eXpanded Nystagmus Acuity Function Research Articles

A New Clinical Method for Visual Function Evaluation Including Estimation and Measurement of Therapeutic Effectiveness: Lessons From Infantile Nystagmus Research.

To translate infantile nystagmus system (INS) research into easily understood, clinically relevant terminology and suggest modifications to research and clinical testing, data and clinical interpretation, and therapeutic choices and evaluation. A clinical method is presented using only three best-corrected visual acuity measurements of patients with INS, whereby (1) a measure of the quality of visual acuity across the visual field is possible; (2) pre-therapy estimates of post-therapy improvements in peak acuity and the high-acuity range of gaze angles are possible; and (3) more realistic visual function outcome measures of therapy are available to the practitioner. The application of the high-acuity field quality spreadsheet to the analyses of patients with INS (before and after therapy) results in a quantitative measure of visual function based on three visual acuity measurements. The clinician can now duplicate adequate functional visual acuity descriptions in patients with INS along with their pre-therapy estimates and outcome measures. Previously, these have only been available to researchers or the rare clinicians who have access to both eye movement data and the expanded nystagmus acuity function analysis of INS waveforms. [J Pediatr Ophthalmol Strabismus. 2021;58(3):188-195.].

Comprehensive analysis of the effect of null zone shifting surgery treatment on patients with infantile nystagmus syndrome

Objective: To characterize the postoperative change of eyes related parameters of patients with infantile nystagmus syndrome(INS), so as to provide a reference for the clinical evaluation of postoperative effect and the rational arrangement of patients' follow-up time after operation. Methods: A retrospective study. Clinical and follow-up data of 17 patients diagnosed with INS at Department of Ophthalmology in Xinhua Hospital, School of Medicine, Shanghai Jiaotong University from June 2014 to December 2016 were collected. All patients with abnormal head posture (AHP) underwent null zone shift surgery. The operative methods were Parks 5-6-7-8, Anderson, Kestenbum 5-5-6-4,null zone shift combined with strabismus correction and vertical null zone transposition. Ophthalmological examination and eye movement were recorded, including best corrected binocular visual acuity (BCBVA), position of the null zone, expanded nystagmus acuity function (NAFX) and foveation time. Single factor repeated analysis of variance, independent sample t test and rank sum test were used for statistical analysis. Results: Among the 17 children, 6 were females and 11 were males. The age at surgery of the patients was 5-11 years.The follow-up time was (14.8±6.0) months. Preoperative BCBVA was 0.382±0.147 (corrected posture), 0.300±0.056 (AHP); foveation time was (0.594±0.011)s;position of null zone was 23.570°±0.118°. The BCBVA at three months after operation was 0.318±0.044 (corrected posture), 0.260±0.045 (AHP); foveation time was (0.950±0.146)s; position of null zone was 5.360°±1.107°. The BCBVA at six months after operation was 0.264±0.039 (corrected posture), 0.230±0.037 (AHP);foveation time was (1.496±0.233) s; position of null zone was 6.070°±1.303°. The BCBVA at twelve months after operation was 0.309±0.039 (corrected posture), 0.250±0.045 (AHP);foveation time was (1.455±0.201) s; position of null zone was 9.290°±8.520°. There was statistical difference between the data of pre-operation and post-operation(all P<0.05). Change of null zone position was identified in six patients after six months.The preoperative NAFX of patients with presence of change of null zone positon was 0.308±0.063 (the primary position), 0.393±0.210 (null zone); BCBVA was 0.450±0.043 (corrected posture), 0.417±0.031 (AHP); foveation time was 0.122 (0.080-1.014)s. The postoperative NAFX of those patients was 0.430±0.090(the primary position), 0.471±0.140 (null zone); foveation time was 0.438(0.170-1.450) s. The data above were lower than that of patients with no regression of null zone[0.523±0.142,0.601±0.110,0.200±0.063,0.250±0.076,0.725(0.230-1.440)s,0.610±0.160,0.680±0.120,0.975(0.380-2.000)s]. The difference was statistically significant(all P<0.05). Conclusions: Null zone shifting surgery is an effective approach for treating INS. Reduction in the null zone position can be observed in some patients at 6 months after operation, which was related to NAFX, BCBVA and foveation time. It is recommended to extend the follow-up time to at least 6 months after the operation. (Chin J Ophthalmol, 2019, 55:13-19).

