Javier González-Pérez

Changes in Corneal Structure with Continuous Wear of High-Dk Soft Contact Lenses: A Pilot Study

Purpose. Despite numerous studies that have considered the effects of extended wear of high-Dk soft contact lenses on ocular physiology, little attention has been paid to the impact of such lenses on central or peripheral corneal thickness and curvature. The present study aims to report the time course of changes in corneal thickness and curvature that accompanies the 30-night continuous wear of new silicone hydrogel soft contact lenses in a neophyte population in a longitudinal study. Methods. Six subjects wore high-Dk lotrafilcon (Dk = 140) on a 30-night replacement schedule for 12 months. Only measurements from the right eye were considered for analysis. Topographical measurements of corneal thickness and curvature were taken. The same parameters were monitored for an additional period of 3 months after lens removal. Results. An almost homogenous increase in corneal radius of curvature was detected for all the locations studied, being statistically significant for the 4-mm cord diameter area. This effect was associated with a progressive thinning effect for the central cornea, whereas midperipheral and peripheral areas did not display such a thinning effect during continuous wear. These effects were still evident for the central cornea 3 months after contact lens wear discontinuation. Conclusions. Continuous wear of high-Dk silicone hydrogel contact lenses is associated with clinically appreciable changes in topographical corneal curvature, whereas only a reduction in corneal thickness is appreciated in the central area. This effect seems to be a result of mechanical pressure induced by these hybrid hyperpermeable materials, characterized by a higher modulus of elasticity. The small sample size compromises the conclusions addressed from this study, and further work will be necessary to confirm the present results.

Central corneal thickness measured with three optical devices and ultrasound pachometry.

Purpose: To evaluate the reliability of three noninvasive pachometry methods against the ultrasound pachometer considered the gold standard. Methods: Central corneal thickness (CCT) was measured using a Paxis ultrasound (US) pachometer, Orbscan II, Pentacam, and Topcon SP-3000 specular microscope in 22 right eyes of 22 healthy adults (7 men, 15 women). Three repeated measures were obtained and then compared to obtain the repeatability of each instrument and the agreement between pachometers. Results: Pentacam is the optical system that renders values of CCT closer to those obtained with US pachometry. Conversely, a specular microscope shows a poorer agreement with US measures, and differences depend on the thickness being measured. The Orbscan system shows a consistent trend toward underestimation of CCT compared with US and Pentacam irrespective of the value measured. Conclusion: Different optical methods used to measure CCT showed significantly different results compared with US pachometry except for the Pentacam system. Clinicians should take into account the fact that specular microscopy might either underestimate or overestimate values of CCT, whereas Orbscan systematically overestimates CCT compared with US and Pentacam.

Further information on the knowledge of topographical corneal thickness.

Central and peripheral corneal thickness has been used increasingly to obtain information about physiologic and clinical conditions of the cornea. In this study, a new method based on ultrasonic pachometry for topographical corneal thickness measurement is described. Results suggest that the technique is reliable for clinical determination of global corneal thickness. Measurements taken by one observer on different sessions (intersession variation) and measurements taken by different observers (interobserver variation) are not significant different (p = 0.586 and 0.273, respectively). This new ultrasound topographical pachometric method can be considered a useful tool for determination of topographical corneal thickness. It has implications for the use of topographical ultrasonic pachometry in contact lenses research, refractive surgery, and management of different pathologic conditions.

