Long-term effect on corneal curvature of corneal collagen cross-linking for keratoconus

Objective@#To determine the effect of corneal collagen cross-linking on the corneal curvature of eyes with keratoconus measured using an Oculus Pentacam® at 2 years and annually thereafter. @*Methods@#This was a descriptive, retrospective study involving patients with keratoconus who had undergone uncomplicated collagen cross-linking using the Dresden protocol from January 2012 to March 2016. Baseline measurements of best-corrected visual acuity (BCVA), maximum K value (Kmax), corneal astigmatism, anterior and posterior elevation map changes were recorded and compared with data taken at 2 and 3 years@*Results@#This study included 32 patients (48 eyes) with a mean follow-up of 28.88 ± 6.23 months. Only 4 patients (6 eyes) had 3-year follow-up data with a mean follow-up of 42.83 ± 4.58 months. When all eyes were considered, significant changes were noted in Kmax, BCVA, and anterior and posterior elevation maps between baseline and 2-year follow-up. Specifically, there were significant decreases in Kmax (p<0.0001) and anterior elevation (p<0.05), and significant improvement in BCVA (p<0.01) while posterior elevation (p<0.0001) was found to have increased significantly at 2nd year follow-up compared to baseline. When only eyes with 3-year follow-up data was analyzed, only BCVA showed significant change (p<0.05). Corneal astigmatism remained stable during the study period.@*Conclusion@#Two to 3 years after collagen cross-linking for keratoconus, corneal curvature parameters and BCVA showed improved and stable outcomes when compared to baseline.

Estudio comparativo de variables corneales entre ojos normales con sospecha de queratocono y con diagnóstico de queratocono / Comparative study of corneal variables among normal, keratoconus suspected and keratoconus diagnosed eyes

OBJETIVOS: comparar el comportamiento de algunas variables corneales mensurables entre pacientes sanos, con sospecha de queratocono y aquellos con diagnóstico de queratocono. MÉTODOS: se realizó un estudio descriptivo de corte transversal a pacientes atendidos en la consulta de córnea y cirugía refractiva del Instituto Cubano de Oftalmología "Ramón Pando Ferrer", entre septiembre del 2012 y marzo del 2013. Se crearon tres grupos: pacientes sanos, con queratocono y con sospecha de la enfermedad. Las variables estudiadas fueron: densidad, coeficiente de variabilidad y hexagonalidad de las células endoteliales, queratometría corneal central, punto corneal más delgado, volumen corneal, elevación corneal posterior y amplitud de cámara anterior. RESULTADOS: no hubo diferencias estadísticamente significativas entre las variables cuantitativas y cualitativas del endotelio corneal en los tres grupos de pacientes; mientras que la amplitud de cámara anterior, la elevación posterior y la queratometría mostraron diferencias entre los tres grupos. No hubo diferencias estadísticamente significativas entre pacientes sanos y sospechosos de queratocono en relación con el punto corneal más delgado y el volumen corneal. Las córneas más curvas, los menores valores del punto más delgado corneal, las cámaras anteriores más profundas y las corneas con menos volumen se encontraron en los pacientes con queratocono. CONCLUSIONES: la amplitud de la cámara anterior, la elevación de la superficie corneal posterior y los valores queratométricos son medidas corneales que pueden considerarse útiles para diferenciar los grupos en estudio.

OBJECTIVE: to compare the behaviors of some mensurable corneal variables among healthy, keratoconus suspected and keratoconus diagnosed patients. METHOD: a descriptive and cross-sectional study was conducted on patients seen at the corneal and refractive surgery service of "Ramón Pando Ferrer", Institute of Ophthalmology between September 2012 and March 2013. They were divided into three groups: healthy patients, keratoconus and keratoconus suspected patients. The variables were density, variability coefficient and hexagonality of endothelial cells, central corneal keratometry, thinnest corneal point, corneal volume, posterior corneal elevation and amplitude of the anterior chamber. RESULTS: there were no statistically significant differences between the quantitative and the qualitative variables of the corneal endothelium in the three groups of patients whereas the amplitude of the anterior chamber, the posterior elevation and keratometry showed differences between the three groups. There was no statistically significant difference between healthy and keratoconus-suspected patients in terms of the thinnest corneal point, and the corneal volume. The most curved corneas, the lowest values of then thinnest corneal point, the deepest anterior chambers and corneas with less volume were found in patients with keratoconus. CONCLUSIONS: the amplitude of the anterior chamber, the posterior corneal surface elevation and the corneal keratometry values are measures that can be considered useful in differentiating the study groups.

