Other Uses of Contact Lenses
ZORAIDA FIOL-SILVA and HAROLD A. STEIN
Table Of Contents
|Although we generally think of contact lenses as cosmetic, there are numerous
other uses for them. Therapeutic contact lenses constitute an important
segment of the contact lens wearing population. Therapeutic lenses
can be soft or rigid, conventional or special design, clear or painted, and
daily or extended wear. When therapeutic lenses, most physicians
think of bandage lenses, typically for the treatment of symptomatic
corneal surface pathology. Although bandage lenses constitute an
important segment of the therapeutic lens population, we must also think
of special design rigid lenses used for the treatment of keratoconus
disease, rigid lenses used in patients with irregular astigmatism of
various etiologies, hybrid lenses (soft and rigid combined), occluder
soft lenses, painted lenses, (numerous uses) and others.|
Technologic advances in both contact lens materials and designs have made possible the development of new and broader contact lens alternatives for the treatment of patients with several anterior segment conditions. Newer alternatives provide our patients not only more but better lens choices.
The most common uses of therapeutic lenses include: bandage lenses, keratoconus design lenses, rigid lenses for the correction of irregular astigmatism of various etiologies, hybrid lenses, and painted lenses (Fig. 1).
|Bandage lenses are a group of soft, thin, highly oxygen permeable lenses
of various levels of water content that are typically fit loosely over
the cornea for various therapeutic purposes. Although years ago several
lenses were in the market exclusively for this purpose, today disposable
lenses are most commonly used. The most common uses of bandage
lenses are epithelial erosions, bullous keratopathy, filamentary keratitis, trichiasis, alkali
burns, penetrating corneal wounds, leaking blebs
after trabeculoplasty, Simmons compression shells, and postsurgical
wound gaps with flat anterior chambers.|
Thin, highly oxygen permeable, (hydrophilic) soft lenses have been used very successfully in the treatment of epithelial corneal erosions. The purpose of the lens is not only to manage pain but also to assist in the healing process of the corneal surface. The lens assists surface healing by protecting the loose epithelium from the mechanical trauma of the eyelid, as well as by preventing adherence of the epithelium to the underlying cornea.
The authors recommend using a highly oxygen permeable, lower water content lens. A tight-fitting lens should be avoided to prevent corneal edema or other complications. Easy tear flow under the lens is very important, and the frequent use of artificial tears is highly recommended. A dry lens will actually make the condition worse.
Pain management is the most valuable use of a bandage lens in patients with bullous keratopathy, although improving visual acuity is often possible and successfully accomplished as well.
Although a tight-fitting lens will likely cause further problems and complications, a very loose-fitting lens should also be avoided because it can actually worsen the symptoms resulting from the constant mechanical trauma of the lens over the corneal surface. Copious use of lubricants or artificial tears is strongly recommended.
Patients with filamentary keratitis also greatly benefit from the use of a bandage soft lens. Regardless of the clinical reason for the filaments, placement of a bandage soft lens will typically help within a relatively short period. In most patients the filaments disappear within a week. Removal of the lens is advocated after the filaments disappear. The frequent use of lubricants is also very important in these patients, both during lens wear and after removal of the lens. A thin, low water content lens is also recommended in these patients.
Although removal of the misdirected eyelashes is the preferred treatment of trichiasis, a soft bandage lens offers valuable temporary relief for this condition, particularly when the misdirected lashes cause direct trauma to the cornea.
Bandage lenses offer protection to the cornea but not the conjunctiva. It is equally important to protect the conjunctiva from the damaging effects of chronic, repeated trauma by the abnormal eyelids and eyelashes. Although patients without corneal involvement are not typically as symptomatic, care should be taken to avoid long-term deformities.
Bandage lenses have proven to be very helpful in promoting re-epithelialization of the cornea in patients with chemical burns. Although the contact lens will not prevent many of the complications of an alkali burn such as symblepharon and conjunctival overgrowth, they will assist in corneal epithelial healing and pain management.
