Isolation of human fetal cones.

PURPOSE: To describe a method for isolating a monolayer of human fetal cone photoreceptors and to compare their structure and ultrastructure before and after preparation. METHODS: Eyes from human fetuses (fetal week 20 to 24) were dissected and the neural retina of the developing fovea identified, cut out and placed on 10% gelatin. A VISX Star excimer laser was used to remove the inner retinal layers. The isolated cone monolayers were cultured for 18 hours and compared with untreated retinas by light microscopy and transmission electron microscopy. RESULTS: Excimer laser ablation removed the inner nuclear and ganglion cell layers leaving a monolayer of fetal cones. These cones survive in culture for at least 18 hours. The laser ablation disorganized the ultrastructure of the synaptic pedicles of these cones, left their plasma membranes intact. CONCLUSIONS: The developing central retina of human fetal eyes provides a source of fetal cones, which can be isolated from inner retinal cells using the excimer laser. Such a monolayer of human fetal cones may be useful for transplantation or biochemical studies.

Reversal of dysthyroid optic neuropathy following orbital fat decompression.

AIMS: To document the successful treatment of five patients with dysthyroid optic neuropathy by orbital fat decompression instead of orbital bone decompression after failed medical therapy. METHODS: Eight orbits of five patients with dysthyroid optic neuropathy were selected for orbital fat decompression as an alternative to bone removal decompression. Treatment with systemic corticosteroids and/or orbital radiotherapy was either unsuccessful or contraindicated in each case. All patients satisfied clinical indications for orbital bone decompression to reverse the optic neuropathy. High resolution computerised tomographic (CT) scans were performed in all cases and in each case showed signs of enlargement of the orbital fat compartment. As an alternative to bone decompression, orbital fat decompression was performed on all eight orbits. RESULTS: Orbital fat decompression was performed on five patients (eight orbits) with optic neuropathy. Optic neuropathy was reversed in all cases. There were no cases of postoperative diplopia, enophthalmos, globe ptosis, or anaesthesia. All patients were followed for a minimum of 1 year. CONCLUSIONS: In a subset of patients with an enlarged orbital fat compartment and in whom extraocular muscle enlargement is not the solitary cause of optic neuropathy, fat decompression is a surgical alternative to bony decompression.

Evaluation of night vision disturbances in contact lens wearers.

PURPOSE: We quantitatively recorded and evaluated night vision disturbances with physiologically dilated pupils. We compared the amount of image degradation experienced in eyes wearing spherical soft contact lenses with the amount of image degradation experienced by subjects wearing spectacles. METHODS: We prospectively evaluated 69 eyes from 35 myopic subjects with no ocular pathology. The subjects ranged in age from 22 to 35 years. We designed a test to quantitatively record image degradation with physiologically dilated pupils in scotopic conditions of dim ambient light. Previously, we have shown that this test accurately measures image degradation. We used this test to compare image degradation between new spherical soft contact lens and spectacle correction. Hyperopes and eyes with greater than 1.50 D of astigmatism were excluded. RESULTS: Adequately correcting myopic refractive error decreased recorded image degradation (P < or = 0.0001). There was no significant difference in the amount of image degradation between spectacle trial frames and new spherical soft contact lenses (P < or = 0.2885). CONCLUSIONS: Our test offers an objective method of assessing night vision disturbances in contact lens wearers. Our results suggest that image degradation, which may contribute to the sensation of glare experienced by some patients, is influenced equally by contact lens and spectacle correction.

Corneal ablation profilometry and steep central islands.

BACKGROUND: Photorefractive keratectomy with large diameter ablations using a uniform laser beam has produced central undercorrections, or "steep central islands" in patients, as seen with videokeratography. METHODS: Using a custom optical profilometer to measure corneal ablation profiles and a VISX excimer laser system, we measured the effect of ablation algorithms, diameter, depth, and dioptric correction on enucleated porcine eyes and living rabbit eyes. Our profilometer was verified using a 43.00 diopter (D) spherical surface and a 35.00 and 43.00 D bicurve test surface as a model for the ablated cornea. RESULTS: The profilometer measured the test surfaces to within 3 microns of predicted values. Photorefractive keratectomies showed over-ablation peripherally and under-ablation centrally which increased with ablation diameter and dioptric correction. Fixed diameter ablations 2 to 6 mm in diameter and 10 to 80 microns deep showed stromal ablation rates vary spatially but not with ablation depth. These spatially variant ablation profiles were used to re-engineer the ablation algorithm and to produce photorefractive keratectomies with improved sphericity. CONCLUSIONS: Steep central islands are caused by the spatial variance of tissue ablated with a uniform laser beam irradiance. This aberration can be corrected by modifying the laser ablation algorithm to correct for the spatial variance of stromal ablation.

