Ординатура / Офтальмология / Английские материалы / Advances in Understanding Mechanisms and Treatment of Infantile Forms of Nystagmus_Leigh, Devereaux_2008

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pathways that use gamma-aminobutyric acid.13,24,28,29 The time course of post-rotational VOR and velocity storage are both prolonged in patients with acquired PAN.13,24,28,29 In contrast, it has been reported that patients with INS actually have abnormally short velocity storage time constants (≈ 1 to 2 seconds).30 The shortened time constant, plus the observation that acquired PAN patients do not have aperiodicity, implies a different, and as yet unknown, pathophysiology in IPAN patients.

In a study of 224 patients with INS, Abadi et al.3 classified 139 (62%) as idiopaths, 63 (28%) as albinos, and 22 (10%) as having other ocular anomalies. Conjugate, uniplanar horizontal oscillations were found in 174 (77.7%), while 32 (14.3%) had a torsional component; 182 (81.2%) were classed as “congenital” nystagmus, 32 (14.3%) as manifest latent

nystagmus, and 10 (4.5%) as a hybrids. PAN was found in albinos. Albino subjects did not show statistically significantly higher nystagmus intensity when compared with the idiopaths (p > 0.01). Of 143 subjects, 105 (73%) had spatial nulls within ±10º of the primary position, although 98 subjects (69%) employed a compensatory head posture. Subjects with spatial null zones at or beyond ±20º always adopted constant head postures. Head nodding was found in 38 subjects (27% of the sample). Horizontal tropias were very common (133 out of 213; 62.4%).3 Abadi and Pascal6 studied 25 subjects with oculocutaneous albinism (16 tyrosinase negative and 9 tyrosinase positive) and 7 with ocular albinism (5 X-linked and 2 autosomal recessive) and found that 12 exhibited IPAN. The nystagmus waveforms encountered during the PAN active phases were either jerk with extended foveation or pseudocycloid,

whereas a variety of oscillations (including triangular and bidirectional) were evident during the quiet phases. For most of the 12 subjects, there was an asymmetric variation in nystagmus intensity during each PAN cycle. None of the 12 demonstrated a convergence null or an abnormal head posture. The authors concluded that IPAN is a common oscillation among humans with albinism and that changes in gaze position markedly influenced the periodicity of the ongoing nystagmus.6

Gradstein et al.7 diagnosed IPAN in 18 (9%) of their 200 patients with infantile nystagmus, although most had not been diagnosed with PAN before referral, despite changing nystagmus reported by referring clinicians. In those 18 patients they found that 5 had ocular or oculocutaneous albinism and 16 had an alternating anomalous head posture (AHP). The PAN cycle was of variable duration, often with asymmetrical rightand left-beating components. Although horizontal jerk nystagmus with accelerating slow phase was predominant, other waveforms were encountered in the active phase of PAN. In the quiet phase (close to null zone), similar, but less intense, oscillations to those in the active phase were characteristic. Half of the patients showed a combination of jerk and pendular waveforms in both phases.7 In another report, the same authors found ocular oscillations consistent with INS evident in 24 of 27 patients with oculocutaneous albinism and Hermansky-Pudlak syndrome (HPS), and half showed PAN.14 They concluded that most patients with HPS have INS, and many have PAN.14

Shallo-Hoffman et al.8 studied 18 patients with INS and found that 7 of the 18 patients had PAN (median cycle: 223 seconds; range: 180 to 307 seconds). The periodicity of the cycles for each adult patient was regular, although the phases within a cycle were often asymmetric. Six of the 7 patients had an AHP, and in 5 of 7 with AHP it was in only one direction (static). Except for one patient, the PAN waveforms had an increasing slow-phase velocity in at least one phase of the cycle; in the other phase they were linear. The authors concluded that the AHP was dependent on, and could be predicted from, the waveforms containing the longest foveation times. Although the waveforms and foveation times may differ among the phases of the PAN cycle, the periodicity of the cycle was usually regular and therefore predictable.8

