New Tests of Distance Stereoacuity and Their Role in Evaluating Intermittent Exotropia

Holmes, Jonathan M.; Birch, Eileen E.; Fu, Valeria L. N.; Mohney, Brian G.

doi:10.1016/j.jaapos.2006.01.099

Cited by 19 publications

(24 citation statements)

References 32 publications

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“…5 Our study does not support this assertion based on the median distance angle of deviation and median distance control score, measured through the course of a single day. Our previous study 14 suggested that there was a overall positive correlation between angle and control score, but that study only documented a single measure of control. In both the present study, and in our previous study, 14 there are notable examples of patients who have large angles and good control and smaller angles and poor control.…”

Section: Discussionmentioning

confidence: 95%

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Variability of Control in Intermittent Exotropia

et al. 2008

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Purpose-Assessing control is thought to be important in the management of intermittent exotropia (IXT), including the decision to perform surgery. The purpose of this study was to assess the presence and degree of any change in control occurring over the course of 1 day using a previously described 6-point clinic control scale, and to evaluate inter-observer and minute-to-minute variability. Design-Prospective case series. Participants-25 patients with intermittent exotropia.Methods-Inter-observer agreement was determined in 17 patients by comparing control scores assessed simultaneously by 2 observers (kappa test). Minute-to-minute variability was observed in the same 17 patients by assessing control twice within 5 minutes. Variability over one day was assessed in 5 of these patients plus 8 additional patients (n=13) by comparing 3 or 4 assessments at least 2 hours apart.Main outcome measure-Control of IXT measured using a 6-point clinic control scale.Results-Inter-observer agreement was high (k=0.94 for distance and k=0.95 for near fixation). Disagreements were no more than one level on the control scale; therefore, for further analysis, change in control was defined as 2 or more levels. For minute-to-minute variability, 4 (24%) of the 17 patients tested twice within 5 minutes showed a change in control: 1 (6%) changed from tropia to phoria at distance, 3 (18%) from phoria to tropia at near. Of the 13 patients assessed over 1 day, 6 (46%) showed change in control, 2 at distance fixation only, 3 at near only and 1 at near and distance.Conclusions-Control of IXT can vary throughout the day, even within minutes, including from phoric to spontaneously tropic, and vice versa. The worst level of control was not always later in the day. This suggests that an isolated assessment of control may not categorize severity of IXT in an individual patient.Intermittent exotropia (IXT) is a common form of childhood strabismus 1, 2 characterized by intermittent divergent misalignment that is often greater at distance fixation. Severity and progression of IXT are currently assessed by determining angle of deviation, stereoacuity, ability to control the deviation and parental reports of frequency. 'Control' may be defined as an estimate of the proportion of time the deviation is manifest and the ease of re-establishing fusion after dissociation. Although the natural history and indications for surgical intervention are poorly defined, 3 it is commonly held that poor control of the exodeviation is a sign of deterioration. 4 On this basis, surgery has been recommended by some authors when the exotropia occurs more than 50% of waking hours or when there is a gradual loss of fusional control as evidenced by an increasing frequency of the exotropia. [4][5][6] Others have suggested that early surgery results in superior sensory outcomes 7, 8 but the timing of surgery for IXT has not been subjected to a randomized clinical trial and prior to such a trial, outcome measures such as control need to be rigorously studied.Until recen...

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Section: Discussionmentioning

confidence: 95%

“…10,14 Inter-observer variability Our underlying hypothesis was that control varies within short periods of time. For this reason we could not rely on sequential assessments to evaluate inter-observer variability.…”

Section: Assessment Of Controlmentioning

confidence: 99%

Variability of Control in Intermittent Exotropia

et al. 2008

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“…6,8,12 The motor convergence necessary to maintain single vision with the larger base-out prisms reduces the ability to make precise adjustments of fine-motor fusion. As we have described previously, 8 this mechanism has been proposed by Holmes et al 6 for patients with intermittent exotropia and Mireskandari et al 12 for patients with macular holes.…”

