REFRACTIVE OUTCOMES OF TORIC LENSES IMPLANTATION AFTER PENETRATING KERATOPLASTY (PK) IN A LONG OBSERVATION PERIOD (CLINICAL CASE)
One of the most significant achievements of ophthalmology in the treatment of corneal pathologies is the development and implementation of Penetrating keratoplasty (PK). The first successful PK operation was carried out by E. Zirm in 1905 [1]. The pioneer of PK operations in the USSR became his successor V.P. Filatov using allomaterials in his work. According to the results of these operations, he noted that corneal transplantation is "a beam of light that cut through the darkness”, the next step in solving the problems of keratoplasty was the opening of the first eye bank [2]. Corneal refraction accounts 60% of the refractive power of the optical system of the eye. Most pathological processes of the cornea lead to a decrease in its transparency, and therefore to a decrease in visual acuity. According to WHO data for 2016, corneal blindness is still among the top three causes of disability after cataract and glaucoma. Moreover, PK still occupies a leading position in the choice of surgical tactics for this type of pathology (3). Keratoconus leads to corneal opacification and is accompanied by a change in its refractive properties. A frequent manifestation of keratoconus is acquired astigmatism, which has a significant effect on visual acuity [4]. In most patients, operations for keratoconus are performed at the age period of 25-40 years. As a result of the eccentric position of the graft relative to the visual axis, patients who underwent PK experience post-ker-atoplastic ametropia. At the age period of50-60years, these patients turn to ophthalmologists with a problem associated with lens opacification - cataract. In this case, the main task of cataract surgeons when performing cataract extraction in patients who previously underwent penetrating keratoplasty is the correction of induced astigmatism and ametropia. Previously, the problem of induced ametropia was eliminated by IOL implantation and spectacle correction with cylindrical lenses. Later, for this purpose, surgeons began to implant toric lenses, which allow to correct the induced corneal astigmatism clearly along the axes. Corneal transplantation results depend on many factors, such as: visual acuity before surgery, astigmatism, and graft transparency. Focusing attention to the induced anomaly of refraction, namely induced astigmatism, it is also important to take into account the position of the graft and the location of the sutures that fix the graft.