Conductive Keratoplasty Monovision for Presbyopia (Nearvision CK)

The ViewPoint CK System has been approved by the FDA (on 02/2004) for the temporary induction of myopia, from -1.00 to -2.00 diopters, for improvement of near vision in the non-dominant eye of presbyopic hyperopes and presbyopic emmetropes with a successful preoperative trial of monovision or history of monovision wear.

Over 80 percent of patients achieved uncorrected distance vision of 20/20 or better alongwith J3 or better near vision i.e. functional vision which allows an individual to perform most routine activities without eyeglasses.

Monovision is a method of presbyopic correction whereby the dominant eye is usually corrected for distance vision and the nondominant eye corrected for near. Monovision treatment performed with conductive keratoplasty is the same procedure as was approved for hyperopia treatment in April 2002, using the same device, same energy, same spot pattern and the same range of correction, but with a refractive target of -1.00 to -2.00 diopters.

The term 'blended vision' was introduced by Refractec with the intent to distinguish monovision achieved with conductive keratoplasty technique from monovision achieved with other methods like contact lens, LASIK etc. This term is unnecessary and is to be avoided as it can misleadingly imply that there is a difference between 'blended vision' and 'monovision'. At FDA's insistence, Refractec has dropped 'blended Vision' from its labeling. Refractec is now marketing this procedure as 'Nearvision CK' for baby boomers. This is another attempt to avoid using the term 'monovision'. Whether it is marketed as 'Nearvision CK' or 'Blended vision CK', the underlyng principal by way of which conductive keratoplasty procedure corrects presbyopia is by creating monovision.

Conductive Keratoplasty (Refractec, Inc. Irvine, CA ) builds upon the principles of thermokeratoplasty, using radiofrequency (RF) energy to reshape the cornea and therefore adjust its refractive characteristics. CK may be performed for low to moderate hyperopia (between +0.75 and +3.00 diopters). To perform the procedure, a handpiece with a Keratoplast Tip delivers controlled RF energy directly to the corneal stroma in a ring pattern. Conductive Keratoplasty creates a purse-string effect that steepens the central cornea through a ring of application spots around the periphery of the cornea. Several studies have concluded that the depth of shrinkage determines the degree of corneal correction. CK seems to be safe, effective, and stable for correcting low to moderate spherical hyperopia in patients 40 years old or older. Uncorrected visual acuity, predictability, and stability are as good as or better than those obtained with other techniques used to correct hyperopia.

The clinical technique of monovision is widely accepted and has a long history of use. In their comprehensive 1996 review, Jain and colleagues concluded that monovision is an effective and reasonable therapeutic modality for correcting presbyopia. They also noted that proper patient selection and clinical screening are essential for monovision success. Currently, monovision may b achieved in our practices by means of contact lenses, intraocular lenses or refractive techniques such as PRK or LASIK. Nonetheless, monovision is not without its limitations. Even in satisfied, successful monovision patients, it is common to find decreased contrast sensitivity and reduced stereopsis in selected patients, and this is, of course, due to the monocular blur. It has also been widely reported in the published literature that patients can experience glare and other night vision difficulties. There are also a few case series and case reports of patients having more severe binocular vision anomalies associated with monovision. Now these monovision related issues serve to emphasize the need to balance good near visual acuity with maintenance of comfortable binocular vision. In essence, the goal or the challenge is to provide or to attain some intraocular blur suppression. It is well known that the quality of this suppression is associated with a number of factors, in particular, the magnitude of the reading addition.

A number of factors contribute to a successful monovision patient. Careful pre-screening of patients is important, along with a contact lens monovision trial or a history of successful monovision contact lens wear. As mentioned previously, it is important to maintain an appropriate level of binocularity, and this can be achieved by limiting the add power. It has been documented that add powers higher than 1.5 to 2.0 diopters can result in a loss of binocular summation and associated problems. Finally, patient education is critical. Patients need to understand, of course, that monovision is a compromise between distance vision and near vision. There are potential for symptoms well documented and, most importantly, there may be a need for continued spectacle use, even though, hopefully, in a successful monovision patient, that dependence on spectacles would be substantially reduced.

AgingEye Times comments:

Monovision can be achieved using many techniques of which Conductive keratoplasty is one. Having gone through the rigors of an FDA approval process, Monovision technique for presbyopia has emerged as a safe and effective way to achieve functional vision. We expect the choice of technique to achieve Monovision (CK or contact lenses or LASIK) to largely depend upon a surgeon's experience with the particular technique and patient preference.

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