Article

SCLERAL LENSES FOR REGULAR CORNEAS

For patients who have normal eyes but fail in other lens modalities, scleral lenses can provide an alternative.

Scleral lenses were first mentioned in the medical literature in 1888 by Adolf Fick, who described glass-blown shells 18mm to 21mm in diameter that could be worn for only a few hours at a time and were designed to protect the eye.1 Polymethylmethacrylate (PMMA) contact lenses were introduced in the 20th century, but due to the absence of oxygen permeability, these lenses resulted in hypoxia, corneal edema, and reduced wear time. Today, higher-oxygen-permeable (higher-Dk) materials are available for GP corneal and scleral lenses, resulting in less corneal compromise. With improved technology, these lenses are lathe cut so that they are reproducible, and lens design changes—no matter how small—can accurately and easily be made.

Scleral lenses are primarily used today for diseased corneas such as:

  1. Keratoconus with and without intracorneal ring segments
  2. Pellucid marginal degeneration
  3. Post-penetrating keratoplasty
  4. Irregular corneal curvature post-refractive surgery such as radial keratotomy (RK), photorefractive keratectomy (PRK), and laser-assisted in situ keratomileusis (LASIK)
  5. Post-keratoprosthesis
  6. Chemical burns
  7. Stevens-Johnson syndrome
  8. Ocular pemphigoid
  9. Symblepharon formation
  10. Graft-versus-host disease
  11. Severe dry eye: Sj√∂gren’s, filamentary keratitis, and limbal stem cell deficiency
  12. Post-infectious ocular diseases such as herpes simplex and zoster

However, scleral lenses also could be used for “regular” corneas. In this article, a “regular cornea” is defined as a cornea that does not have a progressive disease and is “normally shaped.” These include the following conditions and situations:

  1. Refractive errors such as myopia, hyperopia, astigmatism, and presbyopia
  2. Mild-to-moderate dry eye
  3. Recurrent corneal erosions
  4. Athletes involved in fast-action sports for which vision is critical; in such cases, the lenses also provide a “sealed” environment to protect the eye from outside elements or particles
  5. Exposure keratitis

All of the above conditions or situations can be managed with corneal GP lenses, soft contact lenses, and hybrid contact lenses. However, if patients do not succeed with these modalities of wear, scleral lenses provide another alternative.

WHY SCLERAL LENSES?

Scleral contact lenses have many advantages over soft and corneal GP contact lenses. Scleral lenses are filled with a preservative-free fluid reservoir that vaults the entire cornea, and the lens lands gently onto the conjunctiva just past the limbal area. The preservative-free fluid continuously moisturizes the cornea as patients wear the lens throughout the day. As a result, scleral lenses help manage symptoms of dryness, photophobia, burning, foreign body sensation, and cloudy vision.

If a soft toric contact lens is unstable and rotates on the eye, it results in blurred and fluctuating vision. The tear layer between the cornea and the scleral lens will correct the astigmatism on the cornea so that, even if the scleral lens rotates, vision will be stable and clear.

Furthermore, scleral lenses can also be used as a substitute for corneal GP lenses that move excessively or do not center on the cornea. The optic zone of scleral lenses is large (8mm to 9mm) compared to soft and corneal GP lenses, resulting in reduced glare and haloes.

THE FITTING PROCESS

When evaluating a patient for scleral lenses, make sure to obtain the following information:

  1. Keratometry/topography readings
  2. Horizontal visible iris diameter (HVID)
  3. Visual demands
  4. Hobbies and indoor/outdoor activities
  5. Anterior segment evaluation of lid/lash position, meibomian gland disease, tear film stability, and conjunctival and corneal abnormalities

A diagnostic fitting set can help reduce the number of visits needed to finalize the fit of a scleral lens. While it is important to follow the manufacturers’ fitting guides, the principles are the same for all lens brands. First, select the diameter of the lens based on the HVID and on the presence of any conjunctival abnormalities such as pinguecula, pterygium, symblepharon, or glaucoma filtering bleb. Optical coherence tomography (OCT) is helpful in providing a clear view of the landing zone on the conjunctiva to ensure that the lens fits the sclera 360º around without blanching or impingement. Next, adjust the midperiphery. Finally, select the base curve or the sagittal depth to vault the central cornea.