Hosokawa et al.31 found periodicity in the timefrequency distribution in 3 of 13 patients (23%) with INS. One of the 3 patients was diagnosed with pure PAN, and the other 2 patients showed aperiodicity manifested by intensity rather than directional changes. Eighteen of 91 (19.8%) patients with infantile nystagmus who were seen in the Teikyo University School of Medicine were diagnosed with IPAN. The researchers found that face-turning was seen in patients between

the ages of 3 and 9 years. Visual acuity no worse than 20/40 with correction was obtained in all patients, and nearly all had an asymmetric null cycle manifested in an aperiodic alternating head posture.32

The 78 patients with IPAN in our study represent a 15.4% incidence of IPAN in our INS population. The indication for extraocular muscle surgery in 53 patients included strabismus with or without a static AHP or the head posture or nystagmus alone. We performed standard extraocular muscle surgery (recession/resection/myectomy) on patients with strabismus and/or an AHP, while those without such conditions had bilateral horizontal rectus tenotomy with reattachment. The data collected on these patients support the hypothesis that surgical manipulation of the extraocular muscles in patients with oculographically diagnosed INS “improves” the oscillation and visual functions. Interestingly, the nature of the “cycle” is also changed, becoming longer in its duration and null period and showing a predominant change to more favorable waveforms and foveation duration during the null period. Although patients will have absolute improvement in visual acuity, it is in the range of 1 to 3 Snellen lines. Other “measures” of visual function have also been reported to improve after surgery, and probably contribute to visual “well-being.” These include vision in eccentric gaze (gaze-dependent visual acuity), absolute recognition time, and improved binocular field (due to a more normal head posture).1,16,35,36 The clinical and electrophysiologic consequences of extraocular muscle surgery in patients with INS may be due to interruption of the afferent proprioceptive loop, producing a damped peripheral ocular motor response to the nystagmus signal.31,32

Every patient with INS has periods where the nystagmus intensity (amplitude × frequency) is least. It is usually in these quiet periods (null times/zones/ positions) that visual function is best, due to improved foveation quantity and quality during each beat of nystagmus.1,16,35,36 These null times/zones result from a complex combination of unknown afferent and efferent patient characteristics. What we do know about the null period(s) in INS is that there are both static and dynamic components, present to some degree in all patients. The static components that either produce or modify a null/quiet period include a consistent horizontal/vertical/torsional position of gaze (eye in orbit, static gaze angle = Ng) and convergence at near or distance (vergence damping, nystagmus blockage, static convergence = Nv). The static null position for most patients is in the three-dimensional midline (i.e., straight ahead). However, 10% to more than 50% of children have their null zone in an eccentric position of gaze relative to midline (horizontally, vertically, torsionally, or a combination of all three).1,3,5,9,37,38

The null zone/period in patients with INS also has multiple dynamic components. The dynamic components that either produce or modify a null/quiet period include a movement of the null toward a covered eye (causing a clinical “latent component,” dynamic fixing eye = Fe), null movement in the direction opposite of smooth pursuit, optokinetic (OKN) and VOR stimuli (giving the impression of low gain pursuit [saccadic] and “reversal” of OKN-induced eye movements [Dynamic SP−VOR−OKN = E0]), and finally a change over time in both the short term (minutes, periodic/ aperiodic) and over the long term (years, associated with age) [Dynamic (A)PAN = ∆T].1,3,5,9,37,38 Other wellrecognized and highly associated developmental or congenital abnormalities of the visual system affect the oscillation of infantile nystagmus in general and the null/quiet periods in particular. These include high- spatial-frequency vision (acuity) compromise due to optic nerve and retinal disease, heterotopia (and eye dominance), and amblyopia.

We hypothesize that all of the variables listed above— the static components, the dynamic components, and

other visual system factors—combine in a mathematical way to produce the clinical null period we observe and use to guide much of our medical and surgical treatment of this ocular oscillation (Fig. 12.9). It is difficult at this point to describe the details of that mathematical or hierarchical structure, or the neurological mechanisms producing the final null periods associated with INS. The perturbations of the basic INS oscillation as a result of gaze, time, binocular/monocular viewing, acuity, heterotopia, and motion are probably directed by complex developmental connections between the multiple parallel pathways in the afferent visual and efferent vestibular, vestibular ocular, and velocity storage systems. Based on the data from this and other reports of patients with IPAN, we also hypothesize that the rhythmic component of IPAN and the associated head posturing are heavily influenced by associated heterotopia with visual and motor dominance.