Section: Discussionmentioning

confidence: 99%

“…5-7 It has been suggested that distance stereoacuity in intermittent exotropia deteriorates as control of the deviation deteriorates, 5,6 which might be due to the use of accommodative convergence or to the fragility of motor convergence. 4,6,8 Others report distance stereoacuity to be either normal or absent in intermittent exotropia. 7 We previously performed an initial study 8 modeling aspects of intermittent exotropia by inducing exodeviations in nonstrabismic volunteers using base-out prisms.…”

Section: Introductionmentioning

confidence: 99%

Distance stereoacuity in prism-induced convergence stress

Laird

Hatt

Holmes

2008

Journal of American Association for Pediatric Ophthalmology and

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Purpose-In an initial study of prism-induced exodeviation, degraded stereoacuity was not associated with decreased binocular visual acuity, suggesting that accommodative convergence was not recruited. Distance stereoacuity degraded earlier when measured with the Frisby Davis Distance (FD2), than when measured with the Distance Randot (DR). We now describe a follow-up study in which we reversed the prism order and also addressed potential biases of testing order and different measurable levels of stereoacuity to clarify the relationship between exodeviation, distance stereoacuity, and binocular visual acuity.Methods-Convergence stress was induced with base-out prism in 20 adults and increased stepwise. Stereoacuity and binocular visual acuity were measured at each step. Disparities tested were 200, 100, and 60 seconds of arc, and testing was repeated at each prism step.Results-Most subjects showed degraded stereoacuity with the FD2 in contrast to the DR (80% vs 45%, P = 0.02). Reduction of stereoacuity occurred earlier on the FD2 than on the DR (median 18 Δ vs. 40 Δ , P = 0.001). Degradation of stereoacuity was associated with minimal change in binocular visual acuity from baseline to maximal convergence stress (median 20/15 to 20/20).Conclusion-Convergence stress is associated with decreased distance stereoacuity that does not appear to be due to accommodative convergence. Performance on real world stereotests (FD2) is affected more than random dot tests (DR), in contrast to previous findings in intermittent exotropia. There appear to be different mechanisms for decreased stereoacuity in intermittent exotropia and under conditions of convergence stress in nonstrabismic subjects.

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“…Titmus/Wirt Fly test, Randot test and TNO test are among the more popular ones. For the distance stereopsis, the Mentor BVAT SG [12] and Frisby Davis distance stereo test (FD2) [13] are fairly accurate and versatile. However, the distance stereoacuity tests are not commonly available in the clinics and they are relatively expensive.…”

Section: Introductionmentioning

confidence: 99%

A Novel Technique of Measuring Distance Stereo-Acuity Using TNO Chart and Inverted Telescope

Kothari

2017

AOVS

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Purpose: To evaluate the feasibility of the TNO chart for the assessment of distance stereo-acuity using an inverted telescope in normal subjects.Methods: Stereoacuity of 30 emmetropic adult subjects was measured for near. The distance stereoacuity was measured using the TNO chart held at 40 cm and an inverted telescope (Galilean design, 26mm, 2X, Camma Inc. China) in front of the examinee's eyes. Results:The near stereopsis ranged from 60" (seconds of arc) -240" (Median 120"). Distance stereopsis ranged from 4.8" -38.4". Distance stereoacuity could be measured in 14 (47%) subjects. Conclusion:It is possible to measure the distance with an inverted telescope and a TNO chart. Further improvisation is required to design an optimal telescope system with larger field, gradable zoom and measurable inter pupillary distance.

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New Tests of Distance Stereoacuity and Their Role in Evaluating Intermittent Exotropia

Cited by 19 publications

References 32 publications

Variability of Control in Intermittent Exotropia

Variability of Control in Intermittent Exotropia

Distance stereoacuity in prism-induced convergence stress

A Novel Technique of Measuring Distance Stereo-Acuity Using TNO Chart and Inverted Telescope

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