Before applying the lens onto the eye, add fluorescein dye along with saline solution to the lens bowl. The tear film between the cornea and the back surface of the scleral lens can then be evaluated with a cross-section beam via slit lamp examination. This will help identify areas of touch or of low clearance throughout the entire lens. Again, OCT is helpful in more accurately quantifying the amount of corneal clearance.

When prescribing scleral lenses, a Dk of 150 or more is recommended, with a maximum center thickness of 250µm and a central tear film clearance of less than 200µm after settling.2 All of the fitting information can be e-mailed to the consultants at the manufacturing laboratories for evaluation. Their recommendations are often beneficial in achieving a successful fit.

After a lens is dispensed, fluorescein is also used to evaluate tear exchange during follow-up visits after the lens has settled on the eye for a few hours. If fluorescein seeps into the tear film between the lens and cornea, then a toric periphery is needed.

In my experience, there are many advantages of fitting small-diameter scleral lenses compared to large-diameter (≥ 15mm) scleral lenses. These include:

  1. Excellent oxygen transmissibility and low risk of corneal hypoxia, as smaller lenses tend to be thinner compared to very large-diameter scleral lenses.
  2. Reduced likelihood of tear film fogging due to less tear film clearance and less tear film exchange with small-diameter lenses.
  3. Easier application and removal of the lenses.
  4. Less scleral asymmetry closer to the limbus. Smaller scleral lenses can be rotationally symmetric compared to larger lenses, which often need to be rotationally asymmetric. One study showed that when OCT measurements were taken at a 15mm chord, the sagittal depth was more shallow nasally compared to temporally and was slightly asymmetric in shape. These measurements also showed that there was scleral asymmetry closer to the limbus (10.0mm to 15.0mm) that increased approaching the extraocular muscles.3 Scleral lens diameters of less than 15mm can be rotationally symmetric and would not benefit from adding toric landing zones or quadrant-specific designs.3
  5. Conjunctival abnormalities such as symblepharon, pingueculas, and pterygia can be avoided.

EXAMPLE CASES

Following are two cases in which scleral lenses were successfully used in managing normal corneas.

Case 1 A 20-year-old Caucasian female presented to the clinic in 2017 as a new patient to update her soft contact lens prescription. Her chief complaint was progressive worsening of redness and irritation over the last two months during contact lens wear. The symptoms were worse in her right eye than in her left eye. She occasionally discontinued lens wear for one day to get some mild relief, and she used preservative-free tears as needed. Her last comprehensive eye examination was one year ago.

She had a four-year history of frequent replacement soft contact lens wear on a daily basis with occasional extended wear. She habitually wore her contact lenses for 12 to 14 hours a day and would sleep while wearing her lenses on occasion for two consecutive nights. She replaced her lenses on a monthly basis, and her current contact lenses were two weeks old. She used a multipurpose solution for disinfection and changed her case every other month.

Her medical history was unremarkable. She was not taking any systemic or ocular medications. Her family medical history was significant for migraines. Her ocular history included chalazia on both lower eyelids in 2016. She did not have any history of ocular surgery or ocular trauma. Her family ocular history was unremarkable.

Examination Findings The patient’s entrance visual acuities with spectacles were OD –6.50 –0.50 x 005, distance visual acuity (VA) 20/30 and OS –6.50 –0.25 x 160, distance VA 20/30. Her manifest subjective refraction was OD –6.50 –0.50 x 005, distance VA 20/30 and OS –6.50 –0.50 x 160, distance VA 20/30. Topography/keratometry readings were OD 42.66 @ 007/43.14 @ 093, irregular and fluctuating mires and OS 42.48 @ 155/42.88 @ 065, irregular and fluctuating mires.

