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Biomedical subjects

M M Pankratov

Publications and source records attributed to M M Pankratov.

30 records · Page 2Linked to original sources
PubMed1992

Transtympanic endoscopy of the middle ear.

Modern optical technology has made available fiberoptic and rigid endoscopes with diameters of 2 mm and less with acceptable resolution. Endoscopes of small caliber were introduced through a strategically placed myringotomy or an existing perforation to perform exploration of the middle ear as an in-the-office procedure. This technique is now routinely used as an adjunct in the diagnostic evaluation of patients with suspected middle ear conditions. Exploratory surgery of the middle ear may be avoided or definitive procedures may be planned better based on endoscopic findings.

Adolescent↗
PubMed1992

Evaluation of perilymphatic fistulas by middle ear endoscopy.

Transtympanic endoscopy provides a unique opportunity to view the undisturbed contents of the middle ear. Fiberoptic and rigid endoscopes have been used for thorough examination of the middle ear without the need for local anesthetics or surgical trauma. Endoscopy is now routinely used in the evaluation of a perilymphatic fistula and the patient is awake during an intermittent forceful Valsalva maneuver. Oval and round windows in both ears of five cats were studied endoscopically to evaluate surgically created fistulas. Excellent visualization of the defect was obtained in all instances. Endoscopy is a useful office technique for the evaluation of perilymphatic fistula. It reduces the need for surgical exploration and provides a satisfactory examination of the middle ear. Obliteration of the window niche can even be performed through the myringotomy using autologous blood.

Adult↗
PubMed1991

Holmium: yttrium aluminum garnet laser-assisted endoscopic sinus surgery: laboratory experience.

Endoscopic sinus surgery has gained wide acceptance since its introduction into the United States. Complex sinus anatomy and troublesome bleeding have been associated with complications, which vary in severity from synechia to blindness and leakage of cerebrospinal fluid. Endoscopic sinus surgery using a holmium: yttrium aluminum garnet pulsed solid-state laser oscillating at 2.1 microns with fiberoptic delivery was performed in the laboratory, and the results were compared with those of conventional endoscopic sinus surgery. Three beagle dogs, six human cadaver heads, and one calf head were used in the in vivo and in vitro studies to evaluate the bone ablation, tissue coagulation, and hemostatic properties of the holmium: yttrium aluminum garnet laser. Modified endoscopic telescopes for sinus surgery, a newly developed handpiece for fiberoptic delivery, and other surgical instruments were used. The results indicate that the holmium: yttrium aluminum garnet laser and new delivery instrumentation provide good hemostasis and controlled soft-tissue ablation and bone removal. The access to all sinuses in the human cadaver model was very good. The canine in vivo study showed delayed but complete healing on the laser-treated side. Clinical evaluation of the holmium: yttrium aluminum garnet laser is warranted to increase the precision and safety of endoscopic sinus surgery.

Animals↗
PubMed1990

Application of pulsed and continuous wave 1.32 and 1.06 microns wavelengths of the Nd:YAG laser in the canine tracheobronchial tree: a comparative study.

Previous investigations have shown good clinical potential for the use of the 1.32 microns wavelength Nd:YAG laser because its soft tissue absorption is better than that of the 1.06 microns wavelength Nd:YAG laser. The 1.32 microns wavelength Nd:YAG laser has an absorption coefficient in water that is 10 times higher than the 1.06 microns wavelength Nd:YAG laser. A comparative in vivo study of laser soft tissue effects was performed by using the 1.32 microns wavelength and the 1.06 microns wavelength Nd:YAG lasers in a pulsed wave (PW) mode and continuous wave (CW) mode using a non-contact endoscopic delivery system. A standard 5 mm mucosal lesion was made in the canine tracheobronchial tree down to the level of the perichondrium. Soft tissue and cartilage effects were examined by light and scanning electron microscopy, acutely, 1 week and 2 weeks after operation, and a comparison was made between the different laser modalities. To create similar lesions, higher energy was required when using the 1.06 microns wavelength Nd:YAG laser. Soft tissue injury was greater with the 1.06 microns wavelength in CW mode, and no cartilage damage occurred in the PW mode. Soft tissue and cartilage repair after 1 and 2 weeks was better with the 1.32 microns wavelength laser. In comparison, the CO2 laser and the contact Nd:YAG laser proved to be more precise cutting tools than the 1.32 microns wavelength or the 1.06 microns wavelength Nd:YAG lasers. Both Nd:YAG laser wavelengths were useful for coagulation and vaporization of tissues and blood vessels. More studies are needed to determine the effect of the new 1.32 microns wavelengths on endotracheal tumors.

