Corneal surface topography and associated visual performance with INTACS for myopia: phase III clinical trial results. The INTACS Study Group.

OBJECTIVE: To characterize corneal topography with INTACS (KeraVision, Inc., Fremont, CA) an ophthalmic device designed to correct myopia, and relate findings to visual performance. DESIGN: Prospective nonrandomized self-controlled comparative intervention study. PARTICIPANTS/INTERVENTION: Patients were participants in the INTACS FDA phase III clinical trials. MAIN OUTCOME MEASURES: Preoperative and postoperative month 6 videokeratographic corneal topography (EyeSys, Houston, TX) was analyzed for 165 eyes from eight clinical sites. Topographic flattening, asphericity, and surface characteristics were statistically evaluated for relationship to visual acuity, refractive data, contrast sensitivity, and subjective visual symptoms. RESULTS: Corneal radius of curvature flattening was aspheric in nature and increased incrementally and significantly for progressively thicker INTACS (P < 0.05). Comparative stratification analyses suggest potential interactions between existing preoperative asphericity and myopia, postoperative asphericity, and visual performance outcomes. Qualitative symmetric and asymmetric toric topography patterns were related to the postoperative self-reported visual symptoms of "double images" (P < or = 0.05) and "halos" (P < or = 0.10), respectively. CONCLUSIONS: The anterior corneal surface is aspherically flattened (prolately) with INTACS, whereas postoperative corneal asphericity is significantly more prolate than preoperative. Specific qualitative postoperative topography patterns were associated with subjective clinical visual performance.

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.

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.

Lamellar intrastromal corneal tattoo for treating iris defects (artificial iris)

PURPOSE: Defects in the iris are associated with clinically significant optical anomalies, such as glare and peripheral light scatter; however, current artificial-iris technology remains inadequate. The purpose of this study was to explore the practicality of a lamellar intrastromal tattoo technique as a treatment modality to correct optical and cosmetic defects resulting from simulated iris abnormalities in eye-bank eyes. METHODS: Simulated iris defects (abnormally large pupil, sector iridectomy, iridodialysis, and aniridia) were produced in a series of eye-bank eyes. Depending on the simulated iris defect, one or two lamellar channel(s) were created at 50% depth of the cornea via a peripheral incision (1.8 mm) with specialized proprietary instruments (KeraVision, Inc., Fremont, CA, U.S.A.). Commercially available tattoo pigment was inserted through the lamellar channel(s) and blended into the defective region of the iris. RESULTS: The tattoo treatment was relatively simple to perform. Tattoo pigment was inserted uniformly through the small incision, and adequate color blending to match the recipient iris was achieved. The intrastromal tattoo effectively obscured light. CONCLUSION: The lamellar intrastromal tattoo technique appeared to be efficacious for treating different types of iris defects in eye-bank eyes. Further investigation of this technique in nonsighted patient eyes is warranted.

Corneal asphericity in eye bank eyes implanted with the intrastromal corneal ring.

OBJECTIVE: To evaluate the effects of the intrastromal corneal ring, a device developed to reduce myopia, on corneal asphericity in a large set of eye bank eyes. METHODS: Forty-one deturgesced eye bank eyes were implanted with intrastromal corneal rings of five different thicknesses, ranging from 0.25 mm to 0.45 mm. Corneal asphericity, before and after implantation, was examined using two different metrologies. Corneal asphericity profiles were produced from dioptric power data collected from videokeratography. To statistically assess the corneal asphericity differences between exam times for each intrastromal corneal ring thickness, dependent sample confidence intervals (95%) were calculated for the mean differences between preoperative and postoperative measures for each topographic diameter zone. Laser holographic interferometry was used to inspect corneal asphericity in one eye bank eye case study for four intrastromal corneal ring sizes. Wave unit map and geometric zonal spot ray tracing analyses derived from laser holographic interferometry topography were surveyed. RESULTS: Videokeratographic analysis suggested that preoperative corneal shape was prolate, i.e., flattened from central to paracentral cornea. Corneal shape became more prolate with intrastromal corneal ring implantation for all intrastromal corneal ring thicknesses. Laser holographic interferometry demonstrated that prolate asphericity was preserved with the intrastromal corneal ring sizes tested and that optical collection efficiency of the cornea was not diminished. CONCLUSION: Using two different measurement techniques, this eye bank eye study demonstrated that intrastromal corneal rings maintain prolate corneal asphericity.