Slit lamp biomicroscopy revealed clear upper and lower tarsal plates (palpebral conjunctiva) OD and OS and diffuse hyperemia in the bulbar conjunctiva, 2+ OD and 1+ OS. The cornea OD had scattered areas of subepithelial infiltrates in the midperiphery, 2+ superficial punctate keratitis inferiorly, and 5mm of superficial inferior neovascularization; the cornea OS had 1+ superficial punctate keratitis and 3mm of superficial inferior neovascularization (Figure 1).

Figure 1. Appearance of the right and left eyes of the patient in Case 1.

The differential diagnosis included:

  • Contact lens-induced acute red eye (CLARE)
  • Atopic keratoconjunctivitis
  • Chronic hypersensitivity keratitis secondary to meibomian gland dysfunction (MGD)
  • Ocular rosacea
  • Contact lens-related infectious ulcer

We diagnosed chronic hypersensitivity keratitis secondary to MGD. Her eyelid scans showed that she had meibomian gland dropout in both eyes, more severe in her left eye compared to her right eye (Figure 2).

Figure 2. Meibomian gland dropout in the patient in Case 1.

Patient Management She was treated for two months with prescription prednisolone q.i.d. and tapered slowly over two weeks, and we instructed her to discontinue lens wear. After two months, she was refitted into daily disposable contact lenses and experienced no issues for six months. After the six months, she decided to return to her monthly replacement contact lenses even though this was not recommended. We prescribed a hydrogen peroxide care system rather than a multipurpose solution to clean and disinfect the lenses.

After one month of using her frequent replacement lenses, she returned to the clinic with painful, red eyes with infiltrates, 2mm to 3mm of neovascularization in the inferior cornea, and 3+ fluorescein staining in both eyes. She was treated with an amniotic membrane in each eye, two weeks apart. When her corneas were healed, we instructed her to discontinue contact lens wear and performed a thermal pulsation treatment for long-term management. She also started taking omega-3 supplements and using preservative-free artificial tears three times a day.

After three months, she returned to our clinic for a corneal evaluation. Her corneas had 2+ staining with fluorescein in both eyes, with trace infiltrates and 2mm to 3mm of neovascularization. She denied wearing any contact lenses for the past three months. We once again prescribed steroid drops q.i.d. in both eyes and tapered slowly over the next month. Due to her recurrent corneal issues both with and without frequent replacement contact lenses, she was fitted with scleral lenses to manage her ocular surface disease. According to the Tear Film & Ocular Surface Society’s (TFOS) Dry Eye Workshop (DEWS) II report, a therapeutic contact lens is a tertiary treatment for dry eyes after long-term steroid use, amniotic membrane grafts, surgical punctal occlusion, oral secretagogues, autologous serum, eye drops, and ointments.3

The patient’s HVID was 11.0mm; therefore, we fitted a 15.0mm diameter scleral lens. A slightly large lens was selected because of her ocular surface disease. A spherical haptic design was used during trial fitting; as there was no blanching in the conjunctiva both during the fit and after multiple follow-up visits, a toric haptic was not necessary. She used a hydrogen peroxide system for disinfection, preservative-free tears, and a preservative-free saline. She continued to use warm compresses every day for 10 minutes and to take 2g to 3g of omega-3 supplements on a daily basis. She has successfully worn the scleral lenses for one year. Her corneas have remained healthy, and she has fewer dry eye symptoms (Figure 3).

Figure 3. Healthy corneas in the patient from Case 1 after one year of scleral lens wear.

Case 2 A 49-year-old female who had a history of corneal GP contact lens wear for 30 years presented for evaluation for potential refitting into new lenses. Her chief complaint was that her contact lenses—which were four years old—were uncomfortable and that she had to remove her lenses several times a day to clean them so that she could see clearly. She used +2.00D over-the-counter readers with her contact lenses for near work. She was currently using Boston Original Cleaner (Bausch + Lomb) and Clear Care (Alcon). She wore glasses when she was not wearing her contact lenses, but her vision was clearer with her contact lenses.