The occurrence of IPAN is not as rare as previously suggested and can be missed because of long or irregular cycles and the patient’s preference for only one AHP. The changing null period is easier to recognize

using eye movement recordings, but in most clinical environments these are not available. The clinician may be able to diagnose this disorder if an INS patient is examined in the following way: occlude the nonpreferred eye and examine the preferred eye with the head straight and the gaze in primary position over at least 5 to 7 minutes. The examiner looks for a regular or irregular changing oscillation intensity and/or direction. Identification of IPAN, and possibly its waveform characteristics, is essential in cases in which surgical or medical treatment is considered for correction of strabismus, nystagmus, and/or an associated AHP.

At any moment in time (the fourth dimension) the ocular-motor-system abnormality of INS is clinically and electrophysiologically variably expressed. The variability of the oscillation is due in part to a combination of complex visual-system and develop- mental–neurological modifiers. The eye movement abnormality is not present in isolation; it continuously interacts with other ocular motor, vestibular, afferentvisual system, and cognitive factors on a minute-to- minute—as well as a year-to-year—basis.1,3,5,9,36,37 The dynamic nature of this abnormality requires that clinicians and scientists evaluate and study this disease in that fourth dimension of time. This conceptual approach will result in a more profound understanding of the disease and how our therapy changes the visual system of these patients.

References

1.Dell’Osso LF, Daroff RB. Congenital nystagmus waveforms and foveation strategy. Doc Ophthalmol. 1975;39(1):155–182.

2.National Eye Institute. The Classification of Eye Movement Abnormalities and Strabismus (CEMAS): Report of an NEI Sponsored Workshop, 2001. Na-

tional Eye Institute Web site. http://catalog.nei.nih. gov/productcart/pc/viewPrd.asp?id-category= 0&idproduct=52. Accessed January 21, 2008.

3.Abadi RV, Bjerre A. Motor and sensory characteristics of infantile nystagmus. Br J Ophthalmol. 2002;86(10):1152–1160.

4.Hertle RW, Dell’Osso LF. Clinical and ocular motor analysis of congenital nystagmus in infancy. J AAPOS. 1999;3(2):70–79.

5.Hertle RW, Maldanado VK, Maybodi M, Yang D. Clinical and ocular motor analysis of the infantile nystagmus syndrome in the first 6 months of life. Br J Ophthalmol. 2002;86(6):670–675.

6.Abadi RV, Pascal E. Periodic alternating nystagmus in humans with albinism. Invest Ophthalmol Vis Sci. 1994;35(12):4080–4086.

7.Gradstein L, Reinecke RD, Wizov SS, Goldstein HP. Congenital periodic alternating nystagmus. Diagnosis and management. Ophthalmol. 1997; 104(6):918–929.

8.Shallo-Hoffmann J, Faldon M, Tusa RJ. The incidence and waveform characteristics of periodic alternating nystagmus in congenital nystagmus. Invest Ophthalmol Vis Sci. 1999;40(11):2546–2553.

9.Hertle RW, Yang D, Kelly K, et al. X-linked infantile periodic alternating nystagmus. Ophthalmic Genet. 2005;26(2):77–84.

10.Averbuch-Heller L. Acquired nystagmus. Curr Treat Options Neurol. 1999;1(1):68–73.

11.DiBartolomeo JR, Yee RD. Periodic alternating nystagmus. Otolaryngol Head Neck Surg. 1988;99(6):552–557.

12.Leigh RJ, Khanna S. What can acquired nystagmus tell us about congenital forms of nystagmus? Semin Ophthalmol. 2006;21(2):83–86.

13.Leigh RJ, Robinson DA, Zee DS. A hypothetical explanation for periodic alternating nystagmus: instability in the optokinetic-vestibular system. Ann NY Acad Sci. 1981;374:619–635.

