Conclusion and Summary



A number of substances were tested against Ps. pyocyanea (Ps. œruginosa) and their bactericidal concentration determined.



The quaternary ammonium compounds, although bactericidal, are not recommended because of their effect on the cornea.



The mercurial compounds:—thiomersalate 0·005 per cent, and phenylmercuric acetate and nitrate 0·005 per cent., are safe, and are recommended for eserine and sodium fluorescein, which are the most liable to pyocyanea contamination, also for methylcellulose eye-drops, which are liable to contamination by moulds. These compounds are not only powerful bactericides but are also fungicides. Chlorbutol in saturated solution (about 0·8 per cent.) is safe and recommended, but owing to the fact that the solution cannot be heated without detriment to the preservative its use needs great care. Chlorcresol 0·1 per cent, is safe, but in that concentration it causes smarting, and 0·03 per cent, kills pyocyanea within 24 hours. The p-hydroxybenzoates in 0·1 per cent, solution are reliable for most of the eye-drops used except fluorescein. Phenylethyl alcohol is safe in 0·5 per cent, concentration but much quicker in its action at 0·6 per cent., and further clinical trials are needed with this promising preservative.



For cortisone eye-drops 0·9 per cent, of benzyl alcohol, the one used in the original solution, is recommended.



Eye-drops used in hospital wards, outpatient departments and factory medical rooms, should be prepared with bactericidal preservatives, but for eye-drops used by individual patients, a bacteriostatic agent may be permissible. However, for reasons of safety and to make it as foolproof as possible a uniform procedure using a bactericidal preservative is recommended.



Up to now the National Formulary has recommended the use of bacteriostatic agents only. In view of the increasing incidence of eye infections reported by different authorities from many parts of the world, more stringent standards seem desirable.

On the maintenance of sterility in eye-drops.

The study of the pharmacological problems of ophthalmology is a relatively neglected chapter in this specialty. The present paper is an attempt to summarize the results of recent research in the field of ophthalmo-pharmacology. The therapeutic effect of many ophthalmic drugs depends partly or entirely upon their ability to permeate the coats of the eyeball. The conditions which determine a qualitative and quantitative passage of such drugs is the problem of the corneal permeability. Our knowledge of the problems of corneal permeability will improve with the application of the advances made in the allied sciences, especially in physical chemistry. In this actually confusing state of the problem, it seems to the writer that there are three outstanding experimental results. These results are the basis for further research which might bring a harmonious and complete understanding of the present problem, and thus improve the effectiveness of our pharmacological armamentarium.
 The ideal pH of collyria is supposed to be that of tears, namely close to 7–7.4. A considerable deviation of the pH value in ophthalmic solutions causes disturbances necessitating adjusting and buffering. The interest for the pratical application of buffers in collyria centered mainly around three buffer systems, that of Atkins and Pantin, Palitzsch's buffer and Sozirensen's phosphate buffer system. Each of these systems has advantages in buffering certain solutions and disadvantages in others. A thorough comparative study has not as yet been made. The principle of buffering ophthalmic solutions is not uniformly applicable, since the physiological effectiveness of various substances is greater at different pH levels. The ideal collyrium has a pH at which the maximum comfort is associated with the maximum effectiveness. Since each of these maxima is achieved at a different pH level of the solution in use, a compromise approximating midway between the two pH values will often be necessary in order to achieve the maximum comfort with the maximum effectiveness. Another character of a collyrium is its tonicity. Like the pH, the tonicity of the solution is also approximating adequacy if it is close to that of tears, and it was believed to be isosmotic with a 0.9 % sodium chloride solution. As most ophthalmic drugs are heterotonic at the required concentration in distilled water, their solutions require the addition of salts. To render a solution isotonic requires a complex calculation, which can be simplified by the use of Nicola's formula. Most ophthalmic solutions in use are readily contaminated by bacteria, yeasts, molds, and fungi. Therefore the addition of a preservative to collyria is indicated. The most adequate preservative as yet known is a combination of two parahydroxybenzoic acid esters, which secures a satisfactory stability of ophthalmic preparations. The penetration of many ophthalmic drugs can be enhanced by the use of surface active agents; so-called wetting agents or detergents. In many standard antiseptics the bactericidal activity is due in part to their wetting ability. Similarly, local anesthetics have wetting properties that favor the penetration of ophthalmic drugs. Research concerning the applicability of wetting agents in opthhalmic use is in an early stage, but the results are encouraging enough to justify further investigation. The problem of the contact lens fluid involves similar considerations as collyria generally, namely that of the chemical composition the pH, and the tonicity. Disturbances will arise if there is an inadequacy in the lens fluid. As yet there is no adequate lens fluid, and hence the wearing time of contact lenses isUmited. A new field of research for better contact lens fluids was opened by Obrig and Schaeffer by the investigation of the applicabil ity of amino acids in the solution used as the fluid lens. These experiments are in their primary stage. The absorption of the active ingredients from an ointment base depends on the chemical and physical characteristics of the base itself. The best utilization of drugs is obtained with a base in which fat is emulgated in water, and water forms the surface active phase, i. e. with an oil-water emulsion. The average regenerative activity of the corneal tissue is inhibited by local anesthetics. To stimulate “normal” corneal generation through local application, the writer investigated a combination of amino acids for their efficacy in accelerating proliferation. He found that the proliferating cells may utilize these amino acids in the synthesis of new protoplasm, thus stimulating cell neoformation. The rate of regeneration is highly accelerated by the local application of amino acids.

Some aspects of ocular pharmacology.

pupil was dilated a small coloboma of the lens was discovered. There appeared to be a small opacity in the lower part of the lens. The slit-lamp examination with the broad beam showed that the mass had the texture and colour of ordinary uveal tissue, and that there was no vascularization. It merged with the ciliary body without any abrupt edge, and had no irregularity of surface that might be present in a new growth. The vitreous was perfectly normal showing the usual filmns without any trace of infiltration with cells or larger particles. When examined with the narrow beam in optical section, it was seen that the white area seen by focal illumination on the surface of the mass was really a flocculent filamentous deposit on the back of the lens. It extended downwards and was lost in the region of the coloboma. The lens itself, except in the colobomatous area was perfectly clear, and showed the usual sutures and zones of discontinuity. I came to the conclusion that the mass was due to an abnormal development of the ciliary body in the lower sector of the eye, probably a fusion of several processes, and' that there could be no question of sarcomatous growth. Apart from the fact that the lens was obviously implicated in the abnormal picture, the absence of vascularization, the normal aspect of the vitreous, and the normal tension as estimated with the Schiotz tonometer, were evidence against tumour formation. Mrs. D. has now been under observation for six months and no change has taken place in the eye.

https://bjo.bmj.com/content/bjophthalmol/15/11/649.full.pdf

Conservation of eyedrops.

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Conservation of eyedrops.