Unit 6: Amplitude of Accommodation

Punctum Remotum (P.R.)

• The point in conjugation with the retina when accommodation is relaxed.

• It indicates the static refraction of the eye.

• Emmetropia: At optical infinity.

• Hyperopia: Lies in negative infinity, behind the eye.

• Myopia: Lies between optical infinity and the eye.

Punctum Proximum (P.P.)

• The point, measured linearly from the eye, in conjugation with the retina when accommodation is exerted to its maximum.

• Emmetropia and myopia: Positive, in front of the eye.

• Hyperopia: Negative if ametropia exceeds the maximum amount of accommodation available.

Amplitude of Accommodation

• The Punctum Proximum converted to its dioptric value.

• Represents the dioptric difference between the P.R. and P.P.

Range of Accommodation

• The linear distance traversed by the conjugate in moving from the P.R. to the P.P.

• It is the difference between the far point and the near point.

Amplitude of Accommodation

• Represents the maximum amount of accommodation the eye is capable of.

• Influenced by:

  • Original refractive state.

  • Previous use of the ciliary muscle.

  • General health of the patient.

  • Presence of vascular and glandular defects.

• The major influence is the biologically normal decrease in the dynamic focal power of the eye, which accompanies aging.

Decreased Ability to Accommodate

• Results from:

  • Decreased ciliary power.

  • Changes in the index and plasticity of the lens.

  • Loss of elasticity of the lens capsule.

  • Loss of elasticity of the connective tissue in the ciliary body.

lens; innervation

Physical and Physiological Accommodation

• Accommodation is a two-fold process:

  • Physical: Concerns the changes the _____

    undergoes due to its plasticity and elasticity.

    • Measured in diopters.

• Physiological: Concerns the _____of the ciliary muscle and its contraction.

Presbyopia

• recedes with passing years due to the decreasing power of accommodation, which may result from two causes:

  1. Physico-chemical changes in the lens structure.

  2. Physiological power of the neuromuscular mechanism.

plasticity/elasticity; Ciliary muscles

• Physico-chemical Changes

  • Affect the structure of the lens, reducing its ________, preventing changes in lens form necessary for increased refractive power.

  Physiological Changes

  • The _______ and their motor nerve supply deteriorate, reducing the lens' ability to change shape.

Lenticular Sclerosis

• Presbyopia is primarily due to gradual hardening of the lens, resulting in a loss of accommodation.

• ________ : Loss of lens elasticity.

relaxed; maximum curvature

Physical and Physiological Near Points

• Physical near-point: Location of the near point determined by the amount the lens can alter its curvature when the suspensory ligaments are fully ______.

• Physiological near-point: When the lens has reached_____ ____, but the ciliary muscle continues to contract without any further change in the lens.

• active external force

According to Fincham

• Accommodation is not dependent on the release of tension in the unaccommodated state but is caused by an _______ deforming the lens during accommodation.

 loss of ciliary power

Loss of Accommodation

• Caused by a_______, not merely by physical changes in the lens.

• The loss of plasticity/elasticity is a common phenomenon with aging, similar to:

  • Arteriosclerosis: Loss of arterial wall elasticity.

  • Wrinkling of the skin: Loss of skin elasticity.

hardening of the lens capsule

Cause of Sclerosis

• 35% of the lens is composed of soluble protein material, which becomes increasingly insoluble with age, reaching 50% insolubility.

The loss of lens elasticity is due to the _________ and decreased flexibility of the lens material.

• decreases; smaller

Presbyopia and the Degree of Illumination

• Sheard found that presbyopes require greater illumination than non-presbyopes because:

  • Transparency of the ocular media _____ with age.

  • The pupil becomes constantly _____, leading to a marked reduction in visual acuity.

• 15 - (0.25 x age)

• 18.5 – (0.30) × age

• 25 – (0.40) × age

Hofstetter's Formula

• Average:

• Maximum:

• Minimum: