|Year : 1966 | Volume
| Issue : 6 | Page : 233-238
Research and development in ophthalmology
Roland I Pritkin
|Date of Web Publication||17-Jan-2008|
Roland I Pritkin
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Pritkin RI. Research and development in ophthalmology. Indian J Ophthalmol 1966;14:233-8
Of recent years in the never ending battle against blindness, a number of new ideas have been developed for more accurate diagnosis and more efficient treatment in ophthalmic conditions.
Here we shall deal with photocoagulation, intravenous fluorescein in fundus photography of the eye, radioisotopes, electronic devices to enable the blind to decipher reading matter, alpha-chymotrypsin and methods of preserving corneal grafts.
With some of these, new ocular hazards have been introduced, the study of which also constitutes part of research.
| Photocoagulation|| |
The large photocoagulator using a xenon bulb, with the transmission of heat by a series of lenses and prisms will be replaced by a much smaller unit which will have the xenon bulb heat condensed into a beam through a lightweight laser. A hand held, direct view laser photocoagulator is in the process of development. This will make the treatment for the prevention of impending retinal detachment and for sealing small tears and holes a far simpler procedure. Each lesion of the coagulation is accomplished in less than a milli second.
The laser produces a pulse of light energy which is delivered to the eye by being focussed by the lens of the patient's eye to produce a minute coagulation. The retina is "welded" to the choroid by a series of these coagulations through repeated pulses from the laser.
The instrument consists of two interconnected units, the hand held laser head and the power supply. A light source within the head projects a set of crosshairs onto the retina. These crosshairs are exactly aligned with the path of the laser beam and make precision aiming of the device quite simple. When the physician has selected the region of the retina to be coagulated, a trigger is pressed and the power source delivers a surge of electrical current into the xenon flash lamps in the head to activate a precision ruby rod. The laser pulse is generated within the ruby; it passes through an optical system in the head and is reflected into the patient's eye to perform the coagulation.
| Intravenous Fluorescein|| |
Intravenous fluorescein is being used with fundus photography of the eye. As soon as the fluorescein is injected into the vein, it courses through the choroidal blood vessels of the eye. Improved retinal cameras are used to photograph the character of the blood vessels, and if any obstruction is noted, it can be seen and photographed. A 10 cc ampoule containing 5% fluorescein solution is injected into an antecubital vein, and photography must be performed immediately afterwards. In subjects with normal circulation fluorescence appears in the central retinal artery about 8 to 10 seconds after injection of the dye into the vein. Within 1 to 2 seconds after appearance in the central retinal artery, fluorescence is usually seen in most of the retinal arteries, usually appearing first in vessels supplying the macula. Immediately after the arterial phase, fluorescence develops in the retinal background. Venous fluorescence seems to appear first in veins draining the macular area. In diabetic retinopathy more microaneurysmss are visible by this technique than by routine retinal photography. Flameshaped hemorrhages and hard exudates usually do not fluoresce. Cotton wool lesions retain the fluorescence after the rest of the retinal structures are cleared of the dye, in many cases for several hours. This fluorescein method is also of use in determining whether a vascular lesion is actually a retinal hemorrage or might be just a continuity of the vascular system, filling during the later arteriolar phase and sometimes appearing as a microaneurysm except for the short duration of the fluorescence.
| Tonometry|| |
It has been noted that gyycerine taken by mouth will decrease the intraocular pressure. Applanation tonometry is proving more accurate in the measurement of intraocular pressure than the conventional footplate types of tonometers developed during the past 80 years.
The discrepancies in the determination of physiological limits of intraocular pressure if done with the footplate tonometers, may be partially due to the differences in the tonometers used and partially due to the fact that the tonometric readings obtained were transformed into millimeters of mercury with the use of different tables. A comparison of the data concerning the precision of applanation tonometers and the stability of physiological limits of normal intraocular pressure found with their use-with corresponding data obtained by the use of the footplate tonometers demonstrates the advantages of applanation tonometers. In recent years many authors working in the field of glaucoma began to realise the necessity of using applanation tonometry as a more precise method. Goldmann, who took an interest in the problem of tonometric determination of true intraocular pressure (P 0 ) was convinced of the impossibility of receiving exact data of (P 0 ) with the use of the footplate tonometer, and resorted to applanation tonometry. The applanation tomometer proposed by Goldmann is a glass plate connected with a sensitive dynamometer with the help of which pressure is exerted on the cornea so that the diameter of the applanation circle is 3.06 mm. The diameter of the applanation circle is controlled with a slit lamp and the tonometer proper is mounted on the slit lamp. With the use of Goldmann's applanation tonometer a true intraocular pressure can be determined much more exactly than with the use of a footplate tonometer. It has been suggested that the Goldmann tonometer be used for the determination of the eye rigidity, and that these measurements should be performed as follows: Of the two tonometric characteristics necessary for these determinations it was suggested to take the readings obtained with the use of Goldmann's applanation tonometer as the first one, and the data of tonometric examination with the footplate tonometer as the second one. On the basis of the difference of the two tonometric characteristics of the intraocular pressures, the rigidity of the eye examined is calculated. It is quite evident that this recommendation is not entirely right because the principal differences between the applanation and impression tonometers have not been demonstrated. Due to this difference, it is inaxact to correlate results obtained by these methods for computing data on the exact state of eye rigidity.
