EVect of disagreement between refractive, keratometric, and topographic determination of astigmatic axis on suture removal after penetrating keratoplasty

Background/aims—Post-keratoplasty astigmatism can be managed by selective suture removal in the steep axis. Corneal topography, keratometry, and refraction are used to determine the steep axis for suture removal. However, often there is a disagreement between the topographically determined steep axis and sutures to be removed and that determined by keratometry and refraction. The purpose of this study was to evaluate any diVerence in the eVect of suture removal, on visual acuity and astigmatism, in patients where such a disagreement existed. Methods—37 cases (from 37 patients) of selective suture removal after penetrating keratoplasty, were included. In the first group “the disagreement group” (n=15) there was disagreement between corneal topography, keratometry, and refraction regarding the axis of astigmatism and sutures to be removed. In the second group “the agreement group” (n=22) there was agreement between corneal topography, keratometry, and refraction in the determination of the astigmatic axis and sutures to be removed. Sutures were removed according to the corneal topography, at least 5 months postoperatively. Vector analysis for change in astigmatism and visual acuity after suture removal was compared between groups. Results—In the disagreement group, the amount of vector corrected change in refractive, keratometric, and topographic astigmatism after suture removal was 3.45 (SD 2.34), 3.57 (1.63), and 2.83 (1.68) dioptres, respectively. In the agreement group, the amount of vector corrected change in refractive, keratometric, and topographic astigmatism was 5.95 (3.52), 5.37 (3.29), and 4.71 (2.69) dioptres respectively. This diVerence in the vector corrected change in astigmatism between groups was statistically significant, p values of 0.02, 0.03, and 0.03 respectively. Visual acuity changes were more favourable in the agreement group. Improvement or no change in visual acuity occurred in 90.9% in the agreement group compared with 73.3% of the disagreement group. Conclusions—Agreement between refraction, keratometry, and topography was associated with greater change in vector corrected astigmatism and was an indicator of good prognosis. Disagreement between refraction, keratometry, and topography was associated with less vector corrected change in astigmatism, a greater probability of decrease in visual acuity, and a relatively poor outcome following suture removal. However, patients in the disagreement group still have a greater chance of improvement than worsening, following suture removal. (Br J Ophthalmol 2000;84:837–841) Corneal astigmatism after penetrating keratoplasty (PK) is a common complication that can prevent a good visual outcome in an eye with a clear graft and an otherwise healthy visual system. It arises from many causes related to the recipient cornea, 2 trephination of the donor material, trephination of the recipient bed, suturing of the donor cornea to the recipient bed, and during postoperative management. Many procedures are adopted to reduce astigmatism after corneal graft. Selective suture removal is the most common practice adopted postoperatively while the sutures are in place. The eVect of suture removal on post-PK astigmatism has been documented in many studies. The theoretical advantage of selective suture removal is that the surgeon can modify astigmatism while sutures are in place, allowing the patient to receive spectacles or contact lenses between the fifth to seventh postoperative month. However, it should be borne in mind that removal of two adjacent sutures early in the postoperative period could result in slippage and the formation of a step at the graft-host interface. Clinical examination, refraction, keratometry, and topography are the standard tools used to define the sutures to be removed. Refraction and keratometry indicate only one steep corneal meridian while corneal topography can identify one or more steep semimeridians, which are not necessarily 180° apart. In most cases the astigmatism is fairly regular, and refraction, keratometry, and corneal topography indicate the same astigmatic meridian and identify the correct sutures to be removed. However, in some cases, despite the astigmatism being regular, and in most cases where the astigmatism is irregular, refraction, keratometry, and corneal topography are not always consistent in identifying the steep meridians/ Br J Ophthalmol 2000;84:837–841 837 Division of Ophthalmology and Visual Sciences, University of Nottingham, University Hospital, Queen’s Medical Centre, Nottingham NG7 2UH A R S Sarhan H S Dua M Beach