Estudio de la densidad corneal medida con cámara de scheimpflug en sujetos con queratocono
- Autores: Mª. Josefa Fernández García
- Directores de la Tesis: Miguel Ángel Teus Guezala (dir. tes.), Pedro Beneyto Martín (codir. tes.)
- Lectura: En la Universidad de Alcalá ( España ) en 2013
- Idioma: español
- Tribunal Calificador de la Tesis: José Manuel Benítez del Castillo Sánchez (presid.), María Consuelo Pérez Rico (secret.), Carmen Pizzamiglio Martin (voc.), David Díaz Valle (voc.), María Mercedes Cabezas León (voc.)
- Materias:
- Enlaces
- Tesis en acceso abierto en: TESEO
- Resumen
- español
Introducción: El queratocono es una ectasia corneal no inflamatoria, en la que la córnea adquiere una forma cónica debido al adelgazamiento estromal. La transparencia corneal depende de sus características histológicas. Se puede medir mediante el fenómeno de la dispersión de la luz intraocular. El Pentacam es un instrumento basado en la cámara de Scheimpflug que permite obtener imágenes del segmento anterior y la medición de la densidad corneal o dispersión retrógrada de la luz.
Hipótesis y objetivos: Tomando como hipótesis que la densidad óptica corneal medida con cámara de Scheimpflug está alterada en el queratocono, analizamos si la densidad corneal medida con cámara de Scheimpflug en sujetos con queratocono en el ápex y en la periferia media (lo que denominamos "densidad general"), es diferente a sujetos con astigmatismo elevado y la población general. Como objetivos secundarios estudiamos la relación entre la densidad corneal y la severidad de la enfermedad. Estudiamos el valor pronóstico de la densidad corneal con respecto a la evolución de la enfermedad (medida en aumento de dioptrías de astigmatismo corneal). Analizamos la correlación de los valores de la densidad en el centro y en la periferia media en los tres grupos. Medimos la densidad corneal en diversos puntos en córneas sanas con el fin de determinar valores umbrales y un patrón de distribución. Y analizamos la relación entre la densidad corneal y la edad.
Resultados y conclusiones: 1. La densidad corneal en el ápex del queratocono medida con Pentacam fue mayor que en el grupo de sujetos normales y que en el grupo de sujetos con astigmatismo. Estos resultados podrían explicarse por la existencia de alteraciones del tejido corneal en el queratocono que los diferencia del resto. 2. No encontramos diferencias estadísticamente significativas al comparar densidad general en el grupo de queratoconos con el resto. 3. No encontramos diferencias estadísticamente significativas al comparar la densidad en el centro corneal del grupo de sujetos con astigmatismo con el grupo control. Por tanto, el astigmatismo no condiciona diferencias en la medida de la densidad corneal con Pentacam. 4. Encontramos una correlación positiva entre la densidad en el ápex corneal y el grado de queratocono. La transparencia corneal podría ser, de acuerdo con estos hallazgos, un parámetro ligado al deterioro de la enfermedad. 5. No encontramos diferencias estadísticamente significativas al comparar la densidad corneal en sujetos con queratocono y los signos de progresión. Esto podría ser debido a las limitaciones de nuestro estudio por lo que un mayor tamaño muestral y un tiempo de seguimiento más prolongado podrían hacer alcanzar la significación. 6. Encontramos una correlación entre la densidad del ápex o centro corneal y la densidad general en los tres los grupos. 7. El valor de la densidad corneal a diferentes distancias en sujetos sanos es superior al de los estudios previos. No hemos encontrado diferencias estadísticamente significativas al comparar estos valores con el valor en el punto central. 8. Encontramos una correlación entre la densidad general y la edad en sujetos sanos y en el grupo de sujetos sanos y astigmatismo.
