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Biomedical subjects

K K Assil

Publications and source records attributed to K K Assil.

At least 19 recordsLinked to original sources
PubMed2001

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.

Adult↗
PubMed2001

Stability after laser in situ keratomileusis in moderately and extremely myopic eyes.

OBJECTIVE: To evaluate the stability, mechanism, and degree of regression following laser in situ keratomileusis (LASIK) in cases with moderate to extreme myopia after 2 years of follow-up. SETTING: Single-center clinical trial. METHODS: Fifty-two eyes of 38 patients were enrolled in the study. One year follow-up was available for 47 eyes of 35 patients and 2 year follow-up for 39 eyes of 27 patients. Eyes were divided into 2 groups based on the level of preoperative myopia: Group 1, moderate to high myopia > or =15.0 diopters (D) (range -7.0 to -15.0 D, n = 24); Group 2, extreme myopia >15.0 D (range -15.3 to -25.8 D, n = 15). Laser in situ keratomileusis was performed using the Chiron Automated Corneal Shaper(R) microkeratome and the Summit OmniMed excimer laser. Manifest spherical equivalent, mean central keratometry, and central corneal thickness (CCT) were measured preoperatively and 12 and 24 months postoperatively. RESULTS: Group 1 exhibited a mild myopic shift (mean -0.07 +/- 0.28 D; P >.2) and a mild increase in keratometry (mean 0.05 +/- 0.46 D; P >.6), with an accompanying increase in CCT (mean 7.5 +/- 12.2 microm; (P =.006) at 24 months. Group 2 displayed a significant myopic shift (mean -0.7 +/- 0.7 D; P =.001) and a significant increase in keratometry (mean 0.4 +/- 0.5 D; P =.01), with a mild increase in CCT (mean 2.4 +/- 9.7 microm; P =.35) at 24 months. Corneal ectasia was evident in 1 eye in the extreme myopia group. CONCLUSION: The refractive effect of myopic LASIK up to -15.0 D remained reasonably stable during the second postoperative year. Significant regression of the refractive effect occurred in eyes with higher levels of myopia (>15.0 D), with the risk of progressive ectasia. Extreme caution is recommended when myopic LASIK is performed in eyes with higher levels of myopia.

Adult↗
PubMed1999

Improvement of visual function with glare testing after photorefractive keratectomy and radial keratotomy.

PURPOSE: To evaluate the effect of a glare source on visual function in patients after photorefractive keratectomy and radial keratotomy. METHODS: Thirteen patients (22 eyes) who underwent photorefractive keratectomy and 20 patients (40 eyes) who underwent radial keratotomy were evaluated in this cross-sectional study. LogMAR visual acuity and contrast sensitivity were measured. Pupils were measured with the Rosenbaum card. A halogen/tungsten glare source approximated the luminance of headlights of an oncoming car at 100 feet. RESULTS: In the photorefractive keratectomy and radial keratotomy groups, pupils were significantly smaller (P<.01) and the pupillary clearance of the ablation zone in photorefractive keratectomy and the clear zone in radial keratotomy were significantly larger under the glare condition (P<.01). In the photorefractive keratectomy group, visual acuity and contrast sensitivity under the glare condition were significantly higher than in the no-glare condition (P = .02). In the radial keratotomy group, contrast sensitivity under the glare condition was significantly higher than under the no-glare condition (P = .001 to .003). CONCLUSIONS: After photorefractive keratectomy or radial keratotomy, the traditional glare source constricted the pupil and partially masked the optical aberrations, which resulted in an improvement in visual function. A "pupil-sparing" aberration test is needed for evaluation of visual function after refractive surgery.

Adult↗
PubMed1999

Role of clearance and treatment zones in 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.

Adult↗
PubMed1998

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.

Adult↗
PubMed1997

Two-incision radial keratotomy for low myopia with astigmatism.