14.Gradstein L, FitzGibbon EJ, Tsilou ET, et al. Eye movement abnormalities in Hermansky-Pudlak syndrome. J AAPOS. 2005;9(4):369–378.

15.Hertle RW, Dell’Osso LF, FitzGibbon EJ, et al. Horizontal rectus tenotomy in patients with congenital nystagmus: results in 10 adults. Ophthalmol. 2003;110(11):2097–2105.

16.Hertle RW, Yang D. Clinical and electrophysiological effects of extraocular muscle surgery on patients with Infantile Nystagmus Syndrome (INS). Semin Ophthalmol. 2006;21(2):103–110.

17.Wang Z, Dell’Osso LF, Tomsak RL, Jacobs JB. 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. J AAPOS. 2007;11(2):135–141.

18.Holmes JM, Beck RW, Repka MX, et al. The amblyopia treatment study visual acuity testing protocol. Arch Ophthalmol. 2001;119(9):1345–1353.

19.Yang D, Hertle RW, Hill VM, Stevens DJ. Gaze-dependent and time-restricted visual acuity measures in patients with Infantile Nystagmus Syndrome (INS). Am J Ophthalmol. 2005;139(4):716–718.

20.Brigell M, Bach M, Barber C, et al. Guidelines for calibration of stimulus and recording parameters used in clinical electrophysiology of vision. Calibration Standard Committee of the International Society for Clinical Electrophysiology of Vision (ISCEV). Doc Ophthalmol. 1998;95(1):1–14.

21.Dell’Osso. OMLAB Web site. http://www.omlab. org. Last updated December 30, 2007. Last accessed March 3, 2008.

22.Davis DG, Smith JL. Periodic alternating nystagmus. A report of eight cases. Am J Ophthalmol. 1971;72(4):757–762.

23.Korres S, Balatsouras DG, Zournas C, et al. Periodic alternating nystagmus associated with ArnoldChiari malformation. J Laryngol Otol. 2001;115(12): 1001–1004.

24.Leigh RJ, Das VE, Seidman SH. A neurobiological approach to acquired nystagmus. Ann N Y Acad Sci. 2002;956:380–390.

25.Lewis JM, Kline LB. Periodic alternating nystagmus associated with periodic alternating skew deviation.

J Clin Neuroophthalmol. 1983;3(2):115–117.

26.Matsumoto S, Ohyagi Y, Inoue I, et al. Periodic alternating nystagmus in a patient with MS. Neurology. 2001;56(2):276–267.

27.Oh YM, Choi KD, Oh SY, Kim JS. Periodic alternating nystagmus with circumscribed nodular lesion. Neurology. 2006;67(3):399.

28.Furman JM, Wall C 3rd, Pang DL. Vestibular function in periodic alternating nystagmus. Brain. 1990;113(5):1425–1439.

29.Lee MS, Lessell S. Lithium-induced periodic alternating nystagmus. Neurology. 2003;60(2):344.

30.Demer JL, Zee DS. Vestibulo-ocular and optokinetic deficits in albinos with congenital nystagmus.

Invest Ophthalmol Vis Sci. 1984;25(6):739–745.

31.Hosokawa M, Hasebe S, Ohtsuki H, Tsuchida Y. Time-frequency analysis of electronystagmogram

signals in patients with congenital nystagmus. Jpn J Ophthalmol. 2004;48(3):262–267.

32.Hayashi T, Hasegawa F, Usui C, Kubota N. Pathophysiology and diagnosis of congenital periodic alternating nystagmus. Nippon Ganka Gakkai Zasshi. 2003;107(5):265–272.

33.Dell’Osso LF. Biologically relevant models of infantile nystagmus syndrome: the requirement for behavioral ocular motor system models. Semin Ophthalmol. 2006;21(2):71–77.

34.Hertle RW, Chan CC, Galita DA, et al. Neuroanatomy of the extraocular muscle tendon enthesis in macaque, normal human, and patients with congenital nystagmus. J AAPOS. 2002;6(5): 319–327.

35.Hertle RW, Anninger W, Yang D, et al. Effects of extraocular muscle surgery on 15 patients with oculo-cutaneous albinism (OCA) and infantile nystagmus syndrome (INS). Am J Ophthalmol. 2004;138(6):978–987.

36.Wang ZI, Dell’Osso LF. Being “slow to see” is a dynamic visual function consequence of infantile nystagmus syndrome: model predictions and patient data identify stimulus timing as its cause. Vision Res. 2007;47(11):1550–1560.

37.Gottlob I. Nystagmus. Curr Opin Ophthalmol. 2000;11(5):330–335.

38.Reinecke RD. Costenbader lecture. Idiopathic

infantile nystagmus: diagnosis and treatment. J AAPOS. 1997;1(2):67–82.

ABSTRACT

We report 3 patients with acquired nystagmus who were treated with eye muscle tenotomy and reattachment. The first patient had acquired pendular nystagmus (APN) associated with multiple sclerosis (MS) and underwent bilateral medial rectus tenotomies and bilateral lateral rectus recessions to correct exotropia. Eye movements were recorded before surgery, after surgery, and after surgery and treatment with memantine. Following surgery, APN decreased by ≈ 50% and the eXpanded Nystagmus Acuity Function (NAFX) increased by 34%. Measured Snellen acuity increased 100%, from 0.125 OD and OS to 0.25. Saccades were unaffected. After treatment with memantine, APN was damped further by 69%, and NAFX was improved an additional 9%; Snellen acuity increased 60% to 0.4. The second patient had monocular APN associated with MS. The horizontal recti were tenotomized and reattached in only the eye with nystagmus. This resulted in damping of the nystagmus by 66%, and Snellen acuity increased 100% from 0.2 to 0.4. The third patient had downbeat nystagmus of undetermined etiology and preferred a chin-down (up-gaze) head position to diminish symptoms. Asymmetrical superior rectus recessions, to address head position and hypertropia, were combined with tenotomy and reattachment of both inferior recti. Surgery resulted in reduction of vertical nystagmus by 46%, improvement of NAFX values by 17%, and improvement in visual acuity from 20/25

to 20/20. These preliminary results support the view that eye muscle tenotomy may diminish acquired forms of nystagmus and improve vision in selected patients.

Although eye muscle surgery is established as a treatment modality for congenital forms of nystagmus, its place in the therapy of acquired forms of nystagmus is debated. Currently, there is a dearth of studies that evaluate the results of such surgery using reliable methods for measuring eye movements. In this chapter, we report our experience in studying the effects of surgery on the eye muscles of 3 patients with acquired forms of nystagmus. We have used a procedure developed for the treatment of congenital forms of nystagmus—eye muscle tenotomy and reattachment (T&R).1 Partial descriptions of theses cases have been previously published.2,3

CASE REPORTS

Case 1

The first patient had acquired pendular nystagmus (APN) from multiple sclerosis (MS) and underwent bilateral medial rectus T&R and bilateral lateral rectus recessions to correct exotropia (i.e., tenotomy combined with recession). Eye movements were recorded by the scleral search coil technique at three times: before surgery, after surgery, and after surgery and treatment with oral memantine (Figs. 13.1 and 13.2). Following surgery, APN decreased by ≈ 50%, and the eXpanded Nystagmus Acuity Function (NAFX)

5

RE

5

increased by 34%. Measured Snellen acuity increased 100% from 0.125 OD and OS to 0.25. Saccades were unaffected. After treatment with memantine, APN was damped further by 69% and NAFX was improved an additional 9%; Snellen acuity increased 60% to 0.4.

Figure 13.2 Eye speeds for the fixating right eye (case 1) measured pre– and post–horizontal rectus muscle surgery and also after addition of memantine.

Comment: Vertical components of APN were reduced as well as horizontal components, even though surgery was only done on the four horizontal recti. Memantine appeared to have an additive effect to T&R, presumably by a different, central mechanism.

Case 2

The second patient (Fig. 13.3) had uniocular APN in association with MS. Preand post-tenotomy eye movements were studied using digitized video recordings. The horizontal recti were tenotomized and reattached only in the eye with APN; this resulted in damping of the nystagmus by 66% and an increase in Snellen acuity 100% from 0.2 to 0.4. Comment: The addition of gabapentin did not appear to augment effect of T&R in this patient.

