First Clinical Results of a New Generation of Ablative Solid-State Lasers

In the early 2000s, solid-state lasers emerged as an alternative technology to excimer systems in refractive surgery. Despite some technological limits at the time, good clinical results could be achieved with solid-state laser systems. This prospective case series reports clinical outcomes of five eyes treated with a newly developed solid-state laser system (AquariuZ) in three patients. Patients underwent preoperative examination, including corneal topo-and tomography, aberrometry, and confocal microscopy. All patients received a femtosecond LASIK with the Ziemer LDV Z8, a refractive treatment with the AquariuZ solid-state ablation laser, and were then followed up for a period of up to 12 months. The applied aspheric optimized profiles did not induce higher-order aberrations nor spherical aberration in any of these operated subjects. No eye lost BCVA lines throughout the duration of the follow-up. Six months after surgery, the safety index of patient 1 was 5, and for patients 2 and 3, it equaled 1. Confocal laser microscopy imaging findings were comparable to those seen typically for excimer lasers. The obtained results are encouraging and confirm that the new solid-state laser system is safe.

Corneal absorption spectra in the deep UV range

SIGNIFICANCE

Refractive surgery in ophthalmology uses pulsed lasers at 193, 210, or 213 nm. The reason is that most molecular constituents of cornea absorb strongly in this wavelength range. Precise refractive surgery via ablation requires an accurate knowledge of the absorption coefficient at the relevant wavelengths. Yet, the absorption coefficients of corneal tissue reported in literature vary by almost an order of magnitude; moreover, they were measured mostly at the wavelengths mentioned earlier.

AIM

By measuring the corneal absorption coefficient of intact eyeballs stored at different environmental conditions, prepared by following different procedures, and as a function of postmortem time, we determine the absorption coefficient for the entire wavelength range between 185 and 250 nm for as close as possible to in-vivo conditions.

APPROACH

We use a specially designed UV ellipsometer to measure refractive index and absorption coefficient. Specifically, we investigate the temporal evolution of refractive index and absorption coefficient after enucleation of the eyeballs under different environmental conditions and preparation procedures.

RESULTS

Our measurements provide accurate values for refractive index as well as absorption coefficient of cornea in the wavelength range between 185 and 250 nm. We find that the absorption coefficient decreases with time and that neither storage conditions nor preparation procedures but a continuous degeneration of the cornea is responsible for the observed time evolution. We use the measured time evolution to extrapolate refractive index and absorption coefficient to in-vivo conditions.

CONCLUSION

Our measurements of the close to in-vivo absorption coefficient of cornea between 185 and 250 nm allow for a better understanding and modeling of refractive cornea surgery, also at other than the three commonly used wavelengths. In the future, this may be relevant when new pulsed laser sources with other wavelengths become available.

Orcein and Litmus

Orcein was separated into 14 dyes by partition chromatography. Their constitutions were determined mainly by spectroscopy and led to formulae that are derived from 7-amino-2-phenoxazone, 7-hydroxy-2-phenoxazone, and 7-amino-2-phenoxazime, and that were confirmed by syntheses. The major constituent of litmus is assembled polymerically from 7-hydroxy-2-phenoxazone chromophores. The mechanism of formation is elucidated.