Variación de la elevación anterior y posterior de la córnea tras el crosslinking corneal / Changes in the anterior and posterior elevation of the cornea after the corneal crosslinking

OBJETIVO: determinar las variaciones de la elevación anterior y posterior de la córnea con el tratamiento de crosslinking corneal en pacientes con queratocono en el Servicio de Córnea del Instituto Cubano de Oftalmología "Ramón Pando Ferrer". MÉTODOs: se realizó un estudio descriptivo, retrospectivo, a 30 ojos de 30 pacientes con queratocono a los cuales se les realizó el crosslinking corneal. Se recogieron los datos en el preoperatorio a los 6, 12 y 24 meses. Las variables estudiadas fueron: esfera mejor ajustada anterior, elevación anterior, esfera mejor ajustada posterior y elevación posterior. RESULTADOS: la esfera mejor ajustada anterior en el preoperatorio de 7,34 mm permaneció sin diferencia significativa en el posoperatorio y la elevación anterior mostró una reducción estadísticamente significativa de 20,73 µm en el preoperatorio a 14,90 µm al año y 15,93 µm a los 2 años. La esfera de mejor ajuste posterior de 5,94 mm no sufrió modificaciones en el posoperatorio, ni la elevación posterior media de 31,80 µm. CONCLUSIONES: después del crosslinking corneal la elevación anterior disminuye y la posterior se mantiene igual.

OBJECTIVE: to determine the anterior and posterior corneal surface elevation in the corneal crosslinking surgical treatment applied to patients with keratoconus at the corneal service of "Ramón Pando Ferrer" Cuban Institute of Ophthalmology. METHODS: a retrospective and descriptive study of 30 eyes from 30 patients with progressive keratoconus who underwent the corneal collagen crosslinking. Data were collected preoperatively at 6, 12 and 24 months. The studied variables were best fit anterior sphere, anterior elevation, best posterior fit sphere and posterior corneal elevation. RESULTS: the preoperative best fit anterior sphere was 7,34 mm and there was no difference in the postoperative period. The anterior corneal surface elevation showed statistically significant reduction from 20,73 µm in the preoperative period to 14,90 µm in the first year and 15,93 µm in the second year after surgery. There was no changes either in the posterior best fit sphere of 5,94 mm or in the posterior elevation of 31,80 µm. CONCLUSIONS: after the corneal crosslinking, there is a reduction of the anterior elevation and the posterior elevation remains the same.

Configuración del Pentacam en el tamizaje de cirugía refractiva / Pentacam configuration in refractive surgery screening

Objetivo: determinar la consistencia de la configuración manual del Pentacam en el tamizaje de cirugía refractiva. Métodos: se realizó un estudio observacional, descriptivo en el Instituto Cubano de Oftalmología Ramón Pando Ferrer durante el 2012. La muestra quedó conformada por 104 imágenes correspondiente a ojos examinados por el Pentacam que cumplieron los criterios de selección. Se analizaron variables tales como: diámetro para al cálculo de la esfera de mejor ajuste, elevación anterior, elevación posterior y se utilizó la clasificación de ectasias corneales según elevación anterior y posterior para agrupar la muestra. Resultados: del total de la muestra el 45,2 por ciento y el 54,8 por ciento utilizó un diámetro menor de 8 mm, y mayor de 8 mm para el cálculo de la esfera de mejor ajuste, respectivamente. La comparación de media de los dos grupos fue estadísticamente significativa. Según la clasificación de ectasia por elevación anterior y posterior, con un diámetro mayor de 8 mm se duplican en por ciento los exámenes normales y disminuyen los patológicos en un 25 porciento respectivamente. Existen diferencias entre las medias y la desviación estándar de los exámenes evolutivos a un mismo ojo según la configuración automática y manual. Conclusiones: la configuración manual del Pentacam permite tener una consistencia en el tamizaje de cirugía refractiva

Objective: to determine the consistency of manual Pentacam configuration in refractive surgery screening. Methods: observational and descriptive study performed at Ramon Pando Ferrer Cuban Institute of Ophthalmology during 2012. The sample was made up of 104 images of eyes examined by Pentacam equipment, which had met the selection criteria. The analyzed variables were diameter for best fit sphere calculation, anterior elevation, posterior elevation and the classification of corneal ectasias based on anterior and posterior elevations was used in order to group the sample. Results: in the sample, 45.2 percent and 54.8 percent used a diameter lower than 8mm and over 8mm for the calculation of the best fit sphere, respectively. The mean comparison between the two groups was statistically significant. According to the ectasia classification based on anterior and posterior elevations, with the over 8mm diameter, the normal exams doubled in some percentage and the pathological ones decreased by 25 percent, respectively. There are differences between the means and the standard deviations in evolutional exams performed in the same eye, considering the automatic and the manual configurations. Conclusions: manual configuration of Pentacam allows attaining consistency in the refractive surgery screening

