International Newsletter and Forum on Rigid Gas Permeable Contact Lenses, Corneal Shape, Health and Vision
 August 2016
In This Issue
Column
Scleral Lenses
Refractive Surgery
Keratoconus
Treatment Zone Decentration
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Agenda
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Column
Scleral Lens Challenges

It is amazing how scleral lenses have gone 'mainstream' - to some degree - in our field. With that, there is the risk that it is indeed regarded as a mainstream modality. It isn't. Managing scleral lens wear - for ocular surface disease potentially more so than for the irregular cornea - is a serious challenge. Take corneal grafts, for instance. They are quoted by 'allaboutvision.com' as one of the indications for scleral lenses. And they are. But they may represent one of the most challenging of scleral lens fits. The endothelium of a post-corneal transplant eye is typically compromised, and hypoxia is a serious challenge. Careful monitoring of the clarity of the graft is essential. The highest-Dk material you can find may help, together with a reduced central thickness, and minimal clearance. However, then there is the risk of creating too little clearance and potential touch of the lens with the sometimes elevated hinge at the host to donor border, potentially resulting in complications. In other words, scleral lenses for corneal transplants surely is not a stroll in the park. And while we are at it, intraocular pressure (IOP) increase is an uncertainly that we may have to monitor too, potentially. Charles McMonnies wrote a paper for Clinical and Experimental Optometry on 'A hypothesis that scleral contact lenses could elevate intraocular pressure.' And although no more than a hypothesis, and while this is countered by a study by Nau et al in Eye & Contact Lens (stating that immediately the mean central IOP was not different in a scleral lens wearing eye from the mean central IOP in the control eye not wearing a lens), it is still something to consider. Or, as Muriel Schornack put it in her recent webinar for the Scleral Lens Education Society on June 22nd: 'An Ounce of Prevention, A Pound of Cure: Avoiding and Managing Complications of Scleral Lens Wear.'
Eef van der Worp 
Scleral Lenses
Satisfaction
Sure enough, scleral lenses can be a life changing modality for certain patients. Bergmanson et al looked at 'Assessing Scleral Contact Lens Satisfaction in a Keratoconus Population'. An overwhelming majority of lens wearers (soft, piggyback, hybrid and predominantly corneal GP lenses) strongly preferred the comfort and vision of the scleral contact lenses. This cohort of keratoconus patients on average were dry eye suspects, according to a dry eye questionnaire the investigators performed. Midday fogging, at least occasionally, remains an issue, as more than half of the patients reported this phenomenon. In addition to keratoconus, and to a larger degree even, scleral lenses can be of great satisfaction to patients who have PMD. Because of the peripheral ectasia with this condition, fitting such an eye with corneal lenses is often virtually impossible, and scleral lenses in fact can be a very useful non-surgical treatment of last resort for PMD patients; scleral lenses can delay or prevent surgical treatment in these cases. A paper by Rathi et al in Contact Lens and Anterior Eye looks at scleral lenses in the management of pellucid marginal degeneration. The outcome was that scleral lenses can be used successfully in patients with PMD. The most common reason for discontinuation of lens wear was not lens fit, vision or comfort, but difficulty with scleral lens insertion or removal.
Corneal Ectasia
Corneal Elevation after Refractive Surgery
A study by Ying et al iin Contact Lens & Anterior Eye looked at corneal elevation in Chinese myopic patients who underwent refractive surgery. A total of 3000 eyes in 1500 patients were evaluated with the Pentacam instrument. Normal upper limits for corneal elevation in adult Chinese subjects were 4.95μm, 5.25μm, 6.2μm and 11.0μm at the anterior apex, anterior thinnest point, posterior apex and posterior thinnest point, respectively. Younger age, greater anterior corneal astigmatism, lower anterior and posterior keratometry, and shallower anterior chamber depth resulted in greater posterior corneal elevation values. Wang et al, also in Contact Lens & Anterior Eye, compared posterior corneal elevation changes and corneal biomechanical changes post-femtosecond laser-assisted in situ keratomileusis (FS-LASIK) and small incision lenticule extraction (SMILE) procedures using the Pentacam system and the Ocular Response Analyzer. FS-LASIK demonstrated a greater increase in posterior corneal elevation compared to SMILE at 12 months as well as a greater reduction of corneal resistance factor compared to SMILE. 
Keratoconus
Surgery or Contact Lenses?

Want to learn more about keratoconus? Melissa Bernett explains it well in an overview article in Contact Lens Spectrum. Keratoconus is a non-inflammatory, self-limiting corneal disease in which the cornea becomes progressively thinner, more distorted, and steeper in curvature, usually beginning in adolescence- and is a bilateral, yet asymmetric corneal ectasia, she writes. The abnormal curvature of the cornea causes changes in its refractive power in myopia and astigmatism. When managing patients who have keratoconus, it is optimal to consider corneal cross-linking early, especially if disease progression is evident. Contact lenses are advantageous in most patients who have keratoconus. If possible, deferring corneal transplantation until absolutely necessary is the preferred approach it is stated. Photo: Gustav Pöltner 
Scleral Shape
A Road Map to Scleral Mapping

Sheila Morrison explores the topic of the importance of scleral shape, based partly on a number of studies from Pacific University. One of the questions she addresses is: does the amount and orientation of corneal toricity extend across the limbus onto the sclera? In conclusion, she confirms that scleral shape is highly asymmetric and that the asymmetry is not often of the same magnitude as the corneal toricity. Another question is: as practitioners, could we achieve more efficient and appropriate scleral lens fits, with more knowledge about anterior ocular shape? This is answered with a resounding yes. Scleral lens fitting, regardless of design, is based on the sagittal height of the anterior chamber, and quadrant-specific lens modifications are now possible. Through scleral mapping technology, we have the ability to determine the toricity and asymmetry in all eight meridians of the eye, she writes. Can we alleviate scleral lens fogging and end-of-day discomfort by optimizing lens design based on individual scleral shapes? The increased use of back-toric scleral lenses could help to more equally distribute pressure where the lens lands, potentially leading to better comfort. Some reports indicate that changing patients from a spherical to a toric back surface may also decrease fogging. For more related questions like this, and the full report, see link below.
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Orthokeratology & Astigmatism   

Using orthokeratology to correct astigmatism often results in an insufficient visual outcome due to poor centration of the treatment zone or to insufficient correction of the astigmatism. A toric reverse geometry design provides full correction in astigmatic eyes from 1D to 7D of astigmatism power. This case report discusses orthokeratology as a possible treatment in a case with -3.10D of corneal astigmatism. A 22-year-old female complained of dry eye syndrome and fluctuating visual acuity with her current hydrogel contact lenses. After discussing all of the various treatment options, we decided to attempt overnight orthokeratology. Orthokeratology with a standard reverse geometry design resulted in an unstable fit and a toric fluorescein pattern with a flat periphery along the vertical meridian; more importantly, the reverse zone was not landing appropriately in the vertical meridian. An overnight orthokeratology lens with a toric reverse geometry design offered an excellent alternative treatment. 
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I-site is an educational newsletter that is distributed on a monthly basis and provides an update on rigid gas permeable related topics (scientific research, case reports and other publications worldwide). I-site is objective and non-political. Its editor Eef van der Worp, optometrist, PhD, FAAO, FBCLA, FIACLE, FSLS is a lecturer for a variety of industry partners, but is not related to any specific company. Please contact us at: i-site@netherlens.com.