[Comparative analysis of clinical and functional parameters in patients with stable stage II-III keratoconus after implantation of corneal segments and fitting of scleral rigid contact lenses]. / Sravnitel'nyi analiz kliniko-funktsional'nykh pokazatelei u patsientov so stabil'nym keratokonusom II­III stadii posle implantatsii rogovichnykh segmentov i podbora skleral'nykh zhestkikh kontaktnykh linz.

The modern treatment strategy for keratoconus (KC) involves sequential application of medical technologies aimed at stabilizing pathological changes in the cornea and restoring visual acuity. PURPOSE: This study compares the effect of implantation of intrastromal corneal ring segment (ICRS) and fitting of individual scleral rigid contact lenses (RCLs) on visual functions in patients with stage II-III KC after previously performed corneal collagen cross-linking. MATERIAL AND METHODS: The Helmholtz National Medical Research Center of Eye Diseases examined and treated 34 patients (69 eyes) aged 18 to 33 years with stage II-III KC. The study included patients who had previously undergone standard corneal collagen cross-linking. Depending on the type of optical correction, the patients were divided into two groups: patients in group 1 underwent ICRS implantation using a femtosecond laser; patients in group 2 were fitted with individual scleral RCLs. RESULTS: Improvement in clinical and functional parameters was observed in both groups. A higher clinical and functional result was achieved in group 2. CONCLUSION: For patients with stable stage II-III KC, it is advisable to recommend fitting of individual scleral RCLs for visual rehabilitation.

[Changes in the wavefront and peripheral defocus profile after excimer laser and orthokeratology corneal reshaping in myopia]. / Izmeneniya volnovogo fronta i profilya perifericheskogo defokusa posle eksimerlazernogo i ortokeratologicheskogo resheipinga rogovitsy pri miopii.

PURPOSE: This study compares the trends of changes in corneal asphericity, corneal and total aberrations and peripheral refraction in myopic eyes after excimer laser and orthokeratology correction. MATERIAL AND METHODS: Aberrometry (OPD-Scan III; Nidek, Japan) was performed in 63 patients (126 eyes) with moderate and high myopia before and after femtosecond laser-assisted in situ keratomileusis (Femto-LASIK; 88 eyes, group 1) and photorefractive keratectomy (PRK; 38 eyes, group 2). Peripheral refraction (Grand Seiko AutoRef/Keratometer) at 15° and 30° from the center of the fovea was observed in 12 patients of group 1 and in 18 patients with a background of orthokeratology correction (group 3). RESULTS: Corneal asphericity factor Q transitioned to positive values after PRK and Femto-LASIK. Corneal aberrations: root mean square higher order aberration (RMS HOA) increased in both groups, Tilt 1 increased in group 1 and became negative in group 2, Tilt 2 increased in group 2 and went negative in group 1. Trefoil 6 did not change in group 1 and decreased in group 2. Coma 7 and 8 increased synchronously in both groups. Spherical aberrations (SA) increased in group 1, and went negative in group 2. Total aberrations changed to a lower degree, and these changes were not synchronous with the corneal ones; RMS HOA decreased in group 1 (while corneal RMS increased significantly), and in the PRK group it increased, but much less than the corneal. Total SA increased in group 1 and did not change in group 2. Peripheral myopic defocus formed in all cases, after Femto-LASIK the maximum was in the zone of 30º, after orthokeratology lenses - in the zone of 15º. CONCLUSION: Using excimer laser and orthokeratology to reshape the cornea in full accordance with its different profiles have different effects on the wavefront and peripheral refraction of the eye. The internal optics of the eye partially compensates corneal aberrations induced by the excimer laser.

[Optical aberrations of the eyes with various degrees of myopia]. / Aberratsii opticheskoi sistemy glaza pri miopii razlichnoi stepeni.