Change of cornea posterior elevation after laser in situ keratomileusis / 中华实验眼科杂志

Background Keratectasia after laser in situ keratomileusis (LASIK) is one of the serious complications which affect the vision.The measurement of cornea posterior elevation is an important way helping to find this change.Objective The aim of this study was to investigate the change of cornea posterior elevation after LASIK in myopic eyes with astigmatism and affecting factors.Methods A series case-observational study was adopted.One hundred and twenty-seven myopic eyes with astigmatism of 66 patients who received LASIK in 2008 May through 2010 January in Beijing Tongren Hospital were retrospectively analyzed to evaluate the change of cornea posterior elevation following the LASIK.The parameters related to cornea posterior elevation were measured and compared before and 3 months,6 months and 1 year after surgery,respectively,with Oculyzer anterial segment analysis system.Results The height values from posterior cornea highest point,the lowest point and central vertex central elevation zone were (12.20±3.39),(-19.02±7.38) and (1.05 ±3.25) μm respectively before LASIK and were (14.38±3.80),(-18.55±7.11),(2.83±4.81)μm in3 months and (13.99±3.38),(-17.57±6.54),(2.45±4.61) μm in 6 months after LASIK.They were (14.40±3.85),(-17.76±6.00),(2.16±5.00) μm in 1 year after surgery.Significant increases were found in the vertex height and central elevation after LASIK compared with before surgery(highest pointq=6.813,5.594,6.875,all at P＜0.001.central vertex:q=4.488,P=0.002;q =3.530,P=0.013 ;q =2.799,P =0.047).However,no significant difference was seen in various time points after LASIK (P＞0.05).A positive correlation was obtained between the height value of the posterior cornea central vertex with the spherical equivalent (SE),maximum cutting depth or cutting proportion 1 year after LASIK (r =0.295,0.297,0.295,all at P=0.001),and there was a negative correlation between it with residual stroma (r=-0.208,P=0.019).The intraocular pressure (IOP) measured with noncontact tonometry (NCT) was (14.24±3.33) mmHg before LASIK,and those of 3 months,6 months and 1 year were (8.42± 1.90),(8.61 ± 1.64) and (8.76± 1.64)mmHg after LASIK,showing a significant lowing in IOP after LASIK in comparison with before LASIK (q =29.851,28.317,26.337,all at P＜0.001).But no significant change was found in the different time points after LASIK (P＞0.05).There was significant difference in the IOP corrected by Ehlers after LASIK (P＞0.05).The IOP before LASIK had positive correlation with the central elevation of posterior cornea surface 1 year after LASIK(r=0.258,P =0.003).Conclusions The cornea posterior elevation increases slightly early stage after LASIK but retains stable level with lapse of time.The refraction diopter before LASIK is the main factor affecting the posterior corneal shape.To reduce the risk of corneal ectasia,more attention should be paid to the reserving of appropriate corneal residual stroma and smallest degree of eccentricity during the ablation procedure.

Comparison of Anterior and Posterior Elevation, and Sagittal Curvature between Keratoconus and Normal Cornea

PURPOSE: To compare changes of anterior and posterior corneal elevation, and sagittal curvature according to the severity of keratoconus and to compare differences between keratoconus and normal cornea. METHODS: A total of 81 eyes diagnosed with keratoconus and 20 eyes of normal subjects were evaluated with a Pentacam Scheimpflug camera. The keratoconus eyes were divided into 3 groups according to mean keratometer (K): mild (K or =). The following parameters were obtained to evaluate the correlation of keratoconus: corneal thickness, anterior and posterior corneal elevation, and sagittal curvature. RESULTS: Out of 81 keratoconus eyes, 56 eyes were mild, 12 eyes were moderate, and 13 eyes were severe keratoconus. The mean central corneal keratometer, anterior and posterior corneal elevation, and sagittal curvature of the keratoconus eyes were 49.7 D, 22.07 microm, 38.16 microm, 52.76 D and the values increased statistically compared to the normal eyes. Furthermore, the values increased significantly with the severity of keratoconus. ROC curve analysis showed the estimated meaningful value for anterior and posterior corneal elevation and sagittal curvature of keratoconus for diagnosis; there were no diagnostic values for corneal thickness and refractive power. CONCLUSIONS: The index of 5.5 microm for mean anterior elevation, 12.5 microm for mean posterior elevation, and 44.5 microm for mean sagittal curvature using the Pentacam(R) are useful to diagnose keratoconus. Variation of anterior and posterior elevation, and sagittal curvature measured by Pentacam(R) are useful in understanding the process of keratoconus.

