Unilaterally impaired patients can benefit from Boston type I keratoprostheses

Until recently, keratoprostheses were only considered for patients with bilateral severe visual impairment. Previous authors have argued that there is no need to subject patients with unilaterally good vision to a surgery that is associated with a multitude of potential postoperative complications and requires intensive follow-up. However, with the goal of expanding indications for the Boston type I keratoprosthesis, a recent study reported excellent visual outcomes in patients who had preoperative visual acuity better than 20/50 in the contralateral eye. This begs a fundamental question: What is gained by performing keratoprosthesis implantation for patients with unilateral visual impairment?

In this prospective study, researchers assessed the binocular function, including both motor and sensory outcomes, in 17 patients who underwent implantation of a Boston type I keratoprosthesis and had a best-corrected visual acuity of better than 20/50 in the contralateral eye. 

At a mean follow-up of 21 months, all but one patient demonstrated some degree of binocular function, as defined by the demonstration of first-degree fusion with the use of the Bagolini lens test.  Second-degree fusion at near was demonstrated via the Worth-4-dot test in 13 patients, and stereopsis (third-degree fusion) was demonstrated in seven patients. Patients with better postoperative sensory binocular function tended to be of younger age (P = 0.05) and have better postoperative visual acuity (P = 0.006). Five patients were found to have some degree of ocular misalignment. Overall, patients with strabismus had worse binocularity (P = 0.04).

The authors conclude the combined  improvement in vision-related quality of life, improved motor skills, and improved patient safety are important indications for keratoprosthesis implantation in patients with unilateral visual impairment. They note that two of the three patients who regained visual acuity better than 20/80 after surgery without regaining stereopsis had some degree of strabismus diagnosed before surgery. As such, preoperative evaluation should include a careful assessment of visual potential and ocular alignment.