Histological comparison of corneal ablation with Er:YAG laser, Nd:YAG optical parametric oscillator, and excimer laser.

PURPOSE: To use histological techniques to assess and compare the ablation depth, local damage, and surface quality of corneal ablations by a Q-switched Er:YAG laser, an optical parametric oscillator laser at 2.94 microm, a long pulse Er:YAG laser, and a 193-nm excimer laser. METHODS: Human cadaver eyes and in vivo cat eyes were treated with a 6.0-mm diameter, 30-microm-deep phototherapeutic keratectomy ablation and a 6.0-mm diameter, -5.00-D photorefractive keratectomy ablation. Human cadaver eyes were also treated with a 5.0-mm diameter, -5.00-D laser in situ keratomileusis (LASIK) ablation. Fluences and pulse widths used were 200 mJ/cm2 and 70 ns for the Q-switched Er:YAG, 150 mJ/cm2 and 7 ns for the optical parametric oscillator laser (OPO), 500 mJ/cm2 and 50 microseconds for the long pulse Er:YAG, and 160 mj/cm2 and 20 ns for the excimer laser. In the ablation rate study, 12 porcine eyes were ablated by the OPO laser with a range of layers and at different fluences ranging from 60 to 150 mJ/cm2, all using a 1.5-mm spot on the eye. The ablation depth of these acute ablations was evaluated by light microscopy examination. RESULTS: In the acute damage study, light microscopy showed a thin surface layer in all samples with minimal thermal damage except on the long pulse Er:YAG corneas. Transmission electron microscopy revealed less than 0.3-microm surface damage for all specimens of both the optical parametric oscillator and the excimer laser samples with no evidence of collagen shrinkage. Transmission electron microscopy showed damage layers of 0.5 to 3 microm for Q-switched Er:YAG and 3 to 10 microm for long pulse Er:YAG. Scanning electron microscopy showed smooth surfaces in all eyes, although the excimer was the roughest. In the porcine eye study, ablations were produced in both PTK and PRK modes with the ablation rate per layer increasing with the fluence. At 120 mJ/cm2, the average ablation rate was 1.9 microm per layer. CONCLUSIONS: The histology from the short pulse mid-infrared optical parametric oscillator laser at 2.94 microm was comparable to the 193-nm excimer with a smooth, damage-free, ablation zone when performing PRK and LASIK.

Healing after photorefractive keratectomy in cat eyes with a scanning mid-infrared Nd:YAG pumped optical parametric oscillator laser.

PURPOSE: To evaluate the healing characteristics of cat corneas treated with a new scanning mid-infrared laser system. METHODS: Six adult cats were treated with 6-mm diameter photorefractive keratectomy (PRK) corrections. One eye in each animal was untreated as a control and the other was treated with either a -3.00 or -6.00 diopter ablation. The laser was a new Nd:YAG pumped optical parametric oscillator laser at 2.94 microm with a new scanning delivery system. The pulse width was 7 nanoseconds, the repetition rate was 10 Hz, the size of the laser spot on the eye was 1.0 mm, and the fluence was 150 mJ/cm2. Healing of the cat corneas was followed for 4 months. Slit-lamp and corneal topography evaluations were done at each follow-up examination. Histology was performed at the end of the study. RESULTS: The corneal epithelium healed within 1 week. There was no stromal haze in any eye after the epithelium healed. After the first 2 weeks, slit-lamp examination could not identify which eye was treated. Corneal topography showed corneal flattening. Light microscopy at 4 months revealed normal epithelium and increased keratocyte density in the anterior third of the cornea. Electron microscopy showed discontinuities in the basement membrane and hemidesmosomes. The deep stroma and endothelium were normal. CONCLUSIONS: Cat corneas treated with the new optical parametric oscillator laser healed normally with no adverse effects. Increased keratocyte activity in the anterior stroma was the only noticeable response besides the flattening shown by topography.

The second-trimester fetus with isolated choroid plexus cysts: a meta-analysis of risk of trisomies 18 and 21.

