Accomodation

Question 1

Why is accommodation important?

Answer 1

A dynamic process to produce and maintain a focused retinal image

The power of the lens changes to maintain the image.

The lens curvature changes, the lens power changes and focusing changes.

Question 2

The Accommodative Process

Answer 2

There is a change in the shape which leads to a change in the power of the lens

This allows objects at various distance to be focused at the retina.

The only active element is the ciliary muscle, while other parts are passive

Question 3

What is the only active element of Accommodation?

Answer 3

The ciliary muscle, the rest are passive

Question 4

What allows objects at various distances to be focused on the retina?

Answer 4

Change in shape that leads to a change in power of the lens

Question 5

Smooth muscle with parasympathetic innervation

Answer 5

Ciliary muscle

Question 6

In accommodation, the ciliary muscle does what?

Answer 6

The ciliary body contracts and moves forward

The contraction releases the resting tension on the zone less around the lens equator

The lens capsule is able to mold the lens to become more spherical

Question 7

Function of the lens capsule

Answer 7

To mold the lens to become more spherical

Question 8

Biomechanics of the accommodative process

Answer 8

Innervation to the ciliary muscle

Ciliary muscle contracts

Ciliary muscles moves inward and forward

Ciliary ring advances along the ciliary muscle

Choroid and posterior zone lens stretch

Anterior zonular tension decreases, and the zonules relax

Lens capsule mold the crystalline lens, lens becomes more spherical

Lens power increases and focal length decreases

Eye changes focus from distance to near

Question 9

Accommodation occurs when:

Answer 9

The overall power of the lens increases.

Process:

• Equatorial diameter decreases
• anterior lens surface moves forward while posterior surface moves backward
• central anterior radius of curvature becomes more steep
• central posterior radius of curvature decreases
• central thickness increases
• lens sinks 0.3mm due to gravity

Question 10

Parasympathetic pathway to ciliary muscle

Answer 10

Unfocused image on the retina
Blur signals transmitted to visual cortex
Cortical cell produce sensory blur signals
Signal goes to midbrain/oculomotor nucleus/Edinger-Westphal nucleus
Motor command transmitted to ciliary muscle
Ciliary muscle contraction
Crystalline lens deforms to produce an in focus retinal image

Question 11

Where does the parasympathetic pathway start for the ciliary muscle?

Answer 11

Midbrain/oculomotor nucleus/Edinger-Westphal nucleus

Question 12

How is the motor command transmitted to the ciliary muscle?

Answer 12

Oculomotor nerve (CN3) -> ciliary ganglion -> short ciliary nerve -> ciliary muscle

Question 13

Parasympathetic pathway to the ciliary muscle is coupled with..

Answer 13

Pupillary function

Question 14

When there is no accomodation, the anterior and posterior capsule is..

Answer 14

Taught and flat

Question 15

When there is no accommodation, the ciliary muscle is..

Answer 15

Relaxed

Question 16

What type of eye focuses on a distant target with no need for accommodation? What is the convergence?

Answer 16

Unaccommodated Emmetropic eye

Zero

Question 17

With a near object, the object has _________ rays, leading to an unfocused image on the retina.

The optical power in the eye has to ________ to add positive convergent rays.

Answer 17

Diverging

Increase

Question 18

In the accommodative eye, the image is in focus because of the:

Answer 18

Accommodating lens

Question 19

When an eye accommodates from infinity to a target at 1m (100cm) from the eye, it requires ____ of accommodation (100/100)

Answer 19

1D

Question 20

Accommodation is measured in:

Answer 20

Diopters

Question 21

3 physiological changes in accomodation

Answer 21

1. Eye accommodation
2. Pupil constriction
3. Eye converge

AKA Near Reflex

Coupled with parasympathetic innervation from EW nucleus

Question 22

Convergence, accommodation and pupil constriction occur in..

Answer 22

Both eyes.

Even if stimulus is in one eye

Question 23

Reasons for change in pupil size

Answer 23

1. Controls light
2. Modifies depth of focus
3. Varies any optical aberration

Question 24

Corneal reflex in distance in near fixation

Answer 24

Reflex is nasally in distance fixation

Reflex is temporally in near fixation due to convergence

Question 25

Components of Accommodation

Answer 25

Reflex accommodation Vergence accommodation Tonic accommodation Proximal accommodation

Question 26

An automatic adjustment of the refractive state to maintain a focused retinal image

Answer 26

Reflex accommodation

Question 27

When does reflex accommodation occur?

Answer 27

When responding to blur, or reduction in contrast.

Question 28

When and why is reflex accommodation important?

Answer 28

Important for small scanning eye movements/micro saccades Very important because it makes the fine change under binocular and monocular condition

Question 29

The change in accommodation induced during fusion all vergences

Answer 29

Vergence accomodation Leads to convergence accommodation/convergence ratio (CA/C)

Question 30

The refocusing that occurs due to apparent nearness (or perceived proximity) of a target

Answer 30

Proximal accommodation Activated by perceptual cues Stimulated by targets within 3 m of individual

Question 31

"Lead of accomodation" The residual/resting level of accommodation Due to baseline stable innervation input from the midbrain

Answer 31

Tonic accomodation Accommodation at rest (0.5 to 1.5 D) Present even in absence of blur, disparity, and proximal cues Reduces with age

