Accommodation and Convergence
Learning Objectives
● To recount a definition of accommodation
● To identify when AoA should be measured clinically
● To name 3 clinical measures of accommodation
● To recount a step-by-step method for measuring AoA using push up and push
down methods
● To establish a patient’s reading add based on their tentative add
● To evaluate the method for measuring Amplitude of Accommodation by knowing
the sources of error
● To recount a step-by-step method for measuring accommodative facility (D&N)
● To compare a patient’s accommodative facility against norms
● To recognise factors leading to a lag or lead of accommodation
● To recount a method for measuring near point of convergence and know
normative values
1. What is Accommodation?
Definition:
Accommodation is the process by which the eye changes its optical power so that images of
objects at different distances are focused clearly on the retina.
How it happens:
● The ciliary muscle changes the shape of the lens.
● When you look at something near, the lens becomes thicker and more curved →
increases refractive power.
● When you look at something far, the lens becomes thinner → decreases refractive
power.
2. Why is Accommodation Important?
● It allows us to focus clearly at different distances.
● In people over 40–45, the lens becomes less flexible → presbyopia (difficulty focusing
on near objects).
● In clinic, we assess how much accommodation a person has, to decide if they need a
reading addition (Add).
,3. Components of Accommodation
1. Reflex - stimulated by blur, keeps vision in focus
2. Vergence - stimulated by convergence
3. Tonic - resting position in dark
4. Proximal - induced by awareness of near object
Accommodation has several measurable parts:
1. Amplitude of Accommodation (AoA) – how much the eye can accommodate
(maximum ability).
2. Accommodative Facility – how quickly the eye can switch focus between near and far.
3. Accuracy of Accommodation – how precisely the eye focuses on a target. - not
measured routinely
4. Relative Accommodation – how accommodation interacts with convergence (not
covered deeply here).
Amplitude of Accommodation (AoA)
Definition
The maximum focusing power the eye can exert.
→ It’s the difference (in dioptres) between the far point and the near point of
accommodation.
● Far point - furthest point a px can see without blur
● Near point - closest point a px can see without blur
Key point: AoA decreases with age because the lens becomes less elastic.
, Hofstetter’s Formulas
(for expected values up to age 60)
Formula Type Equation Example (Age 30)
Maximum AoA 25 – 0.4 × age 25 – 12 = 13 D
Average AoA 18.5 – 0.3 × age 18.5 – 9 = 9.5 D
Minimum AoA 15 – 0.25 × age 15 – 7.5 = 7.5 D
Clinical Importance
● Essential for calculating near additions.
● Helps identify presbyopia, latent hyperopia, or accommodative problems (e.g.
insufficiency, spasm).
- Generally measure for age group 40
● Low AoA may cause eye strain (asthenopia) or blurred near vision.
Learning Objectives
● To recount a definition of accommodation
● To identify when AoA should be measured clinically
● To name 3 clinical measures of accommodation
● To recount a step-by-step method for measuring AoA using push up and push
down methods
● To establish a patient’s reading add based on their tentative add
● To evaluate the method for measuring Amplitude of Accommodation by knowing
the sources of error
● To recount a step-by-step method for measuring accommodative facility (D&N)
● To compare a patient’s accommodative facility against norms
● To recognise factors leading to a lag or lead of accommodation
● To recount a method for measuring near point of convergence and know
normative values
1. What is Accommodation?
Definition:
Accommodation is the process by which the eye changes its optical power so that images of
objects at different distances are focused clearly on the retina.
How it happens:
● The ciliary muscle changes the shape of the lens.
● When you look at something near, the lens becomes thicker and more curved →
increases refractive power.
● When you look at something far, the lens becomes thinner → decreases refractive
power.
2. Why is Accommodation Important?
● It allows us to focus clearly at different distances.
● In people over 40–45, the lens becomes less flexible → presbyopia (difficulty focusing
on near objects).
● In clinic, we assess how much accommodation a person has, to decide if they need a
reading addition (Add).
,3. Components of Accommodation
1. Reflex - stimulated by blur, keeps vision in focus
2. Vergence - stimulated by convergence
3. Tonic - resting position in dark
4. Proximal - induced by awareness of near object
Accommodation has several measurable parts:
1. Amplitude of Accommodation (AoA) – how much the eye can accommodate
(maximum ability).
2. Accommodative Facility – how quickly the eye can switch focus between near and far.
3. Accuracy of Accommodation – how precisely the eye focuses on a target. - not
measured routinely
4. Relative Accommodation – how accommodation interacts with convergence (not
covered deeply here).
Amplitude of Accommodation (AoA)
Definition
The maximum focusing power the eye can exert.
→ It’s the difference (in dioptres) between the far point and the near point of
accommodation.
● Far point - furthest point a px can see without blur
● Near point - closest point a px can see without blur
Key point: AoA decreases with age because the lens becomes less elastic.
, Hofstetter’s Formulas
(for expected values up to age 60)
Formula Type Equation Example (Age 30)
Maximum AoA 25 – 0.4 × age 25 – 12 = 13 D
Average AoA 18.5 – 0.3 × age 18.5 – 9 = 9.5 D
Minimum AoA 15 – 0.25 × age 15 – 7.5 = 7.5 D
Clinical Importance
● Essential for calculating near additions.
● Helps identify presbyopia, latent hyperopia, or accommodative problems (e.g.
insufficiency, spasm).
- Generally measure for age group 40
● Low AoA may cause eye strain (asthenopia) or blurred near vision.
