Maddox Classification

1. Maddox Classification • Emphasis on motor alignment • Based on empirical clinical observation • Accommodative convergence predominates • Fusional convergence considered a fine adjustment

2. Graphical Analysis • Based on Maddox classification and theory • Allows for a mechanical, static appraisal of accommodation/vergence interaction • Presents a template for "visualization" of these interactions • Provides a quantitative approach to binocular vision analysis

3. OEP Theory • A global model of visual processing • Suggests that most binocular dysfunctions arise from purposeful mal- adaptations NOT inherent weaknesses of a particular system • Suggests mechanisms for progression of binocular dysfunction

4. System Control Analysis • A biomedical engineering model utilizing multiple neural control processes. There is an integration of a host of neural inputs that ultimately affect convergence and accommodation channels • This model allows multiple sources (in the brainstem and more centrally) to influence vergence output • A theoretical model mirroring recent findings on specific physiological processes • This model provides a dynamic representation of accommodation/vergence interaction • This model allows for non-linear stimulus/response characteristics • It suggests mechanisms for progression of binocular dysfunctions 8. it provides a quantitative and dynamic approach to binocular vision analysis

5. Dead-space generator • The “just noticeable difference” to the vergence and accommodative system • Accommodative System: depth of focus • Vergence System: Panum’s fusional area

6. Comparator • Element that compares demand (accommodative or vergence) to the output (response). • When response is sufficient: the comparator will be inhibited • Depends on negative feedback loop from the plant.

7. Summation • A simple, arithmetic summation of the response occurs at these junctions. • Proximal vergence gain (+) fusional vergence gain • Proximal vergence gain (+) blur induced accommodation

8. Control (Integration) Element • Location for gain control and integration of various accommodative and vergence signals • Saturation points for all inputs are set here as well

9. Gain Control • Allows for “tweaking” of signals for accommodation or vergence • Response may be allowed through at full strength (full gain) or it may be cut (gain control)

10. Saturation Element • Allows the control element to say “no more” to the input • Demand may increase, but the output of the control element would remain the same.

11. Adaptation • Inputs of slow (adaptive) accommodation and vergence responses. • Responsible for “re-calibrating” baseline activity of the system • The increase in slow (adaptive) vergence and slow (adaptive) accommodative response to a long-term (10-15 seconds) stimulus at near

12. Cross Links • Where accommodative vergence and convergence accommodation enter the game. • The amount of convergence accommodation gained by 6Δ of fusional convergence is determined by the CA/C ratio. • The amount of accommodative convergence gained by 1.00D of blur-induced accommodation is determined by the AC/A ratio.

13. Plant • “Factory” where orders for accommodation and vergence are filled. • Output from this system also provides NEGATIVE feedback loop to the input part of the diagram. • Allows output to be matched to the real vergence and accommodative demand • When there is feedback, engineers say the system is operating “closed loop”

14. Isolating Accommodative Vergence • Clinically with VonGraefe phoria testing—gradient AC/A • By dissociating the patient with prism, the fusional vergence loop is opened. The prism creates a non-fused environment, so Panum’s fusional area does not exist. As a result, the eyes assume their tonic position and fusional vergence gain goes to zero. • Accommodative & Proximal vergence remain operational • Proximal vergence is controlled, because phorias are measured behind the phoropter w/the patient’s BVA, and subsequently with a series of (—) lenses. Theoretically, proximal vergence is controlled because all tests are done behind the same phoroptor • Thus, Accommodative Vergence is isolated.

15. Isolating Fusional Vergence • A pinhole effectively opens the accommodative loop by creating a situation where the depth of focus is infinite. • (+) lenses are effective at limiting the proximal effect

16. Characteristics of Proximal Vergence • Peak Velocity • 70°/s • Latency • 200-225 ms • Loop type: • closed loop • May set “vergence table” at an early phase, before fusional& accommodative kick in. • up to70% of initial vergence response • May explain why diplopia is not noticed even though 1s may pass before vergence response is complete.

17. Characteristics of Fusional Vergence • Peak Velocity • 20°/s • Latency • 150-200 ms • “Fast” Component • Has leaky integrator which decays over about 10s • Within ~1s, disparity error reduced to Panum’s fusional area • Initial 200ms is pre-programmed (open loop) • “Slow” Component • Under continuous feedback control (closed loop) • Charges up as fast component decays • Loop type: • closed loop • Lower peak velocity than proximal vergence • May not be dominant player at initiation of vergence response

18. Characteristics of Accommodative Vergence • Peak Velocity • 10°/s • Latency • 250 ms • Loop type: • open loop (i.e. not subject to integration or gain control) • Accommodative vergence response has a longer latency than other vergence components • Probably not a dominant player at initiation of vergence response

19. Total (composite) vergence response • Velocity of net response: • 80°/s—90°/s • Latency (stimulus to onset of response): • 150ms—200ms • Time for Completion: • 0.5s—2s