Validation of a Novel Confocal Microscopy Imaging Protocol With Assessment of Reproducibility and Comparison of Nerve Metrics in Dry Eye Disease Compared With Controls.

PURPOSE: The purposes of this study were to assess the reproducibility of a novel standardized technique for capturing corneal subbasal nerve plexus images with in vivo corneal confocal microscopy and to compare nerve metrics captured with this method in participants with dry eye and control participants. METHODS: Cases and controls were recruited based on their International Statistical Classification of Diseases and Related Health Problems (ICD-10) diagnoses. Participants completed the following 3 ocular symptom questionnaires: the Ocular Surface Disease Index, Neuropathic Pain Symptom Inventory, and Dry Eye Questionnaire 5. A novel eye fixation-grid system was used to capture 30 standardized confocal microscopy images of the central cornea. Each participant was imaged twice by different operators. Seven quantitative nerve metrics were analyzed using automated software (ACCmetrics, Manchester, United Kingdom) for all 30 images and a 6-image subset. RESULTS: Forty-seven participants were recruited (25 classified as dry eye and 22 controls). The most reproducible nerve metrics were corneal nerve fiber length [intraclass correlation (ICC) = 0.86], corneal nerve fiber area (ICC = 0.86), and fractal dimension (ICC = 0.90). Although differences were not statistically significant, all mean nerve metrics were lower in those with dry eye compared with controls. Questionnaire scores did not significantly correlate with nerve metrics. Reproducibility of nerve metrics was similar when comparing the entire 30-image montage to a central 6-image subset. CONCLUSIONS: A standardized confocal imaging technique coupled with quantitative assessment of corneal nerves produced reproducible corneal nerve metrics even with different operators. No statistically significant differences in in vivo corneal confocal microscopy nerve metrics were observed between participants with dry eye and control participants.

Optimization of femtosecond lasers using porcine and human donor corneas before in vivo use.

PURPOSE: To demonstrate a safe and effective method of optimizing a femtosecond laser upon installation or for a new procedure before use on patients. In this case, specifically for optimizing settings for intrastromal corneal pocket creation for the presbyopic small-aperture corneal inlay (Kamra) and deep laser in situ keratomileusis (LASIK) flaps for the presbyopic hydrogel corneal inlay (Raindrop). SETTING: Keil LASIK Vision Center, Grand Rapids, Michigan, USA. DESIGN: Experimental study. METHODS: Human donor corneas were used to optimize femtosecond laser settings after initial optimization with porcine corneas. The laser used was the Femto LDV Z4. RESULTS: Pocket settings optimized for porcine corneas were 12.0 mm/s pocket and tunnel at 105% energy; whereas, settings optimized with human donor corneas were 13.0 mm/s pocket and tunnel at 110% energy. Settings optimized with human donor corneas were subsequently applied in vivo to create pockets for the small-aperture corneal inlay. Further adjustment of settings to 14.0 mm/s pocket at 110% energy was still necessary to optimize pockets. No change in settings was necessary when creating deeper corneal LASIK flaps (ie, the same settings could be used for flaps of 110 µm or 180 µm). CONCLUSIONS: After settings were optimized for porcine corneas, further optimization was necessary before successful corneal incisions could be created in vivo for corneal pockets. No further optimization was required when creating deeper corneal flaps for the hydrogel inlay. It is important to emphasize that settings obtained and reported here are not applicable to other femtosecond lasers.