Improvement of Visual Acuity after Surgery for Nystagmus

Improvement of Visual Acuity after Surgery for Nystagmus Alina A. Zubcov, MD,1 Norbert Stark, MD,1 Alexander Weber, MD,2 Sheryl S. Wizov, eOA,3 Robert D. Reinecke, MD3 Purpose: The authors compared the preoperative and postoperative binocular visual acuities and eye movement recordings of patients who underwent eye muscle surgery conSisting of the Anderson-Kestenbaum procedure or the artificial divergence procedure modeled after COppers, or a combination of both procedures, for the treatment of infantile nystagmus with head turn. Methods: Binocular visual acuities and eye movement recordings by electro-oculography (EOG) were compared preoperatively with those done within 3 weeks postoperatively. Shifting and broadening of the minimal intensity zone and foveation time and changing of the waveform were measured. The treatment of 6 of 18 patients was based on the artificial divergence principle; for 7 patients, treatment was in accordance with the Anderson-Kestenbaum principle; and 5 patients had combined procedures. Results: The improvement in binocular visual acuities was two Snellen lines or more in one of six patients in the artificial divergence group and four of five patients in the combined treatment group. The EOG recordings showed shifting of the minimal intensity zone toward the primary position in all three groups. A broadening of the minimal intensity zone occurred mostly in the artificial divergence and combined groups. Increases in foveation time and changes in waveforms from jerk to jerk with foveation were found in three of six patients in the artificial divergence group and in two of five patients in the combined group. Conclusion: With less muscle surgery, the artificial divergence and combined operations gave better vision improvement than the Anderson-Kestenbaum operation. Ophthalmology 1993; 100: 1488-1497

Inherited nystagmus is usually an involuntary, conjugate, and rhythmical horizontal to and fro movement of the eyes. Eye movement recordings allow differentiation of infantile nystagmus from manifest latent nystagmus. I Infantile nystagmus may be present at birth but usually de-

Originally received: November 13, 1992. Revision accepted: March 26, 1993. I

2

Universitatsaugenklinik Frankfurt, Germany. Universitats-Hals-Nasen-Ohren-Klinik, Frankfurt, Germany.

Foerderer Eye Movement Center for Children, Wills Eye Hospital, Department of Ophthalmology, Jefferson Medical College of Thomas Jefferson University, Philadelphia. Dr. Zubcov is currently affiliated with Wills Eye Hospital, Philadelphia. 3

Presented at the American Academy of Ophthalmology Annual Meeting, Anaheim, October 1991. Reprint requests to Robert D. Reinecke, MD, Wills Eye Hospital, 900 Walnut St, Philadelphia, PA 19107.

1488

velops in the first few months oflife. The typical waveform evolution that characterizes infantile nystagmus includes first, a triangular large scanning movement, followed by pendular small amplitude movements, and finally giving way to jerk movements with exponentially increasing velocity of the slow phase with or without foveation, but may be a pseudocycloid or dual jerk2,3 (Fig 1). Most of the waveforms seen in infantile nystagmus have not been reported in acquired nystagmus and seem to represent attempts of the oculomotor control system to increase the foveation period. By definition, the time the retinal image rests on the fovea is called the foveation period and is thought to occur at times when the eye is at minimum velocity. The duration of the foveation period in infantile nystagmus offers a more useful index of normal performance than the nystagmus intensity.2 Other characteristics of infantile nystagmus are a null gaze position of least nystagmus and dampening of nystagmus with convergence (Figs 2A and 2B). At these null

Zubcov et al RE

(\J\J\

LE

(\J\J\

R

10

0 /

PENDULAR

0

Visual Acuity after Surgery for Nystagmus

f\/V\v f\/V\v PENDULAR WITH FOVEATING SACCADE

1 SEC

RE

LE

fYYVl fYYVl JERK

RE

LE

t1'tV1

~

JERK RIGHT WITH FOVEATION

/V\/\ 0fY\ /V\/\ 0fY\ DUAl JERK

PSEUDO CYCLOID

Figure 1. Infantile nystagmus waveforms: pendular, pendular with foveating saccades, jerk, jerk with foveation, dual jerk, and pseudocycloid. Artistic drawing after the original electro-oculogram. Calibration scales are provided on the left hand side of the figure in this and all subsequent figures. R = right; L = left; RE = right eye; LE = left eye.

