A pilot study on the influence of biomechanical properties of the cornea on short-term response to myopic corneal refractive therapy

The authors state that they do not have any proprietary interest in the products named in this article.To study the short-term corneal response to corneal refractive therapy for myopia and correlate it with corneal biomechanical properties as measured with the ocular response analyzer. METHODS: Eight eyes from 8 young subjects were fitted with a reverse geometry contact lens, attempting a myopic correction of -4.00 D. Corneal resistance factor and corneal hysteresis (CH) were measured before contact lens fitting with the ocular response analyzer. These parameters were correlated with the degree of change in apical curvature, simulated keratometry, and central corneal thickness after 3 hours of contact lens wear (effect) and 3 hours after lens removal (recovery). RESULTS: There was a trend toward a faster effect and faster recovery of the orthokeratologic effect for corneas with less resistance in terms of biomechanical properties. Corneal resistance factor did not correlate significantly, however, with any of the topographic and pachymetric parameters. Conversely, CH was significantly correlated with changes in steep keratometry (0.758; P = 0.029) and central corneal thickness (0.755; P = 0.030) during lens wear and with changes in steep keratometry (-0.835; P = 0.010) during recovery. Overall, higher values of CH meant slower effect and recovery of the orthokeratologic effect. CONCLUSIONS: Short-term response of human cornea to corneal refractive therapy is correlated with the biomechanical properties of the cornea. Of the different theories supporting such involvement of corneal response to reverse geometry contact lenses, the most likely one seems to be the one assuming a faster response and faster recovery for corneas with lower resistance. Larger sample studies would be needed to clarify the involvement of corneal biomechanical properties on corneal response to orthokeratology.Supported in part by a grant from the Science and Technology Foundation (FCT), Ministry of Science and Superior Education (MCES), and European Social Fund (ESF) under contract 8281/2002 granted to J.M.G.-M

Long-term changes in corneal structure and tear inflammatory mediators after orthokeratology and LASIK

PURPOSE: To monitor changes in corneal structure and level of inflammatory mediators in tears of myopic patients following orthokeratology (OK) and laser in situ keratomileusis (LASIK). METHODS: Sixty-two myopic subjects were analyzed in this prospective study. Thirty-two had worn Paragon CRT contact lenses and 30 underwent standard LASIK. Thirty-two control subjects were also recruited. Pachometry and corneal topography were performed 12 months after both interventions. Tears were collected and assayed using ELISA for IL-6, IL-8, matrix metalloproteinase-9 (MMP-9), and epidermal growth factor (EGF). RESULTS: Corneal power decreased in the central area and increased in the paracentral area. Simultaneously, there was a central corneal thinning with mid-peripheral thickening for OK. No changes were observed for LASIK. In comparison with controls, IL-6, IL-8, MMP-9, and EGF levels were increased significantly for OK (P < 0.01). Only MMP-9 (P < 0.01) and EGF (P < 0.01) were increased for LASIK. Pro-inflammatory response was found to be associated with the degree of myopia in the OK group. The MMP-9 and EGF upregulation was linked to the presence of iron deposition in both groups, whereas increased levels of EGF were connected with the presence of myopic regression after LASIK. CONCLUSIONS: Both interventions involved important tissue reshaping. The physical presence of a reverse geometry contact lens caused certain markers to change significantly in comparison with no lens wear or LASIK in the long-term response. MMP-9 was significantly higher in tears of subjects presenting iron deposition after OK or LASIK, and EGF levels seemed to play an important role in postoperative refractive outcomes after LASIK.Supported by National Grant PI081380 from Instituto de Salud Carlos III, Spain, awarded to the Ocular Surface and Contact Lens Research Group GI-1750

Short-term corneal response to corneal refractive therapy for different refractive targets

