Biomicroscopic measurement of the optic disc with a high-power positive lens.

PURPOSE: To compare the magnification properties of four different indirect double aspheric fundus examination lenses for clinical disc biometry. METHODS: Experimental study in a model eye. The relationship between the true size of a fundus object and its image was calculated for each fundus lens for an ametropic range between -12.5 and +12.6 D using a slit lamp biomicroscope with adjustable beam length. RESULTS: Equations for determining the correction factor p (degrees per millimeter) were calculated for each fundus lens. The factor can be used in calculations to determine true optic disc size. The total change in magnification of the system from myopia to hyperopia was -21.1% to +24.0% (60-D lens; Volk Opticals, Mentor, OH), -12.9% to +16.2% (Volk super 66 stereo fundus lens), -13.2% to +13.9% (Volk 78-D lens), and -13.3% to +14.0% (Volk super-field NC lens). When the fundus lens position was altered im relation to the model eye by +/-2 mm under myopic conditions, the change in magnification of the system was -4.3% to +5.7% (60-D lens), -4.6% to +6.1% (66 stereo fundus lens), -4.9% to +6.3% (78-D lens), and -5.9% to +7.8% (super-field NC lens). In the hyperopic condition the change was -2.7% to +3.6%, -3.4% to +4.5%, -3.6% to +4.8%, and -4.5% to +6.0%. CONCLUSIONS: The study has shown that the use of a single magnification correction value for each fundus lens may not be appropriate. These findings have important implications for the way in which calculations for determining the true optic disc size and other structures of the posterior pole are performed using indirect biomicroscopy.

Corneal lathing using the excimer laser and a computer-controlled positioning system.

PURPOSE: To present the excimer laser corneal shaping system (ELCS-S), an add-on device to the Keratom, a commercially available 193-nm excimer laser built by Schwind. METHODS: The system is designed for the preparation of donor corneas under sterile conditions using the ultraviolet laser to offer greatest possible flexibility. Lenticules for planolamellar grafting and refractive epikeratoplasty, as well as donor buttons for penetrating keratoplasty can be computer-designed by the surgeon or technician and lathed with the system. RESULTS: Using the excimer laser corneal shaping system (ELCS-S) on human donor corneas, the central surface of the epikeratoplasty lenticule exhibited only narrow, flat concentric notches corresponding to the single lathing steps. Transmission electron microscopy revealed a damage zone of less than 0.3 microm in close approximation to the treated surface. The final thickness revealed a difference of less than +/-53 microm from the intended, initially programmed value. Ultrastructural studies showed the perpendicular stromal surface of the penetrating keratoplasty buttons to be smooth with minimal protrusion of Descemet's membrane. Endothelial injury was observed in a zone averaging between 40 and 100 microm adjacent to the cutting edge only. CONCLUSION: The excimer laser corneal shaping system (ELCS-S) allows a computer-controlled, surgeon-designed, sterile preparation of lamellar and penetrating corneal grafts with the use of the excimer laser. This could offer significant advantages in comparison to presently available systems for lamellar dissection and trephination.

Laser shaping of corneal transplants in vitro: area ablation with small overlapping laser spots produced by a pulsed scanning laser beam using an optimizing ablation algorithm.

Area laser lathing and trephination of donor corneas is used to produce different types of grafts for human transplantation. 193 nm (ArF excimer) laser radiation is used, since this is known to give a non-thermal laser-tissue interaction with a minimal zone of tissue damage. To guarantee the highest degree of flexibility concerning the overall shape of the grafts as well as their thickness profiles, we use a small (compared with the area to be ablated) scanning laser spot. For area lathing of the tissue we have developed a new ablation algorithm (optimized scanning laser ablation, OSLA) that can be applied to lathe and perforate any tissue--with concave (as in this application), convex or plane surface geometry--where surface precision and smoothness are key issues. Using OSLA with the Excimer Laser Corneal Shaping System (a tool for in vitro fabrication of all kinds of corneal transplants like donor buttons for keratoplasty, lamellar grafts for epikeratoplasty and refractive lenticules) enabled us to produce all types of corneal grafts with very high precision. This is considered to be a major improvement towards the production of refractive lenticules.

Impact of growth factors on morphometric corneal endothelial cell parameters and cell density in culture-preserved human corneas.

PURPOSE: Donor corneas can be preserved for < or = 4 weeks in organ culture (31 degrees C) by using modified minimal essential medium (MEM). About one fifth of them have to be discarded, however, as disintegration of the endothelial cell monolayer-enhanced polymegethism, cell loss-occurs. The objective of this study was to investigate whether addition of insulin, dextran, and epidermal growth factor (EGF) makes corneal endothelial cells more viable, stable, and homogeneous. METHODS: Sixteen paired human donor corneas were cocultured in media supplemented with EGF and insulin-like growth factor (IGF) or in conventional modified MEM for 4 weeks. Endothelial parameters were evaluated at the outset and at days 7, 14, 21, and 28 of culture by using an automated digital image-analysis system. RESULTS: No significant differences were observed in the first 2 weeks of culture. Beginning with day 14, however, stabilization of endothelial cell patterns was evident for corneas cultured in supplemented culture media. CONCLUSION: Our data indicate that the addition of growth factors to culture media might increase the percentage of corneas available for transplantation and would also allow a significantly longer period of preservation.

