Article

GP INSIGHTS

GP LENSES FOR NYSTAGMUS

Nystagmus is an ocular condition that is frustratingly difficult to manage, with very few effective treatment options and a lifetime of poor vision for affected patients. The use of GP lenses to maximize vision and minimize the severity of the nystagmus itself is not a new idea; however, research regarding both the mechanism of the GP lens influence and the effectiveness of this as a treatment is limited, and results are mixed.

Benefits of Contact Lenses Compared to Spectacles

The optics behind using contact lenses to improve vision in nystagmus patients is theoretically sound; when wearing spectacles, their eyes frequently look outside of the optical center of their lenses. This induces undesirable prismatic and minification/magnification effects as well as increased chromatic and spherical aberration (Bagheri et al, 2017; Jayaramachandran et al, 2014; Biousse et al, 2004). Other benefits of contact lenses compared to spectacles (less aniseikonia, better peripheral vision, etc.) may also help to increase fusion and to prolong foveal fixation time (Bagheri et al, 2017).

The other reason why GP lenses may be beneficial (and possibly more beneficial compared to soft contact lenses) is due to sensory feedback from lens movement on trigeminal nerve endings in the cornea, conjunctiva, and inner eyelids. Bagheri et al (2017) report improvements in both vision and also in nystagmus frequency, amplitude, and intensity with GP lens wear in a prospective interventional case series of 16 patients who had infantile nystagmus, though Jayaramachandran et al (2014) report no significant difference in vision or nystagmus severity with GP lenses compared to spectacles in a 24-patient randomized, controlled trial. A literature review over the past 20+ years shows similarly mixed results, though study technique is quite varied, and the number of enrolled subjects is always relatively small.

Fitting Challenges

Fitting GP lenses on eyes that have nystagmus can be difficult. Measuring keratometry or topography on moving eyes is challenging, if not impossible in many cases. Application and removal can be difficult depending on the intensity and frequency of the nystagmus and on the dexterity of the patient. GPs are also more likely to decenter and/or dislocate from the eyes, heightening the risk of corneal abrasion as well. Lastly, the constant motion of the GP lens with nystagmus-driven eye movements causes more awareness during lens wear. If poor patient comfort prevents acclimation to GP lens wear, this can lead to lens discontinuation. This is ironic because GP lenses create the sensation-driven neurological feedback loop that may help lessen nystagmus severity.

Despite these challenges, it is still worthwhile to consider GP lenses for patients who have infantile or even acquired nystagmus if the underlying condition/etiology cannot be addressed. It will be interesting to see whether more practitioners attempt GP or even scleral lens fitting in nystagmus patients in the future, with the latter being an exciting option that might provide the benefit of GP optics with less fitting difficulties and better comfort.

Coordination of care with neurologists and neuro-ophthalmologists for GP fitting of nystagmus patients could bring a relatively inexpensive and safe treatment option to patients who are usually left with little or no other hope for improvement and for whom even mild symptom relief is often appreciated. CLS

For references, please visit www.clspectrum.com/references and click on document #280.

Dr. Potter owns a private practice in Sylvania, OH. She has received travel funding from CooperVision and Paragon Vision Sciences. She can be reached at rpotter@personaleyecare.com.