Examination Findings The parameters of her corneal GP lenses were OD base curve 7.48mm, diameter 8.9mm, –11.37D power, distance VA 20/20, plano over-refraction (OR) and OS base curve 7.30mm, diameter 8.9mm, –11.25D power, distance VA 20/25, plano OR. Near VA OD and OS was 20/20 at 16 inches. Her manifest subjective refraction was OD –12.50 –1.75 x 180, add +2.00D, distance VA 20/25, near VA 20/20 at 16 inches and OS –13.50 –1.25 x 175, add +2.00D, distance VA 20/25, near VA 20/20 at 16 inches. Topography/keratometry readings were OD 45.20 @ 007/46.75 @ 097 with irregular mires and OS 45.46 @ 174/46.81 @ 084 with irregular mires.

Slit lamp examination revealed clear lids and lashes OD and OS as well as +1 conjunctival hyperemia OD and OS. Her cornea OD had vascularized limbal keratitis (VLK), with 3 o’clock and 9 o’clock staining; the cornea OS had interpalpebral staining (Figure 4). The lens was clear OD and OS, and the anterior chambers were deep and quiet.

Figure 4. (Left) corneal vascularization OD; (Right) interpalpebral staining OS.

Patient Management This patient was treated with fluoromethalone drops q.i.d. and tapered over a one-month period. She wore soft toric lenses and glasses until her cornea returned to its original shape. We did not refit contact lenses until the patient exhibited an absence of staining on both corneas and until the VLK regressed in her right eye.

Her HVID was 12mm in each eye. We fitted 16.5mm diameter scleral lenses with spherical peripheries. The lenses decentered, and there was mild blanching at 3 o’clock and 9 o’clock. As a result, a toric periphery was used for a better alignment and also to prevent rebound hyperemia; the new lenses centered better. The patient wanted to eliminate her reading glasses, so we ordered center-near multifocal lenses. She has successfully worn these lenses for one year and has functional vision at both distance and near as well as healthy corneas. More manufacturers are also offering decentered optics for multifocal scleral lenses if centration becomes difficult.

Clinical Pearls As both cases show, scleral lenses should not be reserved only for corneas that have progressive diseases. The patients in both of these cases developed corneal disease due to contact lens usage, but their corneal shapes were regular. The first patient had corneal disease from MGD/dry eye that was exacerbated by monthly replacement soft contact lens wear. The second patient developed corneal disease from chronic use of old, poorly fitting corneal GP contact lenses on eyes that were dry. After healing, both patients had “regular” corneas and were successful with scleral lenses.

SUMMARY

The use of scleral lenses for regular corneas is growing. Scleral lenses provide better comfort compared to corneal GP lenses and better vision compared to soft contact lenses, especially as compared to soft toric lenses in patients exhibiting a high amount of astigmatism. However, the scleral lens itself, the care requirements, and the need for a preservative-free solution to fill the bowl of the lens before application makes this modality more costly compared to other contact lens options.

Regardless of cost, the benefits of scleral lenses for patients who have normal corneas—including excellent, stable, and comfortable vision—far outweigh the risks. Offering this contact lens modality will also help differentiate one practice from another. CLS

REFERENCES

  1. Key JE. Development of Contact Lenses and Their Worldwide Use. Eye Contact Lens. 2007 Nov;33(6 Pt 2):343-345.
  2. Michaud L, van der Worp E, Brazeau D, et al. Predicting Estimates of Oxygen Transmissibility for Scleral Lenses. Cont Lens Anterior Eye. 2012 Dec;35:266-271.
  3. van der Worp E, Graf T, Caroline PJ. Exploring Beyond the Corneal Borders. Contact Lens Spectrum. 2010 Jun;25:26-32.
  4. Ritzmann M, Morrison S, Caroline P, Kinoshita B, Lampa M, Kojima R. Scleral shape and asymmetry as measured by OCT in 78 normal eyes. Poster presented at the Global Specialty Lens Symposium, Las Vegas, January 2016.
  5. Jones L, Downie LE, Korb D, et al. TFOS DEWS II Management and Therapy Report. Ocul Surf. 2017 Jul;15:575-628.