Mitsutoshi Ito

Comparison of LASIK using the NIDEK EC-5000 optimized aspheric transition zone (OATz) and conventional ablation profile.

PURPOSE To compare a new ablation algorithm termed the optimized aspheric transition zone (OATz) with the conventional laser ablation profile for correction of myopic astigmatism. METHODS LASIK using OATz profile #6 or using conventional ablation profile was performed on 98 eyes of 53 patients (OATz #6 group) and 111 eyes of 66 patients (control #6 group), respectively. Further, LASIK using OATz profile #5 or using the conventional ablation profile was performed on 109 eyes of 58 patients (OATz #5 group) and 109 eyes of 75 patients (control #5 group), respectively. The effective optical zone, uncorrected visual acuity, manifest refraction, aberrations, contrast sensitivity, and patient satisfaction at 3 months postoperatively were compared between the OATz #6 and control #6 groups and between the OATz #5 and control #5 groups. RESULTS The effective optical zones in the OATz #6 group (6.45 +/- 0.29 mm) or OATz #5 group (6.40 +/- 0.21 mm) were significantly larger than those in the control #6 group (6.33 +/- 0.27 mm) or control #5 group (6.26 +/- 0.25 mm) (P < .01), respectively. Uncorrected visual acuity and manifest refraction were similar in all groups. The changes in contrast sensitivity were significant and favored the OATz #6 (P < .01) and OATz #5 groups (P < .05). The patient satisfaction survey found no statistical difference at 3 months postoperatively. CONCLUSIONS Patients treated with the OATz profiles had better visual quality as measured by contrast sensitivity and also had larger effective optical zones as compared with those treated by the conventional ablation profile.

Detection of cyclotorsional rotation during excimer laser ablation in LASIK

PURPOSE Positionally induced cyclotorsion could be an important factor in the correction of astigmatism during refractive surgery. We analyzed the change in cyclotorsional rotation during excimer laser ablation in LASIK surgery using the NIDEK Torsion Error Detector (TED). METHODS One hundred ten patients (192 eyes) who underwent LASIK for myopic astigmatism, using the NIDEK Advanced Vision Excimer Laser (NAVEX) were measured for cyclotorsion during surgery using the TED system. The manifest refraction of these patients was -6.80+/-2.74 diopters (D) (range: -1.00 to -13.75 D). The iris pattern of the patients eyes in the supine position was recorded via a CCD camera in the EC5000CXII excimer laser system, and it was compared to the iris pattern acquired during OPD-Scan measurement in the sitting position. RESULTS During laser ablation, the degree of cyclotorsional rotation detected by TED was 1.33+/-1.88 degrees (range: -6.33 to 2.99 degrees) clockwise and 1.00+/-1.79 degrees (range: -3.70 to 7.34 degrees) counterclockwise. The absolute degree of torsion error detected by the TED system was 2.33+/-1.16 degrees (range: 0 to 6.21 degrees). CONCLUSIONS The effectiveness of the cylinder treatment can be reduced due to torsion errors. The degree of cyclotorsion constantly changes during laser ablation. Therefore, a monitoring system should be developed for the measurement of torsion error, and this will enable the maximum possible correction of the error during laser ablation.

Picosecond Laser In Situ Keratomileusis with a 1053-nm Nd:YLF Laser

BACKGROUND Excimer laser in situ keratomileusis requires a microkeratome to generate an anterior corneal flap, plus an excimer laser to ablate the underlying stromal tissue. In this paper we introduce the concepts of laser flap formation and in situ keratomileusis using a picosecond laser. METHODS A neodymium-doped yttrium-lithium-fluoride (Nd:YLF) laser with a plano-plano quartz applanation lens was used to generate various patterns of intrastromal photodisruption in human donor eyes to fashion anterior corneal flaps and generate intrastromal lenticules. RESULTS Smooth intrastromal dissections, 6 mm in diameter, were generated 160 microns below the corneal surface when the laser delivered pulses at 1 kHz with energies of either 40 microJ/pulse or 60 microJ/pulse, placed 20 microns apart in an expanding spiral. This enabled us to fashion anterior corneal flaps. The ease of the surgery and quality of the dissection corresponded well, and it was evident that both deteriorated noticeably when the laser pulses were separated by 25 microns or 30 microns, regardless of pulse energy. Using 40 microJ laser pulses placed 20 microns apart we also created a 5-mm diameter, 320 microns thick (130 microns-450 microns deep) stromal lenticule below a corneal flap that was easily extracted when the flap was raised. CONCLUSIONS Anterior corneal flaps were easily fashioned using a Nd:YLF laser. Picosecond laser in situ keratomileusis with a Nd:YLF laser could offer a favorable alternative to combined microkeratome/excimer laser in situ keratomileusis.

