Biomedical subjects

T E Burris

Publications and source records attributed to T E Burris.

23 records · Page 2Linked to original sources

PubMedDate not supplied

Topographic predicted corneal acuity with intrastromal corneal ring segments.

PURPOSE: To evaluate predicted optical quality of the central anterior corneal surface before and after the intrastromal corneal ring segment (ICRS) refractive procedure using a clinical videokeratoscope and software index developed for that purpose. METHODS: Predicted corneal acuity, a topographically derived index provided with the EyeSys System 2000 videokeratscope, representing potential optical quality of the cornea, was assessed preoperatively and at postoperative month 3 in 94 eyes that received an ICRS to treat -1.00 to -6.00 D of myopia. Predicted corneal acuity was calculated by determining the difference between a measured cornea and its best-fit ellipses for reflected ring circumferences within the central 3 mm diameter zone. RESULTS: Preoperative predicted corneal acuity was 20/10 in 92 of 94 eyes (98%). At month 3 after the ICRS procedure, 48 (51%) of moderately myopic eyes were corrected to 20/20 or better, 96% (90 eyes) were corrected to 20/40 or better, and 98% of eyes (92 eyes) had a predicted corneal acuity of 20/10. For the eyes with a predicted corneal acuity of 20/10, spectacle-corrected visual acuity was normally distributed between 20/10 and 20/25. CONCLUSION: Predicted corneal acuity did not change significantly from baseline in eyes with an ICRS. This suggests that topographic irregularities in the central 3 mm of the cornea detectable by predicted corneal acuity software were not induced in the central cornea with the ICRS.

Corneal Stroma↗

PubMedDate not supplied

Characterization of the aspheric corneal surface with intrastromal corneal ring segments.

PURPOSE: Anterior corneal surface asphericity was examined in eyes of Phase II clinical trial participants, before and after intrastromal corneal ring segments (ICRS, Intacs) refractive surgery, and surveyed for relationship to clinical visual performance. METHODS: Aspheric test objects with surface asphericity (Q) ranging from -0.01 Q to -1.44 Q and base radius of curvatures ranging from 7.5 mm to 9.0 mm were measured topographically using videokeratography. Radius of curvature asphericity profile plots were produced for test objects and compared to similar plots created for trial participant eyes (n=25) to quantify corneal asphericity. The potential effects of different amounts of corneal asphericity were assessed using measurement of uncorrected and spectacle-corrected visual acuity and photopic contrast sensitivity. RESULTS: Preoperative corneal asphericity ranged from -0.01 Q to -0.81 Q and postoperative from -0.01 Q to -1.44 Q. Preoperative uncorrected visual acuity was significantly related to corneal asphericity; more myopic eyes tended to have more prolate corneal asphericity. Corneal asphericity was not significantly related to spectacle-corrected visual acuity or photopic contrast sensitivity, before or after surgery. CONCLUSION: Postoperative corneal asphericity values demonstrated that intrastromal corneal ring segments (Intacs) produced a prolate aspheric surface for myopic correction from -1.00 D to -6.00 D. This study indicated that the range of corneal asphericity measured in these 25 eyes, before and after surgery, provided good visual acuity and normal contrast sensitivity.

Biocompatible Materials↗

PubMedDate not supplied

Intrastomal corneal ring segments: reversibility of refractive effect.

PURPOSE: To evaluate the reversibility of refractive effect following removal of the ICRS (intrastromal corneal ring segments; Intacs). METHODS: Data from 34 eyes from which ICRS were removed during United States FDA Phase II and III clinical trials were evaluated with regard to segment size, loss or change of best spectacle-corrected visual acuity (BSCVA), any change of uncorrected visual acuity (UCVA), manifest spherical equivalent refraction, manifest cylinder refraction, stability of manifest cylinder refraction, and subjective visual symptoms. RESULTS: Out of 725 initial or contralateral eyes placed with the ICRS during Phase II and III clinical trials, segments were removed from 34 eyes (4.7%). Other than one (1/725, 0.1%) safety related ICRS removal, 30/725 (4.1%) were due to visual symptoms. ICRS removal was accomplished under topical anesthesia without complications in all eyes. The mean length of time the segments remained in the cornea after initial surgery was 10.3 +/- 5.4 months. At 3 months after ICRS removal, 21 eyes had monitored data available and were within +/-1 line or 10 letters of their preoperative BSCVA. Twenty eyes (20/21, 95%) returned to within +/-1.00 D of their preoperative manifest spherical equivalent refraction. All eyes had a stable refraction at the 3-month examination after removal, and a manifest spherical equivalent refraction within +/-1.00 D of their 1-month examination after removal. Nineteen eyes (19/21, 90%) returned to within +/-2 lines and 16 eyes (16/21, 76%) returned to within +/-1 line of preoperative UCVA. CONCLUSION: The ICRS (Intacs) was easily and safely removed, and eyes returned to preoperative refractive status within 3 months.

Corneal Stroma↗

PubMedDate not supplied

Effects of intrastromal corneal ring size and thickness on corneal flattening in human eyes.

Intrastromal corneal rings can flatten the human cornea, providing a potential new method of keratorefractive surgery. We investigated the effect of implanting various ring sizes of a given thickness in 8.50-mm intrastromal channels dissected in human eye bank corneas. A new intraoperative corneal topography device was used to obtain serial data. Smaller rings with no expansion pressure on the channels were found to induce corneal flattening presumably due to the ring thickness alone. Rings of increasing diameters produced high degrees of corneal flattening at progressively declining rates; this suggests that shear stresses may have expanded the channel due to mechanical stresses placed by our particular experimental technique. Implantation techniques that minimize stress on the outer channel lamellae appear advisable. New ring designs should take ring thickness into consideration along with outer edge configurations that minimize shear stresses on the lamellar channels.

Cornea↗

PubMedDate not supplied

Model of epithelial downgrowth: III. Scanning and transmission electron microscopy of iris epithelialization.

Epithelialization of uveal structures is frequently difficult to diagnose clinically and may require scanning and/or transmission electron microscopy to detect histologically. Since the scanning and transmission electron microscopic findings of progressive iris epithelialization have not previously been described, we examined a cat model of epithelial downgrowth for iris findings from 23 days through 4 months post-implantations of epithelium. Features associated with iris epithelialization included direct contact of iris with implanted epithelium, allowing initially rapid epithelialization of anterior iris structures, and slower epithelialization of posterior iris pigmented epithelium. The morphology of the migrating epithelium progressed from spindle shaped cells with small numbers of pseudopodia and microvillae to confluence of up to five layers of stratified epithelium with numerous surface microvilli. Anterior iris epithelial morphology consisted of cuboidal shaped cells with "looser" cell junctional interdigitations, versus a more squamous appearance of posterior iris epithelialization. A monolayer of lead cells or thin sheets of epithelium may be present well before a clinically apparent multicellular sheet of epithelium is seen.

Animals↗