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.     

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.     

Video-assisted thoracic surgical resection with the neodymium:yttrium-aluminum-garnet laser

Since January 1991, we have performed 79 video-assisted neodymium: yttrium-aluminum-garnet laser resections for pulmonary nodular or interstitial disease. Pathologic examination demonstrated malignancy in 59 patients (32 primary and 27 metastatic), benign nodules in 11, interstitial processes in seven, and granulomatous disease in two. There were 39 men and 40 women with a mean age of 63.4 +/- 12.5 years. Thirty-nine patients underwent resection with the neodymium:yttrium-aluminum-garnet laser alone and 40 had lesions resected with a combination of laser and endoscopic stapling. Laser excision was performed for lesions deep in the substance of the lung or on its effaced surface; both are locations that make stapling alone difficult. Fifteen of 32 patients with a diagnosis of primary lung malignancy underwent open anatomic resections. Pulmonary reserves of the other 17 patients were inadequate for further resection. Operative time, duration of chest tube placement, length of hospital stay, and complication rate were compared with those for 72 patients undergoing video-assisted thoracic surgical resection of nodules with staplers alone. Although operative time for laser-assisted procedures was longer (p < 0.05), there were no differences in duration of chest tube placement or hospital stay compared with stapled resections. The complication rate for laser-treated cases was not higher than for stapled resections and consisted primarily of air leaks lasting 2 to 7 days. The neodymium:yttrium-aluminum-garnet laser is a safe and precise primary or adjunctive tool for video-assisted thoracic surgical pulmonary resection.     

Opacification of the posterior capsule after IOL implantation and its therapy using a picosecond Nd-YAG laser

In a group of 1700 patients after operation of cataract with implantation of IOL the authors found opacification of the posterior capsule in 765 instances (45%). Treatment was provided with a Nd-YAG laser using a picosecond regime. The authors discuss the causes of opacification, successful surgery and its complications.     

Posterior capsule opacification after cataract surgery in patients with uveitis

PURPOSE: To compare the incidence rate of posterior capsule opacification (PCO) after phacoemulsification and standard extracapsular cataract extraction (P/ECCE) in eyes with antecedent uveitis with the incidence rate in eyes without any history of intraocular inflammation. DESIGN: Review of records of 108 eyes of 78 patients with uveitis and 122 eyes of 106 patients with no uveitis who underwent P/ECCE. Rates of PCO were compared by the log-rank test of differences in the Kaplan-Meier survival curves. Proportional hazards regression models provided estimates of the relative risks of PCO among uveitic compared to nonuveitic eyes. MAIN OUTCOME MEASURES: Performance of neodymium: YAG laser posterior capsulotomy was used as a proxy measure for the main outcome of visually significant PCO. RESULTS: Study patients ranged in age from 6 to 81 years (median, 44.5 years) among those with uveitis and 27 to 96 years (median, 68.5 years) among those without uveitis (P = 0.0001). Crude incidence rates for visually significant PCO were 54% over a mean follow-up of 4.3 years in uveitic cases and 40% over a mean follow-up of 3.9 years among nonuveitic cases (P = 0.02). Estimates of PCO incidence (95% confidence interval) in uveitic eyes derived from the Kaplan-Meier models were 38.5% (range, 28.9%-48.2%) at 1 year and 56% (range, 45.8%-66.3%) at 3 years, and estimates among nonuveitic eyes were 11.5% (range, 6.2%-16.8%) at 1 year and 38.4% (range, 29%-47.8%) at 3 years. These rates of PCO among patients with uveitis and those patients without uveitis differed significantly by the log-rank test (P = 0.004). However, after adjusting for the younger age of patients with uveitis, the rates of PCO were no longer statistically different. CONCLUSIONS: The apparent higher rate of PCO in patients with uveitis is primarily due to their younger age at the time of surgery. A moderately increased independent risk of PCO from uveitis cannot, however, be ruled out by this study.     

