Laser in situ keratomileusis for myopia up to -11 diopters with up to -5 diopters of astigmatism with the summit autonomous LADARVision excimer laser system.

OBJECTIVE: To assess the safety and effectiveness of the Summit Autonomous LADARVision active tracking narrow beam excimer laser system for laser in situ keratomileusis (LASIK) correction of myopia and astigmatism. DESIGN: A multicenter, prospective noncomparative case series. PARTICIPANTS: This cohort consisted of 177 eyes corrected for spherical myopia up to -11 diopters (D) and 170 eyes corrected for myopia up to -11 D spherical equivalent with astigmatism up to -5 D. INTERVENTION: Treatments were performed at four sites in the United States using a 6-mm optic zone for spherical myopes and a 5.5-mm optic zone with a 1-mm blend for astigmats. MAIN OUTCOME MEASURES: Visual acuity, subjective refraction, vector analysis, subject satisfaction, intraocular pressure, complications, and adverse reactions. RESULTS: Six-month follow-up was available on 157 spherical eyes and 113 astigmatic eyes. For spherical myopes, uncorrected visual acuity (UCVA) was 20/20 or better in 60.5%, 20/25 or better in 80.3%, and 20/40 or better in 93.9%. The mean spherical equivalent was -0.29 +/- 0.45 D with 75.2% +/- 0.50 D and 94.9% +/- 1.00 D of intended. A loss of two lines of best spectacle-corrected visual acuity (BSCVA) occurred in 0.6%, and no eyes lost greater than two lines of BSCVA. For astigmatic myopes, UCVA was 20/20 or better in 52.0%, 20/25 or better in 74.5%, and 20/40 or better in 94.1%. The mean spherical equivalent was -0.23 +/- 0.49 D with 75.2% +/- 0.50 D and 95.6% +/- 1.00 D of intended. A loss of two lines of BSCVA occurred in 0.9%, and no eyes lost greater than two lines of BSCVA. Vector analysis showed that 99% of the intended cylinder was corrected on average with a mean angle of error of 4.2 degrees. Refractive stability was achieved between 1 and 3 months in 97.5% of spherical eyes and 99.4% of astigmatic eyes and confirmed between 3 and 6 months in 100% of both spherical and astigmatic eyes. CONCLUSIONS: Eyes treated for myopia up to -11 D of spherical equivalent with or without astigmatism up to -5 D show early refractive stability, good UCVA outcomes, no significant loss of BSCVA, accurate correction of astigmatism, and slight undercorrection without a change from the photorefractive keratectomy algorithm and with a single treatment.

Photorefractive keratectomy for low-to-moderate myopia and astigmatism with a small-beam, tracker-directed excimer laser.

OBJECTIVE: To assess the safety and effectiveness of the Autonomous Technologies Corporation LADARVision excimer laser system for photorefractive keratectomy correction of myopia and astigmatism. DESIGN: A multicenter, prospective, noncomparative case series. PARTICIPANTS: The cohort consisted of 467 eyes corrected for spherical myopia and 211 eyes corrected for myopia with astigmatism. INTERVENTION: Treatments were performed at six sites in the United States using a 6-mm ablation zone for spherical myopes and a 5.5-mm zone with a 1.0-mm blend for astigmats. MAIN OUTCOME MEASURES: Visual acuity, subjective refraction, corneal haze, intraocular pressure, complications, adverse reactions, patient satisfaction, and corneal endothelial changes. RESULTS: Twelve-month follow-up was available on 414 spherical eyes and 175 astigmatic eyes. The results for spherical eyes with correction between -1 and -5.99 diopters (D) were: uncorrected visual acuity (UCVA) of 20/40 or better achieved by 98.1%, 20/20 or better by 72%, 1.8% lost 2 lines and 0.3% lost greater than 2 lines of best spectacle-corrected visual acuity (BSCVA); 76.4% were within 0.50 D of the target correction and 94.4% were within 1.00 D. The results for myopia with astigmatism with spherical equivalent correction between -1 and -5.99 D were: UCVA of 20/40 or better in 97.4%, 20/20 or better in 61.7%, 2.5% lost 2 lines and no eyes lost greater than 2 lines BSCVA; 73.9% were within 0.50 D of the target correction and 95% were within 1.00 D. For spherical myopes combined with myopic astigmats corrected for 6 to 10 D, results were: UCVA of 20/40 or better in 93.4%, 20/20 or better in 61.2%, 2.3% lost 2 lines and no eyes lost greater than 2 lines of BSCVA; 67.2% were within 0.50 D of the desired correction and 87.8% were within 1.00 D. Refractive stability was achieved between 3 and 6 months for the spherical and astigmatic groups. No eyes had corneal haze graded as moderate or greater, and there was no significant decrease in endothelial cell density. CONCLUSIONS: Patients treated for 1 to 10 D of spherical equivalent myopia, with or without astigmatism, showed early refractive stability, excellent UCVA, no significant loss of BSCVA, no loss of endothelial cell density, and very low levels of corneal haze to 12 months after surgery.

