Clinical analysis of the neodymium:YLF picosecond laser as a microkeratome for laser in situ keratomileusis. Partially Sighted Eye Study

PURPOSE: To evaluate the use of a picosecond neodymium:YLF (Nd:YLF) laser as a nonmechanical intrastromal microkeratome. SETTING: Universita Cattolica del Sacro Cuore, Rome, Italy. METHODS: An intrastromal spiral disc pattern of picosecond laser pulses was used to create a corneal flap for laser in situ keratomileusis (LASIK) in 14 partially sighted eyes. RESULTS: Flaps with a 6.0 mm diameter and 180 to 200 microns depth were successfully created in most cases. The underlying stroma was treated with a Lambda Physik excimer laser using a 3.5 to 4.5 mm optical zone. Patients were divided into 3 groups for target corrections of 5.0, 10.0, and 15.0 diopters of myopia. Good corneal clarity and refractive undercorrection were recorded in each group 6 months postoperatively. The undercorrection was due in part to the limited optical zone of the laser's delivery system. Some flap decentration was noted. CONCLUSION: This pilot study indicates that the Nd:YLF picosecond laser may be clinically applied for creating corneal flaps for LASIK. Further refinements of the laser delivery system will include enlargement of the flap diameter and improvements in flap centration. The use of a femtosecond laser may expand the capabilities and precision of this technology.     

Wound healing following intrastromal photorefractive keratectomy with the Nd:YLF picosecond laser in the cat

BACKGROUND: We studied the histopathology of the stromal wound healing response in the cat cornea following intrastromal photorefractive keratectomy (IPRK) with the Nd:YLF picosecond laser. METHODS: Intrastromal PRK was performed in the anterior stroma of cat corneas with the Nd:YLF picosecond laser. The cats were sacrificed at predetermined intervals ranging from immediately to 6 months postoperatively. Effects of the laser treatment on the epithelium, Bowman's layer, stroma, and the endothelium were evaluated using light and scanning electron microscopy. No anti-inflammatory agents were used. RESULTS: Intrastromal PRK resulted in no perceptible damage to the corneal epithelium or Bowman's layer either acutely or at 6 months. The corneal stroma showed multiple cavitations immediately after intrastromal PRK, which collapsed over several hours, followed by thinning of the cornea over 2 weeks. At 1 month, the stromal collagen was abnormal with surrounding hypercellularity. The endothelium showed no injury, acutely or at 6 months. No thermal effects on stromal collagen were observed at 6 months, and disruption of the lamellar pattern was not apparent after the cavitation bubbles were reabsorbed. CONCLUSION: Intrastromal PRK can effectively remove stromal tissue without acute damage to the adjacent lamellae, epithelium, or endothelium. There is a transient cellular wound healing response associated with a transient stromal collagen abnormality at 2 weeks to 1 month, which was not apparent 2 months after the procedure.     

Central focal interface opacity after laser in situ keratomileusis

BACKGROUND: The acute onset of a focal central interface opacity with visual loss following LASIK has not been described in the peer reviewed literature. Non-peer reviewed reports of various inflammatory lesions have been recorded. METHODS: We describe three cases in which an acute focal stromal interface opacification was identified within 1 week of laser in situ keratomileusis (LASIK). Each case was performed by a different surgeon on a different day, but using the same method, materials, and the Summit Apex Plus excimer laser. Immediately after surgery, all eyes were normal with good unaided vision. The appearance of the central stromal opacity was associated with acute visual deterioration. Preoperative and postoperative cycloplegic refractions, videokeratography, and postoperative slit-lamp biomicroscopy were performed. Each case was treated with intensive topical corticosteroids. RESULTS: Each case demonstrated a central circular opacity in the interface between corneal flap and stromal bed, with associated variable stromal thinning. Resolution of the pathological process followed 2 to 4 weeks of treatment with topical corticosteroids and subsequent improvement in slit-lamp biomicroscopy, corneal topography, and vision. Etiology was uncertain. CONCLUSION: Central interface opacification is a rare but visually important inflammatory complication of LASIK.     

Removal of flap striae following laser in situ keratomileusis

Androgenablation is the therapy of choice for the treatment of advanced and metastatic prostate cancer. However, in more than half of the patients the disease will ultimately progress within 2 years. Intermittent androgenablation through medical castration maintains the apoptotic potential. By periodically changing phases on and off treatment the quality of life of the patients is improved. Apart from reduced toxicity treatment costs are lowered and tumor progression is possibly delayed. In how far survival is influenced is presently not clear and remains to be evaluated in further clinical trials.     

