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Optometry > Accommodation > Flashcards

Accommodation Flashcards

1
Q

Accommodation

A

The lens ability to change its refractory power in order to focus on objects at different distances.

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2
Q

Accommodation is an _______ response.

A

Involuntary

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3
Q

How does Accommodation occur?

A

This adjustment is brought about by a change in shape of the Crystalline lens.

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4
Q

Positive Accommodation

A

To focus on a near object, it is necessary for the eye to increase its dioptric power.

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5
Q

Negative Accommodation

A

When there is a change in focus from near to distance, resulting in a decrease in dioptric power.

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6
Q

What is the purpose of Accommodation?

A

To neutralise negative vergence from a near object.

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7
Q

How does Accommodation work in Emmetropia?

A

The emmetropic patient can focus the image of the distant object on the Retina with an unaccommodated eye because the Incident vergence at the cornea is 0.

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8
Q

What are the 6 components of the eye that are involved in the process of Accommodation?

A
  1. Cranial Nerve 3
  2. Ciliary Muscle and Ciliary body
  3. Zonules/Suspensory ligaments
  4. The Crystalline Lens
  5. The Elastic capsule of the Crystalline lens
  6. Vitreous
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9
Q

What is the lens like when accommodating distance?

A

Lens is in its flattest, thinnest position.

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10
Q

What is the lens like when accommodating intermediate?

A

Middle of the lens becomes slightly fatter.

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11
Q

What is the lens like when accommodating near?

A

Lens is at its fattest, bulkiest shape

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12
Q

Accommodation in Structures:

Ciliary Body
Zonule
Lens

A

Near Far

Contract Relax
Relax Stretch
Rounds Flattens

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13
Q

What is Helmholz theory of the Accommodation Mechanism?

A

When viewing a far object i.e. not accommodating, the Ciliary muscles relaxes allowing the lens zonules and Suspensory ligaments to stretch and pull on the Crystalline lens, flattening it.

When viewing a near object i.e. accommodating, the Ciliary muscles contract causing the lens zonules to relax which creates tension in the Crystalline lens, making it thicker, rounder and more convex in form.

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14
Q

The source of the tension is…

A

the pressure that the Vitreous and Aqueous humour exert onto the sclera.

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15
Q

What is Schachar theory of the Accommodation Mechanism?

A

This proposed theory focuses on the idea that the lens is associated with increased tension via the Equatorial Zonules.

When the ciliary muscle contracts, Equatorial zonular tension is increased, causing the central surfaces of the crystalline lens to steepen, the central thickness of the lens to increase (anterior-posterior diameter), and the peripheral surfaces of the lens to flatten.

While the tension on equatorial zonules is increased during accommodation, the anterior and posterior zonules are simultaneously relaxing.

The increased equatorial zonular tension keeps the lens stable and flattens the peripheral lens surface during accommodation.

As a consequence, gravity does not affect the amplitude of accommodation and primary spherical aberration shifts in the negative direction during accommodation.

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16
Q

When Unaccommodated, the Anterior and Posterior Crystalline lens radii are…

A

+10.00mm and -6.00mm

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17
Q

When Fully Accommodated, the Anterior and Posterior Crystalline lens radii are…

A

+5.50mm and -5.50mm

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18
Q

What is Coleman theory of the Accommodation Mechanism?

A

He proposed that the lens, Zonule and Anterior Vitreous comprise a diaphragm between the Anterior and Vitreous Chambers of the eye.

Ciliary Muscle contraction initiates a pressure gradient between the Vitreous and Aqueous compartments that support the Anterior lens shape.

The Anterior Capsule and the Zonule form a hammock shape surface that is totally reproducible depending on the circular dimensions.

The ciliary body directs the shape like a suspension bridge but does not need to support an equatorial traction force to flatten the lens.

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19
Q

What is the Near Triad Response?

A

3 motor responses when presented with a near object.

  1. Accommodation
  2. Convergence
  3. Meiosis - Pupil Constriction
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20
Q

What is the purpose of the Near Triad?

A

To ensure the clearest possible perception of light is ascertained.

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21
Q

Amplitude of Accommodation

A

This is the maximum amount of Accommodation that the eye can exert; from the far point where accommodation is fully relaxed to the near point where maximum accommodation is exerted.

22
Q

What is the equation for AoA?

A

Vergence, L at the Eye = 1 / Near point (m)

23
Q

If the far point is at infinity

A

(As in the case of Emmetrope and those wearing Optimal Refractive Correction for DV), then the measurement of the Near point allows the AoA to be determined with ease.

24
Q

An individual can only comfortable exert…

A

50% of the Available AoA.