Extracellular matrix changes in human corneas after radial keratotomy.

Extracellular matrix and basement membrane alterations were identified in human corneas after radial keratotomy. Ten normal and five radial keratotomy autopsy corneas (two at 6 months post surgery, and three at 3 years post surgery) were studied by immunofluorescence with antibodies to 28 extracellular matrix and basement membrane components. Outside of radial keratotomy scars, all studied components had a normal distribution. Of stromal extracellular matrix, only type III collagen accumulated around the scars. The basement membrane around epithelial plugs had a normal composition except for type IV collagen. Its alpha1-alpha2 chains, normally present only in the limbal basement membrane, appeared around all plugs. alpha3 and alpha4 chains were very weak or absent in these areas, contrary to nonscarred areas. This basement membrane pattern was similar to the normal limbal but not to the central corneal pattern. Keratin 3 also had a limbal-like, suprabasal expression in the plug epithelium. The stroma around the scars accumulated tenascin-C, fibrillin-1, types VIII and XIV collagen, all of which were absent from normal corneal basement membrane and extracellular matrix. Only tenascin-C showed less staining in anterior scars 3 years post surgery than 6 months post surgery, but still persisted in posterior scars. Incomplete scar healing was evident even 3 years post radial keratotomy. It was manifested by the accumulation of abnormal extracellular matrix in the anterior and posterior scars and by the limbal-like pattern of type IV collagen isoforms in the basement membrane around epithelial plugs.

Alterations of corneal extracellular matrix after multiple refractive procedures: a clinical and immunohistochemical study.

PURPOSE: To describe the clinical course and alterations of the corneal extracellular matrix (ECM) and basement membrane (BM) in a cornea after hexagonal keratotomy, transverse keratotomies, and keratomileusis. METHODS: Frozen sections of this cornea and of 12 normal corneas were studied by immunofluorescence with specific antibodies. The patient history was analyzed to allow a clinical correlation. RESULTS: In the treated cornea, keratotomy scars and subepithelial fibrosis with neovascularization were seen. Around and beneath the epithelial plugs and along the keratotomy scars, deposits of types III, VI, VIII, and XIV collagen; fibrillin-1; fibronectin; and tenascin-C were found, together with short streaks of types IV (alpha 1-alpha 2) and VII collagen, laminin-1 and -5, entactin, and perlecan. alpha 3-alpha 4 Type IV collagen chains were abnormally absent from the BM around the epithelial plugs. At the edges of the keratomileusis flap, subepithelial fibrosis areas were found, with abnormal deposits of eight different collagen types, perlecan, fibronectin, fibrillin-1, and tenascin-C. The major part of the flap interface did not show ECM abnormalities. ECM alterations outside the scarred areas included the appearance of tenascin-C in the stroma and of alpha 1-alpha 2 type IV collagen in the epithelial BM, and the disappearance of fibronectin from Descemet's membrane. CONCLUSION: Five years after surgery, the treated cornea still presented BM abnormalities at sites of keratotomy scars and epithelial plugs. Several ECM components were abnormally expressed outside the scarred areas, consistent with an ongoing fibrosis in the treated cornea.