PURPOSE: To evaluate the effectiveness of two-incision radial keratotomy (RK) in correcting low-magnitude refractive myopic astigmatism. SETTING: Two clinical study sites, one in St. Louis, Missouri, USA, the other in Caracas, Venezuela. METHODS: Fifty-seven eyes of 43 patients with low-magnitude myopic astigmatism had two-incision RK at one of two clinical study sites. In the initial phase of this series, 10 eyes with amblyopia at the 20/30 level had surgery at one center. Refractive keratotomy was performed with the radial incision placed in the plus cylinder axis of refraction. This axis was verified as the meridian of greatest corneal curvature by standard keratometry and computer-assisted corneal topographic analysis. Two eyes received a second operation (enhancement). RESULTS: Mean follow-up was 11.1 months (range 6 to 12 months). Mean preoperative and postoperative myopic spherical equivalent measured -1.42 diopters (D) +/- 0.51 (SD) and -0.14 +/- 0.39 D, respectively; the mean reduction was 1.28 +/- 0.59 D (P = .0001). Mean preoperative and postoperative refractive astigmatism was 1.41 +/- 0.45 D and 0.48 +/- 0.33 D, respectively (P = .0001). Mean preoperative and postoperative keratometric astigmatism was 1.26 +/- 0.54 D and 0.31 +/- 0.35 D, respectively, a mean reduction of 0.95 D (P = .0001). The surgical meridian was flattened by an average of 2.06 D by keratometry and the orthogonal meridian, by an average of 1.10 D. Preoperative uncorrected visual acuity (UCVA) was 20/40 or better in five (9%) eyes (range counting fingers to 20/40). Postoperative UCVA acuity was 20/40 or better in all eyes (mean acuity 20/25). In the nonamblyopic subgroup mean postoperative UCVA was 20/24. CONCLUSIONS: A limited number of radial incisions placed in the topographically confirmed axis of greatest curvature are effective in the treatment of low-magnitude myopic astigmatism.

Adolescent↗
PubMed1997

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.

Administration, Topical↗
PubMed1996

Liposome-encapsulated (S)-1-(3-hydroxy-2-phosphonylmethoxypropyl)cytosine for long-acting therapy of viral retinitis.

The effect of liposome-encapsulated (S)-1-(3-hydroxy-2-phosphonylmethoxypropyl)cytosine (HPMPC; cidofovir) was evaluated as prophylaxis in a rabbit model of experimentally induced retinitis caused by preretinal inoculation of herpes simplex virus type 1 (HSV-1). Cidofovir (100 micrograms) in liposomes (0.1 mL) was injected intravitreally 10-120 days before retinal inoculation with HSV-1. Twenty-two of 26 eyes pretreated with liposome-encapsulated cidofovir 10-60 days before HSV-1 inoculation were protected from experimentally induced retinitis, and 2 of 5 eyes pretreated 120 days before inoculation were protected. Intravitreal levels of cidofovir were low (0.7 microgram/mL) but detectable 120 days after injection. One 100-micrograms intravitreal injection of liposome-encapsulated cidofovir appears to have a remarkably potent and prolonged (up to 4 months) antiviral effect in this experimental model of HSV-1 retinitis. Since HPMPC is even more potent against cytomegalovirus than HSV-1, liposome-encapsulated cidofovir may prove to be effective local therapy for AIDS patients with cytomegalovirus retinitis.

Animals↗
PubMed1996

Characterization of a central corneal cloudiness sharing features of posterior crocodile shagreen and central cloud dystrophy of François.

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-micron-diameter lacunae were present in the corneal stroma and Bowman's 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 Vogt's or François central corneal clouding or a previously undescribed corneal dystrophy.

Corneal Dystrophies, Hereditary↗
PubMed1995

One-year results of the intrastromal corneal ring in nonfunctional human eyes. Intrastromal Corneal Ring Study Group.