As in most situations in which a bandage lens is used, a thin, highly oxygen permeable lens is recommended and lubrication is very important.
PENETRATING CORNEAL WOUNDS
Bandage soft lenses have been used very successfully in the treatment of patients with small penetrating corneal wounds that have clean edges (without irregularities) and good apposition, without iris prolapse or incarceration. In most instances these are trauma patients (Fig. 2), although the perforations may be seen in some postsurgical patients such as after refractive surgery, radial keratotomy (RK).
The lens provides tamponading of the wound and thus assists in the restoration of the anterior chamber and promotes wound healing. Bandage lenses have also been used after corneal transplantation in patients who have a small wound gape, particularly when resuturing is not possible or is complicated.
GLAUCOMA SURGICAL PROCEDURES
Through the years, bandage lenses have been very helpful in some glaucoma procedures. Flat anterior chambers secondary to a wound leak from a small perforation on the bleb can be resolved with the use of a large-diameter, thin, low water content soft lens. In these cases, the lens will provide a tamponading effect that will facilitate wound closure and healing, thus allowing the reformation of the anterior chamber and providing protection from infection and other complications. In some instances, tissue adhesive has been used very successfully with the bandage lens.
A bandage lens is helpful when the Simmons compression shell is used. In these cases the lens is placed between the shell and the cornea to offer protection from the mechanical trauma of the shell against the cornea.
|Other than the traditionally recognized bandage soft lenses, there are
other therapeutic uses for contact lenses. Some are soft lenses; many
are rigid lenses, typically rigid gas permeable (RGP) lenses. Specialty
lenses are mostly used in situations in which neither spectacles nor
a conventional lens would improve visual acuity or relieve patients from
debilitating symptoms. Some examples are keratoconus, after corneal
transplantation, irregular astigmatism of various etiologies, color
deficiency (particularly red-green), diplopia, anisometropia, cosmetically
unsightly eyes, iris abnormalities with resultant monocular diplopia, photophobia, glare, halos, or decreased vision.|
KERATOCONUS DESIGN LENSES
Patients with keratoconus disease comprise a significant portion of the population of therapeutic contact lens wearers (Figs. 3 and 4). Although patients with early forms of the disease may obtain reasonably good visual acuity with either spectacles or conventional soft lenses, most patients require special design, rigid lenses to obtain functional vision. Eliminating the need for corneal transplantation would be ideal. Because of the high degree of irregular astigmatism and the nature and location of the ectasia that patients with keratoconus have, conventional lens fitting does not provide these patients with either an adequate fit or reasonable comfort or visual acuity.
The purpose of a contact lens in patients with keratoconus is to cover the irregular astigmatism and the distorted anterior surface of the ectatic cornea, thus providing a regular, spherical optical surface in front of the eye. The lens would effectively restore the smooth optical properties of the cornea (Figs. 5 and 6).
There are numerous keratoconus lens designs available in the market. The primary goal of each design is to allow adequate fitting over the diseased cornea with minimal or no direct mechanical trauma to the normal tissue. This is typically accomplished with designs that incorporate several different posterior curvatures in which the central curvature is steeper and the peripheral curves are flatter. Some lenses are bicurved, tricurved, or even multicurved. Aspheric lenses are often used.
Some of the lens designs available today for patients with keratoconus include:
Although some of these lenses may be available in PMMA hard lens material, it is highly recommended that gas permeable materials be used to avoid further compromise on an already diseased cornea.
In the hands of an experienced contact lens fitter, most moderate and many advanced cases of keratoconus can be successfully fitted with contact lenses (Fig. 8). Today, a much lower percentage of keratoconus patients require corneal transplantation, because of the technologic advances and the many contact lens options available.
Significant irregular astigmatism can result from ocular surgery, although it is most commonly seen in patients with penetrating injuries or in patients with significant corneal surface pathology. When the amount and extent of the irregular astigmatism is mild, soft contact lenses can be used successfully. When soft lenses are used, it is recommended that a thick lens be used. The thicker lenses will allow less flexure, thus creating an effective tear-lens layer.
