Purpose: To estimate the possibility of optical correction of an irregular surface of a cornea at primary ectasia (keratoconus) and secondary ectasia (a consequence of radial keratotomy (RKT) and Keratoplasty) for improvement of the maximum of visual acuity. Material and methods: In the study the scleral gas-permeable lenses (SGCL) were fitting by the 60 patients, it was 45 men and 15 women from them. The 46 patients had various stage of keratoconus and 14 patients had the keratectasia after RKT. On the 5 eyes of the patients was carried out keratoplasty earlier. Criteria of successful selection of SGCL considered achievement of steadily high visual acuity, comfort of carrying and the optimal clearance in apical zone, in the limbal and landing zone on the conjunctiva also. The results: In the course of the study, the maximum visual acuity in all patients was achieved with mini-SGKL correction irrespective of type of keratoektasia. All patients observed visual comfort compared with spectacle correction or correction with other types of contact lenses. Conclusion: Scleral gas-permeable contact lenses are the main method of correction at patients with irregular corneas and provide the best visual acuity.
The optical properties of the cornea are determined by its ability to refract and transmit light. Keratoconus changes cornea’s shape, the surface of the cornea becomes irregular, which leads to a violation of light refraction and the occurrence of optical aberrations. The progressing course of the disease and its late detection lead to a delayed start of therapeutic measures, which affects the prognosis of the disease progression and reduces the patient’s quality of life. The quality of visual functions depends on the stage of the process. There are 4 stages of keratoconus (according to M. Asler), each of which corresponds to certain changes in refraction and degree of deformation of the cornea. Early biomicroscopic signs are: “dilution” of the stroma (inhomogeneity of the cornea and a grayish tint in the zone of the developing apex), change in the shape of endothelial cells and clearly visible nerve endings due to longitudinal thickening. In the second stage of keratoconus, the biomicroscopic picture is complemented by the appearance of keratoconus lines (Vogt’s striae). The opacities of the Bowman’s membrane indicate the beginning of the scarring process and the transition of the disease to its third stage. The fourth stage of the disease is characterized by further development of stromal opacities and the occurrence of gross changes of the Descemet’s membrane. Advanced medical equipment for topographic mapping and measuring the cornea makes it much easier for ophthalmologists to diagnose keratoconus and choose more effective treatment methods: crosslinking or surgical treatment. Later it allows to stabilize keratoconus, but does not provide high visual acuity due to the induction of optical aberrations, including high order optical aberrations. Contact lens vision correction is the main way to correct the refractive error resulting from keratoconus. However, the use of corneal gas permeable or soft contact lenses cannot provide high quality vision, additionally causing discomfort associated with their excessive mobility. The use of scleral gas permeable contact lenses is the most effective method of optical correction of all stages of keratoconus and after keratoplasty.
Corneal topography has been widely used in medical practice over recent years and it has helped to detect keratectasias of various genesis more often and in the earlier stages. The emergence of the new polymer materials with high oxygen permeability made it possible to wear scleral contact lenses safely, that also resulted in their popularization. Scleral gas permeable lenses are an effective method of vision correction not only for various ectasias, but also for ametropia, presbyopia and other refractive pathologies. Scleral contact lenses do not directly touch the cornea and the limbus area, whereas tear firm under the lens physically smoothes out all of the existing defects and irregularities of the corneal surface, thus creating a ”cornea-tear-lens“ unified optical system. As a result, visual acuity increases significantly. In addition, scleral lenses ensure excellent comfort starting from the first minutes of wearing due to a larger diameter, no direct contact with the cornea and relatively low mobility. Scleral lenses ensure high visual functions and comfort owing to their specific self-supporting design, which is rested on the sclera. Selection and fitting of scleral contact lenses is simple and can be mastered by any ophthalmologist
Purpose: Evaluation of corneal biomechanical prop¬erties 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 old). Corneal refraction in central zone varied from 48.25 to 56.75 D, values of corneal thickness ranged from 279 to 558 μm. 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 pneumo¬tonometry. IOP indices and values of biomechanical prop¬erties 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 aver¬age 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 aver¬age 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 differ¬ence in dependence on the stage of keratoconus (р>0.473), while in process of disease progression IOPg and IOPp indi¬ces showed statistically significant decrease of mean values. Conclusion. Progression of keratoconus led to a de¬crease in corneal biomechanical properties which deter¬mine reduction of such indices as IOPg and IOPp in contrast to IOPcc.
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