Purpose: to provide a clinical case of recurrent keratoconus from our practice.Materials and method. A patient came to the clinic with a complaint of decreased visual acuity in the right eye. A series of standard instrumental examinations and Scheimpflug keratotopography were performed, and astigmatism of the right eye was diagnosed. Similar examinations were carried out during the patient’s attendance at follow-up examinations.Results. Based on the results of scanning Scheimpflug keratotopography, the diagnosis of keratoconus (forme fruste) was made. On examination after 1 year, there were no complaints of decreased visual acuity and data from the same instrumental examinations indicating keratoconus. After this examination, the patient came 3.5 years later with complaints of a new decreased visual acuity in the right eye. During instrumental examinations and keratopography, data were obtained indicating the presence of posterior keratoconus. After 1 year, a follow-up examination took place without complaints. The data of instrumental studies are identical to the previous visit; keratotopography revealed a decrease in posterior elevation.Discussions and conclusion. It was revealed that the patient was constantly taking the hydroxyurea drug against the background of systemic disease up to the 3rd visit, at the time of the 4th visit she had not taken it for 1 year. There are publications in the literature on the effect of this type of drugs on the collagen of the dermis of the skin, the type of which corresponds to the collagen of the cornea. We hypothesize that drugs may have an effect on the biomechanical properties of the cornea, which requires further in-depth study.

The standard air flow velocity measurement procedure has been developed in order to unify and standardize the measuring instruments used and data processing algorithms, reduce the development time and certify such standard methods. Sources of error in indirect measurements of air flow velocity in the range 3–105 m/s are investigated. The sources of instrumental error of indirect measurements are analyzed – pressure sensors with digital and analog output signals, pitot tube, temperature and relative air humidity sensors, atmospheric pressure sensors. It is shown that the greatest contribution to the instrumental error is made by measuring the pressure difference and atmospheric pressure. The errors of method, which depends on the measurement model, is considered. A new mathematical model of measurements is proposed, which includes optimal expressions for determining the density of moist air and corrections for compressibility and allows to reduce the methodological error, and requirements for the metrological characteristics of the measuring instruments used are developed, ensuring that the total error of indirect measurements of the flow velocity complies with the allowable limits of ±0,2 m/s. Recommendations are given on the use of measuring instruments and algorithms for processing measurement results, which make it possible to reduce the measurement error by 39 % and develop a standard air flow velocity measurement procedure. The standard procedure is relevant for aviation industry enterprises, where the air flow rate is measured by the pneumometric method.

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