Longitudinal Studies and Eye-Movement-Based Treatments of Infantile Nystagmus Syndrome: Estimated and Measured Therapeutic Improvements in Three Complex Cases

ABSTRACTIntroduction and Purpose: To demonstrate the utility of using eye-movement data to reveal the diagnostic characteristics of infantile nystagmus syndrome (INS), determine treatment, and both estimate and document therapeutic improvements in three patients with well-developed foveation periods, fairly broad, lateral gaze “nulls,” head turns, strabismus, and complex, multiplanar nystagmus.Patients and Methods: Infrared reflection, magnetic search coil, and high-speed digital video systems were used to record the eye movements of INS patients, pre- and post-Kestenbaum null-point correction surgery (horizontal or vertical). Data were analyzed and estimations made, using the eXpanded Nystagmus Acuity Function (NAFX) that is part of the OMtools toolbox for MATLAB.Results: In all three subjects (S1–S3), both peak NAFX and longest foveation domain (LFD) improved from their pre-Kestenbaum values. S1: 0.700–0.745 (6.4%) and 25–34° (36%), respectively. S2: 0.445–0.633 (42.4%) and >40° to >50° (10%), respectively. S3: 0.250–0.300 (20%) and 13° to ≫18° (see text), respectively.Conclusions: S1: Even at the high ends of the pre-therapy NAFX and LFD spectra, INS foveation (and therefore, visual-function) improvements may be adequate to justify nystagmus surgery and provide clinical improvements beneficial to the patient. S2: INS foveation improvements in the vertical plane are equal to those originally estimated using the horizontal data in prior patients. S3: Two apparent NAFX peaks can be converted into a very broad peak by surgery based on the preferred lower peak.

Clinical and ocular motor complications of extraocular muscle extirpation for infantile nystagmus syndrome

To describe the effects of extraocular muscle extirpation performed after previous eye muscle surgery in a 20-year-old woman with infantile nystagmus syndrome (INS) for whom we have 19years of follow-up data. Clinical examinations were performed. Eye movement data analysis was carried out using the eXpanded Nystagmus Acuity Function (NAFX) and longest foveation domain (LFD). The patient re-presented to the authors at age 20, 2years after bilateral anterior myectomy of the horizontal rectus muscles, bilateral anterior nasal transposition of the inferior oblique muscle, and bilateral superior oblique recessions. Evaluation revealed deterioration in nystagmus at lateral gaze angles, new incomitant strabismus with severe loss of convergence, limited ductions, saccadic hypometria, slow saccades, and hypo-accommodation. Also, there was a pre- to post-extirpation minimal change of 21% in her peak NAFX, a 50% decrease in LFD, plus a predominant, asymmetric, multiplanar oscillation. It appears that in this patient, horizontal extirpation failed to abolish the nystagmus and caused significant, new, symptomatic deficits interfering with many of the patient's visual functions.

Soft Contact Lenses to Optimize Vision in Adults with Idiopathic Infantile Nystagmus: A Pilot Parallel Randomized Controlled Trial

ABSTRACTPurpose: The optimal management of infantile nystagmus syndrome (INS) is still unclear. Contact lenses (CL) may be superior to glasses in improving visual function in INS but it is not known whether their beneficial effects are due to optical correction alone, or to an additional proprioceptive effect, and whether soft CLs would be as effective as rigid CLs. There is little data on feasibility and and the present study aimed to provide this information.Methods: We completed a pilot Randomized Control Trial (RCT) at a single tertiary referral centre in London, UK. We enrolled 38 adults with idiopathic INS and randomised them to either plano CL (with corrective spectacles if required) or to corrective CL. CL wear was required for a minimum of 2 weeks. Primary outcome measures were feasibility and safety of CL wear in INS; secondary outcome measures were visual acuity and nystagmus waveform parameters.Results: 27 completed the study (27/38,71%). 4 partcipants withdrew due to difficulty with CL insertion/removal and 7 were lost to follow up. CL tolerability was high (24/27,89%) - 2 found the CLs irritant, and 1 had an exacerbation of allergic eye disease. At two weeks, mean improvement in binocular visual acuity from baseline with plano CLs was 0.07 logMAR (95% confidence interval (CI: 0.03-0.11) and 0.06 logMAR with fully corrective CLs (95% CI:0.02-0.1). Mean improvement in the eXpanded Nystagmus Acuity Function (NAFX, a nystagmus acuity function based on eye movement recording) with plano CLs was -0.04(95% CI: -0.08-0.005) and -0.05 with fully corrective CLs(95% CI: -0.09–0.003).Conclusions: CLs are well tolerated, with a low risk profile. Whilst our study was not powered to detect significant changes in BCVA and waveform parameters between treatment arms, we observed a trend towards an improvement in visual function at two weeks from baseline with CLs.