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.

Macular corneal dystrophy type II: Multiple studies on a cornea with low levels of sulphated keratan sulphate

We investigated an individual macular corneal dystrophy (MCD) type II cornea from a 42-year-old woman with markedly reduced antigenic keratan sulphate levels. A characteristic 4.6 Å X-ray reflection was evident, and the mid-stroma contained 30% less sulphur than normal. Close packing of collagen was restricted to the superficial stroma. Abnormally large proteoglycan filaments were noted throughout the extracellular matrix and Descemets membranes posterior non-banded zone, but not its anterior banded zone. Small, collagen-associated stromal proteoglycans were susceptible to digestion with chondroitinase ABC, but not keratanase I or N-glycanase. On occasion, collagen fibrils ranged in size from 20 nm to 58 nm, with preferential diameters of 34 nm and 42 nm. Corneal guttae were evident, as were numerous endothelial inclusions, most probably due to intracellular fibrillogranular vacuoles similar to those found in the stroma. The endothelium expressed reduced anti-keratan sulphate labelling.

Topography-guided Ablation for Treatment of Patients With Irregular Astigmatism

PURPOSE To evaluate the customized aspheric treatment zone (CATz) topography-guided ablation for the correction of irregular astigmatism induced by initial corneal refractive surgery or corneal injury. METHODS CATz ablation was performed on 32 eyes of 28 patients. Each procedure was performed by photorefractive keratectomy (PRK) or LASIK using a NIDEK EC-5000 excimer laser. The eyes had decentered ablations, small optical zones, decreased best spectacle-corrected visual acuity (BSCVA), and asymmetrical astigmatism. Subjective symptoms, uncorrected visual acuity (UCVA), BSCVA, refraction, corneal topography, and higher order aberrations were measured. Mean follow-up was 161.9 +/- 129.9 days (range: 90 to 492 days). RESULTS Data obtained at final postoperative follow-up show that UCVA and BSCVA increased by > or = 2 lines after CATz ablation in 17 and 11 eyes and decreased in 4 and 2 eyes, respectively. Higher order aberrations were decreased in 16 eyes and increased in 1 eye. Topographical maps were improved with decreased surface regularity index (20 eyes) and surface asymmetry index (22 eyes). Seven eyes required further enhancement for residual refractive errors. Thirteen patients (15 eyes) claimed they were satisfied with the outcome, 6 patients (7 eyes) stated that the outcome was lower than expected, and 4 patients (4 eyes) stated they were dissatisfied. CONCLUSIONS CATz topographic ablation effectively improves the quality of vision and symptoms in the majority of patients with irregular corneal astigmatism from previous excimer laser refractive surgery. However, residual or induced refractive errors may need to be corrected with a second operation after CATz.

Ocular integrity after anterior ciliary sclerotomy and scleral ablation by the Er:YAG laser.

PURPOSE To establish the risk of ocular rupture after proposed surgical reversal of presbyopia by anterior ciliary sclerotomy (ACS) or by the Er:YAG laser (HOYA Continuum, Tokyo, Japan). METHODS A total of 45 pig eyes (15 control eyes) were examined. Fifteen eyes were placed into one of two study groups and another 15 eyes were used as controls. One group underwent scleral incisions with the use of a diamond knife, and the other group underwent Er:YAG laser scleral incisions. In both study groups, 8 radial incisions, 2 parallel cuts each at 4 quadrants, 2 mm apart, 4 mm long, and starting 2 mm away from the limbus, were made. A 3-kg steel weight was released from a measured height to the pigs eye, and ocular rupture energy (joules) was measured. RESULTS The mean rupture energy was 26.0 J for control eyes, 15.7 J for the ACS eyes, and 12.2 J for the Er:YAG laser eyes. The ACS and the Er:YAG laser eyes ruptured at significantly lower energies (ACS, P < .001; Er:YAG, P < .001) than the control eyes. Comparison of the ACS group and the Er:YAG laser group showed no statistically significant difference (P = .052) in rupture energy. CONCLUSIONS Scleral incisions by ACS and the Er:YAG laser significantly weakened ocular integrity compared with control eyes. Any patients undergoing ACS or Er:YAG laser scleral incision should be informed of the attendant potential risk after ocular trauma.