Keratoconus and Turner's syndrome.

PURPOSE: To report the association of keratoconus and Turner's syndrome in three patients and to review the ophthalmic manifestations of Turner's syndrome. METHODS: Three patients with keratoconus and Turner's syndrome were identified and reported in a retrospective review. RESULTS: These three cases represent the first series of patients with keratoconus and Turner's syndrome. All three patients underwent penetrating keratoplasty with good visual rehabilitation. None of the patients had other ocular features associated with Turner's syndrome. CONCLUSION: Turner's syndrome is commonly associated with ocular problems. In this series we identify an association of keratoconus with Turner's syndrome. Clearly, a careful ocular examination in this condition with attention to ocular features of Turner's syndrome is important.

Bilateral photorefractive keratectomy with intentional unilateral undercorrection in an aircraft pilot.

An aircraft pilot had bilateral photorefractive keratectomy (PRK) with intentional undercorrection in the nondominant eye for best uncorrected far and near visual acuity (monovision). After PRK, the patient was able to pilot an aircraft with no deleterious effects directly related to surgery. Evaluation of similar cases and further study will allow consensus on whether PRK is appropriate in these patients.

Extracellular matrix alterations in human corneas with bullous keratopathy.

PURPOSE: To uncover abnormalities of extracellular matrix (ECM) distribution in human corneas with pseudophakic and aphakic bullous keratopathy (PBK/ABK). METHODS: Indirect immunofluorescence with antibodies to 27 ECM components was used on frozen sections of 14 normal and 20 PBK/ABK corneas. RESULTS: Fibrillar deposits of an antiadhesive glycoprotein tenascin in the anterior and posterior stroma, epithelial basement membrane (BM), bullae and subepithelial fibrosis (SEF) areas, and posterior collagenous layer (PCL) were revealed in disease corneas. Tenascin in midstroma, which was observed in some cases, correlated with decreased visual acuity. In normal central corneas, tenascin was never found. Other major ECM abnormalities in PBK/ABK corneas compared to normals included: discontinuous epithelial BM straining for laminin-1 (alpha 1 beta 1 gamma 1), entactin/nidogen and fibronectin; accumulation of fibronectin and alpha 1-alpha 2 type IV collagen on the endothelial face of the Descemet's membrane; and abnormal deposition of stromal ECM (tenascin, fibronectin, decorin, types I, III, V, VI, VIII, XII, XIV collagen) and BM components (type IV, collagen, perlecan, bamacan, laminin-1, entactin-nidogen, fibronectin) in SEF areas and in PCL. CONCLUSIONS: The study provides a molecular description of an ongoing fibrosis on the epithelial, stomal, and endothelial levels in PBK/ABK corneas. These fibrotic changes may follow initial endothelial damage after cataract surgery, may be caused by the upregulation of fibrogenic cytokines, and may play a significant role in the progression of bullous keratopathy.

Keratoconus detected by videokeratography in candidates for photorefractive keratectomy.

BACKGROUND: Patients with corneal shape abnormalities should be identified prior to photorefractive keratectomy (PRK). We used videokeratography screening to detect subclinical corneal abnormalities, including keratoconus, which might have been missed by conventional clinical evaluation. METHODS: One hundred forty-six apparently normal myopic eyes (-1.00 to -7.00 diopters [D] with less than 1.50 D of cylinder) of 91 consecutive patients who were candidates for PRK were screened by videokeratography. RESULTS: In 6 of 91 patients (7 of 146 eyes), unsuspected corneal shape abnormalities were detected by videokeratography. Two patients had definite keratoconus and three were classified as keratoconus suspects by inferior corneal steepening (Rabinowitz I-S index ranging from 1.62 to 6.20 D). One patient had early pellucid marginal degeneration. CONCLUSIONS: Keratoconus suspects and contact lens-induced changes resembling keratoconus are present in the "normal" myopic population that presents for refractive surgery. Videokeratographic screening is the only effective means of identifying these and other corneal shape abnormalities.

