The KAMRA corneal inlay (CorneaGen) works on the principle of small-aperture optics. Another way to think about it is pinhole optics, in which the aperture size is reduced to increase the depth of focus by cutting out all the blurry peripheral rays. To you and me, this concept is easy to understand; to some of our patients, however, it might not be. For this reason, it is important to have a few tricks up your sleeve when explaining to patients the difference between monovision and the KAMRA inlay.
Patients who understand photography can relate to the idea of a small-aperture optic because it is the same as changing the f-stop on a camera to enable focus of various objects at different distances simultaneously. For those who are not photography enthusiasts, I will sometimes ask the patient if he or she has ever lost a pair of glasses and made a small circle with the thumb and forefinger in order to be able to see at distance. Most can relate to this easily.
DEMONSTRATION WITH a PINHOLE
Another tactic is to use a pinhole occluder, placing the pinhole on the eye in which the KAMRA inlay will be implanted (see Pinhole Demonstration: Step-by-Step). Immediately the patient can see the difference in reading ability with the inlay compared to what they are currently experiencing.
In addition to showing the patient the improvement in his or her near vision, wearing the pinhole glasses also demonstrates how the KAMRA inlay will not affect distance vision. We can then compare that vision with the pinhole to monovision, so that the patient better understands the amount of distance vision he or she could lose with monovision.
The KAMRA inlay is not a monovision strategy, as the patient is fully binocular at distance, whereas with monovision they are not. The other advantage to the inlay over monovision is that it will last throughout the full progression of presbyopia.
Once patients see the benefits of the KAMRA inlay versus monovision, it is also important to explain to patients that the inlay works best when the inlay eye is a little myopic (-0.75 D). In this range, patients can achieve about 20/25 or 20/20 distance visual acuity and get the full 2.50 D effect at near. On the other hand, we find that patients with a +0.50 D refraction pre-KAMRA inlay, will do well at distance but not nearly as well as they want up close. It is also important that the dominant (non-KAMRA inlay eye) be as close to plano as possible. Otherwise, that eye will drag down the other eye at near.
Pinhole Demonstration: Step-by-Step
1. Determine patient's non-dominant eye and current distance refractive error.
2. Have patient wear trial frame with dominant eye occluded and non-dominant eye slot empty.
3. Ask patient to read lowest line possible on near reading card.
4. Add single pinhole occluder to empty eye slot in front of non-dominant eye.
5. Ask patient to read lowest line possible on near reading card and then look at distance.
6. Add +0.75 D trial lens in front of the non-dominant eye, leaving the pinhole occluder in place. Repeat step 5.
7. Remove pinhole occluder and leave +0.75 D lens in place to demonstrate monovision and repeat step 5.
8. Show patient the difference in his or her vision and how the KAMRA inlay improves depth of focus.
Getting patients to understand the concept of the KAMRA corneal inlay does not have to be difficult. With a brief explanation and use of pinhole occluder to demonstrate the visual scenario with the inlay, most patients will understand the difference between near and distance vision with an inlay and with monovision.
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