30° right and left gaze. Recordings also were done while the patient fixated at 0.33 m. The preoperative and postoperative eye movement recordings were done either with a Tracor RV-275 recorder system (Tracoustics, Inc., Austin, TX) using the method described by Reinecke et al 3 or with an electro-oculogram (EOG) system (Toennies GmbH & CoKG, Wuerzburg, Germany) coupled with a high cutoff at 30 Hz. The preoperative EOG was done the week before surgery and the first postoperative EOG was done within the first 3 weeks after surgery. Foveation times were those periods during which the ocular movement was less than 10° per second and the fovea was believed to be fixating the target. A mean foveation time was calculated from 5 seconds of eye movement recordings. Foveation times less than 40 mseconds could not be measured accurately and were not considered. Nystagmus intensity was calculated as the nystagmus amplitude multiplied by its frequency. The minimum intensity zone, or null zone, was the gaze direction with the lowest nystagmus intensity.

Examinations An eye examination, including a standardized protocol, was completed on each patient 1 day before surgery and

LEFT GAZE

positions, the nystagmus has lower intensity, or the waveform shows a longer foveation period. The gaze angle and convergence typically improve visual acuity. Both mechanisms can be exploited surgically to give better visual acuity and alleviate the anomalous head posture. We compared the preoperative and postoperative eye movement recordings of patients who underwent eye muscle surgery using either the Anderson-Kestenbaum procedure or the artificial divergence procedure, or a combination of both procedures. Our data suggest an explanation for the visual acuity improvements.

J\J\ J\J\

RE

LE

PRIMARY POSITION

J\A J\A

RIGHT GAZE 15-30·

/V)

(1/\

,ooL R

A

L

1 SEC

Materials and Methods Patients All patients had infantile nystagmus with head turn documented by eye and head movement recordings, reliable visual acuity measurements, and eye muscle surgery done to alleviate the horizontal anomalous head position. We used the waveform criteria proposed by Dell'Osso et all to differentiate between manifest latent nystagmus and infantile nystagmus waveforms. 4 Eighteen patients, seen at either the Foerderer Eye Movement Center for Children or the University Eye Clinic Frankfurt, were studied. Methods We recorded 5 minutes of eye movements binocularly in each patient at I-m fixation in primary position and in

Figure 2. Gaze and convergence null angle or minimal intensity zone. In right gaze, nystagmus changes between no nystagmus and jerk right with foveating saccades. In primary position and left gaze, jerk left nystagmus at a higher intensity is seen. Figure 2B shows no nystagmus when viewing at near (with convergence).

1489

Ophthalmology

Volume 100, Number 10, October 1993

1 to 3 weeks postoperatively. The collected data included visual acuities, the angle of the preferred head position, phoria-tropia testing by alternate cover test, and stereopsis measurements (Titmus test). Monocular and binocular visual acuities were measured in primary position and in the preferred head position at distance and at near with the acuity chart directly in front of the patient. The visual acuity measurements were obtained 2 to 4 weeks apart. No therapy for amblyopia was received by any of the patients within the intervening period. An improvement of two Snellen lines or more, corresponding to one octave or more, was considered significant. The distant visual acuities are listed in Tables 1, 2, and 3. The preferred head position was measured while reading small optotypes at distance, near, and at the Harms wall (approximately 2 m) with the "Strabofix after Paul.,,5 Tables 1, 2, and 3 list the head positions measured while reading small optotypes at distance.

rectus muscle on the eye in abduction. In other words, for a left head tum of 30° in a patient tolerating 30-PD base out in front of the left eye before becoming exotropic, we recessed the left medial rectus muscle 5 mm, resected the left lateral rectus muscle 10 mm, and recessed the right lateral rectus muscle 6 mm. If the patient exhibited only an eccentric null position with no null zone at near, the eye muscle surgery according to the Anderson-Kestenbaum principle was performed. 8 ,9 The amount of surgery used was in accordance to that recommended by Mitchell et al lO ifthe head tum was 15 ° and under, and according to Scott and Kraft ll ("augmented Parks") if the head tum was 20° or greater. The Anderson-Kestenbaum procedure is thought to move the eccentric null zone to the primary position and thus alleviate the anomalous head position (Table 2). All operations were performed by one of the authors (RDR, NS, AAZ) using the same techniques.