Asfericidad corneal en una población de adultos jóvenes: Implicaciones clínicas

espanolObjetivos: Determinacion de la relevancia de diferentes componentes opticos oculares en el estado refractivo de adultos jovenes, con especial atencion a la topografia corneal representada por el valor de asfericidad. Sujetos y metodos: Las topografias corneales y biometrias ultrasonicas fueron obtenidas en 109 estudiantes universitarios con diversas formas de error refractivo (rango equivalente esferico: +3,25 D a -11,00 D). Se practica un estudio de regresion para establecer las relaciones entre la asfericidad corneal y el error refractivo, asi como otros componentes opticos oculares relacionados con el mecanismo de emetropizacion del ojo. Resultados: La asfericidad promedio fue -0,23 (DE 0,08, rango: -0,42 a -0,03). Todos los valores se corresponden con la descripcion matematica de la elipse prolata, la mas comunmente aceptada para la cornea humana normal. La correlacion estadistica entre la asfericidad y el error refractivo esferico equivalente no fue significativa, pero existia correlacion significativa de la asfericidad con respecto al radio de curvatura, a la profundidad de la camara vitrea y a la longitud axial. Conclusiones: 1) Los valores de asfericidad apoyan la morfologia generalizada de la cornea prolata como estandar. Se discuten las influencias de esta configuracion en la adaptacion de LC, en la cirugia refractiva o en la capacidad visual del ojo. 2) Los resultados sugieren que, si bien existe relacion entre la longitud axial y la topografia corneal, esta ultima probablemente no participe en los mecanismos de emetropizacion que determinan el estado refractivo del ojo adulto. EnglishPurpose: To determine the relevance of the different ocular optical components in the refractive state of young adults, paying special attention to the corneal topography represented by the asphericity value. Subjects and methods: Corneal topographies and ultrasonic biometries were obtained from 109 university students with different refractive errors (spherical equivalent range: +3.25 D to -11.00 D). A regression study was performed in order to establish the relationships between corneal asphericity and refractive error, as well as other ocular optical components related to the emmetropization mechanism of the eye. Results: The mean asphericity values were -0.23 (SD 0.08, range: -0.42 to -0.03). All the values correspond to the mathematical description of the prolate ellipse, most commonly accepted for the normal human cornea. The statistical correlation between asphericity and equivalent refractive error was not significant, but a significant correlation was found for the asphericity with respect to the radius of curvature, vitreous chamber depth and axial length. Conclusions: 1) The asphericity values support the generalised morphology of the prolate cornea as the standard. The influence of this configuration on the contact lens fit, refractive surgery or the visual performance of the eye are discussed. 2) Results suggest that, although a relationship between axial length and corneal topography actually exists, it is not likely that the latter has implications for the emmetropization mechanisms which determine the refractive state of the adult eye.

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.

Topographic paracentral corneal thickness with pentacam and orbscan : effect of acoustic factor

Purpose: To evaluate the effect of an acoustic factor (AF) on the comparison of central corneal thickness (CCT) and peripheral corneal thickness (PCT) measurements with Orbscan II and Pentacam. Methods: The CCT and PCT at 1, 2, and 3 radial distances from the corneal apex were measured using Orbscan II and Pentacam in 22 right eyes of 22 healthy adults (7 men, 15 women). Three measures were obtained from each 1 of the 25 points measured and then compared to gauge the agreement between both devices at the corneal center and anular areas located at 1-, 2-, and 3-mm distances from the central measurement. Orbscan II readings were considered with and without an AF correction. Results: Pentacam provides statistically significant higher values than Orbscan II does at all the 25 locations analyzed (P<0.001). With a few exceptions, the average difference was fairly constant between 20 and 40 μm for all the corneal locations. A high correlation existed between central readings (r2=0.927; P<0.001) and average thickness at each one of the annular areas being analyzed (r2=0.897 at 1 mm, r2=0.876 at 2 mm, and r2=0.870 at 3 mm); Pentacam minus Orbscan II value averaged for all the points changed from −28±10 to −22±9 μm after the removal of the AF in Orbscan II. Conclusions: Central and peripheral measurements of the corneal thickness obtained with Orbscan II and Pentacam are significantly different. The removal of the AF in Orbscan II renders lower mean differences but decreases the agreement between both systems and potentially induces an overestimation of CCT and PCT by Orbsan II compared with Pentacam.

Comfort and vision scores at insertion and removal during 1 month of wear of Paragon CRT for corneal reshaping.