Purpose: The goal of the present study was to investigate the short-term variations in corneal topography within the first 3 hours of lens wear under open eye conditions, which call be considered an off-label condition in current orthokeratology treatment, and the recovery of the effect during an additional 3-hour period after lens removal.Methods: Fourteen Volunteers were fitted with Paragon CRT reverse geometry rigid gas permeable contact lenses Simulating 2 different refractive targets of -2.00 and -4.00 diopters of myopia correction in the right and left eyes in random order. After the lenses were placed in both eyes. Subsequent measurements of corneal topography were obtained at 30, 60, and 180 minutes: the same measurements were also taken at 30, 60, and 180 minutes after lens removal.Results: Significant flattening of the cornea was evident after 30 minutes of lens wear. Overall, the -4.00 group changes progressed more rapidly than in the -2.00 group, and they also took more time to recover after lens removal. However, for most of the parameters, differences between -2.00 and -4.00 treatments are evident only after 60 minutes of lens wear.Conclusions: Under open eye conditions, the first 30 minutes of corneal refractive therapy are determinant to establish the myopic orthokeratologic effect and changes are almost identical irrespective of the refractive target. After this point, changes are different depending on the refractive target. The recovery was almost as fast as the onset of the orthokeratologic effect, demonstrating that the cornea deforms quickly beneath these lenses and does recover safely and quickly once the lenses are removed.Supported in part by a grant from the Science and Technology Foundation, Ministry of Science and Superior Education, and European Social Fund under contract 8281/2002 granted to J.M.G.-M

Effect of pupil size on corneal aberrations before and after standard, custom LASIK and corneal refractive therapy

PURPOSE: To evaluate the effect of changing the pupil size on the corneal first surface higher order aberrations induced by different refractive treatments (standard LASIK; custom LASIK and corneal refractive therapy). DESIGN: Observational study. METHODS: SETTING: Clínica Oftalmológica NovoVisión, Madrid, Spain. PATIENTS: Eighty-one right eyes with a mean age of 29.94±7.5 years, of which 50 were female (61.7%), were retrospectively analyzed. Corneal videokeratographic data were used to obtain corneal first surface higher order aberrations (HOA) for aperture diameters from 3 to 8 mm using the Vol-CT software. Total Root Mean Square (RMS) and RMS for 3rd to 6th-order Zernike polynomials as well as spherical-like, coma-like, secondary-astigmatism and spherical+coma-like were calculated. RESULTS: We verified an increase of the HOA Total RMS after treatments of 0.014±0.025µm, 0.019±0.027µm 0.018±0.031µm for standard LASIK, custom LASIK and corneal refractive therapy, respectively for 3mm pupil diameter. For the 8mm aperture diameter changes in Total RMS increased by a factor of 50x compared with the variation for the 3mm diameter up to 0.744±0.731µm, 0.493±0.794µm, 0.973±1.055µm for standard LASIK, custom LASIK and corneal refractive therapy, respectively. CONCLUSIONS: The three techniques increase the wavefront aberrations of the cornea and change the relative contribution of coma-like and spherical-like aberrations. For a large aperture (>5mm), corneal refractive therapy induces more spherical-like aberrations than standard LASIK and this more than custom LASIK. However, no differences clinically or statistically significant did exist for narrower apertures. Standard LASIK and custom LASIK did not displayed statistically significant differences regarding to HOA.Objectivo: Avaliar o efeito da alteração do tamanho da pupila nas aberrações de alta ordem da superfície anterior da córnea, induzida por diferentes tratamentos refractivos: cirurgia Laser-Assisted in Situ Keratomileusis (LASIK) standard (LS), cirurgia LASIK personalizada (LP) e terapia refractiva corneal (TRC). Métodos: Foram analisados retrospectivamente oitenta e um olhos direitos de 81 pacientes com uma idade média de 29,94 ± 7,5 anos, 50 dos quais do sexo feminino (61,7%), na Clínica Oftalmológica Novovisión, Madrid, Espanha. Os dados da topografia da córnea foram usados para obter as aberrações de alta ordem da superfície anterior da córnea (SAC) para diâmetros pupilares de 3 a 8 mm, usando o software Vol-CT (Sarver& Associates, Inc). Foram calculadas a raiz quadrática média (RMS) total e as RMS da terceira até à sexta ordens usando os polinómios de Zernike, assim como para as RMS de tipo esférico, comático, astigmatismo secundário e a soma da aberração de tipo esférico com comático. Resultados: Verificou-se um aumento nas aberrações de alta ordem da RMS total depois dos tratamentos de 0,014 ± 0,025 µm, 0,019 ± 0,027 µm e 0,018 ± 0,031 µm para a cirurgia LS, cirurgia LP e TRC, respectivamente, para um diâmetro da pupila de 3 mm. Para um diâmetro pupilar de 8 mm, as alterações na RMS total aumentaram num factor de 50 vezes em comparação com a variação do diâmetro de 3 mm até 0,744 ± 0.731 µm, 0,493 ± 0,794 µm e 0,973 ± 1,055 µm para a cirurgia LS, cirurgia LP e TRC, respectivamente. Conclusões: As 3 técnicas aumentam as aberrações da córnea e alteram a contribuição relativa das aberrações de tipo comático e de tipo esférico. Para aberturas pupilares maiores (> 5 mm), o tratamento TRC induz aberrações de tipo esférico significativamente mais elevadas do que as cirurgias LS e LP. No entanto, não se verificaram diferenças clínicas e estatisticamente significativas para aberturas menores. As cirurgias LS e LP não mostraram diferenças estatisticamente significativas em relação às aberrações de alta ordem.This work was supported by a grant from the Science and Technology Foundation (FCT) of Ministry of Science and Superior Education (MCES) (European Social Funding). António Queirós SFRH/BD/61768/200

