Pterygia cause irregular astigmatism in increasing amounts as they encroach upon the cornea (▶ Fig. 10.1). According to the Blue Mountains Eye Study of 3,564 people aged 49 years or older, 266 individuals (7.3%) had pterygium (or a history of pterygium surgery) and 2,521 (69.5%) had pinguecula present in either eye. 1 Significantly more men than women had both pinguecula and pterygium. There were significant associations between pterygium and increased pigmentation (skin and hair color), decreased skin sun sensitivity, and sun-related skin damage. In a study that examined the prevalence of pinguecula and pterygium in a general population in Spain of 1,155 people age 40 years and older, the prevalence of pinguecula was 47.9% and increased significantly with age. 2 The prevalence of pterygium was 5.9%; this also increased significantly with age. Of interest, after controlling for age and sex, pinguecula was strongly associated with alcohol intake. 2 Fig. 10.1 A mild pterygium nasally OD causing more astigmatism than the fellow eye. The axial map demonstrates central astigmatism (bowtie) with a blue island of flattening overlying the lesion (upper left map). The keratometry view demonstrates the lesion nasally. Irregular astigmatism secondary to radial keratotomy, keratoconus, or decentered hyperopic LASIK may be addressed using specialty corneal transplants or topography-guided surface ablation. This is not the case of irregular astigmatism resulting from pterygium, and not all patients may be good candidates for pterygium surgery. They may live too far from a capable surgeon, lack the financial means, or be wary of surgery. The irregular astigmatism must be corrected nonsurgically to allow them to function. Scleral lenses address irregular astigmatism, dry eye disease, visual function, and pain associated with this condition. Elevated lesions of the conjunctiva such as pingueculae and pterygia 3 often present challenges in fitting the patient desiring refractive correction with contact lenses. These may be a mild pinguecula or conjunctival cyst, more significant, such as in the case of pterygium, (▶ Fig. 10.2 and ▶ Fig. 10.3) or status post trabeculectomy, shunt, stent, or glaucoma implant. Intraocular pressure may be compromised if there is excessive pressure or rubbing over tube shunts or valves. This may lead to conjunctival or tube erosion, increasing the risk of further complications such as endophthalmitis. Elevations on surface of the cornea such as in Salzmann’s nodular degeneration (▶ Fig. 10.4) or severe corneal scarring also complicate lens fitting. Fig. 10.2 Larger pterygia located both nasally and temporally. Fig. 10.3 Topography map corresponding to the ▶ Fig. 10.2. Note the appearance of two bowties 90 degrees apart. Fig. 10.4 Corneal elevations in Salzmann’s nodular degeneration. Another indication for scleral lens fitting is control of ocular surface disease (OSD). 4 Unlike conventional contact lenses, scleral lenses vault the cornea, and land on the scleral conjunctiva. The fluid reservoir continuously bathes and hydrates the cornea. The lens serves as a barrier to protect the corneal and conjunctival surface while blinking. Scleral lenses have also been reported to reduce inflammatory mediators, which may cause pterygium progression. La Porta Weber et al studied osmolarity in a group of 25 patients with OSD. A decrease in tear film osmolarity after 12 months of scleral lens wear was reported. 5 Carracedo and colleagues found statistically significant decreases in tear osmolarity and diadenosine tetraphosphate after patients wore scleral lenses for 6 to 9 hours. 6 Scleral lenses have been found to be beneficial n multiple conditions including ocular surface disease, vernal keratoconjuncitivits, 7 advanced atopic keratoconjuctivitis, 8 graft versus host disease, 9,10 neurotrophic keratitis, graft versus host disease, Steven Johnsons Syndrome, ocular cicatricial pemphigoid, limbal stem cell deficiency amongst others. Scleral lenses do not appear to reduce matrix metalloproteinases, however. 6 Periodic visits for these patients are required to maintain adequate control of OSD, reduce risk of progression, and avoid surgery. 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 and new technologies developed. Corneal topography or Scheimpflug tomography is typically used to assess corneal curvature in corneal gas permeable fitting but is less useful for scleral lens fitting as data is not collected for the limbus or sclera. Anterior segment optical coherence tomography (OCT) is now commonly employed in scleral lens fitting. OCT can be used to measure lens thickness centrally and peripherally, examine lens edges for flaws and causes of discomfort, measure posterior tear film thickness, and assess points of lens bearing to determine the need for design modification. 11 Anterior OCT software contains linear calipers to allow precise analysis of the anterior segment at various sagittal depths. Angular calipers allow measurement of corneal, limbal, and scleral angles to assist in fitting. 