Case 3

The third patient (Fig. 13.4) had downbeat nystagmus of undetermined etiology, oscillopsia, and vertical

RE – Pretreatment

Time (s)

Figure13.3 Case 2: Segments of right eye horizontal nystagmus reconstructed from the digitized videotape recordings. The addition of gabapentin (center) did not appear to augment effect of tenotomy and reattachment.

diplopia from skew deviation; he preferred a chindown (up-gaze) head position to diminish symptoms. Preand post-tenotomy eye movements were recorded by a high-speed digital video system. Asymmetrical superior rectus recessions were done to address head position and hypertropia and were combined with T&R of both inferior recti. Surgery resulted in movement of the NAFX peak from 10º up to primary position, and NAFX values were improved by 17%. Vertical NAFX values increased across the −10º to ±5º vertical range. Foveation time per cycle increased from 88 to 178 milliseconds (102%). Vertical component nystagmus amplitude was reduced by 46%, and frequency was unchanged at ≈ 3 Hz. Visual acuity was improved from 20/25 to 20/20, and the hypertropia was improved. Comment: The vertical NAFX was increased across the −10º to ±5º range, resulting in improved functional vision.

DISCUSSION

To put the present results into context, we provide a brief historical review of the surgical treatment of nystagmus. In 1906, Colburn described attaching the

Figure 13.4 Case 3: Vertical eXpanded Nystagmus Acuity Function (NAFX) values increased across the −10º to ±5º range of vertical gaze postoperatively.

lateral rectus to the periosteum of the orbital wall in an attempt to reduce the amplitude of nystagmus.4 Little else was reported until the early 1950s, when Kestenbaum,5 Anderson,6 Goto,7 and Rama8 described surgical techniques to change gaze angle in order to take advantage of nystagmus null positions, mainly in cases of congenital nystagmus.4 (Infantile nystagmus has now replaced congenital nystagmus as the preferred term and will be used in this chapter except when quoting older literature.) Kestenbaum described a resect– recess operation and, in the second edition of his book,

Clinical Methods of Neuro-Ophthalmologic Evaluation,5 made the following comment (italics added): “The genesis of the nystagmus is not relevant for the indication of surgery. The nystagmus may be an asymmetric nystagmus from infancy or an acquired nystagmus in a demyelinizing disease or a ‘manifested latent nystagmus.’ ”

Anderson6 described recession of yoke muscles in the direction of the slow-phase drift of nystagmus. He came to this idea after observing a change in subjective and objective characteristics of nystagmus in a patient who underwent strabismus surgery.

It had been observed that nystagmus is not infrequently lessened after an operation for strabismus had been performed. One man, aged 22 years, at the time of operation for a left convergent strabismus of at least 60 dioptres, had been worried by the apparent movement of a wall from side to side. It is unusual for patients with congenital nystagmus to be conscious of movement of objects, and this man was conscious only of the movement of walls. Vision was 6/9 in the right eye and 6/12 in the left. Both nystagmus and strabismus had been life-long. The conscious movement vanished after a recession

of each internal rectus muscle and a resection of each external rectus muscle, even though an angle of anomaly of 20 dioptres persisted. (p. 279)

Apparently this was one of the rare patients with infantile nystagmus who had oscillopsia, and the oscillopsia resolved following a bilateral recession–resection (i.e., four-horizontal-muscle) surgery, thus implying an improvement in nystagmus.

Rama,8 in 1953, reported a technique similar to Anderson’s procedure. One year later, Goto7 described combining recession with advancement of the antagonist muscle. Over time, surgical procedures to realign the eyes of patients with nystagmus and gaze nulls became known as “Anderson-Kestenbaum procedures.” (We refer to “nystagmus surgery” as any eye muscle surgery done primarily to damp nystagmus, and “strabismus surgery” as any procedure done primarily to correct ocular misalignment. Often, nystagmus surgery and strabismus surgery are combined in the same patient.)