- English
Keratoconus is a bilateral noninflammatory corneal ectasia in wich the cornea assumes a conical shape due to stromal thinning. Aetiology is unknown. Corneal transparency depends on histologic characteristics, specially on the morfology and homogeneity distribution of collagen fibers. It can be measured by intraocular light scattering, an optical phenomenon that degrades the retinal image. It has two elements: forward scattering (towards the retina) and backscattering (towards the light source).
The Pentacam is a Scheimpflug camera based system that obtains anterior segments images and permits measuring corneal density or backscattered light. Our hypothesis Is that optical corneal density measured with the Scheimpflug camera is altered in keratoconus, so we analyse if corneal density measured with the Scheimpflug camera at the apex and mid periphery, are different than those in subjects with high astigmatism (> 3 diopters (D)) and general population.
As a secondary purpose, 1) the relation between corneal density and the severity of keratoconus is studied. 2) Progression of keratoconus is measured in terms of increasing of corneal astigmatism diopters during a mean period of 34 months (range 11-62 months). 3) Correlation between central corneal density and mid periphery is also analyzed in all groups. 4) Corneal density at differents distances from the center is measured in healthy subjects in order to determine a threshold value and a distribution pattern. 5) The relation between corneal density and age is also analysed.
Apex corneal density in keratoconus was higher than at the center of the control group and the astigmatism group (p= p<0,001 y p=0,001 respectively). Mid periphery corneal density was also higher in keratoconus, but no statistic differences were found. Due to corneal transparency is based on its structural characteristics, these results could be explained because of corneal tissue alterations occurring in keratoconus such as colagen fibers, keratocytes or ground substance alterations as are described in previos studies. No statistic differences were found when comparing central and mid periphery corneal density between the astigmatism group and the control group (p=0,819 y p=0,434 respectively). So, astigmatism itself may not be a confounding variable.
A positive correlation between the severity of keratoconus and corneal density at the apex was found (r=0,213; p=0,043). According to these results, corneal transparency may be a consequence of keratoconus worsening. Corneal density in keratoconus as a progression parameter was studied. Progression was measured as increasing of astigmatism diopters. Corneal density values were higher in those subjects with more increasing of corneal astigmatism, but no statistic significant differences were found (p=0,216 when augmenting 1 or more diopters; p=0,260 when augmenting 2 or more diopters). A larger sample and a longer monitoring period could obtain statistic significant differences.
We found a correlation between apex and mid periphery corneal density in all groups (r=0,465 and p<0,001 for the keratoconus group; r=0,760 and p<0,001 for the astigmatism group; r=0,738 and p<0,001 for the control group). Corneal density at different points was analyzed in order to stablish threshold values and a distribution pattern. Our values were higher than those described in other published studies, but as they do, we also found a decreasing tendency of density values from the apex to the periphery. No significant differences were found in comparing the central corneal density values to some points located at different distances.
The correlation between corneal density and age was studied. There were significant differences between the mid periphery corneal density values and age in controls and the control and astigmatism group (r=0,414; p=0,003 and r=0,374; p<0,001, respectively).
Conclusions:
1. Apex corneal density in keratoconus measured with Pentacam was higher than at the center of the control group and the astigmatism group.
2. No statistic significant differences were found when comparing mid periphery corneal density between keratoconus and contro or stigmatism groups.
3. No statistic significant differences were found when comparing central and mid periphery corneal density between the astigmatism group and the control group. So, astigmatism itself may not be a confounding variable.
4. A positive correlation between the severity of keratoconus and corneal density at the apex was found.
5. No statistic significant differences were found when comparing corneal density and progression (incrasing of 1 or more astigmatism diopters) in keratoconus. A larger sample and a longer monitoring period could obtain significant differences.
6. A positive correlation between apex or central corneal density and mid periphery corneal density was found in all groups.
7. Corneal density at different points in healthy subjects was higher than previous plublished studies. No statistic significant differences were found when comparing corneal density values at the center and at different distances.
8. Statistic significant differences between the mid periphery corneal density values and age were found in controls and controls and astigmatism group.
- español