OBJECTIVE: To assess the risk of trisomy 18 and trisomy 21 associated with isolated choroid plexus cysts diagnosed by ultrasound in the second trimester. METHODS OF STUDY SELECTION: We reviewed the unabridged PREMEDLINE and MEDLINE databases for articles written in the English language regarding second-trimester fetal isolated choroid plexus cysts and trisomies 18 and 21, published in the period 1987-1997. Selection criteria included only second-trimester, prospective studies in which the rate of fetal isolated choroid plexus cysts could be calculated, the number of fetuses with trisomy 18 and 21 was reported clearly, and pregnant women of all ages were included, rather than only those at high risk for aneuploidy due to advanced maternal age. TABULATION AND RESULTS: Thirteen prospective studies, comprising 246,545 second-trimester scans, were selected. Among 1346 fetuses with isolated choroid plexus cysts, seven had trisomy 18, and five had trisomy 21. For each study, a 2 x 2 table was constructed and the likelihood ratio of a positive test was computed. The likelihood ratios for trisomies 18 and 21 were found to be homogeneous (P = .08 for trisomy 18, and P = .16 for trisomy 21). The summary likelihood ratio and 95% confidence interval (CI) for each chromosomal abnormality were calculated using the Mantel-Haenszel fixed effects model of meta-analysis. The summary likelihood ratio for trisomy 18 was 13.8 (CI 7.72, 25.14, P < .001) and for trisomy 21 was 1.87 (CI 0.78, 4.46, P = .16). CONCLUSION: The likelihood of trisomy 18 was 13.8 times greater than the a priori risk in fetuses with isolated choroid plexus cysts diagnosed in the second trimester. However, the likelihood of trisomy 21 was not significantly greater than the a priori risk with isolated choroid plexus cysts. The data supported offering pregnant women karyotyping to rule out trisomy 18 when maternal age at delivery is 36 years or older, or when the risk for trisomy 18 detected by serum multiple-marker screen is more than one in 3000.

Excimer laser instrumentation and technique for human corneal surgery.

The design and development of the instrumentation utilized during the clinical and histopathologic evaluations of the first human eyes treated by argon fluoride excimer laser radiation are described. The laser, optical, alignment, measurement, and control subsystems required for this research were constructed to create a laser beam that has an axially symmetric energy distribution, can be calibrated and measured, can be aligned with the target tissue, and can be manipulated to excise surface tissue. The use of this excimer laser system has demonstrated that a nonuniform superficial lamellar keratectomy can be produced to excise areas of opacified, scarred, or abnormal cornea or to create a new anterior corneal curvature in attempts to correct refractive errors.

Human excimer laser corneal surgery: preliminary report.

The first human trial utilizing the argon fluoride excimer laser at 193 nm to produce a superficial keratectomy in ten human eyes has been described with the histopathological evaluation of four eyes and the longer gross appearance of six eyes at intervals extending to 10 months post-excimer laser treatment. The process of laser superficial keratectomy has proved to be one of the promising areas of surgical intervention for reconstructive or refractive keratoplasty in the future. Intensive investigations need to be undertaken on the corneal wound healing process following laser ablation as well as the nature, and long-term stability of the corneal excisions or induced refractive corrections. It is essential that the optimal laser parameters be established for the various refractive corrections and other corneal surgical techniques, and that pathophysiologic and histopathologic changes that have been induced by the excimer laser-corneal tissue interaction in animals and humans be critically and extensively analyzed.

A prospective, controlled study of maternal and perinatal outcome after intra-amniotic infection at term.