Treatment

Results

The preference of surgery was based on clinical and EOG data related to the minimal intensity zone of nystagmus. Patients with good fusional capabilities, a null zone at near (with convergence), and a gaze angle null were operated on using the artificial divergence procedure after Clippers (Table 1).6 The underlying principle of this procedure is to create the same innervational situation at distance that exists at near, where convergence dampens the nystagmus. We simulate the postoperative situation by giving the patient a prism base out in front of the adducting eye (e.g., for a patient with a left head tum, in front of the left eye). Beginning with 5- to 8-prism diopter (PD) base out, patients usually tolerate the addition of 5 PD every 15 minutes up to 30 to 40 PD. We stop adding prisms when exotropia develops. When moving the adducting eye to divergence with prisms base out, the patient has to converge, and, therefore, the nystagmus decreases and the anomalous head position disappears. If prisms were put in front of the abducting eye, the result would be a worsening of the anomalous head position. The prisms are tolerated well, and an improvement in visual acuity is frequently observed. The treatment is a recess/ resect procedure (ratio 1:2) on the eye in adduction which we calculate according to the amount of prisms tolerated (e.g., for a patient with a left head tum tolerating 40-PD base out, a left medial rectus recession of 4 mm and a left lateral rectus resection of 8 mm would be done). In other patients, the amount of divergence tolerated with prisms base out in front of the adducting eye did not totally abolish the anomalous head position. This group of patients (Table 3), therefore, received a combined artificial divergence/Anderson-Kestenbaum procedure. 7 First, using prisms base out we assessed the amount of artificial divergence tolerated. For the remaining head tum, we calculated the amount of surgery to be done as in the Anderson-Kestenbaum procedure with the exception that we did not operate on the medial rectus muscle of the abducting eye. We operated on the eye in adduction as described above (recess/resect) and recessed the lateral

1490

Artificial Divergence Group Six patients (Table 1) were found to have a convergence null zone (at near) of the infantile nystagmus in addition to a gaze angle null. The mean age of the group at the time of surgery was 6.9 years (1 girl and 5 boys). All patients had good binocular function. Surgeries were performed as described above in the Materials and Methods section. No patient exhibited ophthalmologic problems other than infantile nystagmus. All six patients had orthophoria before the operation, and five displayed an exophoria of 3 to 4 PD only after prolonged alternate cover testing postoperatively. Only one patient (patient 6) displayed an esophoria of 4 PD. Stereopsis (Titmus test) improved in four of the patients (patients 1, 4, 5, and 6). Two patients (patients 3 and 4) did not display any head tum postoperatively. The other four patients showed a head tum of less than 5 0. The binocular visual acuity (Fig 3a) improved in three patients: one Snellen line in two patients (patients 2 and 4) and two or more Snellen lines in one patient (patient 6). Three patients showed no improvement in the binocular visual acuity (patients 1, 3, and 5). Compared with the preoperative EOG results (Table 1), postoperatively all six patients had a broadening of the minimal intensity zone of 20° to 30°. Additionally, three of the six (patients 2, 5, and 6) changed the nystagmus waveform to a longer foveation time. Patient 2 had a change in waveform in primary position from jerk left nystagmus to jerk left with foveation of 160 mseconds/ cycle. Patient 5's foveation time increased from 120 to 160 mseconds/cycle in primary position, and in patient 6 dual jerk changed to dual jerk with foveation of 80 to 140 mseconds/cycle. Patients 1,3, and 4, preoperatively and postoperatively in the primary position, had dual jerk nystagmus waveforms and jerk with foveation, respectively, with the same amount of foveation/cycle. The preoperative and postoperative results of patient 2 are depicted in Figures 4A and 4B. They represent

......

4:\0 ......

M

M

5

6

X = 4/l Titmus rings 1-6

X = 3/l Titmus rings 1-6

X = 4/l Titmus rings 1-9

E = 4/l Rings 1-3

EX = 0 Titmus rings

EX = 0 Titmus rings

EX = 0 Fly and animals A-C positive

1-6

1-3

1-6

0.2 ("E")

0.8

0.8

1.0

0.5 ("E")

0.8

1.0

1.0

down

10° LHT 8° chin

down

20° LHT 5° chin

20° LHT

20° LHT

0°_2° LHT

0°_S ° LHT

0°

0°

2°_3° RHT

EX = 0 Titmus rings

1-8

1.0

15° RHT Very discrete LH tilt RE:RMR recess 3.5 LLR resect 7.0

0.8

LLR resect 5.0

2.5

LE: LMR recess

LLR resect 8.0

4.0

LE: LMR recess

LLR resect 8.0

4.0

LE: LMR recess

LLR resect 8.0

4.0

LE: LMR recess

4.0

X = 3/l Titmus rings 1-8

0.6

EX = 0 Titmus rings

1-6

0.6 LLR resect 8.0

0°_S° LHT

X = 5/l Titmus rings 1-8 LE: LMR recess

Postoperative

Preoperative

20° LHT

EX = 0 Titmus rings

Position

Description of Treatment

Head Turn

Postoperative

Postoperative in Primary

Preoperative

Orthoptic Status

MIZ = -5 to +15° right gaze; pseudocycloid and dual jerk 80-140 msecs/cycle in PP

MIZ = 0° to 25 ° right gaze; jerk right and jerk left with foveation 160 msecs/cycle in PP

