Therapeutic Uses of Silicone Hydrogels

Joel A. Silbert, O.D., F.A.A.O. Dr. Silbert is Professor of Optometry at Pennsylvania College of Optometry and Director of its Contact Lens Programs; he is also Director of Cornea and Specialty Contact Lens Services at The Eye Institute and is Principal Investigator of the CLEK Study (Collaborative Longitudinal Evaluation of Keratoconus), a multicenter study of keratoconus funded by the National Eye Institute. Dr. Silbert is a Diplomate of the Cornea and Contact Lens Section of the AAO, and a former Chair of the Association of Contact Lens Educators.  He has conducted clinical investigations for many contact lens manufacturers, and served as Associate Clinical Editor for the Review of Optometry and Contact Lens Forum.  Dr. Silbert has written numerous articles and textbooks, and has lectured extensively in subjects involving primary eyecare and contact lenses.

Hydrogel soft lenses have long been used for therapeutic applications, primarily for relief of pain, mechanical protection for a denuded or eroded corneal epithelium, and for promotion of ocular healing.  Other less common, but equally important  “therapeutic” uses may include delivery and/or sustained release of topical ocular medications, maintenance of corneal hydration, barrier protection from the action of the lids or lashes, facilitation of complex GP lens tolerance in an otherwise lens-intolerant patient, and even in chemical burn management by slowing or preventing progressive ulceration of deeper corneal tissue.

Traditionally, most practitioners have utilized conventional disposable hydrogels for these therapeutic purposes, due to their widespread availability and low or negligible costs.  However, disposable lenses may be limited in parameters, or possibly inappropriate depending on the therapeutic purpose of their intended use.  For example, some disposable lenses are only available in one base curve, and thus may potentially move excessively and further aggravate a fragile or damaged epithelium, or conversely be too tight, preventing tear and cellular debris exchange.  The use of a steeper fitting lens with less movement may be more appropriate in cases involving pain relief or in splinting of the corneal surface. A lens that provides more visible movement is preferred, however, in cases of a corneal epithelium that is eroded, damaged, or absent.

Additionally, the use of a thin, low water content hydrogel lens may be appropriate for pain management, but be ineffective if the goal is to facilitate sustained drug delivery (which requires a high water content and thicker lens).  Hydrogel disposable lenses are commonly available in mid- to high water content polymers.  While these lenses may appear to move satisfactorily during the first few minutes of lens evaluation, their dehydration on the eye after 30 minutes or longer  may make them behave in a much tighter fashion.  As such, it is important to evaluate these lenses after at least 20 to 30 minutes on the eye, as well as in follow-up visits.

As many therapeutic soft lens applications require regular use and overnight wear for several days (or longer, as in cases of recurrent corneal erosions with or without epithelial basement membrane dystrophy), providing a safer environment under the closed eye through the use of a silicone hydrogel therapeutic lens is far superior in the promotion of healing.  Additionally, the risks of secondary microbial infection, while not entirely eliminated, are greatly reduced with the use of a silicone hydrogel lens.

Currently, the CIBA Vision Night & Day™  silicone hydrogel lens is not only approved for continuous wear for up to 30 days for the general population, but it also has FDA therapeutic lens approval.  Although not a large diameter lens (13.8 mm), it is available in two base curves in a wide array of powers including plano as well.  It does have a stiffer modulus, which will translate into occasional lens awareness for some patients, although this settles rather quickly.  The overall pain relief that it provides is far greater than any minor issues relating to modulus awareness, so this rarely is a problem.  However, in cases where a practitioner is using a Night & Day lens as a bandage lens under a thick, complex design GP lens in a “piggyback” system, patient comfort is often not as great as one would expect.  In those cases, I have gone “off-label” and utilized a silicone hydrogel disposable lens with a lower modulus, such as O2 Optix™ (CIBA Vision) or Acuvue Advance™ (Vistakon) with improved success.  Although not currently approved as a therapeutic lens per se, the O2 Optix lens is approved for overnight wear for up to 1 week, due to its high Dk/t.  I would expect that the newly introduced Vistakon Oasys™ lens (a silicone hydrogel lens of high Dk/t) will also be as useful in these circumstances.
 
