Managing irregular cornea with scleral contact lenses

Fully scleral contact lenses are a good option for achieving successful visual rehabilitation in irregular corneas.

Two subgroups were distinguished in scleral lenses depending on the presence of corneal bearing or not: corneo-scleral or semi-scleral. Recently, the Scleral Lens Education Society (SLS) has defined a more precise differentiation between different modalities of scleral lenses not only based on the lens diameter, but also on the diameter of visible iris of the eye in which the lens is fitted, as detailed in Table 1.1.

SLS supports public education that highlights the benefits and availability of scleral contact lenses.

Researchers found that fully scleral lens of a specific diameter can behave as miniscleral or large-scleral, depending upon the eye on which it is fitted.

This type of lens must always be inserted after being completely filled with saline solution, avoiding the formation of bubbles during the insertion that ultimately could lead to discomfort and poor vision in the patient.

Scleral contact lenses have always been considered suitable for the correction of irregular astigmatism (post-corneal refractive surgery,^2,3 post-keratoplasty4–6), including keratoconus^7-12 and other ectatic disorders,¹³ as they are able to neutralize irregularities with the tear film meniscus that form with the cornea, while maintaining high levels of comfort.

However, there are also other indications feasible for corneo-scleral and fully scleral contact lenses, such as the correction of refractive errors that cannot be corrected satisfactorily with rigid gas-permeable (RGP) corneal or soft contact lenses, the introduction of prismatic corrections, for cosmetic purposes and even in healthy corneas, due to the advantages of this type of lens: less palpebral interaction, great comfort as conjuntictival sensitivity is lower than that of the cornea, no possibility of generating corneal distortion if the fitting is adequate and a simplified fitting process.¹⁴

In addition, the process of insertion and removal of the lens is simplified by the use of a suction cup, avoiding the contact of the fingers with the eye at all times.The scleral Contact lens ICD                                                                                                                                                                                      

The ICD16.5 contact lens (Irregular Corneal Design, Paragon Vision Sciences, distributed by Lenticon, Madrid, Spain) is a fully scleral contact lens that has four differentiated zones allowing a correct centration with no corneal touch and a stable positioning over the conjunctiva (Figure 1).

These zones are: central clearance zone (CCZ), peripheral central clearance zone (PCCZ), limbal clearance zone (LCZ), and scleral landing zone (SLZ) (Figure 1).

The geometry of these zones can be modified to achieve a perfect fitting of the lens independently from the corneo-scleral profile.

Likewise, a peripheral toricity can be added if the conjunctival-scleral profile presents a significant level of astigmatism or to stabilise a scleral lens with toric power to compensate for residual astigmatisms during fitting.

This contact lens is fitted considering the sagittal height instead of keratometry that can be measured using optical coherence tomography (OCT), Scheimpflug cameras, or more precisely with corneo-scleral topographers, such as the Eye Surface Profiler (ESP) from Eaglet-Eye.¹⁵

A central of vault of around 300 µm is required for obtaining an appropriate fitting, with no corneal bearing during wearing due to a potential conjunctival compression of the lens (Figure 2).

This lens is an RGP contact lens manufactured in material HDS 100 from Paragon Vision Sciences.

The material used is a thermoset fluorosilicone acrylate copolymer derived primarily from siloxane acrylate, trifluoroethyl methacrylate, and methylmethacrylate with a water content of less than 1% (Paflufocon D), with a Dk (oxygen permeability) of 100 Fatt.⁹

Results with scleral lens ICD16.5

Our group conducted a study to assess results obtained with the fully scleral contact lens ICD16.5 in corneas with different types of problems.

The study was consecutive and prospective, and was carried out in the Contactology Unit of the Department of Ophthalmology (Oftalmar) of the Vithas Medimar International Hospital in Alicante, Spain.

The study included a total of 42 eyes of 27 patients, 15 men (55.6%) and 12 women (44.4%).

The average age of patients in the stud was 39 ± 12 years (range, 14 to 65 years).

Inclusion criteria for the study were that the participants had no active ocular disease, no severe dry eye, no previous intolerance to soft or corneal gas permeable contact lenses, and they also agreed to and signed informed consent papers.

A prefitting examination also proves to be a valuable step in the process, and our study results bear this out.

