The Near Triad

Synkinesis

Three systems work together as a?

Near Triad

It is essential for clear, single binocular vision at near.

Produce the clearest possible perception of an object.

General purpose of the near triad?

1. Accommodation

2. Convergence

3. Pupillary Constriction

Three components of near triad?

• Stimuli are associated with object distance.

• Retinal blur and disparity provide important information about distance.

• These stimuli can be sufficient to evoke all three near-triad response.

Stimuli for Near Triad? (3)

• Perspective

• Apparent size

• Aberrations

• Psychic or proximal clues

Additional cues that can modify the response? (4)

Blur

Accommodation is primarily driven by?

Retinal Disparity

Vergence is primarily driven by?

Accommodation

Alters the refractive power of the eye.

Positive Accommodation

It occurs when viewing near objects.

Negative Accommodation

It occurs when shifting fixation farther away.

Accommodation

Lens changes allow light rays to form a focused image on the retina.

• 6m

• Emmetrope

At _____m, an _____ has essentially zero accommodative demand.

Retinal Blur

Primary stimulus of accommodation?

Blur provides the primary drive, while other cues may help determine the direction of the response.

Does blur alone stimulate accommodation?

Cornea

It provides most of the eye’s refractive power.

Amplitude of Accommodation

Maximum accommodative response produced with voluntary effort.

Accommodative Insufficiency

Accommodation persistently lower than expected for age.

>2D

In Accommodative Insufficiency, it usually reduced amplitude by?

Asthenopia during near work.

Main symptoms of Accommodative Insufficiency?

Accommodative Fatigue

Accommodative amplitude may initially be adequate.

Accommodative Fatigue

Patient cannot maintain the accommodative response.

Accommodative Fatigue

Blur develops after prolonged viewing.

Accommodative Fatigue

It may represent an early stage of accommodative insufficiency.

Accommodative Excess

Accommodation persistently higher than expected for age.

Accommodative Excess

It can manifest as accommodative spasm.

Accommodative Excess

Reduced negative relative accommodation.

Accommodative Excess

It may involve inability to relax accommodation.

Accommodative Spasm

Inability to relax accommodation.

Accommodative Infacility

Normal magnitude of accommodative response.

Accommodative Infacility

Slowed accommodative dynamics.

Near to far or far to near blur

Common complaint in Accommodative Infacility?

Lag Accommodation

It represents under-accommodation.

Lead Accommodation

It represents over-accommodation.

Convergence

Simultaneous inward rotation of both eyes.

Convergence

It is necessary for binocular fixation on a near object.

Retinal Disparity

Primary Stimulus for Vergence?

Corresponding Retinal Points

Each point on one retina corresponds to a point/region on the other retina.

Binocular Disparity

Difference in the retinal locations of corresponding images.

1. Proximal Convergence

2. Fusional Convergence

3. Tonic Convergence

4. Accommodative Convergence

Components of Convergence? (4)

Proximal Convergence

Convergence in response to perceived nearness.

Fusional Convergence

Convergence that maintains single binocular vision despite disparate retinal images.

Tonic Convergence

Convergence maintained by extraocular muscle tonus.

Accommodative Convergence

Convergence associated with active accommodation.

AC/A

It expresses accommodative convergence in prism diopters per diopter of accommodation.

1. Convergence excess

2. Divergence insufficiency

3. Convergence insufficiency

4. Divergence excess

Four Major Patterns of Convergence Anomalies?

Depth of Focus

It represents the amount of retinal blur that is tolerated.