed by 1 D or less in 97% of eyes (421/435) between 3 and 6 months after implantation and in 99% (343/348) between months 18 and 24. Before surgery, 87% of eyes (390/448) saw worse than 20/40 uncorrected; 24 months after surgery, 55% of eyes (196/358) saw 20/16 or better, 76% (271/358) saw 20/20 or better, and 97% (346/358) saw 20/40 or better. Although two eyes (2/358; 0.5%) lost two or more lines of BSCVA at 24 months; visual acuity in both was 20/20 or better. Intraoperative complications included anterior corneal surface perforation (three eyes) and anterior chamber perforations (two eyes, one during an attempted exchange procedure); all healed spontaneously without suturing and without loss of BSCVA. The ICRS was repositioned in five eyes to increase correction. Postoperative complications in one eye each were infectious keratitis, shallow segment placement, and loss of two lines of BSCVA at two or more consecutive examinations (subsequently regained). CONCLUSIONS The ICRS safely, predictably, and effectively reduced or eliminated myopia of -1.00 to -3.50 D. The refractive effect was stable over time.

Wound healing in response to keratorefractive surgery

Over one million Americans have undergone refractive keratoplasty since the introduction of radial keratotomy into the United States in 1978. There are now a number of alternative techniques available for reshaping the corneal surface to alter ocular refractive errors. Numerous technologic advances in the past decade now enable us to perform these procedures in a safer and more reliable fashion. The ability to control precisely the refractive outcome, however, continues to elude us and appears to be limited, in part, by interindividual variability in the wound healing response. Presently, we review the corneal wound healing response to various keratorefractive approaches and suggest some interventional strategies which might enable us to modulate more precisely our refractive results.

Control of ocular inflammation after cataract extraction with rimexolone 1% ophthalmic suspension

Purpose: To assess the efficacy and safety of rimexolone 1% ophthalmic suspension in controlling intraocular inflammation after cataract extraction. Setting: Twelve independent investigational centers in the United States. Methods: This study comprised 197 patients who had cataract extraction. Postoperatively, patients were randomized to a 2 week regimen of rimexolone 1 % ophthalmic suspension or a placebo. Efficacy was analyzed by monitoring total anterior chamber cells and flare, other parameters of inflammation, and treatment failures. Safety was evaluated by monitoring treatment‐related adverse events and intraocular pressure (IOP). Results: Rimexolone 1 % was clinically and statistically more effective in suppressing cell and flare than the placebo (P < .02). The overall discontinuation rate for treatment‐related adverse events was 5.3% in the rimexolone group and 22.2% in the placebo group. There were no between‐group differences in IOP. Conclusion: Rimexolone 1 % ophthalmic suspension was safe and significantly more effective than a placebo in controlling intraocular inflammation after cataract extraction when used four times daily and continued for 2 weeks.

Fibrin-enmeshed Tobramycin Liposomes: Single Application Topical Therapy of Pseudomonas Keratitis

Treatment of bacterial keratitis requires frequent application of topical antibiotics. We studied the efficacy of a single topical administration of tobramycin incorporated in large multivesicular liposomes and enmeshed in a fibrin sealant on rabbit corneas infected with Pseudomonas aeruginosa. One cornea each of 25 New Zealand albino rabbits was infected with P. aeruginosa. Twenty-four hours later, the animals were randomly divided into five groups of five. Group A received single hourly drops (50 μl) of fortified tobramycin (14.5 mg/ml, total of 17.4 mg). Group B received a single topical application of 3.5 mg tobramycin, in 0.1 ml multivesicular liposomes, enmeshed in a fibrin sealant with an overlaying bandage contact lens. Group C was treated in the same manner as group B without the addition of fibrin sealant. Groups D and E served as nondrug-treated controls, with group D receiving topical fibrin-enmeshed liposomes devoid of tobramycin and group E receiving hourly topical balanced salt solution (BSS) drops. All animals were killed 24 h after initiation of therapy. Significantly fewer colonies of Pseudomonas were present in corneas of all three treated groups, as compared with the two nondrug-treated control groups (p < 0.02). There were significantly fewer colonies of Pseudomonas in groups A and B as compared with group C (p < 0.02). No significant difference was noted between a single administration of topical fibrinenmeshed tobramycin-encapsulated liposomes (group B) and 24 doses of hourly fortified topical tobramycin (group A, p > 0.05). Tobramycin-encapsulated megaliposomes may serve as a useful adjunct in treatment of Pseudomonas keratitis.

Corneal Iron Lines Associated With the Intrastromal Corneal Ring

Corneal epithelial iron lines commonly occur, and their shape is characteristically influenced by the underlying corneal surface topography. We studied a pattern of iron deposition, observed after implantation of the Intrastromal Corneal Ring (KeraVision, Inc., Santa Clara, California). In five of ten patients undergoing placement of the Intrastromal Corneal Ring, an arcuate pattern of epithelial iron deposition was observed eight to 12 months postoperatively. There was no significant clinical or topographic difference over time among the corneas of patients who developed an iron line vs those who did not. Of the five patients with an arcuate epithelial iron line, three underwent explantation of their Intrastromal Corneal Ring at 12 months according to the study protocol. Iron deposition either reverted to a Hudson-Stähli pattern or disappeared in each of these three patients.

