The Gradient AC/A Ratio: What's Really Normal?

Jackson, Jorie; Arnoldi, Kyle

doi:10.3368/aoj.54.1.125

Cited by 25 publications

(6 citation statements)

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“…The AC/A ratio was measured using the gradient method. 13 Fusion was first assessed with worth four-dot test and then near stereoacuity in current refractive correction was measured with Titmus fly stereotest and stereoacuity of o100 s of arc was defined as good. Postoperative, improved stereopsis was defined as a decrease of ≥ 2 octaves at the last follow-up visit or before reoperation, and decreased stereopsis was defined as an increase of ≥ 2 octaves.…”

Section: Methodsmentioning

confidence: 99%

Surgical outcomes of three different surgical techniques for treatment of convergence insufficiency intermittent exotropia

Farid

Abdelbaset

2017

Eye

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PurposeTo determine the outcomes of three different techniques of strabismus surgery in patients with convergence insufficiency intermittent exotropia (CI-X(T)).Patients and methodsSixty-seven patients with CI-X(T) with near-distance disparity (NDD) ≥10 prism diopter (PD) were included in this 1-year follow-up prospective study and were randomly divided into three groups: slanted bilateral LR recession (S-BLR) group in which 22 patients underwent bilateral slanting recession of the lateral rectus (LR) muscle, the I-RR group with 23 patients who underwent improved unilateral medial rectus (MR) resection and LR recession with the amounts of resection and recession biased to near and distance deviation, respectively, and the A-BLR group with 22 patients who underwent bilateral augmented LR recession based on the near deviation. A successful outcome at distant and near was defined as exodeviation between 10 PD of exophoria/tropia and 5 PD of esophoria/tropia. Cumulative probabilities of success, preoperative and postoperative distant, near deviations, and NDD among groups were analyzed and compared.ResultsThe success rate of distant exodeviation, near exodeviation, and NDD in the three groups after 1 year was statistically insignificant (P=0.054, 0.233, and 0.142, respectively). At the 1 year follow-up, vertical pattern strabismus (V and A patterns) was a feature of the S-BLR group, whereas the rate of postoperative overcorrection and undercorrection was significant in the A-BLR and I-RR groups, respectively.ConclusionThe success rate of correction of distant exodeviation, near exodeviation, and NDD was statistically indifferent among the three groups. However, each procedure has its specific postoperative concerns, which should be considered before implementing in patients with CI-X(T).

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Section: Methodsmentioning

confidence: 99%

Surgical outcomes of three different surgical techniques for treatment of convergence insufficiency intermittent exotropia

Farid

Abdelbaset

2017

Eye

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“…Bruce, Atchison, and Bhoola (1995) found a higher group mean AC/A ratio than the present study (see Table 1) although the study by Bruce, Atchison, and Bhoola (1995) used a distance target for AC/A measurement compared with the near target used in the present study. As has been mentioned previously, the effect of proximal stimulation on the relationship between AC/A ratios obtained at different viewing distances is still unclear (Jackson & Arnoldi, 2004;Pankhania & Firth, 2011), and this makes a direct comparison with the present results difficult. It is well established that voluntary effort can significantly affect oculomotor responses in open-loop conditions.…”

Section: Discussionmentioning

confidence: 86%

“…The same study also found no correlation between the response AC/A ratios measured using the target at these two distances (Pankhania & Firth, 2011). Another study did find a significant correlation between the AC/A ratio measured at distance and near (r 2 = 0.2601) and found no significant difference between the AC/A ratios measured using a distance or a near target (Jackson & Arnoldi, 2004).…”

Section: Introductionmentioning

confidence: 82%

Quantifying interactions between accommodation and vergence in a binocularly normal population

et al. 2014

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Stimulation of the accommodation system results in a response in the vergence system via accommodative vergence cross-link interactions, and stimulation of the vergence system results in an accommodation response via vergence accommodation cross-link interactions. Cross-link interactions are necessary in order to ensure simultaneous responses in the accommodation and vergence systems. The crosslink interactions are represented most comprehensively by the response AC/A (accommodative vergence) and CA/C (vergence accommodation) ratios, although the stimulus AC/A ratio is measured clinically, and the stimulus CA/C ratio is seldom measured in clinical practice. The present study aims to quantify both stimulus and response AC/A and CA/C ratios in a binocularly normal population, and determine the relationship between them. 25 Subjects (mean ± SD age 21.0 ± 1.9 years) were recruited from the university population. A significant linear relationship was found between the stimulus and response ratios, for both AC/A (r² = 0.96, p < 0.001) and CA/C ratios (r² = 0.40, p < 0.05). Good agreement was found between the stimulus and response AC/A ratios (95% CI -0.06 to 0.24 MA/D). Stimulus and response CA/C ratios are linearly related. Stimulus CA/C ratios were higher than response ratios at low values, and lower than response ratios at high values (95% CI -0.46 to 0.42 D/MA). Agreement between stimulus and response CA/C ratios is poorer than that found for AC/A ratios due to increased variability in vergence responses when viewing the Gaussian blurred target. This study has shown that more work is needed to refine the methodology of CA/C ratio measurement.

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“…1D that textbooks tell us to expect [4][5][6] and ratios obtained using different methods, which should be the same, rarely correlate. 5,7,8 Importantly, most laboratory research, which is often used to extrapolate to clinical situations, uses response AC/A ratios.…”

Section: Introductionmentioning

confidence: 99%

Convergence accommodation in orthoptic practice

Horwood

2016

British and Irish Orthoptic Journal

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Aim: Orthoptists are familiar with AC/A ratios and the concept that accommodation drives convergence, but the reverse relationship, that of the accommodation associated with convergence, is rarely considered. Methods: This article reviews published evidence from our laboratory which has investigated the drives to both vergence and accommodation. All studies involved a method by which accommodation and vergence were measured concurrently and objectively to a range of visual stimuli which manipulate blur, disparity and proximal/looming cues in different combinations. Results: Results are summarised for both typical and atypical participants, and over development between birth and adulthood. Conclusions: For the majority of typical children and adults, as well as patients with most heterophorias and intermittent exotropia, disparity is the main cue to both vergence and accommodation. Thus the convergence fiaccommodation relationship is more influential than that of accommodative vergence. Differences in 'style' of near cue use may be a more useful way to think about responses to stimuli moving in depth, and their consequences for orthoptic patients, than either AC/A or CA/C ratios. The implications of a strong role for vergence accommodation in orthoptic practice are considered.

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The Gradient AC/A Ratio: What's Really Normal?

Cited by 25 publications

References 4 publications

Surgical outcomes of three different surgical techniques for treatment of convergence insufficiency intermittent exotropia

Surgical outcomes of three different surgical techniques for treatment of convergence insufficiency intermittent exotropia

Quantifying interactions between accommodation and vergence in a binocularly normal population

Convergence accommodation in orthoptic practice

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