PURPOSE.To model the photochemical kinetics of corneal crosslinking with riboflavin (Rf) and confirm the model through measured oxygen concentration experiments under varying energy input conditions by UV-A irradiance and temperature modulation in ex vivo porcine cornea. METHODS.A theoretical model was developed to describe the corneal cross-linking photochemical kinetics of Rf. After instillation with drops of Rf solution in distilled water, deepithelialized porcine corneas were exposed to 365-nm ultraviolet light (UV-A) under varying irradiance and temperature. Oxygen concentration in the cornea at a known depth was monitored during UV-A illumination with a dissolved oxygen fiberoptic microsensor. Data from the oxygen experiments were used to confirm the model. RESULTS.On the basis of the known chemical reactions and diffusion rates of Rf and oxygen into the cornea, the authors developed a theoretical model consistent with corneal oxygen consumption experimental results during UV-A irradiation under different conditions. Oxygen concentration in the cornea is modulated by UV-A irradiance and temperature and quickly decreased at the beginning of UV-A exposure. The time-dependence of both Type-I and Type-II photochemical mechanisms in corneal cross-linking with Rf are discussed.CONCLUSIONS. Using a chemical kinetics modeling approach, the authors developed a simple model that is in agreement with their experimental results on oxygen consumption in the cornea during corneal cross-linking with Rf. It is suggested that the main photochemical kinetics mechanism is the direct interaction between Rf triplets and reactive groups of corneal proteins, which leads to the cross-linking of the proteins mainly through radical reactions. (Invest Ophthalmol Vis Sci.

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Corneal collagen crosslinking was effective in improving the maximum K value, CDVA, and UDVA in eyes with corneal ectasia 1 year after treatment, with an excellent safety profile. CXL is the first approved procedure to diminish progression of this ectatic corneal process.

Microwave keratoplasty reduced corneal curvature and has therapeutic potential as a noninvasive alternative to excimer laser surgical correction of myopia and as a treatment for corneal ectasia.

Drs. Yilmaz and Marshall are paid consultants to Avedro, Inc., and Dr. Muller is president and CEO of Avedro, Inc. No other author has a financial or proprietary interest in any material or method mentioned.

Purpose. This paper describes an advanced system that combines corneal cross-linking with riboflavin with fluorescence dosimetry, the ability to measure riboflavin diffusion within the cornea both before and during UVA treatment. Methods and Results. A corneal cross-linking system utilizing a digital micromirror device (DMD) was assembled and used to measure diffusion coefficients of 0.1% riboflavin in 20% dextran in porcine eyes. A value of (3.3 ± 0.2) × 10−7 cm2/s was obtained for the stroma. Diffusion coefficients for the transepithelial formulation of 0.1% riboflavin in 0.44% saline and 0.02% BAK were also measured to be 4.7 ± 0.3 × 10−8 cm2/s for epithelium only and (4.6 ± 0.4) × 10−7 cm2/s for stroma only. Riboflavin consumption during a UVA treatment was also demonstrated. Conclusion. A new advanced corneal cross-linking system with fluorescence dosimetry of riboflavin has been demonstrated. It is hoped that this method may play a significant role in determining the underlying mechanisms of corneal cross-linking and assist with the development of additional riboflavin formulations. Moreover, dosimetry may prove valuable in providing a method to account for the biological differences between individuals, potentially informing cornea-specific UVA treatment doses in real time.

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The Zeiss SLC measuring system for examining the anterior segment in slit light permits direct digital image storage and analysis. For long-term studies the reproducibility of individual images can be improved. Furthermore, the data can be quickly processed to yield indices which can be used to characterize the cataract: 1) the integral of an axial densitogram as a criterion of average lens opacity, and 2) the difference between the linear regressions of the densitograms of the anterior and posterior lens halves as a criterion of cataract form (e.g., nuclear vs. cortical cataract).