The accommodative-convergence complex — A review
Jan-Tjeerd de Faber in 28th European Strabismological Association Meeting, 2020
Vergence eye movements (the common term for either convergence or divergence) are prerequisites of normal binocular vision. Vergence movements minimize retinal disparity and place the two retinal images of a single object on corresponding retinal points. Analogous to accommodation, vergence movements have been identified as containing the following four features (Maddox, 1886): (1) Fusional vergence, the part of the vergence movement necessary to achieve sensory fusion and avoid diplopia and which occurs in response to retinal disparity. Retinal disparity provides information about both direction and magnitude for the fusional vergence movement needed. (2) Tonic vergence, a continuous effort of convergence, which maintains the eyes in their physiological position of rest. (3) Proximal vergence, the part of the vergence movement initiated by an awareness of a near object. (4) Accommodative vergence (AC), the part of the vergence reflex that occurs solely due to changes in accommodation. If one eye is occluded so that there is no stimulus for vergence movements, and the other eye is presented with an accommodative stimulus, then the occluded eye will make a vergence movement. The process of removing vergence stimuli is referred to as making the vergence system “open-loop”.
Discussions (D)
Terence R. Anthoney in Neuroanatomy and the Neurologic Exam, 2017
Normally the two eyes move together, and their movements are coordinated so that images of an object seen by both eyes fall on exactly corresponding points of the two retinas (e.g., A&V, p. 194). In particular, the images of the focal object fall on both foveas (Ruch and Patton, 1979, p. 453). Since conjugate gaze is often discussed in this context (e.g., A&V, p. 194; DSR&W, p. 356), one might surmise that conjugate gaze refers to all such coordinated movements of the two eyes. This is not usually the intended meaning, however, for most authors do not include movements of convergence and divergence as types of conjugate gaze. Usually, however, this is not stated explicitly, and the only clue available to the reader may be the statement that the eyes move “in the same direction” during conjugate gaze (e.g., DSR&W, p. 356; Adams and Victor, 1981, p. 176). Authors of a neurophysiology text, however, specifically list and distinguish “convergence-divergence” and “conjugate” as two kinds of eye movements used in visual fixation (Ruch and Patton, p. 453). In the 1985 edition of their textbook, Adams and Victor also make this distinction. Unfortunately, they call the convergence-divergence movements “disconjugate” ocular movements (p. 194). not to be confused with dysconjugate gaze or movements (see below).
Accommodating intraocular lenses
Pablo Artal in Handbook of Visual Optics, 2017
However, there are some downsides to the NuLens design. It has been suggested by the developers that the “reversed” principle of ciliary body contraction–induced disaccommodation would necessitate an adaptive period of the visual system.30 A further issue is the convergent eye movement associated with accommodation as near vision would be accompanied by divergence and distance vision by convergence. Potential difficulties with maintaining binocular single vision must not be neglected.31 Furthermore, the developers annotated that a version of the NuLens suitable for small incision cataract surgery should be introduced with regard to the observed steep decline in endothelial cell count observed in the first human study as well as to reduce surgically induced astigmatism.29
Visual function impairment in patients suffering from visually induced motion sickness. A preliminary observational longitudinal study
Published in Hearing, Balance and Communication, 2023
Leonardo Gabriele, Sara De Angelis, Vittorio Roncagli, Marco Tramontano, Leonardo Manzari, Domenico Gabriele
Two evaluation sessions were carried out immediately before (T0) and after 16 weeks of visual rehabilitation training (T1) (Figure 1). Each evaluation aimed to evaluate participants’ visual function and sickness-related symptoms. Visual function evaluation consisted of vergence and accommodative tests, binocular vision, stereopsis and phoria. The function of the vergence eye movement system is to track objects moving in depth, to attain cortical fusion and bifoveation. Visual accommodation is a reflexive physical process in which the lens of the eye adjusts allowing images to become focussed. The stereopsis is the perception of depth produced by the reception in the brain of visual stimuli from both eyes in binocular vision. The phoria is characterized by a latent horizontal and vertical deviation of the visual axes.
Adherence to home-based videogame treatment for amblyopia in children and adults
Published in Clinical and Experimental Optometry, 2021
Tina Y Gao, Joanna M Black, Raiju J Babu, William R Bobier, Arijit Chakraborty, Shuan Dai, Cindy X Guo, Robert F Hess, Michelle Jenkins, Yannan Jiang, Lisa S Kearns, Lionel Kowal, Carly S Y Lam, Peter C K Pang, Varsha Parag, Roberto Pieri, Rajkumar Nallour Raveendren, Jayshree South, Sandra Elfride Staffieri, Angela Wadham, Natalie Walker, Benjamin Thompson
It may be that for treatments based on visual stimulation to be successful, detailed instructions need to be given to patients (and parents/caregivers where relevant) specifying the optimal session length and emphasising the need to continuously view the display for maximum effect. However, continuous viewing must be enforced in a friendly manner to be acceptable to the user, and longer training sessions need to be balanced against the fact that they are less convenient to schedule within the patient’s daily routine. Inconvenient or unpleasant treatments will hinder overall treatment adherence, which can also lead to reduced effectiveness. This balance between training intensity and practicality is an important design consideration for all home-based treatments, and the optimal balance will depend on many factors including patient age, ability, lifestyle factors (e.g. school, work, and/or family responsibilities), the treatment delivery method (e.g. portable versus not portable), and, importantly, the true impact of disrupted play on treatment outcomes, which may vary depending on the condition being treated and the mechanisms underlying the treatment effects. Traditional vision therapy exercises for vergence disorders, for example, are often prescribed with a ‘little but often’ daily regimen to minimise ocular fatigue. But this may not be suitable for all training-type therapies.
Association between post-concussion symptoms and oculomotor deficits among adolescents
Published in Brain Injury, 2021
Sowjanya Gowrisankaran, Ankoor S. Shah, Tawna L. Roberts, Emily Wiecek, Ryan N. Chinn, Karameh K Hawash, Michael J. O’Brien, David R Howell, William P Meehan, Aparna Raghuram
Oculomotor assessment included evaluation of vergence, accommodation, and visual tracking. The following tests were performed to evaluate vergence: eye alignment at distance and near (unilateral and alternating prism cover test); near point of convergence (NPC); vergence amplitudes, including convergence (Positive Fusional Vergence) and divergence (Negative Fusional Vergence) at near (40 cm); and near vergence facility using a prism wedge of 3Δ base in (BI) and 12Δ base out (BO). The following tests were used to evaluate the accommodation system: amplitude of accommodation using the push-up method and monocular and binocular accommodative facility using ± 2.00 D flippers. The developmental eye movement (DEM) test was used to evaluate visual tracking ability. A detailed description of the tests can be found in earlier publications (27,34). Results of oculomotor testing were used to provide vergence, accommodation, and visual tracking deficit diagnoses to each patient, based on criteria described in (Table 1) (17,27).
Related Knowledge Centers
- Accommodation
- Accommodation Reflex
- Eye
- Eye Movement
- Saccade
- Muscle Tone
- Binocular Vision
- Eye
- Stereoscopy
- Vergence-Accommodation Conflict
- Extraocular Muscles