Sylwia Kwasniewska

Morphology of the Trabecular Meshwork within Monkey (Macaca Speciosa) Eyes after Irradiation with the Free-running Nd:YAG Laser

The long-term tissue response of monkey eyes to trabeculoplasty produced at the chamber angle by neodymium:YAG (Nd:YAG) laser (thermal mode) was investigated. Four weeks after irradiation, a monolayer of corneal-like endothelial cells extended over the trabeculum in impact zones, with partial occlusion of intertrabecular spaces; this condition persisted at all subsequent stages of observation (viz, up to 13 weeks). Both primary and secondary degeneration of trabecular endothelial cells occurred predominantly at the posterior border of the juxtacanalicular tissue, and continued throughout the observation period. Lysis and degradation of collagen fibrils were also prominent in this region, and collagen-phagocytosing cells could be seen at all stages. Although activated fibroblasts were marked in this zone, regeneration processes were, in general, less marked than those of degeneration. The significance of these findings in relation to the mechanism by which trabeculoplasty works is discussed.

The effect of transscleral laser cyclophotocoagulation on rabbit ciliary body vascularization

Long-term changes in the vascular network of rabbit ciliary processes induced by Nd:YAG laser cyclophotocoagulation were examined both from a morphological viewpoint and with respect to three-dimensional organization (in vascular casts). Relative changes in intraocular pressure (IOP), monitored within eyes irradiated across one-quarter, one-half, three-quarters, or all of the ciliary body circumference, are discussed in relation to morphological changes. The clinical implications of these findings are considered.

Transpupillar laser phototherapy for retinal and choroidal tumors: a rational approach.

Abstract Background: The physical laws are considered that need to be taken into account for optimal photothermal treatment of solid and vascular tumors, as well as other vascular anomalies of various etiology of the retina and choroid. Optimal irradiation therapy should take into account the distribution of both radiant and thermal energy in tumors, such as retinoblastomas, malignant melanomas and vascular malformations. Strict confinement of the extent of photothermal damage is critical since such pathological entities are frequently located close to the macula or optic nerve head. Methods: A formal treatment of the optical quantities related to these requirements is presented. In this analysis we emphasize the following topics: Arrhenius’ law, the kinetics of protein denaturation, the electromagnetic radiation field, wavelength, laser pulse duration (exposure time), optical properties of tissue, photocoagulation and thermotherapy. Results: Generally, the conditions are best fulfilled when using radiation in the near-infrared range of the electromagnetic spectrum, such as that emitted from the diode (810 nm) and Nd:YAG (1064 nm) laser, because of the good optical penetration properties of this radiation in tissue. The xenon arc lamp was a very effective and particularly appropriate energy source for such purposes, and its withdrawal from the world market may have been untimely. Short wavelength sources of radiation, such as the argon ion (488, 514 nm) or the frequency-doubled Nd:YAG (532 nm) laser, are unsuitable for the irradiation of large vascular structures, as they have poor penetration depths. However, for vascular formations with a short path length (1 mm or less), short wavelength sources appear to be the most appropriate choice. Optical coupling of radiant energy to the eye by means of indirect ophthalmoscopic systems or contact lenses to the eye is crucial. Strong positive lenses may lead to severe constriction of the laser beam which leads to high irradiance within the anterior segment, increasing the chances of it being damaged; with negative contact lenses, such as the –64 D Goldmann type, this danger is reduced. Conclusions: Photothermotherapy is not without risk unless the temperature field can be well adapted to the tumorous structure, as temperature elevations outside a small therapeutic range that affect vital structures are considered to be a risk factor.

Lasers, optical systems and safety in ophthalmology: a review.

This is a review of optical methods related to biomicroscopy and laser treatment of the posterior segment of the eye. Contact lenses can be used to observe optical structures and couple laser radiation into the eye for a vast range of conditions and techniques. A small laser spot size is indispensable for photodisruptive work, though this requires a large beam diameter at the pupil and therefore optical systems and techniques such as scleral indentation which maximize the pupillary beam diameter are preferred. For coagulation work the choice of beam focusing optics is crucial for optimum safety. Vitreous replacement can be used to change the refractive power of the eye and permit new combinations of treatment and optical systems. This review covers many aspects of laser irradiation of the eye. It should be clear that, with the multitude of different procedures and optical systems involved, the laser surgeon is faced with a daunting task in assessing and meeting safety limits.