Enlargement of the photorefractive keratectomy optical zone.

PURPOSE: To evaluate the safety and efficacy of a photorefractive keratectomy (PRK) re-treatment procedure that enlarges the optical zone and treats undercorrection. SETTING: Rotterdam Eye Hospital and Medisch Centrum Alkmaar, The Netherlands. METHODS: This study evaluated 16 eyes that had PRK for myopia with the Summit excimer laser that resulted in a mean undercorrection of -2.82 diopters (D). Patients also reported impaired night vision including difficulty in driving, halos, and stray light and ghost images. These phenomena persisted after spectacle correction of residual refractive error, necessitating further treatment with a larger ablation zone. With a VISX 20/20 excimer laser, the optical zone was enlarged to 6.0 mm and undercorrection treated with a 6.0 mm ablation. RESULTS: At 13.5 months after re-treatment, mean reduction in myopia was 1.70 D, resulting in a residual undercorrection of -1.08 D. In seven eyes, final refraction was within 1.00 D of emmetropia. Only two patients continued to report night-driving problems. CONCLUSIONS: Re-treating undercorrections combined with enlarging the ablation zone resulted in a reduction in myopia from a mean of 2.82 to 1.08 D. Subjective reports of halos and stray light images were decreased in all cases.

Night vision testing in unoperated eyes.

BACKGROUND: We previously described a simple test which evaluates image degradation in post-excimer laser (PRK) patients under scotopic conditions. After refractive surgery, corneal haze, ablation zone decentration, ablation zone/pupillary diameter disparity, and under-correction each result in a characteristic pattern on the Night Vision Recording Chart. METHODS: Using the same method, further studies evaluated night vision image degradation in 118 un-operated emmetropic, myopic, hyperopic, and astigmatic eyes and in 26 contact lens wearers. RESULTS: Scotopic image degradation increases with myopic refractive error, image displacement increases with astigmatism, and contact lens wearers have more image degradation that with spectacle correction. CONCLUSION: Our Night Vision Recording Chart offers a simple, reproducible method to characterize image degradation under scotopic conditions.

Efficiency of disc ablation with lasers of various wavelengths.

In testing the CO2 lasers in CW and pulse mode, the erbium:YAG, the Nd:YAG 1318 microns and 1064 microns, the argon, the holmium:YAG, and the excimer, we found the greatest efficiency in the CO2 CW and pulse mode, and the lowest efficiency in the argon. Data with the holmium:YAG were unreliable because of the early generation laser tested. The Nd:YAG was second only to the CO2 laser, and because the latter has no waveguide, we deemed the Nd:YAG the laser of choice for PLDD.

The barrier function in neodymium-YAG laser capsulotomy.

BACKGROUND: Complications following neodymium (Nd)-YAG laser capsulotomy have been attributed to damage to the capsule and vitreous face. OBJECTIVES: To measure the disruption of the anterior-posterior extracapsular barrier complex induced by Nd-YAG laser capsulotomy and to determine how it might be minimized, using a fluorophotometer. DESIGN: Prospective study of 21 eyes undergoing Nd-YAG laser capsulotomy and cross-sectional comparison with 15 pseudophakic eyes with clear capsules. SETTING: University-based clinical practice. INTERVENTION: Neodymium-YAG laser posterior capsulotomy per study protocol. MAIN OUTCOME MEASURE: Change in extracapsular barrier efficiency as measured by fluorophotometry. RESULTS: Multivariate regression demonstrated that both anterior vitreous disruption and absence of a posterior chamber intraocular lens (aphakia) were significantly correlated with loss of barrier efficiency, whereas capsulotomy size was not. The anterior vitreous was judged to be undamaged in 67% of eyes treated by the study protocol. However, all myopic eyes sustained damage. Opacification of the posterior capsule itself was also associated with mild loss of barrier function even before capsulotomy, compared with the clear-capsule group. Glaucoma occurred more frequently when barrier efficiency was lost postoperatively. CONCLUSION: Damage to the extracapsular barrier complex by Nd-YAG laser capsulotomy is minimized when the anterior vitreous is preserved. The study treatment protocol may be useful in limiting this damage and in reducing complications.

Transconjunctival sinusotomy using the 193-nm excimer laser.