Corneal wound healing after laser in situ keratomileusis in rabbits

BACKGROUND: The aim of this study was to characterize the cell biology of wound healing in rabbit corneas subjected to laser in situ keratomileusis (LASIK). METHODS: Rabbit corneas underwent LASIK with various multizone photoablations or only a lamellar keratotomy followed by repositioning of the flap. We looked for indications for an active wound healing process. Immunohistochemistry for the extradomain A cellular fibronectin (EDA-cFn) or tenascin (Tn) and routine histology were examined. RESULTS: Four days after LASIK or lamellar keratotomy followed by repositioning of the flap, epithelial plugs and prominent keratocytes as well as Tn and EDA-cFn immunoreactions-indicative of a wound-healing process-appeared in the wound margins. Epithelial plugs were less conspicous, and prominent, presumably activated, keratocytes were no longer identified at the wound margin at 2.5 and 5 months after wounding. However, EDA-cFn and Tn immunoreactivities could still be observed. Only the stromal cells located in the periphery of the flap and in relatively close contact with the epithelium were surrounded by scar tissue expressing immunoreactivity for EDA-cFn or Tn. The central corneal stroma was devoid of scar tissue. CONCLUSION: Results indicate that the wound healing reaction after LASIK takes place only at the periphery of the microkeratome wound, leaving the central optical zone clear.     

Corneal reinnervation after photorefractive keratectomy and laser in situ keratomileusis: an in vivo study with a confocal videomicroscope

The purpose of this study was to compare the regeneration of corneal nerves after photorefractive keratectomy (PRK) versus laser in situ keratomileusis (LASIK) in vivo with a confocal videomicroscope. In all, 15 eyes that had undergone PRK and 15 eyes that had been subjected to LASIK were compared with a confocal in vivo slit-scanning video-microscope. The subepithelial nerves were observed preoperatively and at 3, 6, and 12 months postoperatively. In all eyes, good microscope images of the subepithelial nerve plexus could be obtained preoperatively. Because of postoperative light reflection and scattering in the treated area, subepithelial nerve-fiber regeneration could be followed satisfactorily only in seven eyes after PRK and in five eyes following LASIK. In the eyes treated with PRK, recovery of subepithelial reinnervation started from the margin of the ablation zone, being directed toward the center of the cornea. At 8 weeks postoperatively, rarefied subepithelial nerve fibers were visible at the edges, and after 3 months, single nonbranched nerve fibers could be visualized in the center of the ablation zone. At 6-8 months following PRK, subepithelial nerve regeneration seemed to be completed; however, abnormal branching and accessory thin nerve fibers were present without exception. After LASIK, corneal nerve-fiber regeneration followed the same course described for PRK except that regenerated subepithelial nerve fibers were barely visible in the center after 6 months. Further changes in nerve structure were visible for up to 12 months postoperatively. Recovery of corneal sensitivity in humans has been reported to start at 4-6 weeks after PRK and is said to be completed within 6-12 months of surgery. Slit-scanning videomicroscope findings were in accordance with these observations.     

Q-switched 532-nm Nd:YAG laser trabeculoplasty (selective laser trabeculoplasty): a multicenter, pilot, clinical study

OBJECTIVE: To investigate the safety and efficacy of a new laser procedure using a q-switched 532-nm neodymium (Nd):YAG laser, also called "selective laser trabeculoplasty," to lower intraocular pressure (IOP) in patients with open-angle glaucoma (OAG). The laser parameters were set to selectively target pigmented trabecular meshwork (TM) cells without coagulative damage to the TM structure or nonpigmented cells. DESIGN: Nonrandomized, prospective, clinical trial. PARTICIPANTS: Thirty eyes of 30 patients with uncontrolled OAG (OAG group) and 23 eyes of 23 patients with uncontrolled OAG treated previously with argon laser trabeculoplasty (ALT group) were observed for 4 to 26 weeks. Forty-four of the 53 eyes were observed for 26 weeks. INTERVENTION: Patients were treated with the Coherent Selecta 7000 (Coherent, Inc, Palo Alto, CA) frequency-doubled q-switched Nd:YAG laser (532 nm). A total of approximately 50 nonoverlapping spots were placed over 180 degrees of the TM at energy levels ranging from 0.6 to 1.2 mJ per pulse. After surgery, patients were maintained with the identical drug regimen as that before treatment. RESULTS: Both the OAG and ALT groups showed similar IOP reductions over time. Seventy percent of patients in each group responded to treatment with an IOP reduction of least 3 mmHg. At 26 weeks of follow-up, mean IOP reduction was 5.8 mmHg (23.5%, P < 0.001) for the OAG group and 6.0 mmHg (24.2%, P < 0.001) for the ALT group. The untreated eye showed a 9.7% (P < 0.001) reduction of IOP at 26 weeks. However, the IOP difference between the treated and untreated eyes was statistically significant at P < 0.003. Transient IOP elevation of 5 mmHg or greater was seen in 24% of patients. CONCLUSION: The selective laser trabeculoplasty appears to be a safe and effective method to lower IOP in patients with OAG and patients treated previously with ALT. A reduction of IOP can be achieved without coagulation of the TM.     

