Reader and Industry Forum
A Novel GP Contact Lens for Presbyopia
By Dorothy Win-Hall, OD
As soft multifocal contact lens options increase, patients' demands for better quality vision with these lenses or any presbyopic contact lens treatment option also increase. In addition, our near-vision demands will only increase as we continue to need to see fine detail on our numerous digital devices.
Soft Multifocal Limitations
Studebaker (2009) suggested that better vision—or a patient's perception of better vision—with soft multifocal contact lenses compared with monovision correction most likely results from binocular summation and stereoacuity provided by correction of both eyes with similar focal distances. The most common complaints from patients wearing soft multifocal contact lenses are a lack of sharpness at far, near or both distances, which could have several causes, among them:
1. The clinician's choice of prescription power emphasis (e.g., reduced distance power with higher add for better near vision, dominant eye center versus nondominant eye center design, etc.)
2. The patient's refractive error, especially if there is uncorrected cylinder and/or higher order aberration
3. The patient's ability to coordinate eye-brain clarity when viewing through competing prescriptions
4. The patient's visual demands.
There is a limit to the design improvements possible for soft multifocal contact lenses, as they inevitably require simultaneous prescription powers in one lens, which will induce blur at some distance, and the lenses themselves are limited to minimal movement on the eye. In addition, older patients often have increased dry eye symptoms from aging or staring for extended periods trying to bring images into focus. In my experience, few have truly been satisfied with their presbyopic contact lens-corrected vision, and most have either accepted the reduced vision or simply (and begrudgingly) chosen to wear reading glasses over distance-corrected contact lenses.
Is it possible to do better? To answer that, we must think beyond what has already been done. For that, let us turn to the GP option.
Novel GP Design
Translating bifocal GP contact lenses have a remarkable design, but they rely on a patient's lower eyelid to push the lenses up enough for the pupil to access the addition correction on the lower part of the lens. With age, the eyelids lose tension and become more flaccid, making the success of this lens variable. My one experience fitting a patient with a translating bifocal GP lens was not successful because of this limitation. The patient did not have problems with comfort or the functional principle of the lens but simply could not see clearly enough through it. I concluded that if the eye could more stably move and position the lens, perhaps the clarity and success of the presbyopic contact lens would improve.
To accomplish this, I designed a new contact lens that offers multifocal powers with a singlepowered lens. This “accommodating” or “focusable” contact lens, is a single unit, single-powered GP lens that has a large overall diameter (OAD) to provide comfort, improve stability and decrease on-eye lens movement (such as the movement found with the traditional ~9mm OAD lens). The anterior portion of the lens is taller than a standard lens, about 2mm to 3mm, and the anterior midperipheral region has a notched area that is large enough for the eyelids to fit into when the wearer squeezes (as if slightly squinting) the eyelids together. This allows the wearer to effectively lift the lens from the eye, increasing the tear film layer beneath and increasing the lens-to-eye distance, both of which will increase positive power to the eye-lens combination, providing a change in power for near correction.
To test the mechanics of this lens, I fabricated a prototype with an OAD of 10.50mm and an anterior height of ~2.80mm (Figure 1). The base curve and GP lens parameters were fitted for my eye. A generous amount of fluorescein dye was instilled onto the back concave portion of the lens, and the lens was placed on my eye. The lens was not uncomfortable, moved well and sat inferiorly on the eye owing to the increased weight of the thicker lens (Figure 2).
Figure 1. Side view of prototype focusable GP lens with anterior notch for eyelids.
Figure 2. Focusable GP lens on author's eye with fluorescein pooled behind lens. The eye is in a normal, relaxed position.
When the upper and lower eyelids came together to engage the notched portion of the lens, they were able to effectively hold and pull the lens anteriorly from the eye. As shown in Figure 3, the fluorescein behind the lens is no longer visible, as it was released by the lens when it was moved away from the eye. This movement of the lens by the eyelids can be consistently performed and is stable, as both upper and lower lids are involved and working together.
Figure 3. Focusable GP lens on author's eye while eyelids have engaged the notched region and are lifting the lens from the eye.
I used GP lens material for two reason. First, it provides the proper structure for the eyelids to engage with the lens, and second, the material will not dry out, even if the patient keeps his eyes open longer to focus or when the lens is not in contact with the eye during attempts to focus in the slight squinting posture. This makes it ideal for older patients who may experience dry eye.
Although the prototype for this new lens concept is still in a preliminary form, on-eye images demonstrate the functionality of the lens on the eye.
The lens needs further development and testing before it is ready for the general market, but the principle behind this design shows potential for a presbyopic contact lens option that would provide better clarity and utility for the older population without the need for additional near aids, such as reading glasses or magnifiers.
The solution to the challenging and complex visual problem of presbyopia continues to frustrate patients and elude practitioners, but continuing to think outside the box to bring new innovations in vision correction to our patients enables us to do better for them. With the ease of pulling a packaged soft contact lens off of a shelf, it is easy to fall into a one-size-fits-all mentality. We should remember that contact lenses are compact optical devices that require a customized fit for customized performance. CLS
For references, please visit www.clspectrum.com/references.asp and click on document #194.
Dr. Win-Hall earned her optometry degree from the University of Houston College of Optometry where she also completed a Low Vision Residency. She practices in Houston. You can contact her at firstname.lastname@example.org.