Myopia is a not a consequence-free benign change in refractive error. Rather, it is a potentially sight-threatening eye condition. High myopia is a leading cause of blindness and is associated with such comorbidities as retinal detachment, macular choroidal degeneration, premature cataract, and glaucoma (Grossniklaus and Green, 1992; Saw et al, 2005). The earlier the onset, the more time for progression to higher amounts of myopia. It is, therefore, crucial to implement a treatment that decreases myopia progression at as early an age as possible.

Effective contact lens approaches for limiting myopia progression include orthokeratology (ortho-k) and soft multifocal lenses (Walline, 2016). Myopia management with contact lenses is accomplished by providing a myopic blur cue to the retina, which is assumed to act as a retinal cue that slows myopic eye growth (Charman et al, 2006; Smith et al, 2013; Walline, 2016).

Children who have astigmatism pose a special challenge to this type of contact lens fitting. Not only should myopic defocus be in place, both the myopic and the astigmatic refractive errors must be corrected in the same optic. The following discusses astigmatic contact lens options for myopia management, all of which are currently off-label.

Toric Orthokeratology

Spherical ortho-k lenses on astigmatic corneas usually result in poor centration that leads to induced irregular astigmatism, glare, and poor visual outcome. Ortho-k designs require peripheral landing 360º around between the lens and the cornea to prevent tear film squeeze forces from escaping along the steepest meridian in an astigmatic eye (Mountford, 2004). Thus, a toric ortho-k lens is the only option for correction of myopes who have limbus-to-limbus astigmatism (Chan et al, 2009; Korszen and Caroline, 2017). A sagittal height difference between the flat and steep corneal meridians of 30 microns or greater at the landing chord length of the alignment curve suggests that the treatment may benefit from adding toricity to the peripheral alignment curve (Kojima, 2016).

Soft Toric Bifocal Lenses

Most commercially available soft bifocal lenses are center-near designs; however, studies demonstrating effective retardation of myopia have used center-distance designs.

Center-distance toric multifocal lenses are available for myopia management through manufacturing labs that are able to lathe cut soft lenses. These designs typically have the astigmatic correction on the back surface and the multifocal optics on the front surface.

Other Toric Lens Designs

The posterior tear lens behind GP contact lenses effectively corrects high amounts of corneal astigmatism. Bifocal GP lenses are, therefore, ideally suited for myopia management in children who have high amounts of astigmatism (Liu, 2017) (Figure 1).

Many corneal and scleral GP lenses are commercially available in center-distance bifocal designs. Hybrid lenses also are available with bifocal parameters.

Summary

Contact lens-based myopia management treatments exist for all refractive errors, even in cases of significant astigmatism. Gaining proficiency in fitting these modalities will benefit more children who have progressive myopia. CLS

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