| Optical coherence tomography (OCT) is capable of higher speed and resolution than other non-contact corneal imaging modalities. As OCT technology improves, we are finding more and more applications for it in the management of anterior eye diseases and the planning of surgeries. In this study, we discussed the the applications of OCT in evaluating angle closure risk; the clinical diagnosis of keratoconus using OCT pachymetric indices based diagnostic formula; and the application of OCT in designing and observing in a new surgical technique of dual laser-assisted lamellar anterior keratoplasty.Part 1. Anterior chamber angle measurements at the Schwalbe's line with high resolution fourier-domain optical coherence tomographyObjectives:To introduce angle opening distance at Schwalbe's line (AOD-SL) as a parameter to help assess angle closure risks using Fourier-domain optical coherence tomography (OCT).Methods:An 830-nm wavelength Fourier-domain OCT (RTVue, Optovue, Inc.) was used to perform horizontal scans of the nasal and temporal anterior chamber angles in glaucoma subjects. Images were graded by two ophthalmologists who assessed the visibility of landmarks and measured AOD-SL with computer calipers. Schwalbe's line was manually identified by the termination of the corneal endothelium. Gonioscopy was performed by a glaucoma specialist and classified using modified Shaffer system. The correlation between AOD-SL and Shaffer grade were assessed. A cut-off value of AOD-SL for occludability was determined.Results:Thirty five subjects (65 eyes) were enrolled. Schwalbe's line, anterior limbus, angle recess and scleral spur were visible In 97.7%, 99.2%,87.3% and 80.8% of eyes, respectively. Correlation coefficients between AOD-SL and Shaffer grade were 0.80 (nasal) and 0.81 (temporal). The diagnostic cut-off point for AOD-SL was 290?m. The AROC/ sensitivity/specificity values were 0.90/0.80/0.87 (nasal) and 0.90/0.85/0.77 (temporal). Conclusions:The measurement of AOD-SL by Fourier-domain OCT is highly correlated with gonioscopy and may be useful as a noncontact method of assessing angle closure risk.Part 2. Keratoconus diagnosis with an optical coherence tomography-based pachymetric formulaObjectives:To develop an optical coherence tomography (OCT) pachymetry map based keratoconus diagnostic formula. To develop a keratoconus risk scoring table to help clinical screening of keratoconus.Methods:A Fourier-domain OCT system was used to acquire corneal pachymetry map in normal, keratoconus, and forme frusta keratoconus (FFKC) subjects. Five pachymetric parameters were calculated from regions inside the 5 mm diameter zones:minimum, minimum-median, superior-inferior (S-I), superonasal-inferotemporal (SN-IT), and the vertical location of the thinnest cornea (Ymin). These parameters were combined into one formula derived by logistic regression. Keratoconus and FFKC diagnostic accuracy was measured by the area under the receiver operating curve (AROC).Results:One hundred and thirty two eyes from 66 normal,84 eyes from 52 keratoconus, and 22 eyes from 22 FFKC subjects were recruited. Logistic regression formula=-0.036×minimum-0.24×(minimum-median)+0.029×(S-I)-0.025×(SN-IT)-0.0015×Ymin+13.48. Comparing AROC, for keratoconus, the formula was 0.99 which had significantly better accuracy compared with the best single parameter (minimum-median= 0.96, P=0.015); for FFKC, the formula was 0.79 and showed no improvement compared with the best single parameter (minimum-median=0.74, P= 0.43).Conclusions:The OCT corneal pachymetry map based formula improved the diagnosis of keratoconus. It may be useful in the screening of keratoconus in conjunction with standard corneal topography.Part 3. Dual laser-assisted lamellar anterior keratoplasty tophat graft: a laboratory studyObjectives:To develop a dual laser-assisted lamellar anterior Part 3. Dual laser-assisted lamellar anterior keratoplasty tophat graft: a laboratory studyObjectives:To develop a dual laser-assisted lamellar anterior keratoplasty (LALAK) technique, using excimer and femtosecond lasers to perform surgery on eye-bank eyes.Methods:First we compared corneal stromal surfaces produced by deep excimer ablation, femtosecond lamellar cuts, and manual lamellar dissection, and evaluated the effect of excimer laser smoothing with fluid masking. Masked observers graded scanning electron microscopy (SEM) images on a 5-point roughness scale. Then we performed a 6-mm diameter excimer laser phototherapeutic keratectomy (PTK) ablation to a residual stromal bed thickness of 200?m, followed by laser smoothing. We used the femtosecond laser to cut donors in a modified top-hat design with a thin tapered brim, which fitted into a manually dissected circumferential pocket at the base of the recipient bed. Fourier-domain optical coherence tomography (OCT) was used to measure corneal pachymetry and evaluate graft fit.Results:Deep excimer ablation with smoothing (n=4) produced a significantly (p<0.05) smoother surface (grade=3.5) than deep excimer alone (n=4, grade=3.8) or manual dissection with (n=1, grade=3.8) and without smoothing (n=l, grade=4.8). Deep femtosecond cuts (n=2) produced macroscopic concentric ridges on the stromal surface. Experimental LALAK was performed on 4 recipients prepared by deep excimer ablation and 4 donors cut with the femtosecond laser. After suturing good peripheral graft-host match and smooth anterior contour was observed on FD-OCT imaging.Conclusion:These preliminary studies show that the LALAK technique permits improvements in interface smoothness and graft edge matching. Clinical trials are needed to determine whether improved interface smoothness can translate to better visual outcomes. Conclusions1. The Schwalbe's line had higher visibility compared with scleral spur in OCT images. AOD-SL is highly correlated with Shaffer grade and may be useful in assessing angle closure risk.2. The OCT corneal pachymetry map based formula improved the diagnosis of keratoconus.3. LALAK technique permits improvements in interface smoothness and graft edge matching. |
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