Successful surgical management of glaucoma is limited as a consequence of undesired fibroblastic response of episcleral tissues. In 10 rabbit and three human eye bank eyes, we have performed a modified sinusotomy procedure using the 193-nm excimer laser. The technique is minimally invasive. Conjunctiva is pulled over the corneoscleral limbus, and a slit-shaped (1 x 2 mm) excimer beam ablates through conjunctiva and external sclera until penetrating the outer wall of Schlemm's canal, at which time brisk egress of fluid is noted. The conjunctiva is allowed to retract, and a conjunctival bleb is formed. A single suture is used to close the conjunctival defect. Intraocular pressure in the rabbit eye was decreased from 10.0 +/- 1.8 to 4.9 +/- 1.8 mmHg immediately after surgery (p < 0.0001). Histology revealed a partial thickness, smooth-walled ablation consistent with a sinusotomy. This procedure is minimally invasive and may be useful for management of glaucoma, particularly when a substantial component of the impediment to aqueous outflow is external to the trabecular meshwork.

Correction of irregular astigmatism with the excimer laser.

BACKGROUND: Correction of irregular astigmatism has not been possible using available keratorefractive technology. METHODS: The authors used a topographic map as a guide and created a custom excimer ablation program, designed to create a more regular surface. The program consisted of a combination of phototherapeutic and photorefractive ablation patterns. The amount of tissue to be removed was calculated on the basis of the diameter and steepness of the irregular areas of the corneal surface. RESULTS: A more regular surface, as evidenced by topographic analysis, reduced astigmatism, and improved uncorrected visual acuity, was produced. CONCLUSION: Using the corneal topographical map as a guide, excimer laser ablation can be used to create a more regular optical surface with improved visual function.

Evaluation of night vision disturbances.

BACKGROUND: Evaluation of night vision disturbances has relied on subjective responses. We designed a test to more objectively measure night vision disturbances. METHODS: The test consisted of projecting a small circle onto a visual acuity screen. The patient is asked to draw exactly what he sees on an Amsler grid. We evaluated 118 eyes in photopic and scotopic conditions and under different conditions of refractive correction. RESULTS: Image degradation increased in scotopic conditions for myopes (p = .0001), hyperopes (p = .005), and emmetropes (p = .01). Myopic refractive error correlated with size of glare response (p = .001). Astigmatism correlated with decentration of glare response (p = .0001). Decentration increased in scotopic compared to photopic conditions (p = .002). CONCLUSION: Our test offers a simple, convenient way to evaluate night vision disturbances and may offer a means of assessing night vision disturbances in patients considering refractive surgery.

Corneal pachymetric topography.

PURPOSE: The authors developed a system for producing topographic pachymetric maps of the corneal epithelium and anterior scar tissue. METHOD: The system uses high-frequency ultrasound scanning enhanced by digital signal processing. Ultrasonic echo data from consecutive parallel B-scans of the cornea spaced at 250-microns intervals are digitized and stored. Using the I-scan (obtained by computing the analytic signal magnitude of the deconvolved ultrasound signal), layer thickness measurements are made with a precision of 2 microns (standard deviation) at 120-microns intervals along each scan plane. The data are stored as an array, z(x,y), mapping thickness, z, onto horizontal and vertical (x,y) spatial coordinates. Pachymetric maps are then constructed by plotting local thickness, represented by a color scale, against measurement point position. RESULTS: Examples of a normal cornea, a contact lens-wearing cornea, Reis-Bückler dystrophy, and postphotorefractive keratectomy are presented. Areas with significant subepithelial scarring and general epithelial thickening in a subject with Reis-Bückler dystrophy are mapped. Unevenness in the epithelial thickness profile of the cornea in a subject after photorefractive keratectomy is shown, relative to the fellow (untreated) cornea. CONCLUSION: This technique provides the corneal surgeon with a new tool for the topographic evaluation of the thickness of anterior corneal layers in normal and pathologic corneas with high precision. In addition, the technique is not limited to optically transparent tissue.

Diffractive smoothing of excimer laser ablation using a defocused beam.

OBJECTIVE: To determine if excimer laser myopic ablation with a defocused laser image produces a smoother ablation profile than does focused laser light. METHODS: An ArF excimer laser was used to ablate a 5.00-diopter myopic correction in test blocks using both a contracting and expanding iris aperture. Defocused ablation was performed using a contracting iris aperture by translating the target away from the laser source. A confocal laser scanning microscope was used to analyze the surface smoothness at 55x and 275x magnifications. RESULTS: The confocal laser scanning micrographs revealed a series of sharply demarcated concentric ridges in the focused ablation, and less prominent, slightly wavy lines in the defocused ablation performed with a contracting aperture. The focused ablation with an expanding aperture also created concentric ridges toward the periphery, but with slightly smoother edges.