Repair of a late-onset filtering bleb leak using a corneal graft shaped with an excimer laser.

A new method for repairing an area of late scleral necrosis and bleb leak after glaucoma-filtering surgery using mitomycin C (MMC) is described. In a 33-year-old female patient diagnosed with bilateral juvenile glaucoma, a bleb leak occurred 41 months after trabeculectomy with MMC in the left eye. A corneal stromal patch-graft shaped to the desired size using an excimer laser (Excimer-Laser-Corneal-Shaping-System, ELCS-S) was used to cover the scleral defect. This step was followed by water-tight closure of the conjunctiva. During the follow-up period of 12 months the leak remained successfully repaired and the intraocular pressure stayed between 8 and 14 mm Hg without medication. This technique that uses lamellar grafts of very large size should be considered when a surgical repair of a large leaking bleb is required, especially in cases with scleral tissue necrosis.

Midterm visual outcome and progression of diabetic retinopathy following cataract surgery. Midterm outcome of cataract surgery in diabetes.

OBJECTIVE: To assess the influence of cataract surgery on progression of diabetic retinopathy and visual acuity. METHODS: 37 patient eyes with mild to moderate diabetic retinopathy at baseline underwent phacoemulsification and intraocular posterior chamber lens implantation. They were examined 3.3 +/- (SD) 0.7 years after surgery. RESULTS: 83.8% of the eyes showed a better final visual acuity, and 67.6% achieved a final visual acuity of 0.5 or better. The retinopathy remained unchanged in 83.8% and progressed in 16.2% of the eyes. No eye progressed to proliferative retinopathy. CONCLUSION: Phacoemulsification and implantation of a posterior chamber intraocular lens is a safe procedure for patients with mild to moderate diabetic retinopathy.

Retinal detachment after silicone oil removal.

PURPOSE: To evaluate the causes of retinal detachment after silicone oil removal, to define possible risk factors and the anatomical and functional prognosis of this complication. METHODS: 112 eyes that underwent silicone oil removal were included. The group of eyes with retinal detachment after oil removal (18/112 eyes, 16.1%) was compared with the group with no postoperative retinal detachment. RESULTS: The most common cause for retinal detachment after oil removal was anterior PVR (77.8%). Initial PVR detachment, advanced PVR stages, anterior PVR, more preceding operations, aphakia/pseudophakia, myopia and shorter duration of the oil tamponade were significantly more represented in the group of eyes with retinal detachment after oil removal. The prognosis of retinal detachment after oil removal is poor. CONCLUSION: Some criteria could be regarded as risk factors for retinal detachment after silicone oil removal. Improvement of the results should be possible by considering these factors and by control of reproliferations.

A new sponge profile for retinal detachment surgery: design and in vitro-effectiveness.

PURPOSE: To develop a new, calculated design for episcleral sponges to achieve sufficient indentation under avoidance of form related side effects. DESIGN AND METHODS: The new sponge profile consists of two convex halves with different radii, with a calculated optimum relation between inner and outer radius. It was tested on pig eyes and compared with round and half cut sponges. The height of the intraocular buckle was determined by ultrasound (A-Scan, Biovision V Plus), the extraocular height using ultrasound biomicroscopy (Humphrey Biomicroscope System Model 840). RESULTS: The buckle height achieved with the new design showed no significant difference to round sponges, whereas the extrascleral height was significantly lower compared to round sponges (p<0.001). Half cut sponges showed significantly less buckle height compared to round sponges (p<0.001) and to the new design (p<0.02). CONCLUSION: The new design produces sufficient indentation combined with minor change of the outer globe contour. It has the potential to be as efficient as conventional round sponges, but more tolerable for the patient by reduction of form related side effects.

Influence of dorzolamide on corneal thickness, endothelial cell count and corneal sensibility.

PURPOSE: Dorzolamide (Trusopt) is the first topical carbonic anhydrase inhibitor (CAI) that is in clinical use in glaucoma therapy. It is known that CAI have a negative effect on corneal endothelial pumpfunction and therefore on the whole corneal physiology. METHODS: 20 patients with open angle glaucoma or ocular hypertension and an elevated intraocular pressure (IOP) over 21 mmHg and without prior oral CAI-treatment were included in this study. Trusopt was administered t.i.d. as monotherapy and b.i.d. in combination with other topical antiglaucoma drugs. Corneal ultrasound pachymetry, corneal endothelial cell count and aesthesiometry were performed prestudy and on days 1, 8, 15, 30, 60 and 90. RESULTS AND CONCLUSIONS: Mean corneal thickness was slightly increased on day one (statistically non-significant) and returned to baseline measurements at the following visits, no changes in endothelial cell count and corneal anesthesia were found. Topical dorzolamide is not associated with clinically meaningful changes of the cornea.