MIZ = 0° to 25° right gaze; jerk left with foveation 80-100 msecs/cycle

MIZ = 0° to 30° right gaze; jerk right with foveation 120 msecs/cycle in PP

MIZ = 0° to 20° left gaze; jerk left with foveation up to 160 msecs/cycle to no nystagmus in PP

Postoperative MIZ = 0° to 30° right gaze; dual jerk with foveation 120 msecs/cycle in PP

Preoperative MIZ = 20° right gaze; dual jerk with foveation 120 msecs/ cycle inPP MIZ = 15° to 20 ° left gaze; jerk left without foveation in PP MIZ = 20° right gaze; jerk right with foveation 120 msecs/cycle inPP MIZ = 20° right gaze; jerk right with foveation 80100 msecs/ cycle in PP MIZ = 20° right gaze; jerk left with foveation 120 msecs/cycle inPP MIZ = S° to 10° right gaze; pseudocycloid and dual jerk without foveation

EOG Findings

EOG = electro-oculography; EX = exophoria; X = esophoria; LHT = left h ead turn; LE = left eye; LMR = left medial rectus; LLR = left lateral rectus; MIZ = minimum intensity zone; PP = primary position; RHT = right head turn; RE = right eye; RMR = right medial rectus; E = esophoria.

6.5

Astigmatism. hyperopia

Astigmatism. hyperopia

5.6

M

4

6

Astigmatism. hyperopia

4.5

M

Astigmatism. hyperopia

Diagnosis

3

M

9

8

Sex

F

Age at Treatment (yrs)

2

Patient No.

Preoperative with Head Tum

Binocular Visual Acuity

Table 1. Clinical Findings Preoperative and Postoperative Artificial Divergence

~

......

5

M

F

F

F

4

5

6

7

EX = 0

Hyperopia, s/p 4 strabismus surgeries

EX = 0

Idem

E = 411

411 ET

Idem

EX = 0

Hyperopia, 3011 ET ETwith accommodative excess

Astigmatism

Hyperopia, astigmatism

Idem

EX = 0

2011 ET, 311 MET,2l1 right right hypertropia hypertropia

Idem

Postopemtive

EX = 0

PTeopemtive

Orthoptic Status

0.5

0.6

0.6

0.5

0.6

0.6

0.6

0.6 ("E")

0.6 ("E")

0.6

0.6

0.4

Postopemtive in PTimmy Position

0.5

0.4

with Head Tum

PTeopemtive

5° LHT, 3° RHT

Description of Treatment PTeopemtive

MIZ: 0°_5° right gaze; pseudocycloid

MIZ: 0°; pseudocycloid

MIZ: 0°_5° right and 10° gaze; dual jerk and pendular, foveation msecs/cycle

MIZ: 10° right gaze; jerk, pseudocycloid

MIZ: PP jerk, pendular

MIZ: 5 ° right gaze; jerk, pendular, foveation 80 msecs/cycle

MIZ: 0°-10° downgaze; jerk

Postopemtive

EOG Findings

RE: RLR recession MIZ: 20°-25° 9.0 right gaze and RMR resection 6.5 10° LE: LMR recession downgaze; 5.5 jerk LLR resection 10.0 45° LHT 5° 2° LHT, 2° chin RE: RLR recession MIZ: 45° right chin up down 10.0 gaze and 5° RMR resection 8.5 downgaze; LR: LMR jerk, recession 7.0 pendular, LLR resection 11.1 foveation 80 msecs/cycle 0° 20° LHT RE: RLR recession MIZ: 20° right gaze; jerk, 7.0 pendular RMR resection 7.0 LE: LMR recession 5.0 LLR resection 8.0 20° LHT, 10° 8° LHT, 12° RE: RLR recession MIZ: 20° right RH tilt RH tilt gaze; jerk, 7.0 RMR resection 6.0 pseudocycloid LE: LMR recession 5.0 LLR resection 8.0 32° RHT, 10° 5°_7° LHT LE: LMR resect MIZ: 30° right RH tilt 10° gaze and 10° 8.5 chin down LLR recess 10.0 upgaze; dual RE: RMR recess jerk and 6.0 pendular, RLR resect 10.0 foveation 40 msecs/cycle 10 0 RHT 0° RE:RMR MIZ: 10° left recession 5.5 gaze; RLR resection 9.0 pseudocycloid LE: LLR recession 6.0 25° LHT 0° RE: RMR recess MIZ: 40° right gaze jerk, 7.5 RLR resect 9.0 pseudocycloid LE: LLR recess 10.0 LMR resect 5.5

25° LHT 10° chin up

Postopemtive

Head Turn PTeopemtive

EOG = electro-oculography; EX = exophoria; LHT = left head turn; RHT = right head turn; RE = right eye; RLR = right lateral rectus; RMR = right medial rectus; LE = left eye; LMR = left medial rectus; LLR = left lateral rectus; MIZ = minimum intensity zone; ET = esotropia; E = esophoria; PP = primary position; s/p = status post.