Purpose: The goal of this study was to evaluate the pattern of initial adaptation of neophytes to corneal refractive therapy (CRT) for overnight corneal reshaping in terms of comfort and subjective visual performance at lens insertion at night and lens removal in the morning. Methods: Twenty-two young healthy subjects were enrolled in this study. All of them had been trialed to assess adaptation to conventional alignment-fit rigid gas permeable lenses and were only enrolled in this study after a 2-week wash-out period. Visual analog scales for subjective comfort and vision were recorded on a form given to the patient on days 1, 2, 3, 5, 7, 14, 21, and 28. Additionally, the patient attended the clinic on days 1, 7, 15, and 30 after fitting, for follow-up. Results: Successful adaptation was obtained in 21 of the 22 initially enrolled individuals. The average overnight wearing time remained constant during the study at 8 hrs per day. Overall comfort rates increased significantly up to values of 8.02 and 9.12 out of 10 at insertion and removal, respectively (P<0.001). Subjective vision scores also increased significantly at the end of the 1-month study period (P<0.001). Conclusions: Adaptation to CRT is rapid in terms of subjective comfort and vision. Comfort significantly increases by day 5, whereas subjective vision in the morning reaches its maximum by days 15 to 21 and at the end of the day by days 10 to 15. These results are of interest to clinicians to provide evidence-based information to their patients about the expected time to adapt to CRT in terms of self-reported comfort and vision.

Corneal thickness mapping by topographical ultrasonic pachometry

Abstract Ultrasonic measurements of corneal thickness (CT) more than 25 points from a 6-mm diameter area of the central cornea were used to create computerized CT maps. Two subjects were evaluated in different sessions by topographical ultrasonic pachometry. The thickness values were stored as a two-dimensional array z(x,y), whose indices refer to positional coordinates x (in the nasal–temporal direction) and y (in the superior–inferior direction). Pachometric maps were then constructed by plotting thickness values against horizontal and vertical (x,y) position coordinates. Assisted computer interpolation between data points provides color-coded continuous pachometric maps. Data were processed and analyzed separately and an average map was also obtained for each subject. Goodness of fit for the average maps measured by coefficient of determination (r 2 ) was very high in both examples (r 2 = 0.98 and r 2 = 0.99). Fitting standard error was 5.42 μm and 4.17 μm, respectively. Also, points not measured in the ultrasonic evaluation could be automatically predicted from the fitted model. The technique described provides an affordable and reliable method for thickness mapping of full corneal tissue, enabling accurate anatomical evaluation of the changes induced in the cornea by refractive surgery procedures, contact lenses, or disease.

Pigmented corneal ring associated with orthokeratology in Caucasians: case reports

Background:  The aim was to report the appearance of a pigmented ring in both eyes of two patients undergoing overnight orthokeratology.

Comparison of Central Corneal Thickness Measured by Standard Ultrasound Pachymetry, Corneal Topography, Tono-Pachymetry and Anterior Segment Optical Coherence Tomography

ABSTRACT Purpose: To compare central corneal thickness (CCT) measured by standard ultrasound pachymetry (USP), and three non-contact devices in healthy eyes. Methods: A cross-sectional study of CCT measurement in 52 eyes of 52 healthy volunteers was done by a single examiner at Ocular Surface and Contact Lens Laboratory. Three consecutive measurements were done by standard USP, non-contact tono-pachymeter, Pentacam corneal topographer, and Anterior Segment Optical Coherence Tomography (AS-OCT). The mean values were used for assessment. The results were compared using multivariate ANOVA, linear regression, and Pearson correlation. Agreement among the devices was analyzed using mean differences and Bland–Altman analysis with 95% limits of agreement (LoA). Finally, reliability was analyzed using intraclass correlation coefficient (ICC). Results: Mean CCT by ultrasound pachymeter, tono-pachymeter, corneal topographer and AS-OCT were 558.9 ± 31.2 µm, 525.8 ± 43.1 µm, 550.4 ± 30.5 µm, and 545.9 ± 30.5 µm respectively. There was a significant positive correlation between AS-OCT and USP (Pearson correlation = 0.957, p < 0.001), corneal topography and USP (Pearson correlation = 0.965, p < 0.001), and corneal topography and AS-OCT (Pearson correlation = 0.965, p < 0.001). There was a lower correlation between CT-1P tono-pachymeter and the other three modalities. Intraclass correlation coefficients show an excellent reliability between pairs except for CT-1P against the other three instruments that were found moderate. Conclusions: CT-1P tono-pachymeter underestimates CCT measurements compared to Scheimpflug system, AS-OCT device, and USP. Mean CCT among USP, Pentacam and AS-OCT were comparable and had significant linear correlations. In clinical practice, these three modalities could be interchangeable in healthy patients.