In 1979, Dell’Osso and Flynn9 recorded eye movements of 3 patients before and after surgery for congenital nystagmus. In addition to shifting the nystagmus null, they observed broadening of the null region and an overall reduction of nystagmus intensity at all gaze angles. This led them to speculate that the surgery caused “nonlinear changes in ocular motor plant dynamics (i.e., changes in the characteristics of the muscles, tendons, Tenon’s capsule, fatty and scar tissue interactions) as a result of the surgical changing of the points of insertion and methods of attachment of the muscles to the globe.”

Bosone et al.10 found similar results. Subsequently, Dell’Osso et al. showed that eye muscle tenotomy and reattachment (T&R) alone had salutary effects on nystagmus amplitude and velocity in dogs with nystagmus11 and in humans with infantile nystagmus.1,12 A hypothesis evolved that T&R damaged proprioceptive structures in eye muscle tendon that affected the nystagmus oscillation.13

More recently, Büttner-Ennever et al.14 identified two separate sets of ocular motor neurons, one of which participates in proprioceptive feedback that aligns and stabilizes the eyes and has palisade endings located in myotendinous junctions of eye muscles. The cell bodies for these neurons are located around the periphery of the brainstem nuclei. Hertle et al.15 found similar structures more distally at the enthesial (tendino-scleral) regions of eye muscle tendons.

All of the forgoing support the hypothesis that T&R of selected eye muscles should have a beneficial effect on acquired nystagmus by the same mechanism as it does on infantile nystagmus: reduction of small-signal gain of the ocular motor plant by interfering with

proprioceptive tension control.16 Our present results support the view that eye muscle tenotomy may have a role to play in acquired forms of nystagmus of differing etiologies, waveforms, planes of action, and even various neuroanatomic sites of origin. This ability to treat different types of nystagmus supports the hypothesized proprioceptive mechanism of action. Controlled, prospective studies of T&R as treatment of acquired nystagmus are called for so that this therapy can be compared with available pharmacological measures.

References

1.Hertle RW, Dell’Osso LF, FitzGibbon EJ, Thomson D, Yang D, Mellow SD. Horizontal rectus tenotomy in patients with congenital nystagmus. Results in 10 adults. Ophthalmol. 2003;110:2097–2105.

2.Tomsak RL, Dell’Osso LF, Rucker JR, Leigh RJ, Bienfang DC, Jacobs JB. Treatment of acquired pendular nystagmus from multiple sclerosis with eye muscle surgery followed by oral memantine.

Digital J Ophthalmol. 2005;11(4):1–11.

3.Tomsak RL, Wang Z, Dell’Osso LF, Jacobs JB. Combined tenotomy ± Anderson procedure for treatment of acquired vertical nystagmus and infantile horizontal nystagmus associated with diplopia and oscillopsia. ARVO Annual Meeting Abstract and Program Planner. Invest Ophthalmol Vis Science. 2006;47. E-Abstract 2512.

4.Colburn JE. Fixation of the external rectus muscle in nystagmus and paralysis. Am J Ophthalmol. 1906;23:85–88.

5.Kestenbaum A. Clinical Methods of Neuroophthalmologic Evaluation, 2nd ed. New York, NY: Grune and Stratton; 1961.

6.Anderson JR. Causes and treatment of congenital eccentric nystagmus. Brit J Ophthalmol. 1953;37:267–281.

7.Goto N. Nystagmus surgery. Act Soc Ophth Jap. 1954;58:176.

8.Rama G. Strabismo e nistagmo. Rass Ital Ottal. 1953;22:245.

9.Dell’Osso LF, Flynn JT. Congenital nystagmus surgery: a quantitative evaluation of the effects. Arch Ophthalmol. 1979;97:462–469.

10.Bosone G, Reccia R, Roberti G, Russo P. On the variations of the time constant of the slow-phase eye movements produced by surgical therapy of congenital nystagmus: a preliminary report. Ophthal Res. 1989;21:345–351.

11.Dell’Osso LF, Hertle RW, Williams RW, Jacobs JB. A new surgery for congenital nystagmus: effects of tenotomy on an achiasmatic canine and