Article

PRESCRIBING FOR ASTIGMATISM

IS MY CHILD A CANDIDATE FOR ORTHOKERATOLOGY?

There are many opportunities in contact lenses to offer a niche service and to differentiate a practice. Multifocal, scleral, and custom soft contact lenses are some services that can help grow your business. Orthokeratology is another area in contact lenses that allows practices to promote the off-label service of myopia control for a group of patients who have a specific need. As the awareness of orthokeratology effectiveness grows, more and more parents are pursuing orthokeratology for their children; this brings in a wider range of refractive errors, including varying amounts of astigmatism. While moderate-to-high astigmatism can make an orthokeratology fitting more complicated, it does not exclude a child from being a candidate.

Patient Selection

Overnight orthokeratology lenses are indicated for up to 6.00D of myopia correction and up to 1.75D of with-the-rule and 0.75D of against-the-rule astigmatism (Van Meter et al, 2008). However, there are case reports and studies citing management of astigmatism into the range of 3.50D as an off-label treatment (Baertschi and Wyss, 2010; Chen et al, 2013).

When patients and their parents present for an orthokeratology evaluation, many times it’s the expectation management and questions asked that determine patient candidacy rather than the lens design. It’s important to educate parents that many orthokeratology designs are cleared for refractive error correction but are not yet cleared for the purpose of myopia control.

Topographical Analysis

To determine the complexity of the fit, a topographer is an essential tool. When astigmatism is present, we need to know whether the refractive astigmatism matches the corneal toricity and whether the corneal toricity is central or extends limbus-to-limbus, and we need an assessment of symmetry in corneal elevation in the primary meridians.

A lab consultant shared with me that when corneal toricity is considered central, the lab can often correct it by flattening through the astigmatism to create a spherical treatment zone. The lab utilizes topographical elevation maps to determine whether a toric lens design is needed. If the difference in corneal elevation is greater than 30 microns at a chord of 8mm, they recommend using an orthokeratology design with toric peripheral curves to assist in lens centering and stability. Using this simple measurement at the initial evaluation can help better educate patients on the complexity of the fit and set realistic expectations regarding the number of visits and potential lens changes.

Gathering Reliable Data

It can be difficult to gather reliable data when evaluating young kids, and when you’re working with a custom lens, baseline data is very important. The most important data points include refraction, topography measurements, and slit lamp evaluation. If you have an electronic visual acuity screen, utilizing a movie function or frequently changing the letters can help keep their focus during retinoscopy. Taking the time to get a quality objective refraction through retinoscopy and/or auto-refraction will take the pressure off of achieving a consistent subjective refraction.

During topography measurements, an assistant can be helpful to keep a child’s head still or to gently lift the upper lid or lashes with a cotton swab if they are affecting the quality of the scan.

Lastly, during the slit lamp evaluation, pay attention to the eyelid margin and lash direction. Lid margins showing evidence of blepharitis should be treated, and any in-turned lashes or trichiasis should be monitored for corneal staining.

A Great Option

There has never been a better time in contact lenses. Orthokeratology is a service that helps build amazing relationships with patients and their families. We are now able to help more kids than ever before with the growing technology around myopia and astigmatism correction. CLS

The author acknowledges Jennifer Root of Euclid Systems Corporation for her help with this article.

To obtain references for this article, please visit www.clspectrum.com/references and click on document #279.