Laser in situ keratomileusis: literature review of a developing technique

We reviewed papers published in peer-reviewed journals describing techniques and results of laser in situ keratomileusis (LASIK) and summarized the instruments used, nomograms, preoperative and postoperative refractions, predictability, outcome, safety, and complications. We performed a similar review of abstracts published in the abstract books of the 1996 meeting of the International Society of Refractive Surgery, the 1997 meeting of the Association for Research in Vision and Ophthalmology, and the 1997 meeting of the American Society of Cataract and Refractive Surgery. The number of LASIK and photorefractive keratectomy (PRK) patients described in the abstracts were sorted by city. Mean weighted latitudes were calculated and compared for each procedure. The mean preoperative refraction in the papers was -12.59 diopters (D), which was statistically higher than that in the abstracts, -8.71 D (P < .001), and the mean postoperative refraction, -1.10 and + 0.93 D, respectively. The mean percentage of cases within +/- 1.00 D was 67.0% in the papers and 82.5% in the abstracts. Uncorrected visual acuity (UCVA) of 20/40 or better was achieved in 49.2% of eyes in the papers and 83.2% of those in the abstracts; a UCVA of 20/20 or better was achieved in 22.0 and 56.6%, respectively. The portion of eyes that lost two or more lines of best corrected visual was 8.0% in the papers and 0.9% in the abstracts. Complications in the papers included irregular flap (4.0%), incomplete cut (2.5%), free cap (4.9%), perforated lenticule (2.6%), short flap (3.0%), sliding flap (1.4%), interface debris (6.8%), central island (5.3%), decentration (4.7%), epithelial ingrowth (4.3%), induced astigmatism (5.1%), wrinkles (5.9%), haze (8.7%), night vision problems (14.0%), and reoperation (8.2%), Mean latitude for LASIK cases (27.00 degrees +/- 13.73 [SD] was significantly lower than that for PRK cases (42.85 +/- 11.7 degrees). Visual outcomes of LASIK surgery show significant improvements when recent abstracts are compared with published papers. This may reflect continued improvement in the surgical techniques, surgeons' skills, and visual outcomes.     

Gelatinase B and A expression after laser in situ keratomileusis and photorefractive keratectomy

OBJECTIVE: To compare the expression of gelatinases in the corneal epithelium and stroma after laser in situ keratomileusis (LASIK) and photorefractive keratectomy (PRK). METHODS: Rabbit eyes were treated with LASIK (n=11), PRK (n=12), or corneal flap construction (n=12); 4 eyes served as unwounded controls. Zymography was performed on the central epithelium and the stroma 1, 3, and 7 days after surgery to determine the expression of gelatinases. RESULTS: Epithelial expression of gelatinase B in the LASIK group (0%-25%) was lower than that in the PRK group at all time points (50%-100%) and was identical to the corneal flap group. Stromal expression of gelatinases A and B was similar after LASIK and PRK, but was minimal after corneal flap construction at all time points. Epithelial expression of gelatinase A was similar for the first 3 days after LASIK and PRK but not thereafter. CONCLUSIONS: Gelatinase B epithelial expression was up-regulated after PRK but not after LASIK. Gelatinase B stromal expression was up-regulated after both procedures. CLINICAL RELEVANCE: Differences in wound healing and subepithelial scarring after these 2 procedures may be related to gelatinase B.     

