Accommodation

Accommodation

It is the mechanism through which our eyes increase the converging power to focus on the retina when an object is closer than 6 meters.

Accommodation

It is the mechanism by which the eye changes refractive power by altering the shape of the lens in order to focus objects at variable distances.

1. Ciliary muscle contract and move forward.

2. Zonular fiber relax.

3. Medial recti muscles contract.

4. Pupil constricts

5. Pupillary margin of the iris and the anterior surface of the lens move forward.

6. Anterior surface of the lens becomes more convex.

7. Posterior of the lens becomes slightly more convex.

8. Due to gravity, the lens sinks downward during accommodation.

9. Choroid moves forward.

Changes taking place during accommodation? (9)

Far Point

Position of an object when its image clearly falls on retina with no accommodation.

Near Point

Nearest point clearly seen with maximum accommodation.

Range of Accommodation

Distance between far point and near point.

Amplitude of Accommodation

The difference between the dioptric power needed to focus at near point (P) and far point (R).

• Reflex Accommodation

• Vergence Accommodation

• Proximal Accommodation

• Tonic Accommodation

Types of Accommodation? (4)

Reflex Accommodation

Accommodation changes occurring in direct response to reduce quality, or to blurriness of the perceived image.

Vergence Accommodation

Accommodation changes induced by, or associated with changes in accommodation.

Proximal Accommdoation

It is due to the influence or knowledge of apparent nearness of an object.

Tonic Accommodation

Accommodation attributable to the normal bonus of the ciliary muscle.

• Blur image

• Apparent size and distance of object

• Chromatic aberrations

• Scanning movements of eyes

Stimulus of Accommodation? (4)

Reaction Time of Accommodation

Refers to the time between presentation of accommodative stimulus and occurrence of accommodative response.

0.64 seconds

Reaction time of accommodation from far to near?

0.54 seconds

Reaction time of accommodation from near to far?

Pathway of Accommodation of Eye?

• Insufficiency of Accommodation

• Ill-Sustained Accommodation

• Inertia of Accommodation

• Paralysis of Accommodation

Diminished or Deficient Accommodation? (4)

Insufficiency of Accommodation

It refers to a condition where the eyes have a diminished capacity to focus properly on nearby objects.

Insufficiency of Accommodation

This condition is characterized by an inability of the ciliary muscles and lens to increase their optical power to maintain a clear image on the retina when looking at closer objects.

Ill-Sustained Accommodation

It refers to a condition where the eye exhibits a normal initial accommodation response, but cannot maintain this accommodative effort over time.

Ill-Sustained Accommodation

This can result in a progressive decline in the ability to keep a near object in clear focus during a prolonged visual task, such as reading or other close work.

Inertia of Accommodation

It refers to a delay or slowness in the responsive action of the eye’s accommodation.

Inertia of Accommodation

It indicates a sluggishness in the eye’s ability to adjust its focus from far to near, or vice versa.

Paralysis of Accommodation

It is a condition where the eye cannot adjust its focus for different distances because the ciliary muscle cannot contract to change the shape of the lens.

Paralysis of Accommodation

This results in a loss of accommodation, meaning the ability to see objects clearly at various distances is impaired. Paralysis of accommodation can be caused by various factors, including certain medications, trauma, neurological diseases, or it can be a temporary side effect of drugs that inhibit the parasympathetic nervous system.

• Excessive Accommodation

• Spasm of Accommodation

Increased Accommodation? (2)

Excessive Accommodation

It refers to a condition where the eye’s accommodation system is overly active, leading to a greater than necessary focusing effort for near vision.

Excessive Accommodation

This can result in symptoms such as eye strain, headaches, blurred vision, and difficulties in shifting focus from near to distant objects.

Spasm of Accommodation

It is a condition characterized by an involuntary and persistent contraction of the ciliary muscle, leading to excessive focusing power of the lens.

Spasm of Accommodation

This condition can result in a continuous state of near focus, making it difficult to see distant objects clearly.

AC/A Ratio

To measure how much convergence (eye turning in) occurs for each unit of accommodation (focusing effort).

Accommodative Convergence To Accommodation Ratio

AC/A Ratio stands for?