Roy S. Chuck

Optimal wavelength for ultrahigh-resolution optical coherence tomography

The influence of depth dependent dispersion by the main component of biological tissues, water, on the resolution of OCT was studied. Investigations showed that it was possible to eliminate the influence of depth dependent dispersion by water in tissue by choosing a light source with a center wavelength near 1.0 microm. Ultrahigh resolution ophthalmic imaging was performed at this wavelength range with a microstructure fiber light source.

Corneal sensation after laser in situ keratomileusis.

PURPOSEnTo report the time course for the return of corneal sensation following laser in situ keratomileusis (LASIK).nnnSETTINGnUniversity-based retractive surgery practice.nnnMETHODSnTwenty-eight eyes of 18 patients having LASIK were evaluated. Preoperative and postoperative corneal sensation at the nasal flap hinge, at the central cornea, and within the temporal flap edge were measured before and after LASIK for a 3 week period using the Cochet-Bonnet esthesiometer (Luneau).nnnRESULTSnCorneal sensation initially decreased in all 3 positions of the flap measured after LASIK; the greatest decrease was in the central cornea. Near preoperative corneal sensation returned by 3 weeks. The degree of sensation loss did not appear to correlate with the ablation depth.nnnCONCLUSIONnCorneal sensation is significantly decreased for approximately 2 to 3 weeks after LASIK, centrally greater than nasally at the flap hinge or temporally within the flap edge, but it generally returns to near the preoperative level by 3 weeks postoperatively.

Precision and accuracy of an artificial anterior chamber system in obtaining corneal lenticules for lamellar keratoplasty

Purpose: To determine the precision and accuracy of an artificial anterior chamber and a manual microkeratome in obtaining corneal lenticules for lamellar keratoplasty. Setting: Department of Ophthalmology, Cornea, External Diseases and Refractive Surgery Service, University of California Irvine, Irvine, California, USA. Methods: A lamellar keratectomy was performed in 47 human corneoscleral rims. Three lenticule thicknesses (180, 300, and 360 &mgr;m heads) and 3 diameters (7.0, 8.0, and 9.0 mm) were attempted. Diameters and thicknesses were measured by planimetry and pachymetry, respectively. Results: Peripheral lenticule thickness was more likely to be within ±50 &mgr;m of the intended depth in thinner cuts (180 &mgr;m, 9/15 corneas, 60%; 300 &mgr;m, 6/16 corneas, 40%; 360 &mgr;m, 3/12 corneas, 33.3%) (P = .045). Eighty percent (32/40 corneas) were within ±0.5 mm of the expected diameter. Accuracy was best in the 8.0 mm group, with 47.1% (8/17 corneas) within ±0.2 mm of the expected diameter. A thickness/diameter correlation was not observed (rs ≤ 0.28). Conclusions: The precision and accuracy of this system varied according to the attempted thickness and diameter.

Corneal lenticule harvest using a microkeratome and an artificial anterior chamber system at high intrachamber pressure.

Purpose To evaluate the safety and accuracy of a manual microkeratome and an artificial anterior chamber used at high intrachamber pressure to harvest corneal lenticules for lamellar keratoplasty. Setting Department of Ophthalmology, University of California, Irvine, California, USA. Methods forty‐seven human eye‐bank corneoscleral rims were mounted on an artificial anterior chamber. a manual microkeratome was used to perform lamellar keratectomy at a mean intrachamber pressure of 95.8 mm hg ± 4.8 (sd). two thicknesses (300 &mgr;m and 360 &mgr;m microkeratome heads) and diameters (8.0 mm and 9.0 mm) were attempted, and the resultant lenticules were analyzed by pachymetry and digital photography Results In the 9.0 mm/360 &mgr;m group, corneal perforation occurred in 12 of 17 lenticules (71.2%). Except for this group, 24 of 30 corneas (80.0%) showed a less than 0.5 mm deviation from the expected diameter. Neither the horizontal nor the vertical diameter differences were statistically significant (P > .05). The difference between the horizontal and vertical diameters was within ±0.2 mm in 23 corneas (76.7%). Three (10.0%) corneal beds contained a slightly uneven keratectomy margin. Conclusions This system provided accurate and smooth lenticules for lamellar keratoplasty. The precision and accuracy of the obtained corneal lenticules were better than those in previous reports. However, the 9.0 mm diameter/360 &mgr;m thickness head with high intrachamber pressure should not be applied in the clinical setting without further testing. In this laboratory study, a minimal corneal thickness of 588 &mgr;m was required to avoid perforation.

Microkeratome-based limbal harvester for limbal stem cell transplantation: preliminary studies

PURPOSEnTo develop a mechanical device to perform limbal transplantation. This procedure is a valuable surgical technique for management of limbal stem cell deficiency. However, the freehand dissection to obtain donor tissue is laborious and time-consuming.nnnMETHODSnA manual microkeratome (LSK One; Moria/Microtech, Doylestown, Pennsylvania) using a redesigned head (200 microm thickness, 16-mm blade) was used to create partial thickness corneoscleral caps from human donor globes.nnnRESULTSnCorneoscleral caps obtained from human donor globes included a ring of approximately 1 mm of perilimbal sclera in contiguity to the cornea. Scanning electron microscopy showed a smooth cut surface with some chatter at the margins.nnnCONCLUSIONnThis instrument ensures an effective and straightforward method to dissect the area where stem cells have been indirectly localized.

A laboratory model for microkeratome-assisted posterior lamellar keratoplasty utilizing a running graft suture and a sutureless hinged flap.

