Eyeworld

EW INTERNATIONAL 114 October 2016 by Cesar Carriazo, MD relation to the severity of corneal ectasia. Our proposal is not to perform a wedge resection 8,9 as was described years ago. Although this is a similar concept, the wedge creates an effect between the anterior and posterior faces of the cornea that is neither uniform nor symmetrical. We propose performing a cres- cent resection with excimer laser on parallel faces in order to reshape symmetrically both faces of the cornea and to be able to standardize the process depending on the level of keratoconus. We did a computer simulation that allowed us to verify the clinical results we obtained and adjust the settings of the surgical nomogram. Figure 1 shows the first three cases performed. Today, we have 22-month postop follow-up. It shows a significant reduction of the anterior chamber depth and the high order aberrations, especially coma. These changes allow them to gain lines of visual acuity. 7 Based on these results we can safely say that this technique, which we have named corneal lifting, is T he pathogenesis of kerato- conus is multifactorial, with evidence of inflammatory imbalance and oxidative biochemical processes that take place in response to trauma or rubbing of the corneal surface that result in the thinning and scarring of the central part of the cornea. In keratoconus, stromal tissue becomes thinner and loses its normal anatomical structure. It is asymmetri- cally redistributed with the negative effect of steepening or elongating the corneal curvature radii, and this gen- erates a displacement of the anterior and posterior faces of the cornea and, therefore, an increase in the anterior chamber. 1,2 In other words, the progression of keratoconus is accompanied by an enlargement of the anterior chamber due to an increase in the posterior corneal curvature, a thinning of the cornea, and asymmetric and pro- gressive corneal steepening. Currently, corneal ectasia, de- pending on its classification, presents different treatment options: cross- linking, intracorneal rings, lamellar and penetrating keratoplasty. 3 Recognized more than 20 years ago as the only treatment that can direct the course of keratoconus along a less devastating route, cross- linking has a limited effect. Even though some patients, especially those with low-grade ectasia, expe- rience a significant improvement in visual acuity with this treatment, it is not a predictable refractive technique for the management of ectasia. 4,5 As a second alternative, intra- corneal rings are used as an ortho- pedic treatment of ectasia, causing a flattening of the cornea with results that are also hard to predict and are associated with higher-order corneal aberrations due to being positioned in the optical zone of the patients. 6 It is important to mention that the area where the corneal segments are implanted and the adjacent area reduce the size of the real refractive optical zone in these patients. Since this increased thickness creates a flattening of the cornea that reduces corneal aberrations, it is quite far from providing good visual quality for the patient. Today's use of either lamellar or penetrating keratoplasty is not ap- plicable in early stages of the disease and is only advisable when corne- al transparency is compromised, during the more advanced stages where the previously mentioned techniques cannot be used to help the patient. It is important to point out that poor visual acuity and higher-order aberrations in patients with kera- toconus are caused by the irregular astigmatism, and not due to the thinning of the cornea per se. In other words, corneal thinning does not produce poor visual acuity, rath- er decreased visual acuity is caused by the asymmetrical topographies associated with keratoconus. Considering this, and under- standing the biomechanical changes that occur in keratoconus, we can say that to physiologically correct this pathology, we must find a type of surgery that reverses the phenome- non that characterizes this disease— which is the same as saying that the cornea regains its thickness, thus normalizing its curvature radii and returning to its original symmetry. We can therefore state that, conceptually, crosslinking is a more physiologically focused surgical technique than corneal segments. However, I think that neither the predictability observed nor the general results achieved with the use of corneal segments are a satisfac- tory option for refractive surgeons whose end goal is to attain good visual acuity for patients. I also consider that from a phys- iological point of view it is hardly effective to deform a structure that was previously deformed in order to achieve a partial recovery and poor visual acuity. For the reasons above and for the purpose of finding a more physiologically sound approach in the management of keratoconus, we have introduced a new and unique concept for the management of this pathology. 7 Our proposal is to reshape the ectatic structure of the cornea, altering the radius of curvature by performing a crescent resection keratotomy assisted by laser technol- ogy (excimer or femtosecond laser) varying in degree and/or width in Keratoconus: Is it being properly managed? Figure 1 shows the first three cases performed. There was a significant reduction of the anterior chamber depth and the high order aberrations, especially coma. These changes allow them to gain lines of visual acuity. Source: Cesar Carriazo, MD, and Maria José Cosentino, MD continued on page 116

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