Early intervention is key to optimal treatment of nystagmus, emphasised Richard Hertle MD in a keynote lecture at the World Congress of Paediatric Ophthalmology and Strabismus in Hyderabad, India.
Dr Hertle is a world-renowned expert on nystagmus based at Akron Children’s Hospital, Ohio, US. He explained that nystagmus is a neuro-developmental disorder of the ocular motor system that generally starts as an acquired condition at 4 weeks to 3 months of age. Patients often have dynamic vision that changes with anxiety, sleep, medications, state of attention etc. It also differs when checked monocularly versus binocularly and it is therefore important to assess binocular vision.
In addition to eye movement recordings that are crucial for a thorough understanding, all patients should get OCT, visual fields, visually evoked potential, contrast sensitivity, photography and electroretinogram tests for assessing the afferent system, he said.
Infantile nystagmus is caused by an abnormality occurring during a sensitive period of visual development. About 75-85% of patients with infantile nystagmus syndrome have associated ocular pathology, much of which is amenable to treatment. He stressed that similar to amblyopia, it is important to treat nystagmus early when the developing visual system is the most plastic.
A disruption in neural communication between the developing afferent and efferent systems secondary to eye or other ocular motor pathology is the root cause of infantile nystagmus syndrome. This communication can sometimes be restored early as in early cataract surgery for congenital cataracts, which is responsible for visual pathway delays with resultant disruption in neural afferent-efferent communications and subsequent nystagmus.
Optical treatment in the form of contact lenses and glasses are almost as powerful as surgery but are underused, he said. High ametropia should be treated. Among medications, baclofen is generally well tolerated in children and very useful in the up to one-third of patients, who have an additional component of periodicity to their infantile nystagmus syndrome.
Eye muscle surgery is an effective treatment in patients with infantile nystagmus and serves three purposes; to improve an anomalous eye position (strabismus), to improve anomalous head position (eccentric null zones) and, to improve the nystagmus (beat-to-beat foveation, waveform and extent and breadth of the null zone). The cutting of the eye muscles at their insertion on the globe (enthesis) with original insertion site reattachment eye muscles improves nystagmus and gives better visual function.
The current hypothesis is that cutting newly discovered proprioceptive entheseal nerve endings sends signals to the brain, which, in turn “re-boots” the ocular motor system, thus improving the nystagmus. Dr Hertle hopes that his work in this area will help stimulate research on medications that act on these nerve endings, such as his research with topical brinzolamide. Research by him and others has shown significant improvement in waveform characteristics and visual acuity using this topical glaucoma medication.
He also described a nine-operation algorithm for surgical treatment of nystagmus, which produced improvement in multiple measures of visual function (acuity, contrast sensitivity, gaze-dependent vision, visual recognition time) in almost all patients. Between one and three lines of optotype visual acuity improvement occurred in 75% of patients using the PEDIG protocol, binocularly with best correction in place.
Richard Hertle: rhertle@chmca.org