Results of excimer laser photorefractive keratectomy for the correction of myopia.

PURPOSE: This report summarizes the authors' 3-year experience with excimer laser photorefractive keratectomy on 240 eyes of 161 patients. METHODS: With constant laser emission parameters, nitrogen flow across the cornea was used on 79 eyes, whereas 161 eyes had no nitrogen flow. Of the 240 eyes, 74 were operated on without suction ring fixation. Postoperative pain management included patching and oral analgesics in 77 eyes and the use of topical diclofenac or ketorolac and a therapeutic soft contact lens in 163 eyes. Follow-up ranged from 1 month (206 eyes) to 36 months (10 eyes). RESULTS: At 3 months, 88% (144 eyes) had uncorrected visual acuity of 20/40 or better; 86% (151 eyes) had corrected visual acuity to within +/- 1 diopter of intended correction, and 10% (17 eyes) lost two or more lines of best-corrected visual acuity. At 12 months, 89% (122 eyes) achieved uncorrected visual acuity of 20/40 or better, 79% (115 eyes) had corrected visual acuity to within +/- 1 diopter of intended correction, and 4% (6 eyes) lost two or more lines of best-corrected visual acuity. At 24 months, 92% (44 of 48 eyes) had uncorrected visual acuity of 20/40 or better, 86% (44 of 51 eyes) had corrected visual acuity to within +/- 1 diopter of intended correction, and 5% (2 eyes) lost two or more lines of best-corrected visual acuity. At 36 months, 90% (9 eyes) achieved an uncorrected visual acuity of 20/40 or better, 90% (9 eyes) had corrected visual acuity to within +/- 1 diopter of intended correction, and no eyes lost two or more lines of best-corrected visual acuity. CONCLUSIONS: The results obtained with one procedure are within accepted standards of accuracy for refractive surgery, and there is the potential for refinement of the final optical correction. Complication rates are low and are not vision threatening. They included increased intraocular pressure, epithelial "map dot" changes, and recurrent corneal erosion syndrome, "central islands," and others. Photorefractive keratectomy appears to be a safe procedure over the short and medium term.

A retrospective study of disposable extended wear lenses in 100 patients: year 3.

We present the results of the third year of follow-up of a group of 100 patients wearing disposable contact lenses on an extended wear basis. Thirty-seven males and 63 females participated in the study. The mean patient age was 41.76 years (SD: 14.5), and the mean patient follow-up time was 37.73 months (SD: 5.25). Twenty-three patients were lost to follow-up. Most of those lost to follow-up decided to purchase their lenses at discount outlets. A case of recurrent corneal ulcers in a patient wearing lenses obtained from a discount outlet is described. A significant decrease in events defined as complications (14 events) was noted as compared with the second year (32 events) of the study. One corneal infiltrate and one corneal ulcer were noted. Disposable extended wear lenses may be a reasonable means of vision correction in the properly selected patient with appropriate follow-up provided by a well-trained eye care practitioner.

Effect of nitrogen flow on recovery of vision after excimer laser photorefractive keratectomy without nitrogen flow.