Laser vitreolysis: A review

Strands and vitreous adhesion bands can either be dissected noninvasively, transpupillarily by photodisruptive pulses of a Nd:YAG laser, operated in the photodisruptive mode, or invasively using an Er:YAG laser and specialized fibers. The previously used CO2, Ho:YAG, and ultraviolet lasers have become less popular in the recent past. When using the transpupillary method, specialized contact lenses are required. Noninvasive methods avoid the risks incurred with invasive methods, but they require specialized knowledge, which is not available usually in vitreoretinal services. The invasive laser method provides a number of advantages typical of laser-tissue interaction. Advances in electrosurgical methods have opened the door to a new class of miniaturized electrosurgical equipment with which tissue dissection is made possible by plasma due to dielectrical breakdown which allows the pulse energy to be reduced to a very low level, resulting in a highly localized tissue effect. None of these methods has yet been considered for clinical use, mainly because the presently used mechanical methods are thought to be optimal by the majority of vitreoretinal surgeons.

The mechanism of aqueous outflow following trabeculectomy. A light and electron microscopic study.

The morphological effects of trabeculectomy, performed as therapy for a case of chronic simple glaucoma, are described in the two eyes of a patient ten and thirteen months after treatment. Ten months after surgery, a transscleral channel, extending from the position formerly occupied by Schlemms canal to the conjunctiva, is found. This channel is formed from a network of extended fibroblasts and loosely-packed collagenous tissue, and a large number of vessels, including both dilated blood capillaries and lymphatic vessels, develop within it. The sclera and subconjunctiva react differently to the presence of the nylon sutures. The findings support the hypothesis that the formation of an intrascleral outflow route stimulated by surgical intervention plays an important role in lowering IOP after trabeculectomy.

Cyclophotocoagulation in glaucoma therapy.

In a morphological study, the long-term effects of transscleral cyclophotocoagulation on rabbits using the free-running Nd: YAG laser with either a contact or a non-contact delivery system are described. A marked atrophy of the irradiated ciliary processes may be observed. Regeneration of the ciliary epithelial layers is incomplete at least up to 8 months after treatment. The vasucular network is also astrophic, and shows a small regenerative capacity only.

Optical Principles Related to Optimizing Sclerostomy Procedures

A simple probe, consisting of a 200-micrometer uncladded silica optical fiber, advanced from a protecting 22-gauge hypodermic needle, was used to create sclerostomy fistulas both ab interno and ab externo by means of a combined radiation/mechanical effect. Perforation was achieved by exerting gentle forward pressure on the fiber in synchrony with the delivery of radiation pulses. An irradiation protocol suitable for producing such canals in cadaver porcine eyes was delineated using Ho:YAG, Nd:YAG, and diode laser energy sources. Despite significant differences in the pulse energy required for perforation (0.25, 7, and 8 J for the Ho:YAG, diode, and Nd:YAG lasers, respectively), the extent of collateral damage was comparable for each type of laser. The physical mechanisms underlying these findings are discussed.

New Contact Lens for Observation and Coagulation of the Retina and Choroid

The optical performance of a new contact lens for observation and irradiation of the retina and choroid represents a compromise between Goldmanns contact lens and a wide-angle system in regard to magnification, resolution, and size of the field of view.

Transscleral Iridotomy Using a Neodymium: YAG Laser Operated Both With Standard Equipment and an Optical Fiber System - A Preliminary Report: Part II - Light and Electron Microscopic Findings

We report the morphology of transscleral iridotomies applied to human cadaver eyes using a free-running Nd:YAG laser (pulse duration: 20 ms, pulse energy: 1.5-6 J) with and without a fiber optic system. The pigment epithelium, which represents the barrier to the aqueous humor for passing through the iris, is damaged and blasted away over great areas. The mesothelial layer at the anterior surface of the iris is also broken up by the laser beam. Using low pulse energies, the iris stroma is only partially damaged. The destruction of the iris is caused by generation of heat due to absorption of radiated energy.