OBJECTIVE: The intrastromal corneal ring (ICR), a new keratorefractive device designed to correct myopia, was evaluated for safety and efficacy as part of a phase I Food and Drug Administration clinical trial. PATIENTS AND METHODS: Ten patients, each with one nonfunctional eye, underwent surgical implantation of the ICR, which is a split ring composed of polymethyl methacrylate. The eyes were followed up during a 1-year period and were evaluated for wound healing, implant-related inflammation, intraocular pressure, corneal thickness, endothelial cell count, and refractive effects. RESULTS: Wound healing was uncomplicated in all of the patients. No patient experienced implant-associated inflammation or extrusion. Intraocular pressure, corneal thickness, and endothelial cell counts were unaffected by the ICR. Non-sight-threatening intraoperative events included ring decentration and inadequate attachment of a vacuum-centering guide. The ICR reduced keratometrically determined spherical equivalence by an average of -2.5 +/- 1.1 diopters (mean +/- SD). Spherical equivalence, as determined by retinoscopy, was reduced by an average of -2.4 +/- 1.0 D. Results of corneoscopy and computerized videokeratography further confirmed this reduction of myopia. CONCLUSIONS: The ICR may be a safe and efficacious device that offers predictable results with few side effects, and it may be a feasible alternative to current keratore-fractive procedures.

Adult↗
PubMed1995

Long-term therapy for herpes retinitis in an animal model with high-concentrated liposome-encapsulated HPMPC.

OBJECTIVE: To evaluate(s)-1-(3-hydroxy-2-phosphonyl methoxypropyl) cytosine (HPMPC), a potent antiherpes and anticytomegalovirus drug, as a long-term treatment of experimental retinitis in rabbits. METHODS: The drug was first encapsulated into a liposome delivery system in three different concentrations and injected intravitreally. Sequentially, the highest concentration that was shown to be nontoxic to the retina was evaluated in a model of retinitis at 60, 90, 120, 170, and 240 days, after which herpes simplex virus type 1 was inoculated onto the retinal surface. RESULTS: A dose of 1000 micrograms of HPMPC encapsulated in liposomes gives a protective effect for up to 8 months. CONCLUSIONS: Reduced toxic effects and longer-term efficacy compared with free drug was observed. Given the 50 times higher activity of HPMPC against human cytomegalovirus than herpes simplex virus type 1, a single injection of 1000 micrograms of liposome-encapsulated HPMPC may have a very prolonged effect in the treatment of cytomegalovirus retinitis.

Animals↗
PubMed1995

The combined (Genesis) technique of radial keratotomy. A prospective, multicenter study. Refractive Keratoplasty Study Group.

PURPOSE: A prospective, multicenter, clinical study to evaluate a standardized surgical (Genesis) protocol which includes combined-technique radial incisions in patients seeking reduction of their physiologic myopia. The combined incisions were designed to incorporate the safety of the centrifugal incision technique with the efficacy of the centripetal incision technique. METHODS: A total of 375 eyes undergoing radial keratotomy procedures performed in six different clinical centers were analyzed. All procedures were performed in accordance with the Genesis nomograms. The Genesis protocol called for using preoperative screening pachymetry to guide central clear zone size selection, incising the thinnest corneal quadrant first, suturing corneal perforations, and discouraged more than one enhancement procedure, when indicated. Globe fixation technique served as a study variable. RESULTS: Mean follow-up was 6.2 months (range, 1.5-12 months). Mean residual cycloplegic refraction was -0.48 +/- 0.61 diopters (D) (range, -2.50 to +1.50 D); 92% of eyes were within 1 D of the planned goal of -0.50 D and 85% were within 1 D of emmetropia; 14% were myopic; and 1% was hyperopic by more than 1 D. Uncorrected visual acuity was 20/40 or better in 95% of eyes; the remaining 5% retaining myopic refractive errors. A single procedure was performed in 73% of eyes, and 99% received less than two enhancements. Of eyes with no enhancements, 97% had uncorrected visual acuity of 20/40 or better. One study eye (0.3%) had a two-line loss of spectacle visual acuity. There were no invasions of the central clear zone. Globe fixation was a significant predictor for enhancement incidence (P < 0.001) but not for perforation incidence (P = 0.06). Incision sequence was predictive for perforation incidence (P < 0.0002). CONCLUSION: The combined-technique of radial keratotomy, coupled with the Genesis surgical protocol, affords centrifugal incision safety with centripetal incision efficacy. The Genesis nomograms, with a built in refractive outcome goal of -0.50 D provide an acceptable degree of accuracy and predictability while guarding against hyperopic overcorrection.