In most cases, a rigid lens is needed due to the large amount of irregular astigmatism. Rigid lenses will usually provide patients with a better visual acuity. Whenever possible, a thin, spherical gas permeable lens is preferred. The fitting technique may vary, although care should be given to protecting the cornea from lens trauma to the areas of protrusion (Fig. 9). Although a relatively thin lens is recommended, flexure will be a problem if the lens selected is too thin. In patients who cannot tolerate rigid lenses, either piggy-back lenses or a hybrid lens may be used successfully.
The initial lens selection may be difficult because of the inability to obtain accurate keratometric readings. If keratometry is not possible, it may be helpful to use keratometric readings from the fellow eye. Whenever possible, corneal topography is recommended because it is usually helpful in visualizing the cornea of patients with irregular astigmatism. With the use of corneal topography combined with a computerized lens design program, highly specialized lenses may be generated to fit the difficult patient.
The piggy-back lens concept is basically the wearing of both a soft and a rigid contact lens to provide the patient with the good visual acuity of a rigid lens and the comfort of a soft lens. In the piggy-back lens system, the patient wears a soft lens against the cornea, which provides comfort, and a rigid lens over the soft lens to obtain good, useful vision.
Piggy-back lenses are typically used in cases of keratoconus or in patients with irregular astigmatism after a penetrating keratoplasty or as a result of a penetrating injury (traumatic).
Standard soft lenses are applied to create a new anterior surface of the lens/cornea combination. On the surface of the soft lens, the appropriate RGP lens is placed. The rigid lens typically has a steep central posterior curve surrounded by a flatter peripheral zone. The steep central zone stabilizes on the corneal cap while the flatter zone rests on the periphery of the soft lens. Some laboratories will create a custom lens with an anterior depression in the soft lens in order for the rigid lens to fit properly. This feature provides better centration because the rigid lens fit into the shallow depression of the soft lens.
The primary advantage of the piggy-back lens system is comfort. Disadvantages include: cost, extensive patient education, and laborious care and handling of the lenses. A possible complication is decreased oxygen permeability, because there are two superimposed lenses over the corneal surface. This is of particular concern in these patients because the corneas are already diseased and/or compromised.
CONTACT LENSES FOR SPORTS
Generally, soft contact lenses are preferred for any contact sports or athletics because of the danger of the rigid lens being displaced off the cornea or even out of the eye. This has happened so frequently that the National Basketball Association has passed a rule that games cannot be stopped to look for a lens that accidentally pops out of a team member's eye.
Athletes often need rigid lenses to obtain the desired or needed visual results. In these cases, a large-diameter lens must be fitted. These large-diameter lenses can often be tolerated for only 4 to 5 hours at a time.
To provide the best possible fit with increased wearing time, lenses with additional peripheral curves are often used. The larger diameter will provide increased apical vaulting that requires peripheral modifications. Aspherical lenses are best for these circumstances. These may be available in diameters as large as 10.0 mm. Aspherical lenses offer the following advantages: not easily dislodged; better comfort; improved visual acuity; and less photophobia because of the better fit and larger optical zone, therefore, they are better tolerated.
Soft lenses are typically preferred for contact sports because they move the least and are almost impossible to dislodge. Soft lenses will also follow sudden eye movements well, thus improving performance. They also cause less photophobia and are extremely comfortable. Wearing time is flexible with soft lenses. Dust and foreign bodies do not usually affect wear as is the case with rigid lenses, because dust and foreign bodies do not become trapped underneath the lens. Whenever possible, soft lenses are best for soccer, basketball, softball, football, tennis, rugby, cricket, lacrosse, polo, squash, racquetball, skiing, hockey, and other contact sports. The major disadvantage of soft lenses is that the contrast sensitivity is not quite as good as that of RGP lenses.