Perceptual Learning in Children With Infantile Nystagmus: Effects on 2D Oculomotor Behavior.

To determine changes in oculomotor behavior after 10 sessions of perceptual learning on a letter discrimination task in children with infantile nystagmus (IN). Children with IN (18 children with idiopathic IN and 18 with oculocutaneous albinism accompanied by IN) aged 6 to 11 years were divided into two training groups matched on diagnosis: an uncrowded training group (n = 18) and a crowded training group (n = 18). Target letters always appeared briefly (500 ms) at an eccentric location, forcing subjects to quickly redirect their gaze. Training occurred twice per week for 5 consecutive weeks (3500 trials total). Norm data and test-retest values were collected from children with normal vision (n = 11). Outcome measures were: nystagmus characteristics (amplitude, frequency, intensity, and the expanded nystagmus acuity function); fixation stability (the bivariate contour ellipse area and foveation time); and saccadic eye movements (latencies and accuracy) made during a simple saccade task and a crowded letter-identification task. After training, saccadic responses of children with IN improved on the saccade task (latencies decreased by 14 ± 4 ms and gains increased by 0.03 ± 0.01), but not on the crowded letter task. There were also no training-induced changes in nystagmus characteristics and fixation stability. Although children with normal vision had shorter latencies in the saccade task (47 ± 14 ms at baseline), test-retest changes in their saccade gains and latencies were almost equal to the training effects observed in children with IN. Our results suggest that the improvement in visual performance after perceptual learning in children with IN is primarily due to improved sensory processing rather than improved two-dimensional oculomotor behavior.

Effects of augmented tenotomy and reattachment in the infantile nystagmus syndrome.

To test the hypothesis that augmented tenotomy and reattachment surgery (AT-R), which involves placing an additional suture in each distal tendon during the 4-muscle tenotomy and reattachment (T-R) or other infantile nystagmus syndrome (INS) procedures, could increase the beneficial effects of many types of extraocular muscle (EOM) surgery to treat INS. Both infrared reflection and high-speed digital video systems were used to record the eye movements in 4 patients with INS before and after AT-R surgery. Data were analyzed using the eXpanded Nystagmus Acuity Function (NAFX) that is part of the OMtools software. Placement of the augmentation suture did not interfere with Kestenbaum, Anderson, bilateral medial rectus muscle recession, or T-R surgeries. The therapeutic effects of AT-R were similar to but not equal to those from the traditional single-suture surgeries (ie, broadening longest foveation domain [LFD] but no improvement of NAFX peak). The average of the NAFX percent improvements after AT-R was within 31% of those estimated from NAFX values before T-R; the average of the percent broadenings of the LFD values after AT-R was within 16%. The AT-R does not improve the foveation quality in INS above the traditional T-R surgery. It is not improved by an additional suture; indeed, some improvements may be diminished by the added suture. The hypothesized augmented-tendon suture technique (sans tenotomy) has been modified and remains to be tested.

Fusion Maldevelopment (Latent/Manifest Latent) Nystagmus Syndrome: Effects of Four-Muscle Tenotomy and Reattachment

