METHODS

Four patients with congenital nystagmus were prospectively included in our study. The study was approved by our institutional review board. Our inclusion criteria were decreased visual function related to the nystagmus (assessed by best corrected binocular visual acuity worse than or equal to 20/40, but at least 20/400), 18 years of age or older, willingness to participate in the study, and informed consent. Patients were excluded from the study if they were not willing or incapable of using contact lenses (for example, because of poor hygiene, poor compliance, or corneal disease contra-indicating contact lens wear), or if they had an ocular disease sufficient to cause the visual acuity obtained.

All patients underwent complete baseline neuro-ophthalmological, neurological and ocular evaluations, including refraction, slit lamp examination, intra-ocular pressures, dilated funduscopy, confrontation visual fields, extra-ocular movements, characterisation of the nystagmus, and brain magnetic resonance imaging if neuro-imaging was found to be necessary. Contact lens fitting was performed in the contact lens service. All patients were told to wear their contact lenses during the day only. Once the patients were accustomed to their contact lenses, they underwent two evaluations separated by at least one week.

During the first visit, the patients were evaluated with spectacles only, and during the second visit, they were evaluated with contact lenses on (they were asked to wear their contact lenses the week prior to their second evaluation and to come to the eye clinic with contact lenses on). Each evaluation included visual acuity and contrast sensitivity for each eye and with both eyes open. Patients with a null point were asked to avoid their null point position during the evaluation. In addition, a quality of life questionnaire (NEI VFQ-25) was administered to each patient.¹⁰ At the end of the study, the patients were asked whether they subjectively preferred spectacles or contact lenses.

Eye movement recording was performed at each visit with a computer analysed, infrared eye tracker at a sampling rate of 1000 Hz.¹¹ For the first evaluation, the recording was performed with the patients wearing their spectacles. For the second evaluation, the patients wore their contact lenses. The patient fixated a centre target light and read small letters one metre away for 15 seconds. Five to 10 continuous cycles were analysed at the centre of gaze in the middle of each data period of data collection. Frequency, peak amplitude, peak velocity and duration of the foveation period were recorded for each cycle during reading.

RESULTS

Our four patients had congenital nystagmus, two related to albinism (table 1). All had normal funduscopic examinations. All patients had refractive errors corrected with spectacles. Best corrected visual acuity ranged from 20/40 to 20/400. All were fitted with soft contact lenses. All patients subjectively preferred contact lenses to spectacles. Their visual acuity was slightly improved with contact lenses compared with spectacles alone (mean visual acuity OU improved from 20/64 to 20/40). When both eyes were tested separately, contrast sensitivity was improved with contact lenses compared with spectacles alone, but was not improved with both eyes open. Quality of life (VFQ-25) was improved with contact lenses compared with spectacles alone (Mean VFQ-25 score improved from 64.7 to 72.05). Eye movement recording to analyse mean peak amplitude, peak velocity, and duration of the foveation period showed no change in two patients (patients 3 and 4), improvement in one patient (patient 1), and worsening in one patient (patient 2) (table 2). Nystagmus frequency did not change in any patient.

DISCUSSION

This study confirms the positive therapeutic effect of contact lenses in some patients with congenital nystagmus for whom few treatments are available. Much of the clinical improvement observed in our patients may result from a better optical correction of their refractive error with contact lenses than with spectacles, rather than a true damping effect of the nystagmus by contact lens wear. It is also possible that contact lenses had a placebo effect on our patients who strongly believed contact lenses helped them with daily activities. Visual acuity was slightly improved in all patients, and their contrast sensitivity was better with contact lens wear.

All patients had an important refractive error that was most likely better corrected with contact lenses than with spectacles. Indeed refractive disorders are more common in patients with congenital nystagmus than in the general population, and accurate refraction is the best way to improve visual acuity in patients with nystagmus.⁹ However, because of his severe astigmatism, patient 4 used plano contact lenses in addition to spectacles correcting his refractive error, and the slight improvement of his visual function could not be explained by the optical correction itself.

Contact lens wear improved our patients’ quality of life. Indeed, the VFQ-25 questionnaire evaluating patients’ quality of life based on their visual function was improved in all patients. All our patients preferred contact lenses to spectacles alone. They all felt that their visual function self confidence was improved with contact lenses. All emphasised better performance at work, during interactions with a group (such as during teaching), or while driving with their contact lenses on. Their explanation varied from “I feel I can see better” to “I look better without my glasses” suggesting an important placebo effect of the contact lenses. Indeed, it is well known that visual acuity of patients with congenital nystagmus fluctuates with both the mental state (level of attention, excitement, or anxiety) and the visual task.^1,3 Therefore, increasing the confidence of patients with congenital nystagmus may have a significant impact on their quality of life.

In our study, the eye movement recordings showed that contact lenses had no or, at most, a moderate effect on the nystagmus itself. It has been suggested that contact lenses may damp the nystagmus itself,^2,5–8 but this was not observed in three of our four patients. We chose to not use the more sensitive search coil method because of the use of topical anaesthesia and scleral coil used with that technique, which would have made it impossible to isolate and evaluate the proposed effect of the contact lenses via a sensory feed back mechanism.¹ It is possible that a true damping effect would be more obvious in patients with acquired nystagmus and severe oscillopsia than in patients with congenital nystagmus.⁴

There are problems with the use of contact lenses in nystagmus. Fitting is technically difficult and requires multiple measurements of keratometry. Finally, placing a contact lens in a moving eye is difficult, especially when an underlying neurological disease decreases the patient’s level of dexterity. It has been emphasised that the constant motion of the eyes may cause lens slippage with possible irritation of the cornea, but this was not observed in our patients. Since the mass of the lens does not seem to play any role in the treatment of nystagmus, soft lenses are usually preferred to the less well tolerated hard lenses.

In summary, although we could not demonstrate definite changes on eye movement recording, contact lens wear had a positive effect on our patients with congenital nystagmus. Contact lens wear is a relatively safe and inexpensive treatment, and should be offered to patients with nystagmus and decreased vision.