Patients with congenital nystagmus see poorly with glasses. The oscillations of the eyes with spectacles produce constant parallax. With contact lenses, the visual disturbance that is created by the constant eye movements against a fixed spectacle is greatly reduced, thus improving the functional vision. The visual gains for nystagmus patients can be remarkable and can be improved from 20/200 to 20/50 or even better with the use of contact lenses.
As fixation is improved by the corrective lenses, the actual amplitude of the oscillations may decrease. This is particularly noticeable under dim illumination.
Most patients with nystagmus seem to have a large amount of astigmatism. Properly correcting the astigmatism is of utmost importance, particularly when the goal is to improve the patient's overall visual acuity. Some prefer fitting these patients with large-diameter RGP lenses, although some of us prefer to use soft toric lenses, often custom made, with good axis stability. The advantage of the soft lens, which is used whenever possible, is greater axis stability with the nystagmus.
Patients with albinism almost invariably have a significant nystagmus and large amounts of astigmatism. These patients not only benefit from contact lenses for the reasons discussed previously but also benefit from a tinted lens to decrease the photophobia that they have as a result of the translucent iris. Decreasing the photophobia will also enhance their vision, as well as their comfort and functionality.
Orthokeratology is a method of correction of refractive errors using a series of rigid contact lenses to change the shape of the cornea, thus altering the refractive error. It is said to be a system for “sight without glasses.” Orthokeratology has been available for many years although its popularity has varied through the years. With the increasing popularity of refractive surgery, orthokeratology has become somewhat more popular. Its reversibility has made it an attractive alternative to refractive surgery.
The premise behind the system is that progressive flattening of the cornea through the use of a series of flatter fitting lenses will eliminate myopia. The assumption is made that the degree of flattening will be uniform in all meridians. Certainly this is not always the case. Flat fitting lenses worn over a long period may result in a toric cornea.
The advocates of orthokeratology point to its usefulness in treating certain groups of patients who require good vision and cannot wear contact lenses.
With orthokeratology, lenses can be applied as night lenses and removed during the day. The night wearing maintains the flatness of the cornea (retainer effect). Lenses must be reassessed at least every 6 weeks with repeated attention to the refraction. New corneal readings and slit lamp evaluation of the cornea is required. When changes in the corneal curvature occur, new flatter lenses are provided.
Often a retainer plano lens is worn, sometimes for a minimum wearing schedule, to keep the cornea flat. Most ophthalmologists have very limited experience with orthokeratology.
Complications such as over-wear reactions, corneal abrasions, induced corneal astigmatism, corneal warpage, and ocular discomfort from the wearing of such a large, flat lens can occur. The main objections of orthokeratology are (1) corneal complications from the use of overnight contact lens wear (e.g., hypoxia, corneal edema), (2) cost and time expenditure, (3) unpredictable effectiveness and inability to screen patients for accurate patient selection, (4) necessity of a retainer contact lens, and (5) usefulness only in myopic patients.
AFTER REFRACTIVE SURGERY
As refractive surgery has become increasingly popular, the need for specialized contact lens fitting after refractive surgery has increased significantly. There are several uses or needs for contact lenses after refractive surgery: (1) “molding lens” to reshape the cornea and promote healing under the laser-assisted in-situ keratomileusis (LASIK) flap, (2) bandage—to minimize pain in cases of photoreactive keratectomy (PRK) or in cases in which there is any abrasion occurring with LASIK or any other refractive procedure, (3) correction of irregular astigmatism resulting from the surgery, (4) correction of any residual refractive error not corrected by the surgery, (5) treatment of anisometropia in patients that have only undergone surgery in one eye, and (6) others.
Following refractive surgery, patients usually have a very different and distinct corneal anatomy that often makes lens fitting difficult. This is especially the case with patients who have undergone RK and similar procedures. Their corneal anatomy is quite different than that of nonsurgical patients.
