Reader and Industry Forum
Reader and Industry Forum
Blinking With Scleral Lenses: An Analysis of Problems Involved
BY BEZALEL SCHENDOWICH, OD, FIACLE
The purpose of the blink reflex is to clean, refresh, and rehabilitate the outer eye to keep it healthy. Its flushing action with resulting pumping of the canaliculi works only when the eyelids fully, comfortably, and gently close periodically throughout the day. The wiper phenomenon brings new, fresh tears—along with their ocular nutrients—to the surface of the eye and removes partially dried tears along with their debris and other collected environmental foreign substances. This is the key to a white conjunctiva, a sparkling corneal reflex, and healthy lid margins. A full blink additionally squeezes gently on the meibomian glands to assure a rich, fatty component, increasing the tears’ wetting time on the cornea.
Inefficient, incomplete, or infrequent blinking induced by mechanical, volitional, or neurological causes creates a dry environment for the eye that can eventually cause deterioration in the health of the external eye.
A dry or dry-feeling eye can be primary or secondary. An extensive clarification of dry eye disease is not my purpose here—others have and continue to research and write on this developing topic. However, a few words at this juncture will help to bring into focus an important aspect of ocular surface disease. In short, primary dry eye is a lack of tears, and secondary dry eye is the inefficient use of tears produced by the lacrimal gland, the accessory glands of the conjunctiva, and the meibomian glands of the lid margins.
What Causes Dryness During Contact Lens Wear?
A well-recognized cause of secondary dry eye is a contact lens on the eye. But by what mechanisms do the lenses induce dryness symptoms?
Figure 1. Dense deposits on the outer surface of a scleral lens on a non-blinking eye.
A GP corneal contact lens is felt by the upper lid margin at the beginning of the down sweep of the blink; it is felt under the upper lid as the blink continues; and it is felt by the lower lid margin toward the end of the blink. These sensations trigger an avoidance reaction—the completion of the lid sweep across the eye becomes reduced, and the eye subsequently dries. Injection, 3 o’clock and 9 o’clock staining, loss of corneal epithelium, dellen, and further changes result.
Explaining ocular surface drying with a soft contact lens in situ is more difficult. Perhaps we can postulate that the lens, fully hydrated or partially dehydrated, rides on the cornea and protects the surface from the effects of sun, wind, and foreign bodies. This protection reduces the corneal nerves’ perception of sensation. This decreased sensitivity may reduce the blink reflex to the extent that the contact lens, and consequently the ocular surface, becomes dry.
Post-Refractive Surgery Dryness
Before I can begin discussing the ocular surface around and behind a scleral GP lens, I need to comment on the surgically induced, neurologically mediated dry eye. Perhaps the most common adverse reaction to laser refractive surgery is dry eye. Like many self-reported cases of dry eye, this one seems paradoxical. Patients who report experiencing post-surgical dryness, when asked whether they can cry tears, will affirm that they can. So how do we explain the conundrum: is the eye dry or is it wet(-table)?
In fact, both possibilities are true and correct! How can the eye that can cry be dry? The answer is once again relevant to blinking. An eye that does not blink sufficiently is not rewetted on a continuing basis. That eye dries, but when it does infrequently blink, the tear quality is deficient. When tears are present, they will dry on the surface of such an eye abnormally quickly. Tears may be present, but they are not being efficiently used. These patients must be taught to rehabilitate their blink reflex and effectively treat their meibomian glands to reinvigorate their production of meibum.
Figure 2. Trapped debris behind a scleral lens.
The post-surgical eye is a temporarily, neurologically induced dry eye. When the epithelium is ablated or cut to produce a flap, the superficial nerves that mediate the blink reflex are interrupted. Suddenly, the cornea is devoid of protective sensation, and the blink reflex is non-existent. The eye dries and stays that way, irrespective of the necessarily frequent instillation of artificial tears, until the nerves correctly regenerate, if at all.
A scleral lens in situ has an effect on the cornea and external ocular environment that is much more similar to a post-laser cornea than to a cornea covered by a soft contact lens. A scleral lens provides an optimally wet and protected environment, so unlike with wear of a soft lens, the cornea will not dry under a well-fitted scleral lens. But, because the scleral lens shields the cornea from environmental insults as well as the sensation of dryness, it also dramatically reduces the need to blink.
The resulting blinklessness contributes to the symptom constellation of a dry ocular surface. Within hours, the exterior of the lens becomes dry and crusty, collecting deposits of everything normally found in the tears as well as environmental contaminants (Figure 1). The eye begins to redden, and visual acuity becomes noticeably harder to measure. Needless to say, such patients are on their way to developing contact lens-induced papillary conjunctivitis.
Figure 3. Tight lens syndrome.
But, wait, there’s more. A well-fitted GP scleral contact lens is nearly sealed and moves much less compared to a soft lens of similar diameter—but, with a full blink the lens will move. It is this just-perceivable, blink-induced vertical translation that is responsible for just enough pumping and fluid exchange from under the lens to prevent the buildup of cellular debris between the lens and the eye.
A buildup of this debris (Figure 2)—dead, debrided cells, cellular excreta, and a variety of toxins—can cause corneal inflammation and is known clinically as scleral tight lens syndrome or occasionally as toxic lens syndrome (Figure 3).
Resolving the Problem
Tight lens syndrome is essentially a fitting problem—blinking cannot budge the tight scleral lens. Avoiding tight lens syndrome requires that the limbal zone must vault high enough over the limbus to prevent constriction of the limbal vasculature and to provide the limbal stem cells with “breathing space.” The profile of the landing zone and lens edge must be above the plane of the conjunctiva.
Further, you must instruct such patients to place the scleral lens gently onto the eye. The lens must be filled to capacity with saline so that bubbles will not be trapped in the fluid lake.
While the lens is being worn, it must not be rubbed or pressed into the conjunctiva. Patients must learn how to blink fully to allow for the exchange of tears and saline.
Scleral lenses, in any of their incarnations and designs from corneal-sclerals through full sclerals, show their true worth in replacing irregular corneae as the primary refracting surface of the eye without the concomitant likelihood of erosions and desiccation associated with GP corneal contact lenses. They are hardly felt, and there is no balancing of the lens between tense lids. Scleral lenses will not dislodge, ride up under the upper lid, or fall out of the eye. Foreign bodies will not crawl under the lens to annoy and aggravate as they do with corneal lenses. Refraction is sharp and vision is clear as long as the outer surface is kept clean and wetted. Wearing time can be a full day depending upon aspects of the fitting and characteristics of the blink.
But these many benefits of scleral lenses will not be passed onto patients unless the lenses are properly fitted and patients instructed on their proper application, care, and how to blink while wearing them. CLS
As always, my respect and thanks must be expressed to my patients for choosing me to help them confront their visual adversities invoked by their corneal ectasias.
Dr. Schendowich is a member of the Medical Advisory Board of the National Keratoconus Foundation, USA, a Fellow of the International Association of Contact Lens Educators, and a clinical supervisor to Israeli optometry students in the ophthalmology clinic at the Sha’are Zedek Medical Center in Jerusalem, Israel.
Contact Lens Spectrum, Volume: 28 , Issue: June 2013, page(s): 48 - 51