Purpose - to comparatively analyze the wavefront aberrations and biometric parameters of the eyes with various degrees of myopia. MATERIAL AND METHODS: The study included 134 eyes of 67 patients with mild, moderate and high myopia aged 7-28 (mean age 19.3±1.5 years). The following biometric parameters were examined: anterior chamber depth (ACD), lens thickness (LT), axial length (AL), as well as corneal and total aberrations. The parameters were studied on the Galilei G6 system (Ziemer Ophthalmic Systems AG, Switzerland) and the OPD-Scan III aberrometer (Nidek, Japan). Spherical aberration (SA) was estimated as the sum of Z4+Z8+Z12. RESULTS: As the refraction increased, the root mean square higher-order aberrations (RMS HOA) also increased significantly: from 0.24±0.02 µm in mild myopia to 0.45±0.03 µm in high myopia, and in eyes with AL of ≥27.0 mm - to 0.57±0.02 µm (p=0.01). An increase in vertical tilt, vertical coma and vertical trefoil were also observed. Total SA was positive and increased in eyes with moderate myopia compared to those with low myopia (from 0.02±0.01 µm to 0.06±0.02 µm, p=0.02), which coincided with changes in the internal optics of the eye: an increase in ACD and a decrease in LT. At the same time, no differences in corneal aberrations were observed among patients with low and moderate myopia. A significant decrease of SA occurred in high myopia (from 0.06 µm in low myopia to 0.015±0.02 µm in high myopia). The average value of SA was 0.005±0.01 µm in eyes with AL of ≥27.0 mm and appeared to be negative in 40% of cases. The average value of corneal SA was negative (-0.002±0.01µm) in eyes with AL of ≥27.0 mm. This group had predominantly patients with congenital myopia. CONCLUSION: An increase of total positive SA in patients with moderate myopia compared to those with low myopia is associated with changes in the internal optics of the eye (ACD, LT). Significant increase of higher-order aberrations and decrease of SA with the transition to negative values was observed in patients with high axial myopia.

[Experimental study of the effect of corneal hydration and its biomechanical properties on the results of photorefractive keratectomy]. / Vliyanie gidratatsii i biomekhanicheskikh svoistv rogovitsy na rezul'taty fotorefraktsionnoi keratektomii v eksperimente.

Water content in the cornea may affect the outcome of its excimer laser ablation, especially in presbyopic patients with myopic refraction. This hypothesis can be tested by scanning the cornea in the terahertz (THz) range to determine its hydration level. PURPOSE: To study the effect of hydration of the cornea determined by non-contact THz scanning and its biomechanical parameters on the results of photorefractive keratectomy (PRK) in an experiment. MATERIAL AND METHODS: PRK was performed using the Nidek EC-5000 QUEST excimer laser on 8 rabbit eyes. Corneal hydration was evaluated by determining the reflection coefficient (RC) in the THz electromagnetic radiation range before PRK, after 3-5 days, and after 1, 2, 3, and 4 months. Clinical examination included autorefractometry, assessment of corneal thickness and other anatomical and optical parameters of the anterior eye segment (Galilei G6, Ziemer Ophthalmic Systems AG 6.0.2, Switzerland), measurement of corneal hysteresis (CH) and corneal resistance factor (CRF) using the Ocular Response Analyzer (ORA; Reichert, USA), as well as tear production (Schirmer test). RESULTS: The initial water content in the cornea has a significant effect on the thickness of the removed layer, i.e. on the PRK effect, with correlation coefficient of Rs= -0.976 (p<0.01). The correlation between CH and the ablation depth is less pronounced (Rs=0.643), and CRF had no correlation with it (Rs= -0.089). Biomechanical indicators of the cornea depend on its hydration: changes in CH and CRF after excimer laser ablation qualitatively coincide with changes in RC, the correlation coefficient between RC and the initial value of CH is R= -0.619 (moderate negative correlation). CONCLUSION: THz scanning is an effective non-contact technology for monitoring corneal hydration level. The mismatch of the hypoeffect of keratorefractive excimer laser intervention planned for patients with presbyopia with the actual outcome can be caused by individual decrease in the initial water content in the cornea.