Peripheral refraction in myopic patients after Orthokeratology

Purpose: The purpose of this study was to characterize the central and peripheral refraction across the horizontal meridian of the visual field before and after myopic corneal refractive therapy (CRT) with contact lenses. Methods: Twenty-eight right eyes (mean age±SD = 24.6±6.3 years) were fitted with Paragon CRT contact lenses to treat myopia between -0.88 and -5.25D of spherical equivalent. Along with a complete set of examination procedures to assess suitability for treatment, the central and peripheral refraction was measured along the horizontal meridian up to 35º of eccentricity in the nasal and temporal retinal area in 5º steps. Results: Baseline central average spherical equivalent (M) measured by subjective refraction changed from -1.95±1.27D to -0.38±0.67D. Changes in M component ranged between 1.42±0.89D at center to 0.43±0.88D at 20º in the temporal retina (p0.351). Beyond the 25º limit, M component changed in the myopic direction up to -1.11±0.88D at 35º in temporal retina (p0.05 for all eccentricities). Furthermore, the degree of myopic increase in spherical equivalent for 30º (r2=0.573, p<0.001) and 35º (r2=0.645, p<0.001) eccentric refraction was highly correlated with axial spherical equivalent at baseline. Conclusions: CRT inverts the pattern of peripheral refraction in spherical equivalent refraction creating a treatment area of myopic reduction within the central 25º of visual field, and a myopic shift beyond the 25º. In peripheral refraction for 30º and 35º, the amount of myopia induced in terms of spherical equivalent has an almost 1:1 relationship with the amount of baseline spherical equivalent refraction to be corrected.Objectivo: O objectivo deste estudo foi caracterizar a refracção central e periférica através do meridiano horizontal do campo visual, antes e depois da Terapia Refractiva Corneal à miopia (CRT) com lentes de contacto. Métodos: Foram adaptados com lentes de contacto Paragon CRT vinte e oito olhos direitos de 28 indivíduos (com uma idade média ± DP = 24,6 ± 6,3 anos) para corrigir miopia entre – 0.88 e – 5.25 D de equivalente esférico. Juntamente com um conjunto completo de exames para avaliar a possibilidade de tratamento, foi medida a refracção central e periférica ao longo do meridiano horizontal até aos 35º de excentricidade na área da retina nasal e temporal em intervalos de 5º. Resultados: A média do equivalente esférico central no estado inicial (M) medido pela refracção subjectiva mudou de - 1,95 ± 1,27 D para - 0,38 ± 0,67 D. As alterações no componente M variaram entre +1,42 ± 0,89 D no centro e +0,43 ± 0,88 D a 20º na retina temporal (p 0,351), a 25º para ambos os lados da medida da refracção central. Para além do limite de 25º, o componente M mudou no sentido da miopia até – 1,11 ± 0,88 D a 35º na retina temporal (p 0,050 para todas as excentricidades). Além disso, o aumento do valor de miopia em equivalente esférico para 30º (r2 = 0,573, p < 0,001) e 35º (r2 = 0,645, p < 0,001) de refracção excêntrica foi altamente correlacionado com o equivalente esférico do estado inicial. Conclusões: As lentes CRT invertem o padrão da refracção periférica no equivalente esférico da refracção, criando uma área de tratamento na redução da miopia dentro de 25º do campo visual central, e um deslocamento miópico para além de 25º. Na refracção periférica para 30º e 35º, o valor da miopia induzida em termos de equivalente esférico, tem uma relação de quase 1:1 com o valor da refracção do equivalente esférico do estado inicial a ser corrigido.Ministério da Ciência e do Ensino SuperiorFundação para a Ciência e a Tecnologia (FCT) - Bolsa SFRH/BD/61768/200