Elevated lesions of the conjunctiva such as pingueculae and pterygia1 oftentimes present challenges in fitting the patient desiring refractive correction with contact lenses. These lesions can be irritated and thus become inflamed from a contact lens that has a less-than-optimal fit.
Historically, management usually meant fitting a small diameter corneal RGP lens or soft lens which avoided the lesion(s) either by a smaller diameter or vaulting it completely in a large, often custom, design.
Pterygia may result in irregular astigmatism as it grows across the cornea. Irregular astigmatism may not be fully corrected with the use of spectacle lenses. Thus, contact lenses may be recommended but their fitting certainly presents a significant obstacle.
With the increased interest in scleral lenses as a desirable alternative in fitting the irregular cornea or conjunctiva with elevated lesions new strategies are required.
If the lesion is a pinguecula two to three millimeters beyond the limbus then the proven strategy of fitting a smaller diameter lens may be the most straightforward solution. This works well in eyes with a relatively small horizontal visible iris diameter (HVID). This has been defined as a diameter of 11.5 mm or less.2
In a larger eye different approaches may be preferred. A commonly used technique involves notching the edge of the scleral lens thus avoiding direct contact with the lesion. The lens is oriented by the patient to align the notch around the pingcuecula. The notch itself helps to keep the lens situated, however, toric peripheral curves of at least 150 microns difference may be employed, as well.3
Pterygia and Salzmann’s nodular dystrophy can be even more complex as they involve the cornea itself and may affect vision. A unique and successful solution involves a “microvault”. This is a raised dome either on the edge or within the body of the scleral lens. The practitioner describes to the laboratory the exact location and desired height of the vault.
- Axis – “the optical axis location of the center of the microvault relative to the center of the lens and whether the microvault is nasal or temporal” .
- Decentration – “distance from the center of the lens to the center of the micro vault”.
- Width – “equal to the width of the microvault”.
- Depth – “the sagittal depth of the microvault. How high the apex of the vault is above the ocular surface (up to 500 microns).4
Another alternative for especially large or irregular pterygia is the process of impression molding5. This process creates a perfect mold of the eye with all its surface features intact in a twenty-six (26) millimeter diameter. Ophthalmic grade polyvinylsiloxane (FDA approved for the eye) fills a small, circular tray. The tray is inserted into the eye without anesthesia for approximately two to three minutes. The dense PVS hardens to a flexible, rubber-like solid. When removed from the eye a perfect impression is retained. The process is quite painless and quick.
The impression is sent to the lab where it is digitally scanned with up to several million data points. Those data are transformed into several hundred thousand points that are communicated to a lathe which cuts the scleral lens. One lens can take as long as three hours to be cut. The result is a lens that follows the contours, the “lumps and bumps”, of the cornea, limbus, pinguecula or pterygium exactly.
If further refinements are required, the impression process does not need repeating. The practitioner and laboratory can view the digital image in three dimensions and pinpoint exactly where changes are indicated and a new lens can be cut.
Although the cost of impression molding is more expensive initially, the savings in time and materials for the patient, the practitioner and the laboratory is usually justified in the more difficult cases.
As the popularity of scleral lenses continues to grow practitioners will become more familiar with these techniques to improve the comfort and vision in these special patients.
- Bennett ES, Weissman BA. Clinical Contact Lens Practice. Lippincott, Williams & Wilkins. 2005. Sect. II, Chapter 8; 198
- Caroline PJ, Andre MP. Elevated Conjunctival Lesions and Scleral Lenses. Contact Lens Spectrum; February 2017:56
- Zenlens MicroVault. Bausch & Lomb Specialty Vision Products, www.aldenoptical.com. Zenlens_MicroVault_Promo.pdf
- EyePrint Prosthetics. www.eyeprintpro.com Lakewood, Colorado, USA