Role of clearance and treatment zonesin contrast sensitivity: Significance in refractive surgery

PURPOSE To evaluate the relationship between contrast sensitivity, surgical treatment zone, and clearance (ablation or clear zone-pupil diameter) in photorefractive keratectomy (PRK) and radial keratotomy (RK). SETTING Saint Louis University Eye Institute, St. Louis, Missouri, and Hunkeler Eye Center, Kansas City, Missouri, USA. METHODS Thirteen patients had PRK and 20, RK. Contrast sensitivity was measured with the Stereo Optical F.A.C.T. (F.A.C.T.) and VectorVision CSV-1000 (VV) charts. Pupils were measured with the Rosenbaum card. RESULTS In the PRK group, VV contrast sensitivity at 6 and 12 cycles per degree (cpd) correlated with the ablation zone (r2 = 0.18 and 0.22, respectively), while visual acuity and F.A.C.T. contrast sensitivity did not correlate. In the RK group, both VV and F.A.C.T. contrast sensitivity at 6 cpd correlated with clearance (r2 = 0.29 and 0.12, respectively). Pupils were larger with the VV test than with the F.A.C.T. chart because ambient chart luminance was less in the former. CONCLUSION Contrast sensitivity is likely a more sensitive indicator of visual function than acuity in refractive surgery. The VV system unmasks aberrations from the transition zone of ablated and unablated cornea in PRK. Larger samples are needed to determine the critical ablation clearance of the pupil to avoid loss of visual function.

Ultrastructure of picosecond laser intrastromal photodisruption

PURPOSE To investigate the ultrastructure of the corneal stroma after picosecond intrastromal photodisruption with a neodymium-doped yttrium-lithium-fluoride (Nd:YLF) laser. METHODS We performed picosecond intrastromal photodisruption on six human eye-bank eyes using a lamellar technique. Thirty picosecond pulses at 1000 Hz and 20 to 25 mJ per pulse were placed in an expanding spiral pattern, the pulses separated by 15 microns. Three layers were placed in the anterior stroma, separated from each other by 15 microns. In addition, intrastromal radial and arcuate incisions were generated in two living rabbit eyes in a plane perpendicular to the corneal surface. After the procedure, the corneas were processed for scanning and transmission electron microscopy. RESULTS Scanning electron microscopy of the eye-bank eyes demonstrated multiple, coalescing intrastromal cavities forming a layer oriented parallel to the corneal surface. These cavities had smooth inner walls. Transmission electron microscopy demonstrated tissue loss surrounding some cavities, with the terminated ends of collagen fibrils clearly evident. Other cavities were formed by separation of lamellae, with little evidence of tissue loss. A pseudomembrane was present along the margin of some cavities. Although there was occasional underlying tissue disruption along the border of a cavity, there was no evidence of thermal damage or tissue necrosis. The perpendicular photodisruptions demonstrated intrastromal cleavage of corneal collagen similar to diamond-knife incisions, with the exception of intact overlying Bowmans and epithelial layers. CONCLUSION Intrastromal photodisruption with a Nd:YLF picosecond laser induced no thermal necrosis or coagulative change in the region of tissue interaction. Lamellar intrastromal photodisruption demonstrated both tissue loss and lamellar separation when performed with the current treatment parameters, possibly limiting ablation efficiency and predictability.

Efficacy of tobramycin-soaked collagen shields vs tobramycin eyedrop loading dose for sustained treatment of experimental Pseudomonas aeruginosa-induced keratitis in rabbits

We compared the efficacy of a fortified tobramycin-soaked collagen shield to the efficacy of a single loading dose (four 50-microliters drops) of fortified tobramycin eyedrops in the treatment of New Zealand White rabbits with Pseudomonas aeruginosa-induced keratitis. Eyedrop loading-dose efficacy was evaluated with and without lateral tarsorrhaphy. Six hours after a single treatment, significantly fewer Pseudomonas colonies were present in the corneas of all three drug-treated groups as compared to the number of colonies in the corneas of balanced salt solution-treated control rabbits (P less than .006). Although no significant difference was observed between any of the drug-treated groups, lateral tarsorrhaphy was associated with a greater than tenfold decrease in the number of colony-forming units (P = .073). We found no significant difference in efficacy between a collagen shield presoaked in tobramycin, and a single loading dose of tobramycin eyedrops, in the treatment of rabbits with P. aeruginosa-induced keratitis.

CHARACTERIZATION OF A CENTRAL CORNEAL CLOUDINESS SHARING FEATURES OF POSTERIOR CROCODILE SHAGREEN AND CENTRAL CLOUDY DYSTROPHY OF FRANCOIS

A 56-year-old black woman with full-thickness mosaic pattern central corneal cloudiness, similar in appearance to central cloudy dystrophy and posterior crocodile shagreen, underwent corneal transplantation. Atypical features included decreased vision, photophobia, and epithelial involvement, with occasional foreign body sensation. Numerous 0.5-2.0-µm-diameter lacunae were present in the corneal stroma and Bowmans layer, and a saw-toothed lamellar pattern was often evident in the corneal stroma. Soybean agglutinin (SBA), a lectin that binds N-acetyl-galactosamine residues, bound diffusely to stromal foci exhibiting similar size and distribution to the lacunae observed by electron microscopy. An absence of histochemically detectable lipid associated with these lacunae suggests that SBA reacted with glycoconjugates other than glycolipids. Biochemical analyses revealed similar contents of keratan sulfate, chondroitin/dermatan sulfate, and collagen as in normal controls, suggesting that the SBA binding moieties are associated with a glycoprotein or proteoglycan that is structurally or compositionally different from those found in normal cornea. This patient may represent an extreme variant of Vogts or Francosis central corneal clouding or a previously undescribed corneal dystrophy.