The habit of using impression tonometry in the prone position and applanation tonometry in the erect position may also be a factor. However, Goldmann has made some studies with the applanation tonometer, having the patient lie down, and has found them to be no different, with this instrument, than when the patient is in the erect position.
| Radioisotopes|| |
Radioisotopes are undergoing a period of development in which their side effects are becoming better known.
Radiation or surgery in lid tumors has created a controversy. All are agreed that treatment of corneal tumors by radiation may damage the cornea further, and produce a cataract if an exceptionally large amount of radiation is used. If lid tumors show a recurrence, the treatment should be changed to surgery. The concept of radiation injury is not new, however. Sunlight is an example. Man has known about sunlight for a long time. He has known about the effects of fire. However, there is no sensory warning for x-ray and. radium. Manmade detecting devices must be used to help in this matter. Radiation damage is not immediate as it is with fire or sunlight. Radium and nuclear reactors, and cyclotrons which are sources of radiation can cause harm from a distance. Germs cannot do that. They must enter the body. Sunlight may cause harm from a distance, but its effects at the time that it is being received are known to the senses.
The characteristics of radiation hazards are the following: They are not perceived by the senses and there is a delayed effect. They may originate in or out of the body, and may penetrate thick solid material. The permissible dose is the main criterion in the measurement of safety, and there are three factors over which one has control. These are distance, time, and shielding. Distance follows the law of the inverse square. Time has maximum safe time as the basis, and shielding attenuates the radioactive power of a substance. To understand the industrial hazards of radiation, the constituents of matter must be understood.
From the standpoint of the biological effect of neutrons upon the human organism, two actions are important. These are the processes of absorption and scattering. A. stable isotope becomes radioactive on exposure to thermal neutrons. Since neutrons and hydrogen nuclei are of the same mass, the result of an elastic collision between two such particles will be the loss of roughly half of the neutron energy. Radioactive isotopes may disintegrate by several methods. Ionization is a method of interaction of radiation with matter. In this method, a neutral atom splits into positive and negative parts. Matter in the solid, liquid or gas state, can be ionized by charged particles provided they possess sufficient energy to eject electrons from the particular atom or molecule under consideration. Biological damage due to radiation is a consequence of ionization in the body tissue.
Three types of interaction between photons and matter occur; (1) Photoelectric effect, (2) scattering, and this has two varieties, the Compton type and the coherent type, (3) Pair production. In the photoelectric process, all of the energy of the photon is transferred to an orbital electron of an atom. Scattering has two varieties. The Compton type, in which the photon may collide with an electron and impart part of its energy to it, and the coherent type where the photon bounces off the atom or molecule, changing direction without losing energy.
In determining the unit of measurement to solve the problem of endangered health due to particle accelerator such as an x-ray machine or a radioactive isotope laboratory, the following must be considered: (1) For alpha and low beta radiation, the damage would be mainly to the skin. (2) Higher energy beta and gamma would produce a larger dose in the deeper layers of tissue. (3) A roentgen equals 83 ergs absorbed per gram of air. (4) In soft tissue, the amount of energy absorbed per gram is approximately the same as air. (5) Units of measurement based on time are roentgens per minute and milli-roentgens per hour.
A person exposed to infra-red light from a furnace may develop glassblower's cataract with posterior cortical opacity. Later the anterior lamella of the lens comes off and dangles in the anterior chamber. In this type of cataract, the site of damage is not determined by the tissue with greatest absorption, but by the point of greatest intensity of radiation. This is in the lens, when the source is a large surface such as the molten glass in a furnace. One actual hazard of visible and infra-red light is eclipse watching. Steady fixation can cause a hole in the macula where the head is concentrated on such a small area that it is destroyed. This hazard does not occur except during an eclipse, because ordinarily when the full disc of the sun is seen there is so much light entering the eye that it is unable to tolerate the intense light and the lid closes almost involuntarily.
