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Ophthalmology Emphasizing Corneal and Refractive Issues

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Repair the Microdehiscence

The microdehiscence is a topographic result of asymmetric incisons and/or wound healing. Figure A shows a cornea with a trauma involving a small midcorneal perforation at about 6 oclock. This results in localized corneal flattening shown by the “teardrop” shaped rings shown in Figure A which would appear as a blue colored asymmetric spot on corneal topography. Computer interpreted corneal topography is sometimes unreliable in interpreting these patterns and sometimes it pays to examine the ring data for these patterns. Assymetric incisions cause irregular astigmatism  on this basis.

Figure B shows a microdehiscence in the context of a corneal transplant (at about 2 oclock). In this case, the cornea transplant is symmetrical about the visual axis but wound healing is asymmetric with a wound healing problem at the point of the microdehiscence. Figure C shows the pathology of the problem, poor wound healing has resulted in a plug of epithelium  unable to heal because of inadequate suture tension across the graft edge. If this situation were present around the entire graft edge (such as in premature removal of sutures or loosely tied running suture) it would result in the appearance of “thick” graft wound and a steep central corneal curvature. Because of the extra tissue around the edge of the wound, it would be as if the donor were oversized relative to the host opening. This is a good argument for proper wound closure with the torque anti-torque PK wound closure and against premature removal of sutures merely for short term astigmatic correction. If asigmatism occurs during the “sutures in” postop period after PK it is preferable to add a suture to increase tension across the wound and to permanently correct the pathology which caused it.

Figure D shows a corneal transplant approximately 2 months postop with a relatively spherical central cornea and a microdehiscence at about 6 oclock. While one might argue that the microdehiscence is causing no trouble and elect to do nothing, figure E shows the same patient 2 months later. Now the central cornea has a significant astigmatism with the flat axis at about 20 degrees and the microdehiscence has gotten larger at about 7 oclock. Imagine correcting the central astigmatism by removing sutures at 5 ocklock. This would further destabilize the graft edge and while a temporary correction of central astigmatism might result, long stability of the cornea would in all likelihood be compromised. Similarly, adding a suture along the flat axis at 20 degrees would correct central astigmatism  but would not correct the real problem at 7 oclock (the microdehiscence).

Figure F shows the result of adding additional sutures at 7 oclock. The central astigmatism has been improved and the microdehiscence is gone. In figure G the sutures have been removed and the central cornea remains spherical. This shows that the short term objective of reducing astigmatism during the “sutures in” phase of the corneal transplant can be combined with repairing the microdehiscence to produce a stable long term transplant.

The pathophysiology of this repair is also simple to understand. In “normal” wound healing, the wound is filled with and epithelial plug and microfibrils stretch across the wound to pull it closed and exp ell the epithelial plug. When the wound gapes too much the sides cannot be closed by physiologic means. Additional tension across the wound (by means of a suture) brings the edges together allowing nature to take her course.  

Buzard K.: "Repair of the 'Microdehiscence' to Correct Post Keratoplasty Astigmatism", Ophthalmic Surgery, Vol. 20, No. 12, December 1989, pp 876-82.

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