New lens designs, particularly rigid lenses, have been developed to fit these patients. Similar to postkeratoplasty patients, the corneas of these patients have a flat central area surrounded by a steeper periphery. Conventional lenses cannot be successfully fit in most of these patients.
Patients who suffer penetrating injuries to the eye often need or benefit from contact lenses. As mentioned earlier, the correction of irregular astigmatism is best accomplished with the use of a rigid lens. Irregular astigmatism cannot usually be corrected with either spectacles or soft lenses. Most patients with penetrating injuries have resultant irregular astigmatism.
Large ametropias often require contact lenses to avoid anisoconia and diplopia and to achieve functional visual acuity. Monocular aphakia is a common complication of trauma. Restoration of vision is accomplished with the use of a contact lens whenever intraocular lens implantation is not feasible or contraindicated.
Posttraumatic iris abnormalities are another common complication after penetrating trauma: traumatic mydriasis and traumatic partial or total aniridia. These abnormalities are often best corrected with the use of an iris-painted soft contact lens. Lens use in these cases can be beneficial both cosmetically and functionally. Cosmetically, covering an unsightly eye can help the patient recover emotionally and can improve the self-esteem.
Functionally, correcting the iris anomalies can eliminate glare, flare, halos, and monocular diplopia. Strabismic abnormalities often develop after trauma that will often cause diplopia. A black pupil lens can offer occlusion that will eliminate the diplopia.
Thorough evaluation of a posttraumatic patient can identify problems and deficiencies that are often treatable with the use of a contact lens. Combinations can be custom made to treat these patients.
Amblyopia and diplopia are the two primary indications for occlusion therapy. Occlusion therapy has been most commonly done with patches, but contact lenses are a more palatable, cosmetically acceptable option for many patients (Figs. 10 and 11).
The use of occluder lenses in children for the treatment of amblyopia has been somewhat controversial. Conservatives believe that the risks of a contact lens outweigh their benefits. Concerns about infections are the main focus of this controversy. Another concern is hypoxia and the complications associated with extended wear because these very young patients do spend a significant percentage of their days sleeping. They are not often used but, whenever used, they are usually quite successful.
Contact lenses are a very successful tool in the treatment of diplopia, both monocular and binocular. Strabismus, neurologic disorders, and trauma are the most common causes of diplopia. In most cases the diplopia is binocular, although, in trauma cases monocular diplopia associated with iris anomalies is not uncommon. Patients with diplopia are often quite debilitated with the symptoms, and the relief offered by the lenses is usually quite welcome.
Depending on the anatomy of the eye, these lenses can be either an occluder (black-out) lens or a simple black pupil lens. The traditional black-out lens is a soft lens that is painted black and totally opaque on its entire surface. Although successful in providing coverage of the visual axis, thus relieving the symptoms, it is not cosmetically appealing, especially in patients with light colored eyes. The most commonly used type of lens is a clear soft contact lens with a black pupil in the center. The pupillary diameter will vary depending on the patient's pupil diameter and positioning of the eye. Careful attention must be paid to the position of the eye to avoid allowing light and vision through the periphery of the painted pupil. In many cases it is necessary to enhance the occluder effect of the lens, because patients can still see through the lens, and thus symptoms are not eliminated. A technique that can be used with great success is the use of a contact lens with a power that is completely different than the patient's refractive error. This lens (power) will provide some significant blurring of the vision that, together with the blocking effect of the black pupil, will in fact obstruct the vision. Although some patients report some vision out of the eye with the lens, most are able to learn to suppress the image in the covered eye enough to obtain symptom relief.
In patients with monocular diplopia, the symptoms are caused by iris abnormalities that in effect create two different visual axis. In most cases the iris abnormalities are traumatic, although they can be iatrogenic (as in patients with peripheral iridectomies that are not covered by the eyelids). Although rare, monocular “multiplopia” can occur. This is usually seen in trauma patients or in patients that have undergone multiple intraocular surgeries and have several iridectomies that are not covered by the eyelids.
