Pascal Rol

Optical properties of miniaturized endoscopes for ophthalmic use

Endoscopes for use in ophthalmology can now be manufactured with overall intraocular diameters smaller than 0.89 mm. Endoscopes based on gradient-index lenses yield a higher resolution than those making use of ordered fiber bundles having the same diameter. Likewise, endoscopes with optical elements having a diameter of 0.50 mm yield a higher resolution than those with smaller diameter (0.35 mm). Thanks to the miniaturization, a working channel can also be integrated within the tube of the endoscope instead of being a part of the illumination bundle. This allows the design of new endoscopic devices including various surgical instruments. Preference is given to an endoscope with an integrated aspiration/irrigation system or with a fiber for laser therapy. The potential phototoxicity of these systems is briefly discussed.

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.

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.

Internal sclerostomy with the Er:YAG laser using a gradient-index (GRIN) endoscope.

BACKGROUND AND OBJECTIVEnTo show that sclerostomy, a glaucoma filtering surgery, can be performed using an Er:YAG laser. Scarring at the filtering site, a recurrent problem, may be reduced through proper positioning of the sclerostomy by using an intraocular endoscope.nnnMATERIALS AND METHODSnAb interno full-thickness sclerostomies were performed on eye bank eyes with an Er:YAG laser through a custom made optical delivery system. The intraocular laser probe consisted of a low OH silica fiber inserted in a metallic tapered sheathing. A rigid intraocular endoscope based on gradient-index lenses allowed visualization of the filtration site.nnnRESULTSnA clear view of the anterior chamber angle was obtained through the endoscope, allowing for precise location of the sclerostomy. Full-thickness sclerostomies could then be performed at the desired location. Histologic sections showed thermal necrosis less than 50 microm thick in tissue adjacent to the sclerostomy.nnnCONCLUSIONSnA sclerostomy performed with a combined procedure using an Er:YAG laser and intraocular endoscopy increases the speed of the procedure. The use of a high-resolution intraocular endoscope may increase the success rate of ab interno laser glaucoma surgeries.

Optical aids and their application

In this article, we are concerned only with some of the practical problems facing the ophthalmic laser surgeon

Integrated optical fiber systems — some theoretical aspects

SummaryThe specific advantages of a number of integrated optical systems, consisting of optical probes of various shapes and materials, coupled to a number of optical fibers are described. The radiation fields of the various systems vary significantly in their performance and the clinical effects may be expected to vary correspondingly. This is a step forward in the theoretical evaluation of optimal laser microsurgical tools for specific applications.

A New High-Power Biconcave Contact Lens for Observation and Coagulation of the Posterior Segment

A wide-angle, high-power negative contact lens was designed for observation and coagulation of the retina and choroid. The new contact lens has a lateral magnification of 0.44 and a field of view of 64 degrees. Due to the prismatic of its biconcave structure, the field of view may be shifted by tilting the lens, induced eye movements beyond the equator of the retina, or both. Because only a negative refractive surface is required, optical aberrations are significantly reduced. Safety during laser irradiation tasks is increased compared with the use of positive wide-angle contact lenses because the irradiance of the crystalline lens is significantly reduced.

Biconcave Contact Lenses: A Critical Analysis of Their Optical Properties

BACKGROUND AND OBJECTIVEnThe purpose of this experiment was to compare biconcave contact lenses with other contact lenses already used for observation and irradiation of the retina and choroid.nnnMATERIALS AND METHODSnThe optical performance of different biconcave lenses is described in terms of magnification, resolution, and field of view. The optical properties of the eye were taken into account using the Gullstrands model of the human eye.nnnRESULTSnThe performance of biconcave contact lenses represents a compromise between that of Goldmanns and wide angle indirect contact lenses. An upright image, with good peripheral image quality and an intermediate field of view is characteristic of such design. In addition, laser irradiation with large spot sizes is less hazardous when using such negative contact lenses compared to positive lenses of the same absolute refractive power.nnnCONCLUSIONSnBiconcave contact lenses qualify as a complement to planoconcave lenses for chorioretinal observation and irradiation tasks. For the same magnification factor, the field of view is smaller than that obtained with indirect contact lenses but the image degradation in the periphery of the retina is reduced.

Transscleral Iridotomy Using a Neodymium:YAG Laser Operated Both With Standard Equipment and an Optical Fiber System - A Preliminary Report: Part I - Optical System and Biomicroscopic Results

The effects upon the iris of radiation emitted by a Nd:YAG laser working in its thermal (free-running) mode and transmitted through the sclera were studied. The advantages and disadvantages of a fiber optic system, as compared to a conventional optical system, were studied using eight autopsy eyes. It was shown that the conventional optical system as well as a fiber optic system are both able to perforate the iris completely and to blast away or destroy the pigment epithelium. One merit of the fiber optic system as compared to the conventional system is that it requires considerably less energy for the same effect. This is partially because the sclera, when compressed, becomes more transparent and thus transmits a greater amount of laser energy.