11 Various fitting strategies are used to fit lenses in these complicated patients. Simply ordering lens specifications such as optic zone radius, total diameter, back vertex power, and material is not adequate in complicated eyes. Custom specifications including tertiary and secondary curvatures, asphericity, diameter, and optic zone modifications are often required. For simplicity, customization can be categorized in three areas: the optical zone, the transition zone, and the landing zone. Unlike regular corneal gas permeable lenses with back surface powers in alignment with the corneal surface, scleral lenses have a post lens tear reservoir between the posterior lens surface and anterior cornea. The transition zone is located just peripheral to the optical zone chord continuing to the beginning of the presumed or measured landing zone chord. It varies with each manufacturer and design. It has been previously referred to as the limbal or intermediate zone. It is described by its radius of curvature and its width. The landing zone is located peripheral to the transitional zone and begins from the primary functional diameter and ends at the lens edge. It may also be a planar (flat) surface placed at various angles from the transitional zone to the edge of the lens. Also described as lens haptics. It is described by its radius of curvature and its width. These zones can be customized to maintain good functional vision and minimal discomfort despite elevated lisions. Techniques specific to fitting patients with pterygium and conjunctival elevations include adjusting the lens diameter, notching the lens, and custom vaulting techniques. A standard corneal gas permeable lens diameter of 9.0 to 9.5 mm may encounter the elevated lesion, and prolonged contact may cause irritation, inflammation and discomfort. If the lesions are encroaching significantly onto the cornea, it is possible to fit a gas permeable lens inside the lesion’s borders by decreasing the lens diameter. If the lesion is a pinguecula 2 to 3 mm beyond the limbus, a 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. This has been defined as a diameter of 11.5 mm or less. 2 Alternatively, if the elevation is located at the limbus, increasing the diameter to vault the elevation may be more successful. Scleral lens fitting categories and diameters are described in ▶ Table 10.1. Lens diameters (mm) Corneo-scleral 12.9–13.5 Semi-scleral 13.6–14.9 Mini-scleral 15.0–18.0 Full scleral 18.1–24.0 or greater Source: Reproduced with permission of Contact Lens Spectrum, published October 2010. Contact Lens Spectrum is published monthly by PentaVision LLC, ©2010 All rights reserved. Visit www.clspectrum.com for more information. In patients with peripheral corneal or conjunctival lesions, evaluation of peripheral fitting characteristics is essential. Conjunctival blanching and impingement must be avoided in these patients. 12 Blanching is a whitening of the conjunctiva due to lens pressure on the tissue. Changing the peripheral curves or using a nonrotationally symmetrical lens may alleviate blanching. 13 Impingement occurs when the edge of the lens focally pinches into the conjunctival tissue. Impingement can occur as a result of a very steep landing zone with minimal contact with the conjunctiva except for the very edge of the lens. Conjunctival staining and hypertrophy may be evident after lens removal. To alleviate impingement, flatten the scleral landing zone periphery or increase the edge lift. It is also possible to increase the overall diameter of the lens to bear the weight more evenly on the conjunctival surface. For a large irregular elevation, it is possible to at the edge of the scleral lens to avoid direct contact. The patient is instructed to align the lens notch is a specific position to avoid the conjunctival elevation. The notch itself helps to keep the lens situated. Additionally, however, toric peripheral curves of at least 150-μm difference may be employed 2 (▶ Fig. 10.4). The first step is to measure the length and width of the conjunctival abnormality with a slit beam of the biomicroscope or using scleral topography/profilometry. The height and width of the conjunctival abnormality with the scleral lens on the eye are then measured. The scleral lens is marked with a sharpie or dry erase marker with the lens on the eye. Be sure to inform the patient that the lens is being marked and not the eye. Finally, measure the marking on the lens after the scleral lens is removed. Consult the preferred laboratory consultant to discuss the notch and send the measurements and/or the lens to the laboratory. Notching is performed manually and is not precisely reproducible. When inserting the scleral lens with a notch, it is important to place it on the eye with the correct orientation. Be sure to inform the staff person who is training the patient on scleral lens application and removal, as well as the patient, about the need for proper lens orientation. Pterygia and Salzmann’s nodular dystrophy can be even more complex as they involve the cornea itself. Irregular astigmatism may reduce 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 (▶ Fig. 10.5). The practitioner describes to the laboratory consultant the exact location and desired height of the vault. The following must be specified 14: The 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.” The amount of decentration—“distance from the center of the lens to the center of the microvault.” The width—“equal to the width of the microvault.” The depth—“the sagittal depth of the microvault: how high the apex of the vault is above the ocular surface (up to 500 μm).” 6 Fig. 10.5 Image of focal vault within the lens.
10.2 Fitting Strategies
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