To examine the waveform and clinical effects of the four-muscle tenotomy and reattachment procedure in fusion maldevelopment nystagmus syndrome (FMNS) and to compare them to those documented in infantile nystagmus syndrome (INS) and acquired nystagmus. Both infrared reflection and high-speed digital video systems were used to record the eye movements in a patient with FMNS (before and after tenotomy and reattachment). Data were analyzed using the eXpanded Nystagmus Acuity Function (NAFX) that is part of the OMtools software. Model simulations and predictions were performed using the authors' behavioral ocular motor system model in MATLAB Simulink (The MathWorks, Inc., Natick, MA). The model predicted, and the patient's data confirmed, that the tenotomy and reattachment procedure produces improvements in FMN waveforms across a broader field of gaze and decreases the Alexander's law variation. The patient's tenotomy and reattachment plots of NAFX after surgery versus gaze angle were higher and had lower slope than before surgery. Clinically, despite moderate improvements in both peak measured acuity and stereoacuity, dramatic improvements in the patient's abilities and lifestyle resulted. The four-muscle tenotomy and reattachment nystagmus surgery produced beneficial therapeutic effects on FMN waveforms that are similar to those demonstrated in INS and acquired nystagmus. These results support the authors' prior recommendation that tenotomy and reattachment nystagmus should be added to required strabismus procedures in patients who also have FMNS (ie, perform tenotomy and reattachment on all unoperated muscles in the plane of the nystagmus). Furthermore, when strabismus surgery is not required, four-muscle tenotomy and reattachment may be used to improve FMN waveforms and visual function.

A new measure of nystagmus acuity.

To construct a new visual acuity measuring function for congenital nystagmus (CN) patients by studying the relationships between acuity, velocities and positions of the eye. After assessing the relationship between acuity, movement velocities and positions of the eye separately, a new function, which we call the automated nystagmus acuity function (ANAF), was constructed to measure the visual acuity of CN patients. Using a high-speed digital video system working at 500 frames per second, each eye was calibrated during monocular fixation. Twenty-six recorded nystagmus data were selected randomly. Using nystagmus waveforms, the best vision position (foveation period) and visual acuity were analyzed in three groups of subjects, and then all outputs were compared with the well-known expanded nystagmus acuity function (NAFX) and ANAF. Standard descriptive statistics were used to summarize the outputs of the two programs. Foveation periods were brief intervals in the CN waveform when the image was on or near the fovea and eye velocity was relatively slow. Results showed good visual acuity happened during the period when velocity was low and the eye position was near the zero position, which fitted the foveation periods. The data analyzed with NAFX and ANAF had a correlation coefficient of 0.934276, with an average error of -0.00973. The results from ANAF and NAFX analyses showed no significant difference. The NAFX manually identifies foveation eye positions and produces accurate measurements. The ANAF, however, can be calculated simply using the factors eye position and velocity, and it automatically calculates the ANAF without the need to manually identify foveation eye positions.

Quantifying Nystagmus in Infants and Young Children: Relation between Foveation and Visual Acuity Deficit

Nystagmus eye movement data from infants and young children are often not suitable for advanced quantitative analysis. A method was developed to capture useful information from noisy data and validate the technique by showing meaningful relationships with visual functioning. Horizontal eye movements from patients (age 5 months-8 years) with idiopathic infantile nystagmus syndrome (INS) were used to develop a quantitative outcome measure that allowed for head and body movement during the recording. The validity of this outcome was assessed by evaluating its relation to visual acuity deficit in 130 subjects, its relation to actual fixation as assessed under simultaneous fundus imaging, its correlation with the established expanded nystagmus acuity function (NAFX), and its test-retest variability. The nystagmus optimal fixation function (NOFF) was defined as the logit transform of the fraction of data points meeting position and velocity criteria within a moving window. A decreasing exponential relationship was found between visual acuity deficit and the NOFF, yielding a 0.75 logMAR deficit for the poorest NOFF and diminishing deficits with improving foveation. As much as 96% of the points identified as foveation events fell within 0.25° of the actual target. Good correlation (r = 0.96) was found between NOFF and NAFX. Test-retest variability was 0.49 logit units. The NOFF is a feasible method to quantify noisy nystagmus eye movement data. Its validation makes it a promising outcome measure for the progression and treatment of nystagmus during early childhood.

A new algorithm for automated nystagmus acuity function analysis

AimsWe developed a new data analysis algorithm called the automated nystagmus acuity function (ANAF) to automatically assess nystagmus acuity function. We compared results from the ANAF with those of the...

