G. Kounis

Corneal Hydration Monitored by Laser-induced Breakdown Spectroscopy

BACKGROUND Corneal hydration is an important factor in laser corneal ablation. In photorefractive keratectomy (PRK), corneal ablation rate and final ablation surface quality are strongly dependent on corneal hydration. We used a spectroscopic technique for monitoring corneal hydration during PRK. METHODS Hydroxyethlymethacrylate (HEMA) was employed for corneal hydration modeling. Hydrated HEMA samples were irradiated with a pulsed Nd:YAG laser (1064 nm, 10 mJ/pulse, pulse duration 15 nsec). Successive emission spectra corresponding to different degrees of hydration were recorded on a gated optical multichannel analyzer. The weight of the sample and hence its water content was monitored during the entire procedure with a sensitive balance. One rabbit and one human cornea were used to demonstrate the spectral analogy between the model and corneal tissue. RESULTS The most noticeable dependence on water content of the substrate was that of atomic emission lines of Ca at 393 nm and 396 nm. CONCLUSION Plasma emission spectra exhibited significant dependence on sample hydration. This dependence can be used for estimation of water content of irradiated model material and real cornea.

Tono-Pen XL tonometry during application of a suction ring in rabbits

BackgroundThe purpose of this study is to evaluate the use of Tono-Pen XL in measuring IOP during the application of a suction ring in rabbit eyes with manometrically controlled IOP.MethodsTono-Pen XL was calibrated against direct manometry in 10 rabbit eyes. A suction ring was then applied in 4 rabbit eyes and the IOP was determined manometrically during suction ring application at 350 mmHg vacuum pressure. Finally, in 6 catheterized rabbit eyes the IOP was measured with Tono-Pen XL during suction ring application at suction vacuum from 350 to 650 mmHg, while keeping actual IOP stable at 30 mmHg and 60 mmHg.ResultsLinear regression analysis revealed that the Tono-pen XL was reliable for IOPs between 10 and 70 mmHg (R2 = 0.9855). Direct manometry during suction ring application showed no statistically significant variation of Tono-Pen XL readings when the incanulation manometry intraocular pressure changed from 30 mmHg to 60 mmHg and no statistically significant correlation between suction vacuum and IOP measurements.ConclusionTono-Pen XL measurements are unreliable during the application of a suction ring on living rabbit eyes even when the actual IOP is forced to be within the validated range of Tono-Pen XL measurements. This inaccuracy is probably related to altered corneal and scleral geometry and stress.

Contact transcleral photodynamic cyclo-suppression in human eyes: a feasibility study

OBJECTIVE To evaluate the safety and efficacy of contact transcleral ciliary body photodynamic treatment (CB-PDT) with verteporfin in human eyes. DESIGN Prospective interventional case series. PARTICIPANTS Five glaucomatous blind eyes of 5 patients. METHODS Verteporfin (6 mg/m(2)) was infused in bolus and then the ciliary body was irradiated transclerally with a fibre optic device. Twelve spots were placed 360° and 0.5 mm behind the sclerocorneal limbus. Laser power was 80 mW and irradiation time was 3 minutes. RESULTS The average intraocular pressure reduction was 30% after the first month and remained below pre-treatment levels throughout a 3-month follow-up. No serious adverse events were reported. CONCLUSIONS CB-PDT for refractory glaucoma was safe and efficient in human eyes; larger studies are required to evaluate its possible clinical role.