Purpose. To evaluate changes in anterior corneal curvature and graft stability with different sized donor buttons in a laboratory model of posterior lamellar keratoplasty. Methods. Thirty-six human eye bank corneas (18 donors and 18 recipients) were mounted on an artificial anterior chamber. A manual microkeratome was used to create a hinged anterior lamellar keratectomy. A 7.0-mm diameter posterior lamellar disk (posterior stroma, Descemets membrane, and endothelium) was then trephinated from the recipient cornea. Three different sizes (7.0, 7.25, and 7.5 mm) of donor buttons were compared. They were sutured into the recipient bed with a running 10-0 nylon suture and covered by the host corneal flap. The flap was replaced without sutures. The resulting endokeratoplasty was analyzed by computerized videokeratography and tonometry. Results. Regular postoperative astigmatism was present in all cases. There was an average increase in astigmatism of 1.47 ± 1.49 diopters (D) postoperatively. The mean change in the average keratometry readings was −5.12 ± 6.12 D. The grafts and flaps maintained watertight seals with average leak pressures of 66.9 ± 46.4 mm Hg. Although donor buttons oversized by 0.5 mm had the least change in average keratometry reading, those oversized by 0.25 mm had the best stability at high pressure. All groups had little change in astigmatism. Conclusion. The optimal sized button of those tested would be either oversized by 0.25 or 0.5 mm. This new surgical technique may result in lower risk of high and irregular astigmatism in the management of corneal endothelial disorders.

Phototherapeutic keratectomy for superficial corneal fibrosis after radial keratotomy.

We report on 4 patients who developed superficial corneal fibrosis after radial keratotomy. All 4 were treated successfully with manual debridement of the epithelium and manual excision of the fibrous scar, followed by phototherapeutic keratectomy.

Ablation spectra of the human cornea

Ablation of human corneal tissue with 193 nm excimer laser energy generates fluorescence in the near ultraviolet and visible regions of the spectrum. The fluorescence spectra from five human corneas were collected during ablation in vitro. We find that the fluorescence spectrum changes continuously as the cornea is ablated from the epithelial surface towards the endothelium. We reduced the dimensionality of the large data set resulting from each cornea by a principal components analysis. The three most significant principal component eigenvectors suffice to describe the observed spectral evolution, and independent analysis of each tissue sample produces a similar set of eigenvectors. The evolution of the calculated eigenvector weighting factors during ablation then corresponds to the observed spectral evolution. In fact, this evolution is qualitatively consistent between corneas. We suggest that this spectral evolution offers promise as a real-time surgical feedback tool.

Evaluation of a microkeratome-based limbal harvester device for limbal stem cell transplantation.

Purpose. To assess the cut quality and reproducibility using a novel microkeratome-based limbal harvester. Methods. An enlarged microkeratome head and stainless steel blades were coupled with a nitrogen gas–driven turbine (15,000 blade oscillations/min) of a microkeratome. A large, 16-mm-diameter suction ring was attached to the globe. A lamellar sclerokeratectomy using head depths of 170 and 200 &mgr;m was performed in human donor research eyes. Obtained lenticule thickness was measured by ultrasound pachymetry and the bed size by planimetry. Histologic and scanning electron microscopy (SEM) analyses of the samples were performed. Results. Central lenticule thickness was 294 &mgr;m (standard deviation [SD] 37) for the 170 head and 277 &mgr;m (SD 91) for the 200 head (p = 0.720). Lenticule diameter was larger in the horizontal meridian using the 170 head (12.8 mm [SD 0.8] vs. 11.9 mm [SD 0.7], p = 0.028), but similar in vertical meridian (12.0 [SD 0.6] versus 11.4 mm [SD 0.6], p = 0.093). Histology showed a multilayer epithelial cell pattern at the lenticule periphery. The SEM showed a smooth cut surface in both the stromal bed and the lenticule. Conclusion. Cut reproducibility and quality are similar to those found using standard microkeratomes for corneal lamellar cuts. This system ensures, in a straightforward way, the presence of epithelial cells in the edges of a mechanical sclerokeratectomy for limbal stem cell transplantation.

Effect of age on the refractive outcome of myopic photorefractive keratectomy.

Purpose: To evaluate the effect of age on the outcome of myopic photorefractive keratectomy (PRK). Setting: University‐based refractive surgery practice. Methods: A retrospective analysis of 197 eyes that had PRK for myopia was performed. Four groups of patients were compared: Group 1, patients <30 years (n = 35); Group 2, patients 31 to 40 years (n = 56); Group 3, patients 41 to 50 years (n = 47); Group 4, patients >50 years (n = 59). The percentage of eyes with an uncorrected visual acuity of 20/20 or better and 20/40 or better and the percentage of eyes with spherical correction within ±0.5 and ±1.0 diopter (D) of the attempted correction were derived for each age group. The percentage of patients overcorrected and undercorrected by 1.0 D or more in each age group was also calculated. Results: The difference between the percentage of patients who achieved a visual acuity of 20/20 or better in Group 4 and in the younger groups was statistically significant at 3 months (P = .02) but not at 6 months (P = .70) and 12 months (P = .55). The difference between the percentage of patients who achieved an acuity of 20/40 or better was not significant at any time. The difference between the percentage of patients who were within ±0.5 D of intended correction in Group 4 and in the younger groups was statistically significant at 3 months (P = .001), 6 months (P = .006), and 12 months (P = .008); the difference between the percentage of patients who were within ±1.0 D of intended correction was not significant at any time. The difference between the percentage of patients overcorrected and undercorrected by 1.0 D or more in Group 4 and in the younger groups was not significant at any time. Conclusions: In the 3 younger groups, age did not significantly affect visual outcome or predictability. However, there was a significant difference between Group 4 and the 3 younger groups in predictability of the refractive outcome at 3, 6, and 12 months. Age may play a role in the outcome of refractive surgery.