15

7.5

17

6

F

3

Hyperopia, astigmatism s/p strabismus surgery papillae and maculae coloboma Hyperopia, astigmatism, ET

20

F

Oculocutaneous albinism, hyperopia

Diagnosis

8

2

F

Age at Patient Treatment (yrs) No. Sex

Binocular Visual Acuity

Table 2. Clinical Findings Preoperative and Postoperative Anderson-Kestenbaum Procedure

w

...... ~

EX = 0 EX = 0 Titmus rings 1-8 Titmus rings 1-8

EX = 0 Titmus rings 1-5

6.5

5

F

M

4

5

1.2

0.6 ("E")

0.4 ("E")

1.0

1.0

0.6 ("E")

Postoperative in Primary Position

0.8

1.0

0.6

0.3 ("E")

Preoperative with Head Tum

LHT

25°-30°

25° RHT

30° RHT

25° RHT

up

30° LHT 20° chin

Preoperative

=

0°

7.0

10.0

RE:RMR recess 6.0 LE: LMR recess 5.0 LLR resect 10.0

5.0

LE: LLR recess

RE:RMR recess 5.0 RLR resect

5.0

LE: LLR recess

10.0

4.0

RE:RMR recess 5.0 RLR resect

RE: RMR recess 4.0 RLR resect 8.0 LE: LLR recess

LMR recess 7.0

LE: LLR resect

7.0

RE: RLR recess

Description of Treatment

=

MIZ = 25° right gaze; dual jerk, foveation 40 msecs/ cycle inPP

MIZ = 25 ° left gaze; jerk, foveation 160 msecs/ cycle inPP

MIZ = 30° right gaze; bidual jerk, foveation 60 msecs/ cycle inPP MIZ = 20° left gaze; jerk, foveation 120 msecs/cycle inPP MIZ = 30° left gaze; jerk, foveation 120 msecs/ cycle inPP

left medial rectus; MIZ

MIZ = -5 ° to +25°; dual jerk, foveation 100 msecs/cycle in PP

MIZ = -10° to +25°; jerk, foveation 160 msecs/cycle in PP

MIZ = -5° to 25°; jerk, foveation 120 msecs/cycle in PP

MIZ = -10° to +25°; jerk, foveation 120 msecs/cycle in PP

MIZ = -5 ° to +30°; bidual jerk, foveation 120 msecs/cycle in PP

Postoperative in Primary Position

EOG Findings

Preoperative with Head Tum

left eye; LLR = left lateral rectus; LMR

0°_5° RHT

0°_5° RHT

0°_5°

0°

Postoperative

Head Turn

EOG = electro-oculography; EX = exophoria; E = esophoria; LHT = left head turn; RE = right eye; RLR = right lateral rectus; LE = minimum intensity zone; PP = primary position; X = exophoria; RHT = right head turn; RMR = right medial rectus .

X = 4A Titmus rings 1-8

X = 4A EX = 0 Titmus rings 1-8 Titmus rings 1-8

EX = 0

EX = 0 AnimalsA-C

8

X = SA

EX = 0 Animals A

Postoperative

F

Hyperopia, astigmatism

Preoperative

3

7

6

Diagnosis

Orthoptic Status

F

M

Age at Treatment (yrs) Sex

2

Patient No.

Binocular Visual Acuity

Table 3. Clinical Findings Preoperative and Postoperative Combined Artificial Divergence and Anderson-Kestenbaum Procedure

Volume 100, Number 10, October 1993

Ophthalmology

2 had a papillar and macular coloboma; and patients 2, 3,6, and 7 had strabismus or had had strabismus surgery. Patient 5 displayed esophoria preoperatively. In the patients with binocular vision, stereopsis did not change postoperatively. Patients 4 and 5 displayed a residual head turn greater than 5 0. The others did not show a head turn greater than 5° postoperatively. The binocular visual acuity (Fig 3b) improved only one Snellen line in only one patient (patient 2). Preoperative and postoperative EOG results (Table 2) document a change of the minimal in-

AnHiclal Divergence Group

f

)

I ~

1.1

0.11 0.7 0.5 0.3

0.5

0.3

A

0 .7

0 .11

1.1

Preope.... lv. vl~ ecully

RE

~

§

II

J

LEFT GAZE

R

Anderson-Kestenbaum Group 1.1

I

20·

1tAJ\ 1 sec

0.11 LE

0.7

J\J\

0.5

PRIMARY POSITION

M M

RIGHT GAZE 15-20·

~

IYl IYl 60-80 mSle ro.eatt on

NEAR

0.3

0.5

0.3

B

0 .7

0.11

1.1

PreopeI'8IlYe vi'" ecutty

Combined Group

f )