Factors determining the refractive effects of intrastromal photorefractive keratectomy with the picosecond laser

PURPOSE: To determine the relationship between laser parameters and tissue removal with picosecond laser intrastromal photorefractive keratectomy (ISPRK) and to assess the effect of the parameters on the healing process and the long-term refractive changes. SETTING: Medical Laser Center Lübeck, Germany. METHODS: A modified Intelligent Surgical Lasers (ISL) 2001 system with a cone angle of 30 degrees was used for in vitro investigations of the laser effects in water and on the porcine cornea. Photographic methods were used to determine the plasma volume and to investigate the thickness of the intrastromal bubble layer as a function of the laser pulse energy, the number of layers in which the pulses were applied, and the layer separation. The data were used to calculate the amount of tissue removal. Histologic evaluation was done by polarization microscopy after Sirius-red staining. RESULTS: The laser pulses produced a sponge-like appearance of the stroma in a layer extending through about one third the corneal thickness, accompanied by mechanical distortions of the stromal lamellae. Thermal changes were weak. Tissue removal was impaired by the cavitation bubbles from preceding laser pulses. The amount of evaporated tissue depended only weakly on laser pulse energy and number of layers in which the pulses were applied. The maximum amount of tissue that could be evaporated without damaging the outer corneal layers was a 10.0 microm thick layer. With a 6.0 mm optical zone, the tissue removal produced an immediate refractive effect of only 0.85 diopter. CONCLUSIONS: Intrastromal PRK does not work as originally envisioned because the amount of evaporated tissue is very small. The greater long-term refractive changes observed in animal experiments and clinical studies must therefore be due to the healing response of the cornea. Because the refractive effects are strongly influenced by the healing response of the cornea, they are poorly predictable.     

Mucous gland adenoma of the trachea resected with an endoscopic neodymium: yttrium aluminum garnet laser

We report a case of mucous gland adenoma of the trachea in a 73-year-old male revealed by bronchoscopy. The tumor was resected with a contact neodymium: yttrium aluminum garnet (Nd-YAG) laser after five years of observation. The tumor was histologically peculiar because it presented numerous cystically dilated, or irregularly shaped mucus-filled glands lined with cuboidal or tall columnar cells. In some parts, the lining cells of the tumor showed papillary proliferation. We diagnosed this tumor as a mucous gland adenoma of the trachea. We review the clinical features of this rare tumor and discuss the usefulness of the laser in the diagnosis and the therapy.     

Prevention of posterior capsule opacification with the CO2 laser

BACKGROUND AND OBJECTIVE: Posterior capsule opacification (PCO) is a common complication after cataract extraction, despite the modern surgical techniques and lenses being used for this procedure. Its prevention challenged many investigators, because the current treatment of choice, capsulotomy with Nd:YAG laser, is associated with sight-threatening complications. In the present study, the authors investigated two approaches of preventing PCO using the CO2 laser. MATERIALS AND METHODS: A 15-W CO2 laser with a 17- or 18-gauge hollow probe was used on 20 sheep eyes and 14 rabbit eyes. Lens extraction was done by phacoemulsification. In the equatorial treatment study, the anterior chamber was filled with either air or a viscoelastic substance, and laser burns were applied to the equator of the lens capsule and to the peripheral anterior capsule to destroy the epithelial cells. In the capsulotomy study, a primary posterior capsulotomy was created by delivering 1 to 3 laser shots to the capsule behind an implanted intraocular lens (IOL). RESULTS: The CO2 laser was satisfactory in sheep eyes after filling the anterior chamber with air. In rabbit eyes, however, it was technically impractical to work with air. Using a viscoelastic material to maintain the anterior chamber, the hollow probe of the CO2 laser becomes plugged up and therefore is unable to affect the ocular tissue. However, by combining viscoelastic and air pumping, both the destruction of the lens epithelial cells and the creation of a central posterior opening behind a capsular-fixated IOL was repeatedly achieved. CONCLUSION: Using the CO2 laser for destruction of lens epithelial cells and the creation of controlled posterior capsulotomy is feasible and practical. A different design of the probe (closed gauge) is required to enable it to operate clinically in a fluid or viscoelastic environment.     

Osteonecrosis after contact neodymium:yttrium aluminum garnet arthroscopic laser meniscectomy

OBJECTIVE: The purpose of this report is to describe two cases of osteonecrosis that occurred after arthroscopic meniscectomy with a contact neodymium:yttrium aluminum garnet laser system. The patients developed increasing knee pain and disability 5 months and 6 months after laser meniscectomy. MR imaging showed subchondral osteonecrosis in the femoral condyle and tibial plateau immediately adjacent to the site of laser meniscectomy in both patients. One patient required a total knee replacement to alleviate knee symptoms, and the other patient required a tibial osteotomy and surgical elevation of collapsed tibial articular surface. CONCLUSION: To our knowledge, this complication of laser arthroscopic meniscectomy has not been reported in the radiology literature. The clinical and MR imaging features of this important complication are described and possible causative mechanisms are discussed.     