Animals↗
PubMed1988

[A universal laser for intraocular treatment].

The creation of a single apparatus incorporating the different lasers applicable to intraocular pathology derives from the idea of possessing the means, with one device, of objectively comparing the effects and parameters of various lasers in order to pursue a more precise line of treatment. This has led to our fabrication of the universal intraocular laser. The word universal means the ability of the machine to act on each kind of intraocular tissues with all of the various infrared or other-colored radiations, as well as with different modalities. The unit is transportable. It only requires a source of electric power (110 or 220 V) and includes an independent cooling system. The Nd: YAG laser has selectable operating parameters: pulsed or continuous excitation, Q-switched or mode-locked mode, mirror or fiber optic transmission. It is used also as the basic system of the coloured module. The colour module can provide the three clinically useful radiations: green, red, yellow. The green (532 nm) is obtained by transmission of the I.R. beam brought a birefringent crystal (KTP). Red (650 nm) and yellow (575 nm) come from two incorporated dye lasers excited by the green radiation.

Equipment Design↗
PubMed1987

A step-zoom probe for laser endophotocoagulation: I. Design.

A step-zoom probe for laser endophotocoagulation of the eye has been developed, using fiber optics and a gradient index (GRIN) rod lens. It provides the operator with five or more focused spots ranging in size from 50 to 500 microns, and the spot size on the target is independent of the media filling the vitreous cavity, i.e., fluid or air. Each spot is located at the waist of the beam and therefore can be easily placed on the target, reducing the potential for overtreatment. A prototype model is currently undergoing animal testing.

Animals↗
PubMed1985

Calculation of an IOL from the wide-angle optical model of the eye.

Currently used paraxial formulas for calculating the power of an intraocular lens (IOL) ignore the pupillary aperture of the eye (3.5 mm) and assume that the locations of the principal planes of the crystalline lens and cornea are known. For calculating IOL performance, only the axial point in the field is considered. The eccentricity of the ocular optical system and the probable error in the IOL centering are also ignored. The use of a wide-angle optical model of the aphakic eye for computation of the IOL would result in values that approach more closely those in the real eye. The performance of the implanted IOL could then be calculated in conditions that are much closer to reality. To obtain information on the precision required in preoperative measurement of the asphericity of the cornea, we have studied the effect of corneal asphericity on IOL performance.

Cornea↗
PubMed1984

An optimized zoom ophthalmoscope.

An indirect ophthalmoscope that could provide higher magnification (up to 15X) would offer definite advantages in fundus diagnosis. If it could also supply an erect fundus image, it could advantageously replace the surgical microscope in vitrectomy operations. The surgical microscope requires the use of a contact lens, which restricts the surgical techniques and may damage the corneal epithelium, and it reduces image brightness when the magnification is increased. In contrast, an indirect ophthalmoscope does not require a contact lens and keeps the image brightness constant regardless of magnification. Increased magnification can be obtained in an indirect ophthalmoscope by incorporating telescopes in the ophthalmoscope oculars. The possible use of two telescopic systems, Keplerian and Galilean, and the problems of stereopsis and image inversion are discussed. A new, optimized ophthalmoscope is described, with Keplerian telescopes, that provides a range of magnifications from 2X to 15X as well as options for an erect or inverted fundus image.

Humans↗
PubMed1984

Automation in krypton laser photocoagulation.

Histologic study of lesions produced by krypton red (647.1 nm) and krypton yellow (568.2 nm) laser lights reported here suggests advantages in alternating these two wavelengths in photocoagulation. Selection of the best wavelength to be used in a given location on the retina should result from pre-determined absorbance conditions in that location. The feasibility of the relative measurement of absorbance in different fundus locations by measurement of the relative reflectance is discussed. Instrumentation for these measurements and for switching from one wavelength to the other is described. Instrumentation for the possible expansion of krypton laser applications to clinical problems in the anterior segment also is suggested.

Animals↗
PubMed1983

Astigmatism of oblique incidence in the human model eye.

Two cylindrical lenses of equal power, one positive and one negative, were used to correct astigmatism of oblique incidence in a wide-angle optical model of the human eye. Tangential and sagittal vergences were calculated at different visual angles from the posterior pole to the peripheral retina. The positive cylinder was placed with its axis parallel to the tangential meridian while the negative cylinder was placed with its axis parallel to the sagittal meridian. Improvement in the quality of the retinal image at different angles of incidence was obtained by varying the angle between the axes of the correcting cylinders. Corresponding gains in resolution have been calculated and confirmed by peripheral fundus photography.

Astigmatism↗