I ~

C

1.1

A

0.11

LEFT GAZE

0.7 0.5

RIGHT GAZE

15-20·

RE

0.3

0.3

0.5

0.7

0.11

LE 1 sec

~1Ye vI.uII ecutty

Figure 3. Comparison of preoperative and postoperative visual acuity in the artificial divergence group 3 (A), in the Anderson-Kestenbaum group 3 (B), and in the combined group 3 (C).

drawings of the original recordings. Notice the waveform in primary position changed from jerk left to jerk left with foveation to no nystagmus and the broadening of the null zone from the primary position to 20° right gaze.

Anderson,Kestenbaum Group Seven patients with infantile nystagmus displayed only an eccentric null position and had a standard AndersonKestenbaum procedure. The six girls and one boy had a mean age at surgery of 9.4 years. Operating techniques were as previously described in the Materials and Methods section. Patient 1 had oculocutaneous albinism; patient

1494

PRIMARY POSITION

B

Foveation 160 msee/eyele to no nystogmus

••

Figure 4. Illustration of the original electro-oculogram. Preoperative eye movements of patient 3. A,in 15 0 to 20 0 right gaze, there is no nystagmus (minimal intensity zone) to jerk right with 60 to 80 mseconds/cycle foveation. In primary position and left gaze, jerk left without foveation is detected at a higher intensity. Notice the left head turn. B, no head turn, patient looks straight ahead after the recess-resect procedure was done on the left eye. The left medial rectus muscle was resected and the left lateral rectus was recessed (arrow). Postoperative eye movement recordings show no change in the nystagmus in right gaze. In primary position, jerk left with 160 mseconds/ cycle foveation is shown; unchanged nystagmus waveform in left gaze compared with preoperative recordings is shown. See the broadening of the minimal intensity zone, now extending from 20 0 right gaze to primary position.

Zubcov et al . Visual Acuity after Surgery for Nystagmus tensity zone from lateral gaze to primary position, or close to it if a residual head tum was still present. The nystagmus waveform did not change. Figures 4A and 4B of patient 3 depict the typical preoperative and postoperative eye movement recordings of this group. Notice that the minimal intensity zone moved from 15° to 20° right gaze to primary position. Now at 15° to 20° right gaze, the nystagmus is jerk right with a greater intensity.

Artificial Divergence Combined with AndersonKestenbaum Group Five patients (3 girls and 2 boys) had a mean age of 6.5 years in this group (Table 3) at the time of surgery. All patients had stereopsis which improved in two patients (patients I and 5).. Patient 2 displayed exophoria but other patients were orthophoric. No residual head tum greater than 5° was found postoperatively. The binocular visual acuity (Fig 3C) improved two Snellen lines or more in four of the five patients (patients I, 2, 4,and 5) but did not change in patient 3. Preoperative and postoperative EOG showed a broadening of the minimal intensity zone by 30° to 35° in all patients. The foveation time/cycle increased in primary position in two of five patients (patients I and 5).

Discussion Binocular Visual Acuity Improvement The usual indication for surgery of infantile nystagmus is the elimination of the anomalous head position assumed by patients to use the eccentric minimum intensity zone where the nystagmus is least and permits the best visual acuity. The functional benefits of surgery for manifest latent nystagmus have been described elsewhere. 4 We compared three different surgical procedures used to treat infantile nystagmus as to the patients' improvement in binocular visual acuity. The first group consisted of six infantile nystagmus patients operated, as suggested by Clippers, according to the artificial divergence principle.6 Two of six patients improved their binocular visual acuities by one Snellen line (patients 2 and 4) and one patient's postoperative binocular visual acuity improved by four Snellen lines (patient 6). Three patients were unchanged (see Fig 3A). The second group was comprised of seven patients treated with the classic AndersonKestenbaum 8 •9 surgical procedure. Postoperative binocular visual acuities, as seen in Figure 3B, show only a nonsignificant improvement of one Snellen line in one of seven patients (patient 2). The other six patients' binocular visual acuities did not improve. In the third group, the patients had a combined artificial divergence and Anderson-Kestenbaum surgical procedure, as suggested first by Roggenkamper. 7 Binocular visual acuities in four of five patients improved by two Snellen lines or more (patients I, 2, 4, and 5); they remained unchanged in one patient (Fig 3C).