BACKGROUND: Excimer laser (VISX) photorefractive keratectomy was performed using nitrogen flowing through the ocular fixation ring. It was felt that eliminating nitrogen flow may provide faster early visual rehabilitation. METHODS: Two groups of 50 consecutive eyes underwent photorefractive keratectomy with (N2 flow) and without (no N2 flow) nitrogen flow, and were evaluated at 1 month postoperatively. RESULTS: There were more under- or overcorrections exceeding 1.00 diopter (D) in the N2 flow than in the no N2 flow groups. Eighteen eyes in the N2 flow and 11 in no N2 flow groups saw 20/50 or less, without correction. Fourteen eyes in the N2 flow and nine eyes in the no N2 flow groups lost two or more lines of best spectacle-corrected visual acuity. Four eyes in the N2 flow and none in the no N2 flow groups increased more than 1.00 D of astigmatism. CONCLUSION: The elimination of nitrogen flow in photorefractive keratectomy performed with the VISX laser appears to improve visual results in the early postoperative period.

A two-year experience with excimer laser photorefractive keratectomy for myopia.

PURPOSE: This report summarizes the authors' 2-year experience with excimer laser photorefractive keratectomy (PRK) on 160 eyes of 128 patients. METHODS: All eyes were treated with an excimer laser: fluence, 160 mJ/cm2; frequency, 5 Hz; ablation zone diameter, 5.0 to 5.5 mm; and depth per pulse, 0.21 to 0.27 microns. A suction fixation ring was used in all eyes either with nitrogen flow (79 eyes) or without nitrogen flow (81 eyes) across the cornea. Follow-up ranged from 1 month (152 eyes) to 24 months (12 eyes). RESULTS: At 3 months, 82% (139) of eyes achieved an uncorrected visual acuity of 20/40 or better; 83% were corrected to within +/- 1 diopter (D) of intended correction and 30% lost one line of best-corrected visual acuity. At 6 months, 88% (124) of eyes achieved an uncorrected visual acuity of 20/40 or better; 84% were corrected to within +/- 1 D of intended correction and 15% lost one line of best-corrected visual acuity. At 12 months, 91% (71) of eyes achieved an uncorrected visual acuity of 20/40 or better; 84% were corrected to within +/- 1 D of intended correction and 17% lost one line of best-corrected visual acuity. At 24 months, 100% (12) of eyes achieved an uncorrected visual acuity of 20/40 or better; 91.6% were within +/- 1 D of intended correction and 0% lost one line of best-corrected visual acuity. CONCLUSIONS: In eyes with a follow-up of 6 to 24 months, 77% to 100% achieved an uncorrected visual acuity of 20/40 or better and 84% to 92% were corrected to within +/- 1 D of the intended correction. The authors conclude that excimer laser PRK appears to be a safe procedure capable of correcting the eyes of patients with low to moderate myopia with approximately the same degree of accuracy as radial keratotomy.

A retrospective study of disposable extended wear lenses in 100 patients: year 2.

We present the results of the second year of follow-up of 100 patients wearing disposable contact lenses on an extended wear basis. Thirty-seven males and 63 females participated in the study (mean age: 41.1 years +/- 13.88 (mean +/- 1 standard deviation); and the mean patient follow-up time was 26 months +/- 4.9). A total of 13 patients were lost to follow-up. Seventeen patients discontinued extended wear yet continued to wear soft lenses on a daily wear basis--the reasons for this finding are discussed. A significant decrease in the number of events defined as complications (32 events) was noted when compared to the first year of follow-up (136 events). Seven corneal infiltrates occurred during the second year, compared to 6 such events during the first year of the study. Additional complications included: giant papillary conjunctivitis (6 cases), corneal staining (5 cases), and corneal abrasions (4 cases). Disposable extended wear soft contact lenses offer a reasonable means of vision correction in the properly selected patient. At the same time, caution should be exercised in the fitting and wear of these lenses.

A comparison of excimer laser (308 nm) ablation of the human lens nucleus in air and saline with a fiber optic delivery system.

