Temporary Keratoprosthesis Vitrectomy
by  C. Douglas Witherspoon, MD

Originally published in "VitreoRetinal Surgery & Technology-The Newsletter of Vitreoretinal Surgeons,"Volume 1, Number 1, January/February 1989

Temporary keratoprosthesis (TKP) vitrectomy is a useful approach to the treatment of patients with severe posterior segment disease combined with corneal opacification. Such patients include those with severe combined anterior and posterior segment trauma; retinal detachment combined with pseudophakic bullous keratopathy or graft failure; and fulminant bacterial endophthalmitis....  We believe TKP deserves greater consideration relative to the alternatives of no surgery, consecutive penetrating keratoplasty and vitrectomy, limited vitrectomy, endoscopy or eneucleation.

Planing, Preparation
After ultrasound/VEP/ERG evaluation and thorough patient counseling, initial surgical steps include conjunctival peritomy and isolation of the rectus muscles on traction sutures if scleral buckling is anticipated. A Flieringa ring to aid in TKP emplacement is optional.

A 6-mm infusion cannula is secured to the sclera, 3.5mm posterior to the limbus and usually in the inferotemporal quadrant, avoiding abnormal anterior structures.  If choroidal detachment, scarring or retinal detachment is suspected anteriorly, insertion of the infusion cannula is delayed until after trephination of the cornea to allow for direct viewing of the anterior structures prior to emplacement.  In any case, the infusion cannula is not turned on until it can be ascertained that the tip of the cannula is in the vitreous cavity and free of any obstructing material.  We prefer the use of gas-forced liquid infusion to allow for rapid and accurate changes in intraocular pressure often necessitated by this procedure.   

The recipient corneal bed is best created with a vacuum trephine.  The trephine is usually centered on the cornea, even in the presence of freshly closed lacerations which will be contacted.  An 8-mm recipient bed is used for the Lnaders-Foulks-Mannis keratoprosthesis (8.2mm, hard plastic); a 7-mm bed is used for the 7.5-mm Eckhardt silicone-rubber prosthesis. The Eckhardt TKP is said to be disposable, although it may be reused several times.  It is relatively more difficult to insert, but upon insertion it provides an excellent view of the peripheral vitreous cavity. Emplacement of all keratoprosthesis requires an aphakic eye and is best achieved with stabilization of the TKP by an assistant; for example, slight downward pressure with a cotton-tipped applicator as the Landers prosthesis is rotated....

Most injuries requiring TKP vitrectomy involve considerable disorganization of the anterior segment in the form of iris loss, hyphema, lens laceration and ciliary body laceration.  Not infrequently, the retina is highly detached and approaching the anterior segment.  After trephination of the cornea, meticulous open-sky reconstruction of the anterior segment, including viewing of the infusion cannula, is advisable prior to TKP emplacement.

Vitrectomy Proceeds
Once the TKP is secured to the cornea, closed posterior vitrectomy can take place as usual.  The four-strut Landers TKP requires no supplemental contact lens, but scleral depression is necessary to completely view the retinal periphery.  The Eckhardt TKP requires a supplemental contact lens.  Air-fluid exchange causes the Landers prosthesis to fog with water vapor; however, a small amount of viscoelastic material placed on the internal surface of the prosthesis will provide an adequate view.  Following vitrectomy, scleral buckling may be performed in the usual fashion, preferably prior to corneal transplantation.

Using optimal donor tissue, we have achieved late graft clarity in over 80% of stable eyes, which is comparable to elective transplantation.   Silicone oil keratopathy has not been a significant problem when the use of silicone oil has been essential for retinal reattachment.

With proper attention to details, severely damaged eyes may be salvaged with TKP techniques.  Many of these eyes would otherwise be lost because of delayed or inadequate surgery.  The decision for attempted reconstruction or for enucleation can then be made in a timely manner, in keeping with the surgeon's experienced judgment and the patient's perceived wishes....

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