A significant binocular visual acuity improvement was seen in four of five patients in the combined operation group and in one offive in the artificial divergence group. In the Anderson-Kestenbaum group, none of the seven patients improved significantly. We were biased toward choosing the patients with best binocular potential in the artificial divergence and the combined surgical groups, but the preoperative binocular visual acuities in the combined and Anderson-Kestenbaum groups did not differ significantly (Student's t test; P ~ 0.4). Postoperatively, a significant difference was found (P ~ 0.03). Currently, the most frequently used surgical procedure for the alleviation of the anomalous head position was suggested in 1953 independently by Anderson 8 and by Kestenbaum. 9 Since then, for patients with a head tum greater than 25 0, the four-muscle operation has been modified by the suggestions of Calhoun and Harleyl 2 in 1973 and Scott and Kraft I I in 1984. Scott and Kraft reported the improvement in binocular visual acuity in more than two thirds of their 32 patients as no more than one Snellen line. Only four oftheir 32 patients showed an improvement in binocular visual acuity of more than two Snellen lines. KommereW 3 reported no change in binocular visual acuities in his group of 28 patients. The artificial divergence and the combined group had the best results in terms of functional benefits of surgery for infantile nystagmus. We concur with Kaufmann and Kollingl4 and Sendler et ail S who reported better visual outcome with the artificial divergence procedure: 13 of 25 and 5 of 17 patients, respectively, had significantly improved binocular visual acuities postoperatively. In the combined group, three of five patients showed some improvement in the binocular visual acuities compared with Sendler et ail S who saw significant improvement in two of three patients.

Electro-oculogram Results We focused particular attention on the following eye movement parameters: intensity of nystagmus, waveform, and foveation time (Fig 5). We demonstrated a shifting and broadening of the minimal intensity zone toward the primary position in all three groups. Here, again, the artificial divergence and combined groups displayed an increase of the minimal intensity zone from a null point to a null zone of approximately 30°. The Anderson-Kestenbaum group showed only a modest increase in minimal intensity zone compared with the other groups. This broadening of the minimal intensity zone has been reported by Dell'Osso et al 16 and was thought to be responsible for the improvement in binocular visual acuities noted in some patients after this procedure. Our study showed a broadening of the minimal intensity zone in the artificial divergence and combined groups and only a modest enlargement in the Anderson-Kestenbaum group. This concurs with the binocular visual acuity improvements in the artificial divergence and combined groups versus the Anderson-Kestenbaum group. In the artificial divergence group, we found an increase in foveation time in one patient (patient 5) from 120 to

1495

Ophthalmology PRIMARY POSITION

LEFT GAZE

N\

RE

RIGHT GAZE 15-20·

J\A J\A

M

LE

Volume 100, Number 10, October 1993

tOOL t R

L

A

SIC

LEFT GAZE

RE

LE

B

PRIMARY POSITION

I\JVV\ I\JVV\

••

RIGHT GAZE 15-20 0

fV\M fV\M

Figure 5. Illustration of the original electro-oculogram. Preoperative eye movements of patient 3. A, minimal intensity zone nystagmus in right gaze, without nystagmus. In primary position and left gaze, jerk left at a higher intensity is depicted. Notice the left head turn. B, notice the straight head. The surgery consisted of recess-resect in both eyes; the recession is marked with an arrow. See the translation of the minimal intensity zone from 20° right gaze to primary position.

160 mseconds/cycle. Foveation developed in two other patients (patients 2 and 6). Patient 2 changed the waveform jerk without foveation to jerk with 160 mseconds/ cycle foveation and patient 6 from dual jerk to dual jerk with 80 to 140 mseconds/cycle offoveation. Three patients did not change the foveation time or the waveform. In the combined group, we could demonstrate an increase in the foveation time from 60 to 120 mseconds/cycle (patient I) and 40 to 100 mseconds/cycle (patient 5). In the other three patients, the foveation time or waveform did not change. In none of the seven patients in the AndersonKestenbaum group did the foveation time change. Of the five patients who displayed changes in foveation time, the binocular visual acuities also increased in four. In patient 5 only in the artificial divergence group, there was no change in binocular visual acuity. Attention to the possible importance of waveform as a variable, along with the nystagmus intensity for the assessment of visual acuity, has been drawn by DelrOsso et a1. 16 ,1 7 In their two patients, there was no change in waveform after eye muscle surgery.

