Options for the moderate-to-high astigmat
Soft toric lenses have been shown to be successful in low, moderate, and high astigmatism.17,18 With expanded parameters of daily disposable lenses ranging from -0.75 D to -2.25 D, very few patients have prescriptions outside of what is currently available. Multipackaged lenses expand the available parameters to -2.75 D cylinder. The latest designs offer multiple stabilization zones resulting in a lens that remains rotationally stable in primary as well as extreme gazes.
Toric ortho-k lenses are emerging in most marketplaces. These modified designs provide on average -2.50 DC correction while also offering myopia control for those with higher amounts of compound myopic astigmatism.13
When corneal cylinder exceeds -2.50 D, back-surface toric GPs become an outstanding option. Fitting them empirically is straightforward, efficient, and extremely successful.12 For smaller corneas, the saddle method of fitting the cornea 0.50 D steep in the flat meridian and 0.50 D flat in the steep meridian is highly effective. For average and large corneas, the Mandell-Moore method of fitting the flat meridian 0.25 D flat and the steep meridian flatter than K on a sliding scale as the cylinder increases is equally successful. Find an online calculator tool at http://www.gpli.info/mandell-moore/ to aid in designing your initial bitoric lenses.
These patients achieve excellent vision which may be superior to that of soft lenses. In fact, a study by Michaud showed that 4/10 current soft toric lens wearers chose to wear toric GPs for improved vision.12 This dispels the myth that a previous soft lens wearer will not adapt to corneal GPs.
When patients have struggled with standard multipackaged soft lenses and GP options, it may be time to consider custom soft lenses, hybrids, and scleral lenses. Some patients with atypical corneal diameters may experience more stable fitting and vision with a custom soft lens with a custom diameter. Additionally, new designs offer lens powers that are nearly limitless in sphere and extend to -10.00 D in cylinder.
For patients who have struggled with vision stability with soft lenses and do not tolerate corneal GPs, SynergEyes Duette hybrid is an excellent option. Duette has been shown to offer excellent astigmatic correction when corneal cylinder and refractive cylinder are similar.14
In addition, the development of scleral lenses for the regular cornea offer virtually limitless power options and high-quality vision correction. Newer regular cornea scleral GPs are similar in size to soft lenses and can be designed with toric peripheries or haptics to stabilize lens rotation as well as front toric optics to correct any residual astigmatism for patients with high astigmatic corrections.15,21
There are now as many options for the astigmatic patients as there are for the spherical patient.
Figures 1 (top) and 2 (bottom). Pretreatment topographies showing significant with-the-rule (WTR) astigmatism.
The patient’s mother is very concerned about myopic progression in her daughter. The patient has increased from -2.75 D to -4.00 D in a year. However, she also has -2.25 D cylinder.
After discussing options of soft toric, GP or ortho-k, the parent opted for ortho-k for multiple reasons including myopia control, gymnastics, and swimming. The parent strongly preferred no lens wear for sports. Topographies were sent electronically to the manufacturer along with spectacle prescription, and lenses with enhanced toric peripheries were designed. Spherical ortho-k lenses were ordered empirically.
OD: -4.00-2.25 x 007; 20/20 ; SimKs 42.05/44.13
OS: -3.00-2.25 x 178; 20/20; SimKs 41.88/44.08
See Figures 1 and 2.
The lenses provided very centered treatment zones. See Figures 3 and 4.
At one year, the vision remained 20/25 unaided with a -0.25 DS refraction to 20/20 in each eye. See Figures 5 and 6 for post-treatment topographies.