Diagnosis of ocular herpes

Diagnosis of herpetic and metaherpetic keratitis in the absence of typical features of the clinical manifestation of the process is very difficult. In these cases, it is necessary to conduct laboratory tests. The most common method is cytological examination of the conjunctiva and the method of fluorescent antibodies, which are used in the diagnosis of viral conjunctivitis. In addition, with herpes, in addition to specific changes in the epithelial cells of the conjunctiva, lymphocytes, plasma cells and monocytes are found in the scraping. Despite the obvious practical importance of these laboratory diagnostic methods, they cannot always satisfy the ophthalmologist. Currently, an intradermal test with an antiherpetic vaccine has become increasingly used for diagnostic purposes.

The vaccine is a preparation obtained from strains of the herpes simplex virus types I and II, inactivated with formalin. The active principle of the vaccine is specific antigens of the virus. 0.05 ml of the herpes polyvaccine is injected into the skin of the inner surface of the forearm, and the same dose of the control antigen from uninfected material is injected into the skin of the other forearm. If after 24 hours the area of skin hyperemia arising in the zone of the herpes polyantigen injection is 5 mm larger than on the control side, the test should be considered positive.

There is also a focal allergic test with an antiherpetic vaccine proposed by A. A. Kasparov et al. (1980). It is indicated as a diagnostic etiologic test in patients with frequent relapses of conjunctivitis, keratitis, iridocyclitis and other clinical forms of ophthalmic herpes, with sluggish processes. The test is very important, due to the fact that it is assessed by the presence of an exacerbation of the inflammatory process in the eye (increased pericorneal injection, pain, the appearance of new infiltrates in the cornea, precipitates, newly formed vessels in the cornea and iris). These signs of an outbreak of the process require urgent active treatment measures in the form of increased desensitizing and specific antiviral therapy.

There are a number of contraindications to the test, which include an acute process in the eye, the presence of infectious and allergic diseases, diseases of the endocrine system, tuberculosis, and kidney diseases.

A focal test, which in some cases can also cause a general reaction, should be carried out only in a hospital setting. The test method involves injecting 0.05-0.1 ml of an antiherpetic vaccine into the skin of the forearm. If the above signs of exacerbation of the process in the eye are absent after 48 hours, the injection of the drug is repeated in the same dose after 1-2 days. The diagnostic value of the focal test is 28-60%, which apparently depends on the localization of the inflammatory process in the membranes of the eye. For the sake of objectivity, it should be noted that the test is considered positive not only in the case of an exacerbation of the inflammatory process, but also in the presence of an improvement in the condition of the eye, which is assessed by using a number of ophthalmological methods, from the biomicroscopy method to functional methods of examining the organ of vision. The most conclusive method of etiological diagnosis of herpetic keratitis is to conduct an experiment with grafting a rabbit's cornea or introducing material taken from a human's affected cornea into the brain of a mouse. The development of a clinical picture of herpetic keratitis in a rabbit or the development of encephalitis in a patient following the introduction of the material indicates a viral infection.

Significant difficulties are associated with the diagnosis of viral iridocyclitis occurring in isolation, without clinical symptoms from the cornea. The role of viral infection in the pathology of the vascular tract has not been sufficiently studied. It is believed that patients with herpetic iridocyclitis make up 17-25% of the total number of patients with iridocyclitis. The infectious agent can penetrate into the eye in two ways (from the outside through the corneal epithelium and then into the uveal tract and hematogenously). Young people and children are most often affected. In 17% of cases, iridocyclitis is bilateral and in 50% it recurs. The development of iridocyclitis is usually preceded by factors characteristic of ophthalmic herpes. These include fever, hypothermia, the appearance of herpetic eruptions on the skin and mucous membranes in various parts of the body. Iridocyclitis often occurs in the eye that has had herpetic keratitis in the past. Among the clinical manifestations of herpetic iridocyclitis, as with other types of iridocyclitis, acute and sluggish forms can be distinguished. The acute form is observed less often. It is characterized by sharp pain, pronounced injection of the eyeball of a mixed nature, fibrinous effusion in the anterior chamber of the eye. The sluggish clinical form, observed much more often, is characterized by mild pain or even its complete absence, insignificant injection of the eyeball. It is characterized by the appearance of centrally located large precipitates of a greasy type, fibrinous deposits on the posterior surface of the cornea, herpetic granulomas in the iris with subsequent tissue atrophy in the places of their localization. In this case, the iris in the affected areas becomes thin, discolored, acquiring a mottled (pockmarked) appearance.

When granulomas are localized in the pupillary margin area, stromal posterior synechiae occur. The pupil is resistant to the action of mydriatics. The process is accompanied by active fibrinous effusion into the vitreous body, development of pronounced opacities. With iridocyclitis, complicated cataracts and, which is quite typical, secondary increase in intraocular pressure may develop. with a decrease in the coefficient of ease of outflow of intraocular fluid and the appearance of gonioscopic changes. Quite often, iridocyclitis occurs with hypervascularization of the iris and recurrent hyphema. Practical experience convinces us that the hemorrhagic component in the general clinical picture of any iridocyclitis should always be alarming in terms of herpes infection; other pathogens of the inflammatory process usually do not have such an ability to cause vascular reactions.

However, it cannot be said that the listed symptoms of viral iridocyclitis are of a purely pathognomonic nature. The same changes, expressed to one degree or another, are inherent in serous-fibrinous iridocyclitis of tuberculous etiology, iridocyclitis developed on the basis of streptococcal infection, iridocyclitis of sarcoidosis origin. In this regard, it is not easy to carry out the etiological diagnosis of herpetic iridocyclitis. It is necessary to identify other symptoms, in particular, to determine the sensitivity of the cornea, which can be reduced in herpetic iridocyclitis. An important role is played by the ascertainment of a characteristic conjunctival cytogram, determined in a scraping from the conjunctival epithelium. A positive immunofluorescence reaction in the conjunctival epithelium is taken into account when using the appropriate antiherpetic serum.

Finally, we should not forget about the possibilities of the intradermal test with antiherpetic polyvaccine. It has proven itself in cases of isolated iridocyclitis with a sluggish course and relapses. When diagnosing this allergic reaction, we should remember about the possibility of exacerbation of the process in the case of herpes infection, which requires the appointment of desensitizing agents and increased antiviral treatment.

In herpetic iridocyclitis with pronounced neurotropism of the herpes simplex virus, changes in the central and peripheral nervous system, decreased tempo adaptation, and changes in the visual field of both the diseased and healthy eyes may be observed. Herpetic infection from the iris and ciliary body can spread directly along the anatomical continuation both anteriorly and posteriorly with the development of posterior corneal herpes and bullous herpetic keratitis, the occurrence of focal chorioretinitis, optic neuritis, retinal periphlebitis, and secondary exudative retinal detachment. However, in herpetic infection, the listed pathology does not have any specific differential diagnostic features and can only serve as an aid in establishing an etiological diagnosis.

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