BACKGROUND: Photoablation with excimer lasers has demonstrated precise tissue cutting and minimal thermal damage. Potential ophthalmic applications of these lasers include remodelling of the corneal surface, glaucoma treatment, and phacoablation. Ablation of human lens with a 308 nm XeCl excimer laser light delivered through a fiber has been demonstrated in preliminary experiments. Intraocular delivery of laser light must be done in a fluid medium to preserve the integrity of ocular structures. However, little information is available on the effect of the fluid media on the ablation process. Therefore, a series of experiments was conducted to determine whether the ablation of human lens nucleus at 308 nm via a fiber differs in air and saline media. METHODS: Ablation of human lens nuclei (n = 30) was conducted with a XeCI excimer laser (308 nm) coupled to a 600 microns core size fiber. Irradiation was performed at 2.8 mJ/cm2 energy density and 20 Hz. The fiberoptic was brought to contact with the lens nucleus and remained fixed for the duration of irradiation. Variables consisted of the medium (air or saline) and number of pulses delivered (100 to 10,000). Following establishment of the tissue shrinkage ratio, the depth of each crater and the tissue volume removed were measured histologically. The histological features of nucleus ablation in air and in saline were also examined with both light and scanning electron microscopy. RESULTS: Light microscopy revealed that the average zone of thermal damage adjacent to the crater is thinner in the presence of saline (60 microns, SD = 6 microns) than it is in air (90 microns, SD = 12 microns). In both media, the thickness of the zone of thermal damage is greater at the surface than it is at its base. Following irradiation in air, deep sharpedged craters with smooth walls are formed. Craters formed by irradiation in saline are characterized by reduced depth and irregular walls. For the same number of pulses applied (500, 1000, and 2000), the mean depth of ablation per pulse in air (8.6 to 2.7 microns/pulse) was greater by approximately a factor of two than that in saline (4.10 to 1.30 microns/pulse) at P < .01. However, the mean ablated volume removed per pulse was greater in saline (0.00250 to 0.00150 mm3/pulse) than in air (0.00120 to 0.00080 mm3/pulse), for the same number of pulses (1000, 2000) at P < .01. CONCLUSIONS: In comparing the data for the same number of pulses applied in air and in saline, it appears that the depth of crater formed by irradiation in air is deeper than that in fluid. The overall volume ablated is greater in fluid than it is in air at 1000 and 2000 pulses. Additionally, the zone of thermal damage is thinner in the presence of saline than it is in air. Smoother crater shapes were observed following irradiation in air than in saline. These results suggest that under this specific experimental setup, the ablation in saline is different from that in air.

The use of the SoftPerm lens for the correction of irregular astigmatism.

We evaluated the performance of the SoftPerm combined rigid gas permeable (RGP) and hydrogel lens for the visual correction of 49 eyes (30 patients) with irregular astigmatism. Follow-up was up to 15 months. An attempt was also made to compare the SoftPerm lens to its predecessor, the Saturn II lens. The most common etiology for irregular astigmatism was keratoconus. Others etiologies were penetrating keratoplasty and refractive surgery. Visual acuity improved significantly. Only two eyes were best corrected to 20/20 before fitting whereas, 13 eyes saw 20/20 after fitting. The rate of lens replacement was 0.22 lenses per eye per month. A variety of complications occurred, including corneal staining, abrasions, and edema. Complications also reflected the relative difficulty of handling of the lens, yet no vision threatening complications occurred. Overall, the SoftPerm lens is a vast improvement over the Saturn II and is a reasonable means of correction of irregular astigmatism.

One-year results of excimer laser photorefractive keratectomy for myopia.