INTACS before or after laser in situ keratomileusis: correction of thin corneas with moderately high myopia.

PURPOSE Intrastromal corneal ring segments (INTACS Micro-Thin Prescription Inserts by Addition Technologies, Fremont, Calif) were inserted as a combined surgery with laser in situ keratomileusis (LASIK) in six eyes with thin corneas to correct moderately high myopia. METHODS INTACS were implanted before LASIK (INTACS-LASIK) in three eyes and after LASIK (LASIK-INTACS) in three eyes. Mean preoperative manifest spherical equivalent refraction was -7.88 diopters. Mean follow-up was 306 days. RESULTS No intraoperative complications occurred. The LASIK-INTACS eyes were slightly more overcorrected than the INTACS-LASIK eyes because of the enhanced performance of INTACS in the thinned corneal tissue. Induced astigmatism by INTACS per se was less in the LASIK-INTACS eyes than in the INTACS-LASIK eyes. At last examination, uncorrected visual acuity was better than 20/25 in all eyes. Best spectacle-corrected visual acuity was within 1 line of the preoperative value in all eyes. CONCLUSION Both methods resulted in significant improvement in visual acuity and refraction. Based on our limited experience, however, LASIK followed by INTACS is preferred for reasons of safety, convenience, and lower induced cylinder.

Endothelial Cell Surface-associated Keratan Sulfate after Excimer Laser Photoablation of the Anterior Rabbit Cornea

PURPOSE The expression of keratan sulfate on the surfaces of corneal endothelial cells is altered when the cells are responding to injury. The purpose of this study was to investigate whether excimer laser surgery affected corneal endothelial cells and the levels of keratan sulfate associated with them. METHODS We performed 14 bilateral, transepithelial phototherapeutic keratectomies in rabbits using a Nidek EC-5000 excimer laser. Ablations were 6 mm in diameter and 50 microm, 150 microm, or 240 microm deep. At various times following surgery the endothelium was immunolabeled for keratan sulfate and examined by scanning electron microscopy. Four untreated corneas were also examined. RESULTS Three days after surgery, endothelial cells were not flat but were rounded or domed, a finding that was more pronounced after deeper ablations. No rounded cells, however, were seen at post-operative day 12. Keratan sulfate immunolabel was elevated on endothelial cells 3 days after surgery. By postoperative day 36, its expression was normal under the 50-microm ablations, but remained elevated under one of two 240-microm ablations. CONCLUSIONS Corneal endothelial cells take on a rounded appearance in the early stages after excimer laser photoablations in rabbits, especially after deeper ablations. The apical surface of the endothelium also transiently expresses elevated levels of cell surface-associated keratan sulfate following surgery. These changes appear to be responses to some aspect of the surgery, and may have physiological implications.

Histology and ultrastructure of picosecond laser intrastromal photorefractive keratectomy (ISPRK)

Picosecond intrastromal ablation is currently under investigation as a new minimally invasive way of correcting refractive error. When the laser pulses are placed in an expanding spiral pattern along a lamellar plane, the technique is called intrastromal photorefractive keratectomy (ISPRK). We performed ISPRK on six human eye bank eyes. Thirty picosecond pulses at 1000 Hz and 20 - 25 (mu) J per pulse were separated by 15 microns. A total of 3 layers were placed in the anterior stroma separated by 15 microns. The eyes were then preserved and sectioned for light, scanning and transmission electron microscopy. Light and scanning electron microscopy reveals that picosecond intrastromal ablation using an ISPRK pattern demonstrates multiple, coalescing intrastromal cavities oriented parallel to the corneal surface. These cavities possess a smooth appearing inner wall. Using transmission electron microscopy, we noticed tissue loss surrounding some cavities with collagen fibril termination and thinning of collagen lamella. Other cavities we formed by separation of lamella with little evidence of tissue loss. A pseudomembrane lines the edge of some cavities. Although underlying tissue disruption was occasionally seen along the border of a cavity in no case was there any evidence of thermal damage or tissue necrosis. Ablation and loss of tissue in ISPRK results in nonthermal microscopic corneal thinning around some cavities whereas others demonstrate only lamellar separation. Alternative patterns and energy parameters should be investigated to bring this technology to its full potential in refractive surgery.