1496

In 1989, Bosone et al 18 analyzed the preoperative and postoperative EOGs of five patients who underwent the Anderson-Kestenbaum procedure. They showed that the time constant of the slow phase increased after surgery in two of five patients. In these patients, visual acuity also improved. It is not surprising that Snellen visual acuity is low in patients with nystagmus because of the undesirable image movements with large peak-to-peak amplitudes and velocities as high as 100° per second. 2 The central nervous system, faced with the problem of attaining the best possible vision of a constant oscillating eye, seems to use a strategy aimed at maximizing the time spent by the object of regard on the fovea. The visual acuity is determined by the duration of time the retinal slip velocity is low. 19 Abadi and Worfolk2 showed a correlation between the duration of time below or equal to 10° per second and the improvement in vision. A positive correlation between the foveation time and the binocular visual acuity is confirmed by our data. The postoperative increase in foveation time is probably responsible for the increase in binocular visual acuity. Our study shows that the Anderson-Kestenbaum procedure translates the minimal intensity zone toward the primary position, broadens it moderately (10°), and does not have an effect on the nystagmus waveform . The binocular visual acuities did not significantly improve. Conversely, the artificial divergence and combined procedures, which can be used only in patients with good binocular function, demonstrated a translation of the minimal intensity zone toward the primary position and a broadening of the minimal intensity zone up to 20° to 35°, as well as a change in waveform and an increase in duration of foveation. In terms of functional result, the combined group had the greatest improvement in binocular visual acuities. Comparing the amount of surgery, the artificial divergence group with the least amount (2 muscles) and the combined group (3 muscles) had better functional results than the Anderson-Kestenbaum group (4 muscles). Follow-up will be necessary to determine the stability of these results. Sendler et aIlS reported a persistent improvement in visual acuity and head turn after 3 years in several patients. It seems reasonable to recommend the artificial divergence procedure for all patients with infantile nystagmus and head turn with good binocular function. If the fusional convergence is not capable of fully alleviating the head turn, a combined procedure should be considered.

References I. Dell'Osso LF, Schmidt D, Daroff RB. Latent, manifest latent, and congenital nystagmus. Arch Ophthalmol 1979;97: 1877-85. 2. Abadi RV, Worfolk R. Retinal slip velocities in congenital nystagmus. Vision Res 1989;29: 195-205.

Zubcov et at . Visual Acuity after Surgery for Nystagmus 3. Reinecke RD, Guo S, Goldstein HP. Waveform evolution in infantile nystagmus: an electro-oculographic study of 35 cases. Binocular Vis 1988;3:191-202. 4. Zubcov AA, Reinecke RD, Gottlob I, et aI. Treatment of manifest latent nystagmus. Am J OphthaImol 1990;110:160-7. 5. Economopoulos NK, Damanakis AG. Modification of the Kestenbaum operation for correction of nystagmic torticollis and improvement of visual acuity with the use of convergence. Ophthalmic Surg 1985;16:309-14. 6. Clippers C. Probleme der operativen Therapie des okularen Nystagmus. Klin Monatsbl Augenheilkd 1971; 159: 145-57. 7. Roggenkamper P. Combination of artificial divergence with Kestenbaum operation in cases of torticollis caused by nystagmus. In: Reinecke RD, ed. Strabismus II. Orlando: Grone & Stratton, 1984;329-34. 8. Anderson JR. Causes and treatment of congenital eccentric nystagmus. Br J Ophthalmol 1953;37:267-81. 9. Kestenbaum A. A nystagmus operation. In: Acta XVII Concilium Ophthalmologicum (Canada, United States), 1954. Vol. 11;1071-8. 10. Mitchell PR, Wheeler MB, Parks MM. Kestenbaum surgical procedure for torticollis secondary to congenital nystagmus. J Pediatr Ophthalmol Strabismus 1987;24:87-93. 11. Scott WE, Kraft SP. Surgical treatment of compensatory head position in congenital nystagmus. J Pediatr Ophthalmol Strabismus 1984;21 :85-95.

12. Calhoun JH, Harley RD. Surgery for abnormal head position in congenital nystagmus. Trans Am Ophthalmol Soc 1973;71 :70-87. 13. Kommerell G. Nystagmusoperationen zur Korrektur verschiedener Kopfzwangshaltungen. Klin Monatsbl Augenheilkd 1974;164: 172-91. 14. Kaufmann H, Kolling G . Operative Therapie bei Nystagmuspatienten mit Binokularfunktionen mit und ohne Kopfzwangshaltung. Ber Dtsch Ophthalmol Ges 1981 ;78: 815-19. 15. Sendler S, Shallo-Hoffmann J, Mlihlendyck H. Die Artifizielle-Divergenz-Operation beim kongenitalen Nystagmus. Fortschr Ophthalmol 1990;87:85-9. 16. Dell'Osso LF, flynn JT, DaroffRB. Hereditary congenital nystagmus. An intrafamilial study. Arch Ophthalmol 1974;92:366-74. 17. flynn JT, Dell'Osso LF. Surgery of congenital nystagmus. Trans Ophthalmol Soc UK 1981;101:431-3. 18. 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. Ophthalmic Res 1989;21: 345-51. 19. Dickinson CM, Abadi RV. The influence of nystagmoid oscillation on contrast sensitivity in normal observers. Vision Res 1985;25: 1089-96.

1497