25
Q

Standard reading distance is..

A

33-40cm

26
Q

Standard reading angle is..

A

45’ Down

27
Q

Amplitude of Accommodation Test -

A

For age 50yrs and Under

Push-Up/Pull-down method using the RAF rule.

28
Q

What are the logistics of AoA?

A

AoA gradually decreases with advancing age, and causes patients over the age of 45yrs to experience difficulty with near work and require reading glasses.

29
Q

The Measurement of AoA can help identify…

A

The appropriate reading add required to alleviate the patient’s near visual problems.

30
Q

AoA at age 55-60 becomes __

A

0

31
Q

If you obtain a measure for AoA in patients over 60yrs of age then..

A

You are measuring their Depth of Focus and NOT Accommodative Amplitude.

32
Q

Push-Up Amplitude

A

Method in which a target is brought closer and closer to the patient’s eyes until it first blurs.

33
Q

Pull-down Amplitude

A

Method in which you pull the target away from the patient’s eyes until it first becomes clear.

34
Q

Sheard’s Technique

A

Modification to Pull-down method which involves inserting a -4.00D lens before the eye before the test is carried out.

This alternative involves using increasing amount of minus spherical lens power until distance vision blurs.

35
Q

Explain the procedure for AoA:

A

1) Room lights on
2) Patient wears optimal distance correction if required.

3) Explain:
“I am going to measure your focusing power.”

4) You should sit directly in front of the patient to allow a simultaneous, unobstructed view of the 2 eyes.
5) Place RAF rule against patients face
6) Angle RAF rule down to mimic reading position.
7) Roll the barrel so that the lines of the text are facing the patient.
8) Illuminate reading card of RAF rule by directing an anglepoise lamp over patients’ shoulder so there are no shadows.
9) Occlude LE and measure RE

10) Ask:
Look at the smallest print you can see. I am going to move it closer. Tell me when it first becomes blurred.”

11) Push card slowly towards the patient – When they report blur Ask:
“Try and make it clear again.”

12) Push card forward until blur is sustained = Push-up Amplitude

Note this value in dioptres using RAF rule

13) Push card further forward and then pull it slowly away from the patient and Ask:

“In a moment, I am going to ask you to close your eyes. When you open them there will be a letter/target right in front of your eyes. At the start, it will be too close for you to name but I will start to move it away. It is very important that you tell me what the letter is as soon as you can see it.” = Pull-down Amplitude

Note this value in dioptres using RAF rule

 Repeat with LE and then BE

36
Q

How to calculate the AoA from RAF Rule?

A

Average of both values

37
Q

What to do if AoA is being measured on Older Presbyopes?

A

If the test is to be performed on Older Presbyopes they should wear a partial addition like +1.00 for 45-55yrs to ensure they can see the stimulus at the end of the near point rule.

38
Q

Amplitude can be artificially raised by…

A

Depth of focus i.e. Small pupils

39
Q

How to minimise Depth of Focus error in young patients?

A

Can put -3.00DS lens in front of young patients eyes so the Near point is moved further away from the spectacle plane.

40
Q

If Amplitude is more than 1.50DS lower than expected for Age (read off RAF rule) then ________

A

Accommodation Insufficiency is suspected.

41
Q

Binocular Amplitude are always higher than monocular by ___

A

1-2D as the Convergence response helps to induce Additional accommodation = Convergence Accommodation

42
Q

The patient IS presbyopic if..

A

The Amplitude of Accommodation is reduced to a level below 5.00D in a patient aged over 40yrs wearing optimal distance correction but who has difficulty reading,

43
Q

What is Presbyopia?

A

Where there is a normal age-related reduction in AoA and thus reaches a point where clear near vision cannot be sustained.

44
Q

Presbyopic Sxs normally occur in mid-40’s when…

A

Amplitude reaches around 3D.

45
Q

The Near Triad is under the control of the

A

Edinger-Westphal nucleus

46
Q

The Afferent limb of the reflex

A

is through the Optic Nerve

47
Q

The Efferent limb

A

involves the Edinger Westphal nucleus and the Oculomotor nerve.

48
Q

https://www.ncbi.nlm.nih.gov/books/NBK542189/

A

https://www.ncbi.nlm.nih.gov/books/NBK542189/

49
Q

Synkinesis

A

Coordination between the 3 motor responses

50
Q

Tonic Accommodation

A

The natural refractive state of the eye in darkness is low Myopia (-1.00DS) or when viewing down a Microscope.

51
Q

Tonic Accommodation

A

Dark Focus

Instrument Myopia

Optometry (41 decks)

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