Surface morphology following photorefractive keratectomy.

To examine the effects of surface dehydration on corneal surface morphology before and after photorefractive keratectomy, corneas of fresh porcine eyes were deepithelialized and then immediately fixed or treated according to one of six protocols (four eyes per protocol): dehydrated under the illumination of an operating microscope; dehydrated and then rehydrated with topically applied balanced salt solution; photorefractive keratectomy; photorefractive keratectomy followed by surface dehydration; or photorefractive keratectomy followed by dehydration and subsequent rehydration. Surface smoothness (S) was measured with an image analysis system. The surfaces of the unablated corneas were smooth (S = 0.992 +/- 0.002), and dehydration did not significantly (P = .7) influence the morphology. After ablation, dehydration resulted in apparent fragmentation of the superficial lamellae, with consequent roughening of the surface (P = .0001). Rehydration was only partially successful in reducing surface irregularity. We conclude that corneal dehydration during and following photorefractive keratectomy roughens the corneal surface and should be carefully avoided.

Ablation rates and surface ultrastructure of 193 nm excimer laser keratectomies.

PURPOSE: To determine whether photorefractive keratectomy can be performed at lower energies than are currently employed in clinical trials. METHODS: Fresh pig corneas were ablated using a clinical excimer laser to study the effects of various energy densities (100-200 mJ/cm2) and beam diameters on ablation rates and on the surface ultrastructure of the ablated cornea. RESULTS: A 20-mJ increase in energy density was associated with a 0.03 micron per pulse increase in the ablation rate. A nearly linear increase in the pseudomembrane thickness occurred with increasing energy densities (r2 = 0.83) or decreasing ablation area diameter (r2 = 0.86). CONCLUSIONS: Our findings suggest that fluences less than those currently used in clinical trials (160-180 mJ) are capable of ablating tissue while producing thinner electron-dense pseudomembranes on the corneal surface. The relationship between pseudomembrane thickness and clinical factors such as reepithelialization and postoperative haze remains to be determined. Operating at lower fluences does have the advantages of allowing larger diameter ablations, reducing possible shockwave damage, and reducing the maintenance requirements for the laser.

Orbital fat removal. Decompression for Graves orbitopathy.

BACKGROUND: Orbital decompression has been used to describe surgical procedures that remove some portion of the orbital walls to reduce pressure on the orbital contents. Substantial morbidity associated with these procedures includes infraorbital anesthesia, worsened extraocular motility, globe displacement, and blindness. The authors believe that orbital contents also may be decompressed by removing orbital fat. METHODS: Eighty-one patients with nonactive Graves orbitopathy were selected for orbital fat decompression based on the presence of proptosis and associated signs and symptoms to avoid bone removal. Soft-tissue analysis by computed tomography (CT) scan showed distended pockets of fat extending into the intraconal space, which were removed through medial-upper and lateral-lower anterior orbitotomies. Decompression with bone removal was reserved for those few patients with compressive optic neuropathy unresponsive to medical treatment and those patients with residual deforming exophthalmos after fat removal. RESULTS: One hundred fifty-eight fat decompressions were performed on 81 patients over 9 years. The authors measured an average reduction in proptosis of 1.8 mm (range, 0-6.0 mm). The greatest average reduction in proptosis (3.3 mm) was produced in patients with preoperative Hertel measurements of greater than 25.0 mm. Morbidity was limited to temporary motility impairment of the inferior oblique in two patients. CONCLUSION: The concept of orbital decompression can include removal of orbital fat to reduce proptosis, eliminate symptoms, and improve appearance with far less morbidity than when bone decompression is used as the primary decompressive procedure.

Soft tissue effects of the THC:YAG laser on canine vocal cords.

Recently, a laser based on a thulium-holmium-chromium (THC) doped Yttrium-aluminum-garnet (YAG) rod has been developed that produces light of 2.15 microns wavelength and can be transmitted through a low OH- silica fiberoptic cable. This wavelength falls on one of the peaks of the energy absorption spectrum of water. Thus, the THC:YAG laser eliminates the disadvantage of a cumbersome delivery system found in the CO2 laser while still providing precise cutting and minimal tissue injury inherent in lasers emitting light absorbed by water. We evaluated the soft tissue effects of this laser on canine vocal cords. Ablative lesions were produced by the THC:YAG laser and histologically examined on postoperative days 1, 7, and 28. Results indicate that the depth of tissue penetration is easily controlled and the healing response to tissue injury is comparable to that of the CO2 laser. The THC:YAG laser should prove to be a superior laser for use in otorhinolaryngology, especially when adapted to a flexible endoscope.