BACKGROUND: Excimer laser photorefractive keratectomy for the correction of myopia is presently under investigation in the United States by the Food and Drug Administration (FDA). The Phase II-B FDA study is being conducted on 75 normally sighted myopic eyes utilizing three currently available excimer lasers. This report presents the 1-year results on 12 myopic eyes treated with the VISX excimer laser system at the Ellis Eye Center at Cedars-Sinai Medical Center in Los Angeles under the Phase II-B FDA protocol. METHODS: Twelve eyes of 12 patients with myopia between -1.75 and -5.00 diopters underwent 193 nm argon/fluoride excimer laser photorefractive keratectomy. The epithelium was mechanically removed, and fixation was accomplished with a suction ring which provided nitrogen flow across the corneal surface. The computer controlled corneal ablations were 5.00 mm in diameter and were accomplished with an iris diaphragm closing from large to small. RESULTS: The preoperative spherical equivalent myopia was -3.50 D (SD = 1.02) and the postoperative myopia was -0.25 (SD = 0.48). Eleven of the 12 patients achieved an uncorrected visual acuity of 20/30 or better and were corrected to within +/- 0.50 D of emmetropia. All corneas demonstrated a mild reticular subepithelial haze which was barely visible at 1 year. There were no vision-threatening complications and none of the eyes experienced a loss of best corrected visual acuity. CONCLUSIONS: In this small trial, the excimer laser appears to be capable of accurately changing the refractive power of the cornea for the correction of myopia with minimal side effects. Only when larger numbers of patients undergo the procedure will we be able to determine the safety and efficacy of photorefractive keratectomy as a refractive surgical procedure.

A retrospective study of disposable extended-wear lenses in 100 patients.

A retrospective evaluation of 100 patients who wore disposable extended-wear contact lenses is presented. The patients were selected at random and were fitted with one of three lens brands approved for extended wear. There were 37 males and 63 females in the study. The mean age was 40.1 years (range, 14 to 76 years). Sixty-seven of the patients wore nondisposable extended-wear soft contact lenses before being fitted with disposable lenses. Complications were noted and included two instances of infectious ulcerative keratitis and six cases of peripheral corneal infiltrates. It is believed that the rate of complications is due to the ongoing hypoxic effect of prolonged use of extended-wear or other contact lenses and may be improved by providing a greater variety of lens fitting parameters. Disposable extended-wear lenses may be a reasonable means of vision correction in the appropriately selected patient and with proper follow-up. At the same time, caution should be exercised in the fitting and wear of disposable extended-wear lenses.

The use of Saturn II lenses in keratoconus.

We studied Saturn II contact lenses in keratoconus patients who were intolerant to other available contact lenses. A total of 24 patients, who were followed for up to 15 months, participated in the study. Visual acuities improved significantly following fitting with the Saturn II contact lens; whereas only one eye in the series was correctable to 20/20 before fitting, eight eyes were corrected to 20/20 following fitting. A great number of lenses had to be replaced during the study because of deposit formation and tearing at the interface (rate of replacement: 0.52 lenses per eye per month). A variety of complications occurred during lens wear, resulting in only six eyes wearing the Saturn II lens at the close of the study (out of 46 eyes that had started wearing the lens). Discomfort due to tightness of the peripheral segment was the most common cause of lens discontinuation. We conclude that the Saturn II lens was inadequate for fitting patients with advanced keratoconus.

Excimer laser ablation of the human lens at 308 nm with a fiber delivery system.

A 308 nm excimer laser has been used with a fiber delivery system to perform ablation of the human lens. Preliminary results demonstrate the system's ability to ablate lens nucleus and cortex selectively, preserving the anterior and posterior capsules. The total delivered energy necessary to ablate a human lens ranged from 35 to 63 joules. Laser tissue interaction and ablation rates were computed for the different components of the human lens (capsule, cortex, nucleus) for the operatively useful energy densities (fluences). Operative experience suggests that cortex and nucleus can be ablated while preserving the capsule if an adequate irrigation and aspiration system is developed. These results also suggest that this modality may be adequate for performing endocapsular cataract extraction. Laser tissue interactions were also computed at variable distances between the fiber tip and tissue. As this distance increased, the spread of the beam increased and a significant increase in energy was necessary to induce tissue ablation. This was due to the decrease in fluence with increasing distance to the target tissue and/or the absorption and scattering of the delivered energy within a short distance from the fiber tip by the ablated material. Evidence of a sonic effect was also present.