Effects of Acetazolamide on Infantile Nystagmus Syndrome Waveforms: Comparisons to Contact Lenses and Convergence in a Well-Studied Subject

Aim:To determine if acetazolamide, an effective treatment for certain inherited channelopathies, has therapeutic effects on infantile nystagmus syndrome (INS) in a well-studied subject, compare them to other therapies in the same subject and to tenotomy and reattachment (T&R) in other subjects.Methods:Eye-movement data were taken using a high-speed digital video recording system. Nystagmus waveforms were analyzed by applying an eXpanded Nystagmus Acuity Function (NAFX) at different gaze angles and determining the Longest Foveation Domain (LFD).Results:Acetazolamide improved foveation by both a 59.7% increase in the peak value of the NAFX function (from 0.395 to 0.580) and a 70% broadening of the NAFX vs Gaze Angle curve (the LFD increased from 20° to 34°). The resulting U-shaped improvement in the percent NAFX vs Gaze Angle curve, varied from ~60% near the NAFX peak to over 1000% laterally. The therapeutic improvements in NAFX from acetazolamide (similar to T&R) were intermediate between those of soft contact lenses and convergence, the latter was best; for LFD improvements, acetazolamide and contact lenses were equivalent and less effective than convergence. Computer simulations suggested that damping the central oscillation driving INS was insufficient to produce the foveation improvements and increased NAFX values.Conclusion:Acetazolamide resulted in improved-foveation INS waveforms over a broadened range of gaze angles, probably acting at more than one site. This raises the question of whether hereditary INS involves an inherited channelopathy, and whether other agents with known effects on ion channels should be investigated as therapy for this condition.

Eye-Movement-Based Assessment of Visual Function in Patients with Infantile Nystagmus Syndrome

Infantile Nystagmus Syndrome (INS) is an ocular motor system dysfunction characterized by the rhythmic to-and-fro oscillations of the eyes. Traditionally, the assessment of INS visual function solely focused on null- or primary-position visual acuity. Our purpose is to use the past four decades of INS research to introduce a more complete assessment of visual function in patients with INS. All eye-movement data were obtained using high-speed digital video, infrared reflection, or scleral search coil systems. We have introduced four important aspects of a more complete INS visual function assessment: the eXpanded Nystagmus Acuity Function and visual acuity measurements in primary position; broadness of the eXpanded Nystagmus Acuity Function peak and high-acuity field; target acquisition time; and gaze-maintenance capability. Visual function in patients with INS is multifactorial and the simple assessment of primary position visual acuity is both inadequate and may not be the most important characteristic in overall visual function. A more complete visual function assessment should also include primary and lateral gaze eye-movement and visual acuity examinations, target acquisition time and gaze holding.

Extending the eXpanded Nystagmus Acuity Function for vertical and multiplanar data

We updated and extended the functionality of the eXpanded Nystagmus Acuity Function (NAFX), for application under more diverse circumstances, improving its clinical predictive value. The original NAFX “ τ-surface” of minimum-necessary-foveation times had been individually calculated for each combination of position and velocity limits. We have replaced it with an idealized mathematical function that repairs the irregularities in its surface due to idiosyncrasies in the subject data used for the initial calculations. To extend applicability to multiplanar data, we combine horizontal and vertical eye-movement data into a single waveform using vector summation. Torsional eye movements have little effect on visual acuity and are ignored. Age-related visual acuity relationships, derived from population data, more accurately relate the NAFX value to acuity for individual patients. Using the same patient fixation data that established the original NAF and NAFX functions, we verified that the updated NAFX yielded equivalent results for uniplanar data. For biplanar data, the results were also comparable to those of uniplanar data of the same magnitude. The updated NAFX yields greater accuracy in prediction of potential visual acuity for subjects of all ages, for uniplanar and multiplanar nystagmus, extending the objective, direct measure of post-therapy waveform improvement, allowing selection of the best therapy for a wider range of nystagmus patients.

Using the NAFX to Measure the Effectiveness over Time of Gene Therapy in Canine LCA

