Step Your (Scleral) Game Up – Utilize Scleral Lens Toricity
This Scleral Lens Monthly is for you, the experienced scleral lens practitioner, who is fitting scleral lenses with success. However, sometimes we all run into scenarios where the scleral lens fit could be improved. (See Figure 1 below.) This is how to step your scleral game up.
It has been established that scleral shape is not rotationally symmetric or spherical, but rather non-rotationally symmetrical exhibiting an irregular shape.1 Although corneal and scleral toricity are not associated,2 the sclera, similar to the cornea, may have steep and flat meridians.3 The flattest curvature is typically observed nasally and the steepest curvature temporally.1 However, scleral shape varies from patient to patient, each quadrant within an individual eye, and from right eye to left eye. Scleral asymmetry starts at the more symmetrical limbus and increases in asymmetry towards the extraocular muscles.4 Researchers indicated that measurements by OCT at a 15mm chord demonstrated low toricity. 4 In a different study, scleral toricity was 100 µm on average.5 Based on this information, some practitioners advise that scleral lens diameters of 14.5mm or less can be rotationally symmetric, and scleral lens diameters greater than 14.5mm may benefit from back surface toricity or quadrant specific designs.4
An optimal alignment in all meridians on the scleral is essential. Scleral lenses, especially larger diameter lenses, have to land in both principal meridians. Toric, or quadrant specific, landing zones can help to achieve ideal scleral alignment and have numerous advantages. Incorporating back surface toricity can help improve lens decentration, reduce lens distortion,1 reduce excessive debris,1 reduce the formation of air bubbles, decrease conjunctival prolapse, improve localized conjunctival vessel blanching6-7 and lens impingement.8-9 In turn, your patients will experience improved comfort, increased wearing time, overall satisfaction, better visual quality and enhanced optical correction,10-12 which all lead to long term successful scleral lens wear!
Clinically, we often observe inferior temporal lens decentration with thinning of the fluorescein pattern in the superior nasal quadrant.13 This decentration is induced by scleral asymmetry which increases towards the extraocular muscles. A well centered scleral lens is especially important when integrating multifocal optics or higher order aberrations. In order to improve lens centration and stabilization, use back surface toricity.
It has been reported that applying a scleral lens with spherical haptics on a toric sclera will not exhibit an ideal fit and will have a with the rule appearance.14 The lens will touch the horizontal meridian and will lift off in the vertical meridian. A helpful tip is to evaluate the scleral lens outside of the slit lamp. Evaluate for areas of compression, impingement and edge lift using a penlight. Have the patient look in different directions to get a complete view. After scleral lens settling, it is helpful to ask the patient how the lens feels, and to localize any discomfort if present. In my experience, patient responses are often very accurate and correspond with the scleral lens fit. Then administer fluorescein and evaluate the lens using a slit lamp with a slit beam and white light to identify landing patterns. If a patient is demonstrating any of the symptoms listed above, apply a lens with back surface toricity to determine if symptoms improve. Some manufacturers have lenses that include back surface toricity within the diagnostic fitting set. Most manufacturers can design lenses with back surface or quadrant specific toricity.
Now that you have some additional tools for scleral lens success, go step your (scleral) game up!
Figure 1: Significant compression with blanching of blood vessels.
Image courtesy of Tom Arnold, OD, FSLS
1. van der Worp E. A Guide to Scleral Lens Fitting, Version 2.0 [monograph online]. Forest Grove, OR: Pacific University; 2015. Available from: http://commons.pacificu.edu/mono/10/.
2. van der Worp E, Graf T, Caroline PJ. Exploring beyond the corneal borders. Contact Lens Spectrum. 2010;25(6):26-32.
3. Jedlicka J, Johns LK, Byrnes SP. Scleral contact lens fitting guide. Contact Lens Spectrum. 2010;10:30–36.
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8. Schornack MM. Toric haptics in scleral lens design: a case series. Poster presented at the Global Specialty Lens Symposium. Las Vegas, 2013 January, 27-29.
9. Mahadevan R, Jagadeesh D, Rajan R, Arumugam AO. Unique hard scleral lens post-LASIK ectasia fitting. Optom Vis Sci. 2014;73:136–142.
10. Visser ES, Visser R, Van Lier HJ. Advantages of toric scleral lenses. Optom Vis Sci. 2006;4,233–6.
11. Visser ES, Visser R, Van Lier HJ, Otten HM. Modern Scleral Lenses, Part I: Clinical Features. Eye & Contact Lens. 2007;1:13–6.
12. Visser ES, Van der Linden BJ, Otten HM, Van der Lelij A, Visser R. Medical applications and outcomes of bitangential scleral lenses. Optom Vis Sci. 2013;90:1078–85.
13. Caroline PJ, Andre MP. Why scleral lenses do not center? Contact Lens Spectrum. 2014;29(8):56.
14. DeNaeyer, G. Today’s scleral lens. Review of Cornea & Contact Lenses, supplement to Rev Optom. 2012 (06):18-22.
Dr. Melissa Barnett is a Principal Optometrist at the UC Davis Eye Center in Sacramento, specializing in anterior segment disease and specialty contact lenses. Dr. Barnett is the Past President of The Scleral Lens Education Society. She lectures and publishes extensively on topics including dry eye, anterior segment disease, contact lenses and creating a healthy balance between work and home life for women in optometry.