Effect of surface photorefractive keratectomy and laser in situ keratomileusis on the corneal endothelium

PURPOSE: To investigate endothelial cell loss in pairs of fresh human autopsy globes following high-diopter myopic photorefractive keratectomy (PRK) or laser in situ keratomileusis (LASIK). SETTING: Center for Research on Ocular Therapeutics and Biodevices and Magill Laser Center for Vision Correction, Storm Eye Institute, Charleston, South Carolina, USA. METHODS: In the first part of the study, 12 globes had either -10 diopters (D) multizone surface PRK or -10 D single-zone LASIK. In the second part, three groups of 5 globes each had -15 D, -20 D, or -25 D multizone-blend LASIK procedures. Fellow globes in both groups were used as untreated controls. Corneoscleral buttons were excised from all globes. Following 7 days in corneal organ culture, the endothelial surface was stained with two vital dyes: calcein-AM and ethidium homodimer. Fluorescence microscopy was used to obtain endothelial cell counts. RESULTS: The mean dead cells per square millimeter (cells/mm2) were 0.94 in the -10 D PRK treated corneas compared with 0.91 in the fellow untreated eyes (P = 0.06(. The mean dead cells/mm2 in the -10 D single-zone LASIK-treated corneas and in the fellow untreated eyes were 0.61 (P = 0.88). The mean dead cells/mm2 in the -15 D, -20 D, and -25 D multizone-blend LASIK-treated corneas were 3.08, 2.33, and 5.55, respectively, compared with 3.49, 1.92, and 5.01 in the fellow untreated eyes (P = 0.276, P = 0.339, and P = 0.427, respectively). Dead cell counts for treated and control paired corneas were highly correlated in all treatment groups. CONCLUSIONS: No significant endothelial cell loss occurred after -10 D PRK or LASIK corrections up to -25 D. Although this study has limitations that prevent direct extrapolation to the clinical situation, it does afford a comparable clinical correlate for endothelial cell toxicity following a typical excimer laser ablations.     

Corneal topography of photorefractive keratectomy versus laser in situ keratomileusis. Summit PRK-LASIK Study Group

OBJECTIVE: This study aimed to compare qualitative patterns of corneal topography early in the postoperative course after excimer laser photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK) when used for the treatment of myopia of 6.0 to 15.0 diopters. DESIGN: The study design was a prospective, multicenter, randomized clinical trial. PARTICIPANTS: A total of 64 eyes were treated with PRK and 54 eyes were treated with LASIK. INTERVENTION: Using the Summit Apex excimer laser, patients received either PRK or LASIK using a single pass, multizone excimer laser ablation. Computer-assisted videokeratography was performed at designated postoperative examinations. MAIN OUTCOME MEASURES: Videokeratography maps at 1 and 3 months after surgery were classified using a standard classification scheme. The association of topography patterns to loss of spectacle-corrected visual acuity was tested. RESULTS: At 1 month, for the PRK (n = 60) and LASIK (n = 51) groups, respectively, 63.3% and 19.6% of eyes fell into one of the four optically irregular groups (central island, keyhole, semicircular, or irregularly irregular; P < 0.001). At 3 months, for the PRK (n = 49) and LASIK (n = 39) groups, respectively, 36.7% and 10.3% of eyes fell into one of the optically irregular groups (P = 0.004). Comparing the 1- and 3-month examination results in the PRK and LASIK groups, respectively, 19 (42%) of 45 eyes and 11 (31%) of 36 eyes had a change in topography, generally to an optically smoother pattern. The irregular groups, taken together, were associated with a greater tendency toward loss of spectacle-corrected visual acuity of two or more Snellen lines (P = 0.01). There also was greater tendency toward loss of spectacle-corrected visual acuity in the PRK group that diminished with time (P < 0.01 at 1 month, P = 0.05 at 3 months). CONCLUSIONS: After treatment for moderate-to-high myopia, LASIK topography patterns generally are more regular than are PRK patterns. This may be a result either of masking of underlying topography perturbations by the lamellar corneal flap, thus mitigating induced topography changes, or differences in surface wound healing. This study suggests that more rapid return of spectacle-corrected visual acuity found in patients treated with LASIK may be a result of more regular topography patterns early in the postoperative course.     