Therapeutic hydrogel lenses are very useful in pain management of a wide array of conditions.  These include:  Filamentary keratitis (elimination of filaments after several days), bullous keratopathy (use larger diameter silicone hydrogels for continuous wear), acute episodes of Thygeson’s superficial punctate keratitis (use a thin low water disposable or a silicone hydrogel of lower modulus, plus a mild soft steroid topical drop (Zylet by Bausch & Lomb is useful here in that is combines lotoprednol plus tobramycin). 

As noted previously, patients with recurrent erosions due to epithelial basement membrane dystrophies need both pain relief and splinting of the corneal epithelium during the repair process.  As cells are not tightly conjoined, the action of the lids, particularly during eye-opening in the morning, is often responsible for initiating a recurrent episode.  Thus, in addition to lubrication, long-term treatment with a continuous wear lens is desirable, if the patient is not having PTK or stromal puncture therapy.  One should avoid the use of an ultrathin disposable hydrogel lens, as they may wrinkle and not provide adequate splinting function.  However, the use of a thicker, silicone hydrogel of stiffer modulus is preferred, and the Night & Day™  lens is ideal for this purpose.

In the arena of post-surgical applications, therapeutic bandage lenses are very useful in cases of wound leakage (positive Seidel’s sign in extracapsular cataract extraction, or in the case of a wound leak after penetrating keratoplasty, or after a leaking bleb in advanced glaucoma, or even in cases of a perforated cornea).  In these instances, the application of a silicone hydrogel lens facilitates the sealing of the wound.

Bandage lenses are routinely utilized in surface ablation refractive surgical procedures, such as PRK, PTK, Lasek, and more recently in epi-Lasik cases.  The use of a silicone hydrogel lens is superior in that it provides increased oxygen flux compared to conventional hydrogel lenses, speeds wound healing, greatly assists in pain relief during the re-epithelization process, and provides for some retention of medication in the eye during the few days after surgery.  A study by Szaflik, Ambroziak, and Szaflik looked at 30 patients having unilateral LASEK, who were fitted with Night & Day (CIBA Vision, lotrafilcon A) silicone hydrogels for 3 to 4 days of continuous wear status post surgery.  The authors reported very good lens movement, with an average of 80% of patients showing normal or trace conjunctival hyperemia, good to very good comfort in an average of 77% of patients, and symptoms of pain rated as “absent” or “mild” in an average of 99% of patients during the trial with lotrafilcon A (1).   In another study, the same authors looked at the use of a silicone hydrogel lens as a bandage lens for a variety of anterior segment disorders in 70 eyes from 70 patients, for which therapeutic bandage lenses worn overnight were indicated, with the majority of cases being painful bullous keratopathy (47 eyes, or 67%).  The lens was worn for periods ranging from 7 to 30 days continuously, along with appropriate concomitant therapies.  Subjective comfort was evaluated for 7 days to 18 months after lens fitting.  91% of the total eyes (64 eyes) showed improvement in the clinical condition, and 94% of patients (66 eyes) reported comfort when wearing the lens as “good” or “very good”(2). 

As noted, the therapeutic application of silicone hydrogels also includes their use as part of a piggyback system for problematic cases in which GP lens tolerance is a major issue.  As many patients with keratoconus and other irregular corneal conditions require thick and highly-powered lenses which can mechanically aggravate an already challenged corneal epithelium, the use of a silicone hydrogel lens under a GP lens can facilitate lens wear as well as protect the cornea.  In patients who have been wearing GP lenses only, with good visual acuity and borderline physical lens tolerance, use a silicone hydrogel lens of plano or very low power under the same GP lens, to test whether lens comfort improves.  If so, the patient will likely prefer this system, and the GP lens can be reordered in a hyper-Dk lens material for final lens dispensing (3).

References

1. Szaflik JP, Ambroziak AM, Saflik J.  Therapeutic use of a lotrafilcon A silicone hydrogel soft contact lens as a bandage after LASEK surgery.  Eye & Contact Lens, 30(1):59-62, Jan 2004.
2. Ambroziak AM, Szaflik JP, Szaflik J.  Therapeutic use of a silicone hydrogel contact lens in selected clinical cases. Eye & Contact Lens.  30(1):63-67, Jan 2004.
3. O ’Donnell C, Maldonado-Codina C.  A hyper-Dk piggyback lens system for keratoconus. Eye & Contact Lens, 30(1)44-48, Jan 2004.