Question 32

Factors that affect accommodation

Answer 32

``` Blur Convergence Proximal issues Pharmacology Minus lens Diseases ```

Question 33

Retinal image factors to accommodation

Answer 33

Contrast Spatial frequency Retinal image motion

Question 34

Nonretinal factors to accommodation

Answer 34

Mood Voluntary effort Target luminance Training

Question 35

Type of medication sued best for antagonizing accommodation

Answer 35

Muscarinic blockers

Question 36

Prevent acetylcholine from binding

Answer 36

Muscarinic blockers

Question 37

Common used muscarinic blockers

Answer 37

Tropicamide and cyclopentolate

Question 38

Has a very short half-life and should not be used to determine the cycloplegic refraction

Answer 38

Tropicamide

Question 39

Effective with sufficient half-life, commonly used in kids

Answer 39

Cyclopentolate

Question 40

Other muscarinic blockers used that produce mydriasis and loss of accomodation

Answer 40

Atropine (iritis) Homatropine Scopolamine

Question 41

A sympathomimetic that causes mydriasis but has no significant effect on accomodation

Answer 41

Phenylephrine (adrenaline)

Question 42

Other drugs that affect accomodation

Answer 42

``` Alcohol Ganglion blockers Antidepressants Stimulants Marijuana Carbonic Anhydrase Inhibitors Antihistamine Morphine ```

Question 43

Conditions that affect accommodation

Answer 43

``` Diabetes Traumatic Brain Injury (TBI) Multiple Sclerosis Myasthenia Gravis Botulism Down syndrome Glaucoma Iritis Iris Sphincter tear Eye trauma Adie’s tonic pupil Encephalitis Syphilis Neuro-ophthalmic lesions ```

Question 44

Gradual age-related irreversible loss of accommodative amplitude

Answer 44

Presbyopia

Question 45

When is presbyopia usually reported?

Answer 45

40-45 years of age

Question 46

Complete loss of accommodate, due to presbyopia, usually by

Answer 46

50-55 years

Question 47

There's about a _____ loss of accommodation per year due to presbyopia

Answer 47

2.5 D

Question 48

Complaints related to presbyopia

Answer 48

receded near point of accommodation blurred vision discomfort and asthenopia at near.

Question 49

Contributing factors and biochemical changes that lead to the decrease of accommodation

Answer 49

lens thickness and size increases springiness of capsule decreases (thickens) anterior surface curvature increases stiffer lens ciliary muscle remains stable cortex stiffens zonules become less dense (number of them)

Question 50

Factors that do not change in presbyopia:

Answer 50

Zonules still have their elasticity Ciliary muscle still functions Motor neuronal pathway still functions

Question 51

How do you treat presbyopia?

Answer 51

Plus lenses

Question 52

Forms of treating presbyopia

Answer 52

Bifocals, reading glasses, mono vision or bifocal contact lenses, or surgical correction

Question 53

Typical add powers based on age:

Answer 53

Early 40s - +1.00 to+1.25 45 - +1.50 50 - +2.00 55 - +2.25 60 and above - +2.50

Question 54

Other accommodative conditions

Answer 54

Accommodative excess Accommodative infacility Accommodative insufficiency

Question 55

Result of other accommodative conditions

Answer 55

Result of medication, illness, or accommodative anomaly

Question 56

Treated with proper distance correction and VT

Answer 56

Accommodative excess

Question 57

treated with Proper correction and VT

Answer 57

Accommodative infacility

Question 58

Treated with proper distance correction and additional plus lenses

Answer 58

Accommodative insufficiency

Question 59

Amount of convergence induced by a change in accommodation

Answer 59

AC/A Accommodation convergence/Accommodation Ratio

Question 60

A change in accommodation is accompanied by a change in:

Answer 60

Vergence

Question 61

In accommodation there is:

Answer 61

Convergence

Question 62

With no accommodation there is:

Answer 62

Divergence

Question 63

Abnormal AC/A ratios are seen in:

Answer 63

Binocular problems

Question 64

2 ways of measuring AC/A ratio

Answer 64

Gradient determination Near-far (calculated) determination

Question 65

Gradient determination of AC/A ratio

Answer 65

Phoria is measured at the same near distance (40cm), but with different lenses to change the accommodative demand This can be done in the phoropter or with Modified Thorington, through the subjective refraction Remind the patient to keep the near point target clear to maintain accommodation. Have the patient read the letters Measure the phoria Then measure the phoria again through -1.00D lenses added to the refraction The difference in prism diopters between the phoria with the subjective and the phoria with the -1.00 is the change in convergence That is – this is how convergence responses to the accommodative stimulus

Question 66

Gradient determination of AC/A calculation

Answer 66

(Phoria with minus lens power - baseline Phoria)/absolute power of addition minus lens

Question 67

What is the expected gradient determination of AC/A

Answer 67

3/1 to 5/1 Or 4:1 with SD +/- 2

Question 68

Near-far/calculated AC/A ratio

Answer 68

PD(cm) + NFD (P'near -Pdistance) PD = interpupillary distance in cm NFD = near fixation distance in meter P'near = near Phoria (eso is plus and exo is minus) Pdistance= distance Phoria

Question 69

Calculated near-far AC/A is usually ________ than the gradient AC/A because of:

Answer 69

Larger Due to the proximal vergences that influence the near phoria

Question 70

A high AC/A ratio means: A low AC/a ratio means:

Answer 70

Excess convergence with accommodation Low convergence with accommodation