A study was made of the outcome for mothers and their neonates with both clinical and bacteriologic evidence of intra-amniotic infection at term. Samples of amniotic fluid from patients with intra-amniotic infection showed greater than 10(2) colony-forming units per milliliter of a high-virulence isolate, whereas samples from control patients showed no growth or low-virulence isolates only. Control patients were uninfected during labor and were matched on the basis of gestational age, interval from rupture of membranes to delivery, and mode of delivery. There were 67 matched pairs. The mean interval from diagnosis of intra-amniotic infection to delivery was 3.1 +/- 2.2 hours (+/- SD). Mothers with intra-amniotic infection had a significantly longer hospital stay and greater fever index after delivery than did control patients. Intrapartum bacteremia was documented in six of 50 (12%) women with intra-amniotic infection. The cesarean birth rate was 36%. There was one case of probable septic shock and one of postpartum hemorrhage among women with intra-amniotic infection. Infants in the intra-amniotic infection group had a significantly longer hospital stay than did the control infants. Among 59 infants for whom blood culture results were available, bacteremia was documented in five (8%) with intra-amniotic infection. Definite radiographic evidence of pneumonia was present in 4%; there were no cases of meningitis. There was one perinatal death in the intra-amniotic infection group. Overall, the maternal and perinatal outcome after intra-amniotic infection at term was excellent.

Active annular-beam laser autocollimator system.

An autocollimator using an axicon and a beam expander telescope to generate a 12.5-cm. o.d. annular beam of helium-neon laser light with high (25:1) diameter-to-width ratio has been developed. It is used with a two-axis, electromagnetically actuated mirror assembly to acquire automatically and maintain dynamically autocollimation from a nearby but separately mounted annular mirror. The servo system controls beam alignment even though angular vibratory motions of the annular mirror make it appear to tilt relative to the autocollimator as much as 7 mrad at frequencies below 300 Hz. This paper describes the optical system and the alignment sensing and control system.

Automatic theodolite for pre-launch azimuth alignment of the saturn space vehicles.

The inertial guidance system in the Saturn 1B and Saturn 5 space vehicles is aligned in azimuth prior to lift-off by a Perkin-Elmer high precision, automatic alignment theodolite. This special theodolite, designated the AALT-SV-M2, acquires and locks onto the autocollimated images from each of two porro prisms mounted within the instrument unit on top of the S4-B booster stage of the vehicle. A separate retroreflecting prism on the skin of the instrument unit near the porro prisms is also tracked to eliminate the effects of vehicle sway. The theodolite itself is located in an underground hut between the crawler-ways about 232 m from the base of the vehicle. Six of these theodolite systems have been built by Perkin-Elmer under contract to NASA. These units have been used successfully in all the Saturn launches to date; they have consistently achieved better than the required alignment accuracy of +/-2 sec of arc for all missions. In this paper, we describe the theodolite and its function as an integrated electrooptical system. The means employed to separate the various return images into the proper channels and to generate the required error signals are discussed.

High Precision 10-cm Aperture Penta and Roof-Penta Mirror Assemblies.

10-cm aperture penta and penta-roof-type mirror assemblies of unusually high precision and stability for this aperture have been designed and fabricated by Perkin-Elmer Corporation. These assemblies, which are part of the internal optical alignment monitoring subsystem of a large (122-cm) aperture telescope, provide 90 degrees deviations within +/- 1 sec of arc. In order to minimize degradation of the reflected wavefront due to variations of the thermal environment, each assembly is constructed of optical quality Cer-Vit mirror plates contacted to Cer-Vit blocks which establish and preserve the proper angular relationships between the reflecting surfaces. Thermal, vibration, and shock tests of prototype units have confirmed their inherent resistance to adverse environmental influences. In this paper, the method of construction of these prototype units is described and the results of various tests are given. Since the reflecting surfaces of the mirrors are dielectric coatings which maximize reflectivity in the 0.9-0.95-mu wavelength region but have very low reflectivity at visible wavelengths, a real-time, electrooptical interferometric technique was developed for evaluating with near-infrared radiation the wavefront deformation caused by one of these assemblies. This experimental technique is also described.

A 50.83-cm focal length, f/1 catadioptric objective.

A catadioptric objective system of the Flügge type has been developed for experimental use by the U.S. Army. Major features of this objective are its large aperture and EFL [both 50.8 cm (20 in.)], its compact package configuration in spite of these dimensions, and the high image quality achieved with a simple three component system over a 2.8 degrees field of view. In this paper, the optical and mechanical designs of the objective are described, and some results of laboratory tests of a prototype lens are presented.