This review presents a historical analysis of the development of visual acuity research methods, examines in detail the principles of construction of optotypes and charts for visual acuity examination as well as describes the advantages and disadvantages of modern eye charts. Such attention to this topic is justified by the fact that visual acuity is the main parameter characterizing the state of the eye. Therefore, the study of visual acuity remains one of the most important methods of assessing visual functions. The generally accepted systems for visual acuity examination, despite the simplicity of their operation, do not have a sufficiently high sensitivity, and the optotypes that are used do not make it possible to adequately assess the functional state of the eye.

Purpose: Evaluation of corneal biomechanical properties and their influence on IOP indices in patients with keratoconus.

Material and methods. The study included 194 eyes with keratoconus (113 patients aged from 23 to 36 years). Corneal refraction in central zone varied from 48.25 to 56.75 D, values of corneal thickness ranged from 279 to 558 pm. Patients were divided into 4 groups according to Amsler classification: I stage - 40 eyes; II stage - 78 eyes; III stage - 54 eyes and IV stage - 22 eyes. Standard ophthal-mological examination was carried out including pneumotonometry. IOP indices and values of biomechanical properties were evaluated by dynamic bidirectional pneumatic applanation and pneumatic impression.

Results. Study of corneal biomechanical properties in patients with keratoconus showed a decrease of such biomechanical indices as corneal hysteresis (CH) on average to 8.42±1.12 mm Hg, corneal resistance factor (CRF) -to 7.45±0.96 mm Hg, coefficient of elasticity (CE) - 5.35± 0.87 mm Hg. Values of these indices strongly depended on the stage of keratoconus. In the whole sample, the average corneal compensated IOP (IOPcc) amounted to 15.08± 2.43 mm Hg, Goldman IOP (IOPg) was 11.61±2.37 mm Hg and pneumatic tonometry IOP (IOPp) was 10.13±2.94 mm Hg. IOPcc indices didn't have any statistically significant difference in dependence on the stage of keratoconus (р>0.473), while in process of disease progression IOPg and IOPp indices showed statistically significant decrease of mean values.

Conclusion. Progression of keratoconus led to a decrease in corneal biomechanical properties which determine reduction of such indices as IOPg and IOPp in contrast to IOPcc.

The world-wide use of scleral contact lenses has dramatically increased over the past 10 year and has changed the way that we manage patients with corneal irregularity. Successfully fitting them can be challenging especially for eyes that have significant asymmetries of the cornea or sclera. The future of scleral lens fitting is utilizing corneoscleral topography to accurately measure the anterior ocular surface and then using software to design lenses that identically match the scleral surface and evenly vault the cornea. This process allows the practitioner to efficiently fit a customized scleral lens that successfully provides the patient with comfortable wear and improved vision.

A scleral contact lens (SCL) can be defined as a lens that only rests on the sclera. Raised from the cornea and limbus, the total diameter must be greater than the horizontal visible iris diameter (HVID) and the extension of the limbus. Currently, the most commonly used lenses are scleral lenses with a diameter between 15.0 and 17.0 mm, the so-called mini-scleral lenses. The existing nomenclature of scleral lenses is based only on HVID and total diameter. It is therefore important to further differentiate smaller minisclera lenses from lager ones.

The use of contact lenses (CLs) in children and adolescents is a topical subject that attracted even more attention during recent years due to the improvement of materials and types of CLs. According to research, more than 2 million children and adolescents use soft CLs in the USA alone. This results from both broad medical indications for the prescription of CLs and social reasons. The age at which contact lenses can be recommended for children is also an important subject that is being under debate. While some ophthalmologists believe that children can be introduced to soft contact lenses from the age of 12 years old, others think that the minimum age should be 14 years old. Some doctors, however, are against using contact lenses in children. Optometrists, not having the right to conduct cycloplegia, prefer to prescribe contact lenses to adolescents over 14 years old. On the other hand, the selection of CLs for children and adolescents does not depend on age, but on the indications for their application.

The technology of contact lenses coloring is viewed as a way of giving soft contact lenses the tone that is different from the usual one. Various methods for coloring soft lenses are reviewed; their advantages and disadvantages are outlined. Application features depending on the desiredresult are described. Differences between tinted, colored and decorative lenses are given.

The structure of the primary ophthalmologist appointment at the outpatient department has changed over the last 10-20 years. Universal computerization, the use of tablets and smartphones, being in air-conditioned rooms are accompanied by an increase in the number of patients with complaints of eye redness, dryness and discomfort. The use of vital dyes for biomicroscopy of the eye anterior segment is a simple and informative method for the early detection of diseases of conjunctiva and cornea. Practical recommendations regarding the use of fluorescein in the daily ophthalmic practice, diagnostic features of obtained patterns in diseases of the eye anterior segment as well features that help to assess the fit of contact lenses are given in the article.