In patients with monocular diplopia, the type of occluder lens needed is usually different, because the goal of therapy in these patients is to create a single pupil. These patients typically require an opaque iris-painted lens that will cover the entire iris and creates a single, central, clear pupil. These types of lenses are usually more complex to fit but are usually quite successful.
Approximately 8% to 10% of males and 0.5% of females have some impairment in color vision ranging from a mild deficiency to an almost complete impairment. The defect is most commonly in the red-green range. Although yellow-blue deficiencies are seen, they are much less common.
The X-Chrom lens can be used successfully to treat these patients (Fig. 12). The X-Chrom lens transmits light in the red zone from 590 to 700 nm (spectrum of white light is 380 to 760 nm), thus improving color discrimination in patients with partial impairment in the red-green range. The lens is bright red, usually rigid, and fitted to the nondominant eye. The other eye either remains uncovered or is fitted with a conventional lens for the correction of any ametropias that the patient might have (the X-Chrom lens can be obtained in any power, so that it can also correct any refractive error). The uncovered eye will perceive a red-green object as usual, but the eye with the red lens will perceive the red wavelengths of light and will absorb the green wavelengths. The brain now receives two different intensities. By a rapid self-learning process, the patient can identify both colors properly.
We have significant experience with this lens with reasonably good results. Although the lens does not correct the color defect, it does permit patients to make a discriminatory judgment of color. During the initial patient evaluation, it is very helpful to use a trial lens to evaluate effectiveness. Patients can often improve their results in the Ishihara plates from properly identifying 1/15 plates to identifying 10/15 to 13/15 correct plates. Proper color discrimination is very important in numerous professions such as: electrical engineers, uniformed forces, artists, painters, printers, decorators, and all those professions in which color discrimination is important.
A word of caution to patients wearing the X-Chrom lens: This lens has detrimental effects on space localization of moving objects and other aspects of binocular vision. Persons operating moving vehicles wearing a tinted lens over one eye may experience hazardous distortions of the positions of perceived objects and may, therefore, be dangerous drivers in certain circumstances. Conservative judgments are justified until the extent of the hazards is better understood.
Ideal lens fitting involves special attention to avoiding excessive lens movement and decreasing lens thickness to improve visual results. Otherwise, techniques used for fitting any other conventional rigid lens should be applied. Motivation is quite important because the lens may be cosmetically undesirable (bright red lens in only one eye) and there is an adaptation period that the patients must undergo. The use of bright ambient light is highly recommended to maximize results.
THERAPEUTIC USES OF PAINTED LENSES
Painted contact lenses have a variety of uses: cosmetic, therapeutic, handling, and informational. Although a valuable tool in total patient care, the therapeutic use of tinted lenses is, unfortunately, not often considered.
There are several basic categories or types of painted lenses that can be obtained, considering that multiple variables can be incorporated into any of these lenses. As a general rule, soft (hydrophilic) lenses are used for painting in therapeutic lenses (although rigid lenses may be used rarely). The broad categories of tints include: translucent (Fig. 13); opaque (iris) (Fig. 14), with or without pupillary opening; clear or black pupil; clear lens with black pupil only (Fig. 15), totally black (occluder) (Fig. 16) lens, and others. Although some lenses are commercially available (with predetermined colors and options), others are custom made for each patient. The type of lens chosen for each patient will be dictated by the patient's needs and desires. As a general rule, custom made lenses will be more costly and take longer to obtain but usually accomplish a better cosmetic result and, therefore, greater success. Painted lenses can be obtained with or without refractive power, depending on the patient's needs.
Indications for the use of therapeutic painted lenses include: covering corneal scars, creation of a pupil, pupillary occlusion, diplopia, heterochromia, phthisis, amblyopia, aniridia, and photophobia.
While evaluating a patient for a painted lens, we must take into consideration not only the obvious cosmetic or clinical deformities but also the patient's realistic needs, desires, and expectations. It could be quite frustrating if unrealistic expectations are set or the patient's needs are not met.