To use ocular motility recordings to determine the changes over time of infantile nystagmus syndrome (INS) in RPE65-deficient canines with Leber Congenital Amaurosis (LCA) and assess the time course of the recalibration of the ocular motor system (OMS). Nine dogs were treated bilaterally with AAV-RPE65. A second cohort of four dogs was treated with AAV2.RPE65, an optimized vector. Their fixation eye movements were recorded before treatment and at 4-week intervals for 3 months, by using high-speed (500 Hz) digital videography. The dogs were suspended in a sling and encouraged to fixate on distant (57 inches) targets at gaze angles varying between +/-15 degrees horizontally and +/-10 degrees vertically. The records for each eye were examined for qualitative changes in waveform and for quantitative changes in centralisation with the expanded nystagmus acuity function (NAFX) and compared with ERG results for restoration of receptor function. First group: Before treatment, five of the dogs had clinically apparent INS with jerk, pendular, or both waveforms and with peak-to-peak amplitudes as great as 15 degrees . One dog had intermittent nystagmus. At the 1- and 2-month examinations, no change in nystagmus waveform or NAFX was observed in any of the initial dogs, while at 10 weeks, one dog treated bilaterally with the standard dosage showed reduced nystagmus in only one eye. The other eye did not respond to treatment, as confirmed by ERG. This result was unexpected since it was previously documented that unilateral treatment leads to bilateral reduction of INS. The other dog treated with the standard dosage showed no reduction of its small-amplitude, high-frequency pendular nystagmus despite positive ERG responses. Second group: Only one dog of the four had clinically detectable INS, similar in characteristics to that seen in the affected dogs of the first group. Unlike any previous dog studied, this one showed a damping of the nystagmus within the first 4 weeks after treatment. In all but one of the cases in which OMS recalibration occurred, as measured by the clinical appearance of nystagmus and by quantitative measurement using the NAFX, the improvement was apparent no sooner than 10 weeks after treatment. Longer term, dose-related studies are needed to determine the minimum necessary degree of restored receptor functionality, the duration after rescue for recalibration of the OMS, and the conditions under which recalibration information can successfully affect the contralateral eye.

Infantile nystagmus syndrome: Broadening the high-foveation-quality field with contact lenses

We investigated the effects of contact lenses in broadening and improving the high-foveation-quality field in a subject with infantile nystagmus syndrome (INS). A high-speed, digitized video system was used for the eye-movement recording. The subject was asked to fixate a far target at different horizontal gaze angles with contact lenses inserted. Data from the subject while fixating at far without refractive correction and at near (at a convergence angle of 60 PD), were used for comparison. The eXpanded Nystagmus Acuity Function (NAFX) was used to evaluate the foveation quality at each gaze angle. Contact lenses broadened the high-foveation-quality range of gaze angles in this subject. The broadening was comparable to that achieved during 60 PD of convergence although the NAFX values were lower. Contact lenses allowed the subject to see "more" (he had a wider range of high-foveation-quality gaze angles) and "better" (he had improved foveation at each gaze angle). Instead of being contraindicated by INS, contact lenses emerge as a potentially important therapeutic option. Contact lenses employ afferent feedback via the ophthalmic division of the V cranial nerve to damp INS slow phases over a broadened range of gaze angles. This supports the proprioceptive hypothesis of INS improvement.

Wavelet Analysis in Infantile Nystagmus Syndrome: Limitations and Abilities

To investigate the proper usage of wavelet analysis in infantile nystagmus syndrome (INS) and determine its limitations and abilities. Data were analyzed from accurate eye-movement recordings of INS patients. Wavelet analysis was performed to examine the foveation characteristics, morphologic characteristics and time variation in different INS waveforms. Also compared were the wavelet analysis and the expanded nystagmus acuity function (NAFX) analysis on sections of pre- and post-tenotomy data. Wavelet spectra showed some sensitivity to different features of INS waveforms and reflected their variations across time. However, wavelet analysis was not effective in detecting foveation periods, especially in a complicated INS waveform. NAFX, on the other hand, was a much more direct way of evaluating waveform changes after nystagmus treatments. Wavelet analysis is a tool that performs, with difficulty, some things that can be done faster and better by directly operating on the nystagmus waveform itself. It appears, however, to be insensitive to the subtle but visually important improvements brought about by INS therapies. Wavelet analysis may have a role in developing automated waveform classifiers where its time-dependent characterization of the waveform can be used. The limitations of wavelet analysis outweighed its abilities in INS waveform-characteristic examination.