Spontaneous disappearance of Elschnig pearls after neodymium:YAG laser posterior capsulotomy

Posterior capsule opacification (PCO) from Elschnig pearl formation is a common complication of extracapsular cataract extraction. After PCO treatment by neodymium:YAG (Nd:YAG) laser posterior capsulotomy, Elschnig pearls may undergo hyperproliferation at the edge of the capsulotomy, which may close it. We have seen six eyes in five patients who presented with spontaneous disappearance of Elschnig pearls, resulting in a perfectly clear posterior capsule several years after an Nd:YAG posterior capsulotomy. Possible causes include (1) falling of pearls into the vitreous through the capsulotomy; (2) phagocytosis of pearls by macrophages; (3) cell death by apoptosis.     

Effect of intraocular lens design on neodymium:YAG laser capsulotomy rates

The activity of alkaline phosphatase (AP) was studied in adults of highly active (HA) and low active (LA) Drosophila melanogaster strains and their F1 hybrids, both under normal conditions and after a heat shock (38 degrees C). Under normal conditions, the HA strain expressed a higher AP activity compared to that in the wild-type strain Canton-S and dominated in respect to this character. The AP activity showed a sexual dimorphism, as it was higher in females of both strains. Heat shock (38 degrees C) induced no alterations in the AP activity of D. melanogaster.     

Incidence of retinal detachment after cataract surgery and neodymium: YAG laser capsulotomy

The objective of this retrospective study was to determine the incidence of retinal detachment (RD) in patients following cataract extraction with intraocular lens placement and after neodymium:YAG (Nd:YAG) laser capsulotomy. This study comprised 1092 patients (1168 eyes) who had cataract extraction and related procedures between January 1986 and December 1992 identified from the coding and billing database. Of the 1092 patients, 215 (244 eyes) had had Nd:YAG laser capsulotomy. Their charts were reviewed for incidence of RD, and these data were correlated with age, sex, axial length, surgical complications, and other surgical procedures done at the time of cataract extraction. The incidence of RD following phacoemulsification alone was 0.75% (6/799), with a mean time between cataract extraction and RD of 11.6 months. The cases of RD after extracapsular cataract extraction, combined phacoemulsification and trabeculectomy, combined extracapsular cataract extraction and penetrating keratoplasty, and combined phacoemulsification and anterior vitrectomy were too few to draw any conclusions. The incidence of RD following Nd:YAG laser capsulotomy was 0.82% (2/244), with a mean time of 32 months between cataract surgery and capsulotomy and 13.5 months between capsulotomy and RD. There was a statistically significant higher incidence of RD after posterior capsule rupture and anterior vitrectomy than after uncomplicated phacoemulsification (2/12 versus 6/799). In conclusion, the rate of RD after uncomplicated phacoemulsification was less than or similar to the rate found in other recent studies. It was not statistically different from the rate following phacoemulsification and Nd:YAG laser capsulotomy (0.82%). This study confirms the increased risk of RD following posterior capsule rupture and anterior vitrectomy.     

Probabilistic laser safety: ocular damage models for Q-switched neodymium and ruby lasers

International standards for the protection of the eyes from the hazards of laser radiation define a nominal ocular hazard distance as a distance beyond which an individual would not be expected to suffer any adverse biological effects. The nominal ocular hazard distance, and any associated hazard zones, are calculated using a deterministic technique. This technique does not consider the likelihood that an eye will be irradiated, or the probability that if any eye is exposed, then some level of ocular damage will result. An alternative method of hazard assessment, without compromising safety, is to adopt a probabilistic approach in which the ultimate safety criterion is that the expectation of someone receiving ocular damage must be less than some acceptable risk level. An important element in this assessment is an ocular damage model, which predicts the probability with which a laser exposure will cause permanent eye damage. This paper describes a rationale for the use of the minimum ophthalmoscopically visible lesion as a threshold criterion for the development of ocular damage models. A brief review of existing ocular damage threshold data for Q-switched neodymium:YAG and ruby lasers is presented, and ocular damage models for these lasers systems are derived.     