Adult↗
PubMed1995

Pilocarpine-associated allograft rejection in postkeratoplasty patients.

Corneal allograft rejection is a major cause of graft failure. Identifying possible risk factors for rejection may improve chances for successful outcome. We report three cases of graft rejection associated with the use of post-operative pilocarpine at different concentrations. Pilocarpine was used to treat persistent epithelial defects or raised intraocular pressure. The patients were managed until their rejection episodes resolved. In each case, graft rejection ensued in a quiet eye after initiating treatment with pilocarpine, without other change in medications. Each graft rejection episode resolved with discontinuation of pilocarpine and administration of prednisolone acetate. We propose that if pilocarpine does indeed diminish corneal allograft immune privilege and enhance graft rejection, the mechanisms may include induced intraocular inflammation and altering of anterior chamber associated immune deviation. This is the first report implicating a topical ophthalmic medication with possible corneal allograft rejection.

Aged↗
PubMed1994

A combined incision technique of radial keratotomy. A comparison to centripetal and centrifugal incision techniques in human donor eyes.

PURPOSE: To evaluate and compare the extent of corneal flattening and the anatomy of the incision grooves produced by centrifugal, centripetal, and combined incisions in a human donor eye model. METHODS: Twenty-seven eyes, divided into three groups of nine, received eight-incision radial keratotomy using the centrifugal, centripetal, or combined incision technique. Corneal curvature was evaluated using a topography system, and the anatomy of the incision was assessed by light microscopy and scanning electron microscopy. RESULTS: The average central corneal flattening at the 3-mm clear zone was 4.16 +/- 1.47 diopters (D) for centrifugal incisions; 7.71 +/- 2.77 D for centripetal incisions; and 9.26 +/- 1.75 D for combined incisions. The difference in corneal flattening between eyes that received centrifugal versus either centripetal or combined incisions was significant (P < 0.01), whereas the difference between combined and centripetal incisions was not significant (P = 0.174). Anatomic differences were observed within the incision grooves produced by the three techniques. CONCLUSION: The authors describe a novel combined incision technique of radial keratotomy that provides the potential safety of a centrifugal incision with the effect of a centripetal incision.

Aged↗
PubMed1994

Retinal toxicity of the antimetabolite 5-fluorouridine 5'-monophosphate administered intravitreally using multivesicular liposomes.

BACKGROUND: Liposome-encapsulated 5-fluorouridine-5'-monophosphate (FUMP) has been shown to inhibit proliferative vitreoretinopathy in a rabbit model. Liposome encapsulation extends the intravitreal half-life of this antiproliferative drug by a factor of 28 times. METHODS: The current study investigated the retinal toxicity of intravitreal injections of 10, 50, and 100 micrograms FUMP as free drug or within liposomes in rabbits. Evaluation included ophthalmoscopic examination, electroretinography, and histologic analysis by light and electron microscopy. RESULTS: No electroretinographic evidence for toxicity of FUMP was found. Light and electron microscopy showed only mild transient vacuolization in the outer segment layer, without inflammation. Empty liposomes incurred no toxic effects on the retina. CONCLUSIONS: Our results suggest that liposome-encapsulated FUMP may be non-toxic to the retina at doses that inhibit proliferative retinopathy.

Animals↗