Posterior elevation maps and mean power keratometric maps to evaluate keratoconus and guide Intacs implantation: a step towards improving Intacs nomogram

Introduction: Keratoconos is a cornea disorder that affects young people and is a contraindication for refractive surgery; it could be treated with contact lens, corneal transplantation or with intracorneal ring segments (Intacs) insertion. Purpose: To compare mean power keratometric maps and posterior elevation maps in delineating keratoconus characteristics and guide Intacs implantation. Methods: 23 eyes with keratoconus, 12 subjects, cone area, cone radii, cone peak area and coordinates were measured using both maps and were compared using t test. Statistical significance was defined as p<0.05. Correlations were assessed with PearsonÆs coefficient. Results: Mean cone area was 17.65 mm² ± 4.63 and 35.68 mm² ± 9.72 in posterior elevation map and mean power keratometric analysis respectively (p 0.00). Both posterior elevation and mean power keratometric maps finds a similar percentage split between centre cones (CC) and de-centered cones (DC) of 78:22. However, 9% cases were found not to match after case to case evaluation. Conclusion: Based on the cases that not matched the cone centration, we suggest a new way to define the cone centre using the mean power keratometric map. Therefore, it should be review the decisions to implant symmetric rings vs. asymmetric rings using posterior elevation map. A new parameter is discussed ½cone peak centration¼ in de-centered cones (DC).

Introducción: El queratocono es una enfermedad que afecta individuos jóvenes y es una contraindicación para realizar cirugía refractiva; se puede manejar con lentes de contacto, queratoplastia o anillos intraestromales (Intacs¼). Propósito: Comparar los mapas topograficos mean power keratometric y elevación posterior en la delineación de las características del queratocono y guiar el implante de Intacs. Métodos: Se evaluaron 23 ojos con queratocono en 12 sujetos. Se midió el area del cono, el radio del cono, el area del pico del cono y sus coordenadas, en ambos mapas y se compararon usando la prueba t. La diferencia estadística se definió como p<0.05. Se realizaron correlaciones con el coeficiente de Pearson. Resultados: La media del ßrea del cono fue de 17.65 mm² ± 4.63 y 35.68 mm² ± 9.72 en el analisis con el mapa de elevación posterior y el mean power keratometric respectivamente (p 0.00). En ambos mapas se encontró un porcentaje de distribución similar entre conos centrados (CC) y conos descentrados (DC) de 78:22. Sin embargo, en la evaluación caso a caso, en 9% de los casos no hubo concordancia. Conclusión: Soportados en los resultados de la no concordancia con respecto a la centración del cono, se sugiere una nueva manera de definir el centramiento del queratocono usando el mapa mean power keratometric¼ y por tanto la decisión de implantar Intacs¼ simétricos o asimétricos sobre el modo tradicional con elevación posterior. Se discute un nuevo parametro la centración del pico del cono en DC.

The Early Change of Posterior Corneal Sureace after LASIK Sugery

PURPOSE: To evaluate posterior corneal surface elevation after LASIK in relation to the residual stromal bed thickness and the ablation percentage. METHODS: 363 eyes that underwent LASIK were examined retrospectively. The range of their refractive error was from -1.5 to -10.0 D. We obtained their corneal topography with Orbscan II and pachymetry preoperatively, and at one week, one month, two months, and three months postoperatively. The patients were divided into four groups based on the residual stromal bed thickness: Group I; 145 eyes with less than 250 micrometer, Group II; 129 eyes with 250~300 micrometer, Group III; 79 eyes with 300~350 micrometer, and Group IV; 13 eyes with more than 350 micrometer. We also grouped them based on the ablation percentage per total corneal thickness: Group A; 16 eyes with less than 10%, Group B; 166 eyes with 10~15%, Group C; 149 eyes with 15~25%, and Group D; 35 eyes with more than 25%. RESULTS: The extent of increase in the post-LASIK posterior corneal surface elevation correlates with residual corneal bed thickness and the ablation ratio per total cornea. In contrast, posterior corneal elevation values for Group IV were 0.025+/-0.005 mm preoperatively, 0.038+/-0.007 mm at 1 weeks, 0.037+/-0.010 mm at 1 month, 0.03+/-6 0.012 mm at 2 months, 0.036+/-0.009 mm at 3 months. In Group A, the values at the same times were 0.029+/-0.009 mm, 0.043+/-0.012 mm, 0.039+/-0.013 mm, 0.040+/-0.013 mm, 0.038+/-0.010 mm. CONCLUSIONS: The extent of increase in the post-LASIK posterior corneal surface elevation correlates with residual corneal bed thickness and the ablation ratio. There were no statistically significant changes in postsurgical posterior corneal surface elevation, however, if the residual corneal thickness remained more than 350 micrometer or the ablation percentage was lower than 10%.