In all cases, a very complete pre-fitting examination was carried out that included: filiation data, uncorrected and corrected visual acuity, manifest refraction, biomicroscopy, corneal topography with the Sirius system (CSO), ocular aberration measurements with the iTrace system (Tracey Technologies) and previous anterior segment examination by optical coherence tomography with the 3D OCT-1000 system (Topcon).

The patient was evaluated after 1, 3, 6 and 12 months of contact lens wear to check the success of the fitting.

In our study, a total of 25 eyes with keratoconus (59.5%) were fitted, four of them with previous implantation of intracorneal ring segments and 10 with previous corneal collagen crosslinking, six eyes with irregular cornea after previous LASIK surgery (14.3%), two eyes with irregular cornea after radial keratotomy surgery (4.8%), three eyes after keratoplasty (7.1%, one eye with endothelial corneal decompensation (2.4%), two cases of dry eye (4.8%), and two eyes with myopia magna (4.8%).

The mean sagital height required for the fitting was 4294.12 ± 292.56 μm (4,000 to 4,900 μm) and the mean optical power was –6.96 ± 6.95 D (–21 to +4 D).

After 1 hour of wearing the lenses, the mean apical vault measured by optical coherence tomography was 299.4 ± 85.56 μm (201 to 420 μm).
Concerning the visual outcomes, a significant improvement in decimal visual acuity was achieved with the contact lens after 1 month of wearing compared to that obtained with glasses before fitting (p < 0.001), without significant changes occurring during the rest of the follow up (Figure 3).
This is consistent with the results of previous studies using the same model or other models of scleral contact lenses.^2–15

There was a tendency to an increasing positive over-refraction during the follow up, although it did not reach statistical significance (p = 0.17).

This change was consistent with a slight anterior (p = 0.91) and posterior corneal flattening (p = 0.37), which did not reach either statistical significance.

Moreover, the noted change is in agreement with current studies reporting the level of corneal molding induced by fully scleral contact lenses.16,17
In our study, we detail that a small but statistically significant pachymetric increase was also observed at 3 months of wearing (minimum thickness p = 0.001, central thickness p = 0.08), without significant changes afterward (minimum thickness p = 0.86, central thickness p = 0.88).

This minimal pachymetric increase has been reported by other authors18 and does not seem to be related to problems of clinically relevant hypoxia as high Dk material has been used.

Vincent et al. concluded in a prospective study that, although a small amount of corneal swelling was induced following 8 hours of miniscleral lens wear (on average <2%), modern high Dk miniscleral contact lenses that vault the cornea do not induce clinically significant corneal edema or hypoxic-related posterior corneal curvature changes during short-term wear.

Regarding ocular high-order aberrations, there was a significant reduction, especially of the primary coma, as indicated in Figure 4. This also has shown to be consistent with the significant gain in corrected distance visual acuity that has been achieved with the contact lens.

The tolerance of the contact lens was good in all cases, with the following complications or difficulties reported:

• Abandonment of fitting: 3 cases (6.8%) due to poor tolerance as a consequence of an excessive lens indentation throughout the day

• Lens power adjustments required during the first month (8 cases, 18.2%)

• Adjustments of the scleral landing zone due to lens fogging (5 cases, 11.4%) or excessive scleral indentation (2 cases, 4.5%)

• Episodes of occasional conjunctival hyperemia (tobradex, thealoz, recugel) (5 cases, 11.4%).

Conclusions
In conclusion, the fully scleral contact lens ICD16.5 is a good option for achieving a successful visual rehabilitation in irregular corneas, especially if previous fittings with other types of contact lenses have failed.

This type of lens is able to provide a significant increase in visual acuity combined with a significant improvement in visual quality, maintaining high levels of comfortability.

The fitting process of these lenses is relatively simple and can be highly optimized by introducing the appropriate changes in the different zones of the lens. ■

Disclosures:

David P. Piñero Llorens, PhD
E: dpinero@ipass.es
Dr. Piñero Llorens is researcher/lecturer, Department of Optics, Pharmacology and Anatomy, University of Alicante, Alicante, Spain and Department of Ophthalmology, Vithas Medimar International Hospital, Alicante, Spain.

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