Annulo-aortic ectasia for example refers to a proximal dilatation of the aortic root and its diagnosis is based on the increase in aortic wall diameter. It occurs in Marfan syndrome, in which the cornea also thins and flattens read: Keratoconus and the Marfan paradox. This is supported by the inspection and proper interpretation of curvature and elevation maps of keratoconic eyes. A mild inferior steepening is often found as a topographic sign in early forms of keratoconus: The curvature map left shows a mild inferior steepening. One should not interpret this as an area of local protrusion.
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Annulo-aortic ectasia for example refers to a proximal dilatation of the aortic root and its diagnosis is based on the increase in aortic wall diameter.
It occurs in Marfan syndrome, in which the cornea also thins and flattens read: Keratoconus and the Marfan paradox. This is supported by the inspection and proper interpretation of curvature and elevation maps of keratoconic eyes. A mild inferior steepening is often found as a topographic sign in early forms of keratoconus: The curvature map left shows a mild inferior steepening.
One should not interpret this as an area of local protrusion. On the contrary, this area of the cornea is located in a more posterior plane than its superior counterpart, as shown on the vertical crossectional image taken by the Scheimplfug camera red arrow , and also demonstrated on the elevation map, which reveals a more negative elevation relative to the best fit sphere. This change in corneal curvature occurred in a patient after a number of years of vigorous eye rubbing.
The red area corresponds to a zone where the local curvature is more pronounced: The orange-red area seen in the axial map of the left eye corresponds to a zone where the local curvature is more pronounced this area is located in a plane posterior to its superior counterpart. The elevation map reveals that the elevation is more negative inferiorly. There is no protrusion here. This patient sleeps on his left side, with his head pressed against his hand and forearm. As a result, he developed chronic ocular irritation, which in turn prompted him to rub his left eye vigorously with the knuckles of his index finger, often upon awakening.
The repeated trauma accounts for the corneal deformation seen. From our clinical evaluation of hundreds of keratoconus patients, the first perceived visual symptoms leading to the diagnosis of early keratoconus occurs after 2 to 3 years of intense and repeated eye rubbing. In response to eye rubbing, the buckling and flexure of the corneal fibrils may occur in association with the slippage between collagen fibrils at the cone apex.
The repetitive local trauma alters the viscosity of the ground substance and initiates a temporary displacement of ground substance from the corneal apex. The zone exposed to the trauma from the fingers is often located inferiorly with regards to the geometric center of the cornea. As this zone is located in the paracentral inferior area, this results in a superior flattening and inferior steepening. These changes should not be considered ectatic, as they are isometric, as illustrated in the diagrams below.
Schematic representation of the change in the corneal profile caused by repeated trauma. The initial corneal profile is depicted by an arc of a circle A. It has a constant curvature the green arrow corresponds to the radius of curvature. Repeated trauma exerted on the corneal surface results in asymmetric curvature redistribution B.
Schematic representation of the approximation of the corneal profile vertical cross section obtained with the Scheimpflug camera of the Pentacam topographer.
The profile is symmetrical and can be grossly approximated by a circle the cornea is naturally slightly aspheric, but we will neglect this aspect here. The vertical profile of a keratoconic cornea cannot be grossly approximated by a circle. The vertical asymmetry is the result of the concomitant superior flattening and inferior steepening. It does not correspond to an ectatic protrusion.
The biomechanical alteration causes buckling of the corneal dome, which results in a relative backward position of the inferior steepened cornea arrow. On the axial map, the red zone is not protruding: it is simply steeper, and as such located in a more posterior plane than the flatter superior corneal area. This figure shows the vertical cross section of a keratoconic cornea, for which two different circles have been used to approximate the superior flatter and inferior steeper hemi-corneal profile.
After years of vigorous rubbing, the corneal distortion can become very pronounced, leading to severe irregular astigmatism. While the alteration of the corneal profile is difficult to appreciate in the magnified picture, it is clear that it does not resemble a major protrusion or an ectasia. While the inferior part of the cornea sags and steepens, the superior part of the cornea flattens.
The sagging of the cornea contributes to the vertical inferior displacement of the thinnest point, which is one of the earliest signs of the permanent warpage caused by eye rubbing. Clinical Example This patient was referred for the management of mild keratoconus detected during a recent refractive surgery suitability assessment for low myopia.
Scheimpflug corneal topography revealed the presence of bilateral inferior steepening, more pronounced in the right eye. This patient admitted to rubbing his eyes frequently with his right hand, massaging vigorously in a horizontal motion. He would do so particularly when tired, in the mornings, and under the shower.
There is no protrusion here, as demonstrated by the raw image of the vertical slice taken by the Scheimpflug camera. On the contrary, this is more indicative of warpage of the corneal wall, caused by repeated trauma inflicted by the particular rubbing technique.
The corneal central zone is flattened larger radius of curvature, lower keratometry to compensate for the inferior third of the corneal surface which is concomitantly steepened shorter radius of curvature, higher keratometry. There is no stretching or corneal tissue distension. At this stage, there is no marked corneal thinning. When this particular technique of rubbing is employed, the cornea rubbed by the thumb is usually more affected.
The pulp of the thumb and index finger is softer than the knuckles, and one could predict that if a different technique had been used grinding movements with knuckles , the deformation and thinning would have been more pronounced. The inferior steepening seen in keratoconus should not be confused with and is not synonymous with ectatic protrusion.
Many cases of keratoconus are reported in this website. They all share a history of eye rubbing which preceded the onset of keratoconus. The diagnosis of keratoconus can be life-changing but should not be regarded as tragic.
The disease can be prevented and arrested by the cessation of eye rubbing.
Managing Corneal Warpage
Submit Receive an email when new articles are posted on this topic. Never before have we had so many options available for our patients who desire freedom from spectacles. This is true for all refractive error conditions including astigmatism and presbyopia. However, providing new alternatives to our habitual long-term contact lens wearers poses new challenges. Long-term contact lens wear can alter corneal physiology and corneal topography and can cause transient but substantial refractive error changes. The ultimate goal of rehabilitation is to prevent unnecessary lens re-orders, time and, more importantly, over- or under-corrections after refractive surgery. Operating on or fitting a changing cornea is essentially like chasing a moving target.
Warpage o moldeo corneal
LEBOW, OD The goal of refitting corneal warpage is to return normal radial symmetry to the cornea by distributing lens mass evenly over the corneal surface. Patients with corneal warpage are rarely aware of their problem, and typically overwear their lenses without the benefit of spectacles to use when lenses are off the eye. Visualizing the changes topographically not only helps to define the problem, but also enables the patient to participate in its resolution. Patient History Patient C. She presents with a history of being refit two years ago with RGP lenses that were never comfortable. Wearing time is reduced from all day wear to a maximum of eight to 10 hours. Post-lens wear keratometry shows a moderate cylinder