Whenever the cornea is exposed to a welding light the individual may get an actinic keratitis, or flash burn. of the cornea. It is not necessary to look at the light from a welding arc to receive its deleterious effect. A man working with a furnace must protect his eyes from infra-red radiation and should wear protective goggles in the same way that the welder does. An overdose of x-rays, therapeutic ultra-violet, micro-wave diathermy and radar can do damage to the eye. The effects of electromagnetic radiation upon the eye and its variations of pathologic disease caused by each band of radiation and the effects on the retina must not be taken lightly.
| Alpha-Chymotrypsin|| |
The use of alpha-chymotrypsin has been further developed to make lens removal in cataract extraction much easier. Whereas in an ordinary forceps extraction 10% pull with the forceps and 90% push with the lens hook is exerted, the process is reversed when alpha-chymotrypsin solution is injected over the lens in a cataract extraction.
| Electronic AIDS for the Blind|| |
An electronic pencil has been developed for reading any book printed in the Roman alphabet. This has enabled blind persons to read books other than those printed in Braille. Subsequently an electronic pencil was developed for the Cyrillic alphabet. This makes it possible to train blind persons to translate scientific articles or books from Russian into English, and has added a new occupation for the blind. The American Foundation for the Blind is presently searching for added vocations for the blind, particularly those with additional sensory, physical or mental handicaps.
For several decades the imagination of investigators has been kindled by the idea of enabling blind people to read any textbook, not only those printed in Braille. An attempt had been made to enable the blind to read printed matter by deriving photoelectric signals from the text to be read and translating them into audible output. Reading machines based on this concept can be divided into two categories: the direct translation machines and the recognition machines. In the direct translation machines a standing head or probe which contains photoelectric elements behind a vertical slit is moved over the typed or printed line. Whenever a portion of the letter appears within the slit an audible signal is produced, the pitch of which depends upon the location of that letter portion within the slit. If several portions of a letter appear simultaneously within the slit, a composite signal is sounded. The reading speed of these machines is limited by the fact that most letters produce not one, but a sequence of composite signals which tend to merge into a buzzing sound and to lose their identity beyond the speed of about forty words per minute. This fact restricts severely the usefulness of these machines which would otherwise be quite desirable because of their simplicity, small size, and moderate cost.
In the type of machine called the recognition machine the scanning process is such that as a result the identity of each letter is established. This scanning result is then used to sound off pre-recorded phonetic equivalents of these letters in an effort to produce an output close to English. Since in the English language the relationship between a letter symbol and its phonetic equivalent often depends on the context, close approximation of English in such machine represents a very complex problem. Thus, while the reading speed of such machines could be made quite satisfactory, they arc quite complex. The direct translation machine and the recognition machine, therefore, had to be exploited to the extreme to finally develop an integrated direct translation machine, and this is the machine that has finally been developed, but it is believed that it can be improved still further.
| Recent Advances in Cornea Surgery|| |
Some recent advances which facilitate corneal surgery include.
(a) An improved automatic corneal trephine.
(b) Refinements in the use of an operation telescope and microscope.
(c) A simplified method for preserving donor eyes for use in lamellar corneal transplantation.
(d) A sterile kit for the long term preservation of donor eyes.
There are currently four techniques for the preservation of donor corneas: (1) freezing, (2) dessication, (3) dehydration, (4) use of polyvinylpyrrolidone combined With freezing. A small glass is now available into which has been fitted expanded styrene containing 1.5 gm. of molecular sieve and 11 cc. of anhydrous glycerine. The cornea with a rim of sclera is immersed and hermetically sealed in this vial, which has been sterilized by dry heat. Donor material may then be preserved for an indefinite period of time at room temperature. When the cornea is ready to be used for lamellar grafting it is removed from the glass container and placed in an antibiotic solution for reconstitution or rehydration.
Most artificial cornea studies prior to 15 years ago were concentrated on full thickness plastic implants that had the appearance of collar buttons. These implants were eventually extruded like any other foreign body. It was found that to keep implants in the cornea indefinitely, it must lie as deeply as possible in an intra-lamellar stromal pocket, and have wide skirt-like appendages. This is a more hopeful type.
| Summary|| |
The large photo-coagulator will be replaced by a much smaller laser unit for heat transmission from the xenon bulb, making sealing of retinal tears an easier process.
Intravenous fluorescein is being used with fundus photography of the eye.
Applanation tonometry is proving more accurate in the measurement of intraocular pressure than the conventional footplate types of tonometers.
Radioisotopes are undergoing a period of development in which their side effects are becoming better known. Radiation or surgery in lid tumors has created a controversy.
The side effects of radioisotopes are becoming better known.
Treatment of corneal tumors by radiation may damage the cornea further and produce a cataract. If lid tumors show a recurrence, the treatment should be changed to surgery.
The field for reading by blind persons has been increased by devising electronic pencils with the help of which Roman and Cyrillic alphabets can be "read". Books from other languages can thus be translated into English.
New methods for preservation of cornea for lamellar surgery are presented.