Holmium laser resection of the prostate versus neodymium:yttrium-aluminum-garnet visual laser ablation of the prostate: a randomized prospective comparison of two techniques for laser prostatectomy

Prospective studies were conducted at used-tire sites in Illinois during 1994-1995 in an effort to isolate arboviruses from mosquitoes, particularly Aedes albopictus (Skuse) and Aedes triseriatus (Say). Three isolates of Potosi virus were obtained from Ae. albopictus collected at a waste tire site in Jasper County during 1994 and 1995. Also, a single isolate of Cache Valley virus was obtained from Ae. albopictus collected at the Jasper County site during 1995. These are the first records of arbovirus isolations from Ae. albopictus in Illinois and the first isolate of Cache Valley virus from this mosquito species. During 1994, two isolates of La Crosse virus were made from Ae. triseriatus collected at a used-tire site in Peoria County in proximity to the residence of a human La Crosse encephalitis case. This is the first evidence in Illinois that indicates increased risk to humans living near used-tire sites, which may serve as foci for production of Ae. triseriatus, the vector of La Crosse virus. Tire removal and improved environmental sanitation at such sites may greatly reduce the abundance of vector mosquitoes, and, therefore, the risk of arbovirus transmission.     

Incidence, causes, and neodymium:YAG laser treatment of pupillary capture

OBJECTIVE: To report the incidence of and factors associated with pupillary capture after cataract surgery and evaluate the outcomes of treatment with the neodymium:YAG (Nd:YAG) laser. SETTING: Unit of Ophthalmology, University of Edinburgh, and Royal Infirmary of Edinburgh Trust Hospital, Edinburgh, United Kingdom. METHODS: This prospective study comprised 792 consecutive patients having cataract extraction by one surgeon from 1989 to 1993. Outcome measures were incidence of pupillary capture associated with eye disease and treatment, surgical technique, and intraocular lens (IOL) placement and style; postoperative progress; and results of Nd:YAG treatment. RESULTS: Pupillary capture developed in 30 of the 764 patients (3.9%) having implantation of a posterior chamber IOL a mean of 14 weeks postoperatively (range 2 to 44 weeks). The incidence was significantly higher in eyes with angle-closure glaucoma, combined glaucoma and cataract surgery, can-opener capsulotomy, manual extraction, sulcus IOL implantation, large-optic IOLs, and one-piece IOLs. Neodymium:YAG laser treatment was successful in 8 of 12 eyes. CONCLUSION: Pupiliary capture may be anticipated and when recognized at an early stage, treated successfully with an Nd:YAG laser in most cases.     

A study on gelatin capsule brittleness: moisture tranfer between the capsule shell and its content

Variation in moisture content of the capsule shells either due to the change of storage conditions or the moisture transfer between the capsule shell and its contents may lead to undesired physical properties, such as capsule brittleness and stickiness. DMP 504, a developmental bile-acid sequestrant, is a strongly basic anion-exchange polymer which contains randomly distributed primary, secondary, tertiary, and quaternary amine groups in their hydrochoride salt form. The alkylammonium groups which comprise this polymer form a random network containing a high level of branching and a low level of cross-linking. DMP 504 is very hygroscopic and has a tendency to gain or lose moisture with ease. The transfer of moisture from the capsule shell to DMP 504 powder contained in a hard gelatin capsule can be expected, and if a low water content of the capsule shell is achieved, the capsules become brittle and fracture easily. The sorption isotherm for DMP 504 was generated by storing the drug substance under various relative humidity conditions. After equilibrium, the moisture contents for the samples of individual isotherm points were measured by thermogravimetric analyses. This report applies the sorption-desorption moisture transfer (SDMT) model to predict the equilibrium relative humidity in a system containing DMP 504 in hard gelatin capsules and to establish target loss on drying values for DMP 504 and the capsule shell. Application of this SDMT model resulted in finding a solution to the brittleness problem. The moisture levels of capsule shells and contents for two formulations in a 12-month stability program are also reported here. Results of this study further demonstrate that the SDMT model can be used as a tool to guide the formulator to select optimal initial moisture contents for the empty capsule shell and the formulation to avoid the incidence of brittle capsule problems.