Combining recessions (nystagmus and strabismus) with tenotomy improved visual function and decreased oscillopsia and diplopia in acquired downbeat nystagmus and in horizontal infantile nystagmus syndrome

To investigate the effects of combined tenotomy and recession procedures on both acquired downbeat nystagmus and horizontal infantile nystagmus. Patient 1 had downbeat nystagmus with a chin-down (upgaze) position, oscillopsia, strabismus, and diplopia. Asymmetric superior rectus recessions and inferior rectus tenotomies reduced right hypertropia and rotated both eyes downward. Patient 2 had horizontal infantile nystagmus, a 20 degrees left-eye exotropia, and alternating (abducting-eye) fixation. Lateral rectus recessions and medial rectus tenotomies were performed. Horizontal and vertical eye movements were recorded pre- and postsurgically using high-speed digital video. The eXpanded Nystagmus Acuity Function (NAFX) and nystagmus amplitudes and frequencies were measured. Patient 1: The NAFX peak moved from 10 degrees up to primary position where NAFX values improved 17% and visual acuity increased 25%. Vertical NAFX increased across the -10 degrees to +5 degrees vertical range. Primary-position right hypertropia decreased approximately 50%; foveation time per cycle increased 102%; vertical amplitude, oscillopsia, and diplopia were reduced, and frequency was unchanged. Patient 2: Two lateral, narrow high-NAFX regions (due to alternating fixation) became one broad region with a 43% increase in primary position (acuity increased approximately 92.3%). Diplopia amplitude decreased; convergence and gaze holding were improved. Primary-position right exotropia was reduced; foveation time per cycle increased 257%; horizontal-component amplitude decreased 45.7%, and frequency remained unchanged. Combining tenotomy with nystagmus or strabismus recession procedures increased NAFX and visual acuities and reduced diplopia and oscillopsia in downbeat nystagmus and infantile nystagmus.

A Review of the Tenotomy Nystagmus Surgery: Origin, Mechanism, and General Efficacy

Tenotomy nystagmus surgery neither “weakens” nor “strengthens” the extraocular muscles; it is not strabismus surgery. Tenotomy effectively decreases the gain of the ocular motor plant to small, non-saccadic signals and was hypothesized to be efficacious for other types of nystagmus in addition to infantile nystagmus; it has subsequently been shown to damp various types of acquired nystagmus (pendular and jerk, horizontal and vertical) and reduce their associated oscillopsia. The eXpanded Nystagmus Acuity Function now allows visual acuity improvements to be estimated prior to surgery—something never before possible. More research into proprioceptive tension control should provide non-surgical methods to achieve the therapeutic improvements of tenotomy.

Effects of tenotomy on patients with infantile nystagmus syndrome: Foveation improvement over a broadened visual field

To investigate the effects of four-muscle tenotomy on visual function and gaze angle in patients with infantile nystagmus syndrome (INS). Eye movements of nine patients with infantile nystagmus were recorded using infrared reflection or high-speed digital video techniques. Experimental protocols were designed to record the patients' eye-movement waveforms, pre- and post-tenotomy, at different gaze angles. We used the eXpanded Nystagmus Acuity Function (NAFX) to measure tenotomy-induced changes in the nystagmus at primary position and various gaze angles. The longest foveation domains (LFD) were measured from fitted curves. Peak-to-peak nystagmus amplitudes and foveation-period durations were also measured. All measurements were made unmasked. All seven patients with narrow, high-NAFX, gaze-angle regions showed broadening of these regions of higher visual function. Three patients showed moderate NAFX improvement (13.9-32.6%) at primary position, five showed large improvement (39.9-162.4%), and one showed no NAFX change (due to his high pretenotomy NAFX). Primary position measured acuities improved in six patients. All patients had reductions in nystagmus amplitudes ranging from 14.6 to 37%. The duration of the foveation period increased in all nine patients (11.2-200%). The percentage improvements in both the NAFX and the LFD decreased with higher pretenotomy values. In addition to elevating primary position NAFX, tenotomy also broadens the high-NAFX regions. This broadening effect is more prominent in patients who had sharp pretenotomy NAFX peaks. Four-muscle tenotomy produces higher primary position NAFX increases in infantile nystagmus patients whose pretenotomy values are relatively low, with the improvement decreasing at higher pretenotomy values. The tenotomy procedure improves visual function beyond primary position acuity. This extends the utility of surgical therapy to several different classes of patients with INS for whom other procedures are contraindicated. The pretenotomy NAFX can now be used to predict both primary position acuity improvements and broadening of a patient's high-NAFX range of gaze angles.