Posterior capsule polishing with the neodymium:YLF picosecond laser: model eye study

PURPOSE: To determine the ability and threshold energy of the neodymium:yttrium-lithium-fluoride (Nd:YLF) picosecond laser to achieve micron-level polishing of a latex posterior capsule facsimile (PCF) as an alternative to laser capsulotomy to treat posterior capsule opacification. SETTING: University of Rochester Medical Center, Rochester, New York, USA. METHODS: A solid-state, mode-locked Nd:YLF picosecond laser was used to polish a latex PCF in contact with a poly(methyl methacrylate) intraocular lens (IOL) in an experimental model eye. Eight study groups were treated at different energy levels ranging from 5 to 15 microJ. All treatments were done at least three times in different latex capsules and lenses. An atomic force microscope was used to measure IOL damage and an interferometric surface analysis microscope to assess the polishing effect on the PCF. The IOLs were further subjected to a scatter analysis to assess the optical significance of the damage produced. RESULTS: The latex PCF revealed a polishing effect with all energy settings used. The IOLs were damaged with all energy settings but 5 microJ. Energy settings higher than 5 microJ caused significantly more polishing effect to the latex and damage to the lenses. At the 10 microJ energy level, a single parameter with no depth produced a relative polishing depth of 3.01 microns +/- 0.10 (root mean square +/- SD). At this energy, the damage to the IOLs was 188 +/- 20.52 nm, and it was associated with typical craters over the surface at regular intervals that corresponded to each individual laser pulse. CONCLUSION: This model documented the feasibility of achieving micron-level precision in excising material with the picosecond laser and showed that posterior capsule polishing should be feasible and safe in human eyes.     

Transepithelial photorefractive keratectomy for treatment of thin flaps or caps after complicated laser in situ keratomileusis

PURPOSE: To report transepithelial photorefractive keratectomy treatment of corneal irregularities produced during laser in situ keratomileusis (LASIK) in which there is a thin flap or cap associated with central corneal scarring or epithelial ingrowth that threatens vision. METHODS: Case reports. The thickness of the abnormal corneal flap or cap and associated scarring or epithelial ingrowth is estimated at the slit lamp or measured with an optical pachymeter. If residual myopia is sufficiently high to allow complete ablation of the flap or cap in the central cornea, a transepithelial photorefractive keratectomy is performed in which the epithelium is completely ablated with the excimer laser in phototherapeutic keratectomy mode; residual myopia is corrected using photorefractive keratectomy. RESULTS: This method was used successfully in two eyes of two patients in which a thin cap was associated with a transverse cut through the central cornea or a donut-shaped flap associated with epithelial ingrowth in the central cornea. In both cases, the abnormal cap or flap was ablated, central corneal clarity restored, and visual function improved. CONCLUSION: Transepithelial photorefractive keratectomy may be effective in treating central corneal thin cap or flap abnormalities associated with LASIK.     

Prospective comparison of single-zone and multizone laser in situ keratomileusis for the correction of low myopia

OBJECTIVE: This study aimed to determine whether there is a true difference in predictability between single-zone and multizone laser in situ keratomileusis (LASIK) for the correction of low myopia or whether any difference in predictability is because of a need for separate clinical nomograms for the two treatments. DESIGN: A prospective, randomized, clinical trial. PARTICIPANTS: Fourteen surgeons and 190 eyes of 95 patients with myopia who desired surgical correction of myopia ranging from -2.00 to -7.00 diopters (D) participated. INTERVENTION: Fellow eyes of patients with myopia undergoing bilateral simultaneous LASIK were randomized to single-zone and multizone ablation. Astigmatism was not corrected at the time of LASIK. MAIN OUTCOME MEASURES: Predictability, postoperative videokeratography, and contrast sensitivity were assessed at 3 months after surgery. RESULTS: At 3 months, r2 values relating laser setting to change in spherical equivalent refraction were 0.78 for single-zone and 0.76 for multizone ablation; mean outcome with respect to intended was -0.84 D (0.65 standard deviation [SD]) for single-zone and -0.62 D (0.78 SD) for multizone eyes (P = 0.035). There was no relationship between single-zone and multizone ablation and the likelihood of asymmetric postoperative videokeratography (P = 0.83). The only difference in contrast sensitivity was a significantly greater decrease in log contrast for multizone eyes at 12 cyc/deg under undilated conditions. CONCLUSIONS: There is no true difference in predictability between single-zone and multizone LASIK for the correction of low myopia. Separate clinical nomograms for single-zone and multizone LASIK should eliminate the difference in predictability that was observed in this clinical trial.