[Wavefront and accommodation parameters under different conditions of correction in myopia and hyperopia]. / V.V., Parametry volnovogo fronta i akkomodatsii v raznykh usloviiakh korrektsii pri miopii i gipermetropii.

PURPOSE: To compare the wavefront and accommodation parameters without correction and in soft contact lenses (SCL) in natural and cycloplegic conditions in eyes with myopia and hyperopia. MATERIAL AND METHODS: A total of 142 myopic (mean -5.6±1.4 D) and 48 hyperopic (mean +3.5±1.1 D) eyes were examined in 95 patients aged 5-32 years (mean age 16.9±0.9 years) to compare the wavefront aberrations without correction and with different SCL before and after cycloplegia (two drops of cyclopentolate hydrochloride 1%). The device was set up for 4 mm zone for both narrow and wide pupils. To compare the accommodation parameters under different correction conditions, 85 patients aged 8-23 years (mean age 14.9±0.6 years) with average myopia of (-)5.27±1.4D (123 eyes) and average hyperopia of +3.53±1.2 D (46 eyes) were chosen from the study group. Among the measured parameters are objective accommodative response (OAR), relative accommodation reserves (RAR), pseudoaccumulation amplitude (PA), higher-order aberrations: RMSHOAs, 6-9 Trefoil, 7-8 Coma, spherical aberration (SA). RESULTS: In myopic eyes with SCL Coma 7 decreases, Coma 8 increases with transition to positive values, and Trefoil 9 increases. In hyperopic eyes, trefoil 6 decreases, Coma 7-8 go negative. In myopic or hyperopic eyes with SCL, SA goes from positive to negative. In both myopia and hyperopia, accommodation and PA rates are higher in SCL than in glasses. CONCLUSION: SCL change certain wavefront parameters for myopia and hyperopia in different ways. The accommodation parameters in SCL are elevated in both myopia and hyperopia. The negative spherical aberration induced by contact lenses improves the accommodative response. The revealed features should be considered in the development of correction methods that target refractogenesis.

[Wavefront aberrations and accommodation in myopes and hyperopes]. / Aberratsii volnovogo fronta i akkomodatsiia pri miopii i gipermetropii.

AIM: to comparatively investigate accommodation, pseudoaccommodation, and higher-order aberrations in children and young adults with myopia and hyperopia. MATERIAL AND METHODS: A total of 39 myopic (the mean error of (-)5.2±1.5 diopters) and 53 hyperopic (the mean error of (+)3.1±1.15 diopters) eyes of 46 patients aged 5-20 years (11.6±0.6 years on average) were enrolled. Examination included evaluation of the objective accommodative response, relative accommodation reserves, pseudoaccommodation volume (calculated as the difference between the (+)3.0-diopter lens that is necessary for cycloplegic reading at a 33-cm distance and the weakest possible plus lens that enables reading), and higher-order aberrations (HOA), particularly the root mean square (RMS) value, vertical and horizontal trefoil, vertical and horizontal coma (coma7, coma8), and spherical aberration (SA). RESULTS: Both objective and subjective parameters of accommodation were reliably lower in myopia as compared to hyperopia, while wavefront aberrations (RMS HOA, vertical trefoil, coma7) and pseudoaccommodation - reliably greater. SA was found to be reliably more pronounced in those myopes, who demonstrated larger volume of pseudoaccommodation. At the same time, there was a mismatch in wavefront parameters of myopes and hyperopes at different levels of accommodation and pseudoaccommodation. In myopic eyes, vertical trefoil decreased down to negative values as the accommodative response improved. In contrast to that, in hyperopic eyes with large volume of pseudoaccommodation, SA decreased below zero. CONCLUSION: Myopia has been shown to be associated with reduced accommodation parameters as well as stronger HOA and pseudoaccommodation. Wavefront and accommodation parameters interrelations differ in myopic and hyperopic eyes. The nuances revealed should be taken into account when developing correction methods that purposefully influence refractogenesis.