AOV - final

What is the unique relationship between the accommodation and vergence systems? important

Accommodation and vergence systet are closely linked systems, which interact to keep things single and clear, especially during near vision. If we increase convergence, we will also increase accommodation!!!

• Near target → accommodation increases to keep the image clear.

• Near target → convergence increases to keep the image single.

• one cannot be tested without the other when evaluating function!!

Accommodation and vergence systems are assessed using the same four clinical domains

• posture

• amplitude

• range/reserves

• facility

What are the 4 aspects measured for both accommodation and vergence? What do these measure?

• Posture

  • Accommodation: lead vs lag (MEM/binocular cross cylinder)

  • Vergence: phoria/alignment

• Amplitude

  • Maximum ability

  • Accommodation: NPA

  • Vergence: NPC

• Range / reserves

  • How much extra response can be exerted or relaxed while maintaining function (clear/single binocular vision)

  • Accommodation: PRA/NRA

  • Vergence: PRC/NRC BI/BO fusional reserves (PFV/NFV

• Facility

  • Flexibility/speed/sustainability of changing response

  • Accommodation: lens flippers

  • Vergence: BI/BO prism flippers

describe what happens during accommodation (zonules, lens etc)

near target → zonules relax → lens width increases (accommodated lens)

distant target → zonules strained → lens width decreases

How do you measure the 5 aspects of accommodation?

• Posture

  • Binocular cross cylinder

  • MEM retinoscopy (monocular estimate method near retinoscopy

• Amplitude

  • NPA

• Relative accommodation

  • NRA/PRA at near

  • PRA at distance

• Facility

  • accommodative flippers

  • ±2.00 DS flippers first

  • ±1.00 DS only if patient cannot clear ±2.00

• Convergence accommodation

  • AC/A

what are 4 factors that stimulate accommodation. give clinical examples

1. blur → not focusing at the right distance, changing focusing target according to distance

2. Proximal awareness (if it’s up close I’ll likely have to read it) → awareness of something being close

3. Vergence movements → convergence stimulates accommodation

4. tonic accommodation → in the dark, or with no clear target, the eye rests at baseline focus (tonic accommodation) rather than true optical infinite

what innervates accommodation system? What neutransmitter acts on what receptor in what muscle(s)? What is the antagonistic pathway to accommodation

parasympathetic innervation

ACh mediated; muscarinic receptors; ciliary muscle and sphincter pupillae

sympathetic innervation

noradrenaline-mediated; relaxes ciliary muscle and dilates pupil

what impacts accommodation ability (can name like 3) … prob not that important and kinda obvious

1. AGE!

2. luminance → in dim light the accommodative response is reduced relative to accommodative demand

3. neurological deficit → ex CNIII probs

4. ametropia (ex. refractive error I think)

amplitude of accommodation in ppl with refractive error…. From best to worst. Why

myopes → emmetropes → hyperopes

myopes are good at accommodating because the power of their lens is already too high (focused Infront of retina). Less accommodation of the lens needed to view things at close distances.

what test measures combined evaluation of accommodation and vergence

Convergence accommodation (AC/A)

what is the binocular cross cylinder technique? What does it measure? How does it work? How to correct

measures accommodation posture (how accurately is the accommodative system focusing relative to where the visual stimuli is located?)

• patient observes a cross target at habitual reading distance (40 cm)

• binocular

• +/- 0.5D cross cylindrical power (at 90 degrees)

• if addition isn’t enough or eye is under-accommodated = horizontal lines clearer

  • referred to as lag

  • add until vertical lines are clearer

• if vertical lines are clearer the eye is over-accommodated

  • referred to as lead

  • add minus until horizontal lines are clearer

why are amplitude accommodative tests performed monocularly? (NPA)

If you did it binocularly, the result could be contaminated by vergence/fusion factors

what is a normal NPA value?

NPA ≥

15D − 0.25 × age

what are the normal facility values (prob not that important)

• monocular: 11 cpm ± 5; adults about 8 cpm

• binocular: 10 cpm ± 5; adults about 8 cpm

what are 5 accommodative dysfunctions and their signs? -important i think

1. insufficiency (not accommodating enough)

• high lag, low amplitude, poor facility

1. excess (accommodating too much)

• no log/maybe lead, high amplitude, fails + facility

1. spasm (stuck in accommodative state)- neurological parasympathetic NS dysfunction - overstimulation

1. ill-sustained (not strong enough)

2. infacility (too slow to change focus)

• slow facility

what could be some causes of the following:

A 21 yo university student presents to you with symptoms of intermittent blurred vision in lectures especially towards the end of semester and after looking close for lengthy periods

• accommodative excess or spasm

• accommodative infacility

define vergence

a vergence is the simultaneous movement of both eyes in opposite directions to obtain or maintain single binocular vision

what is vergence measured in?

prism dioptres

the vergence system can be affected by many factor. name 3 categories and give some exampeles

1. Anatomical factors

• EOM insertion

• size, shape of globe

2. Neurological

• any lesions affecting innervation of CNIII, IV, VI

3. general

• fatigue, alc, medication

what is tonic vergence?

baseline convergence of the eyes without visual stimuli or acommodation

• wiuthout tonic vergence, vergence sits aat

what do these tests measure?

vergence posture

how accurately are the eyes pointing relative to where the visual stimulus is located?

what is PRC and NRC? what does it measure. How to record

positive relative convergence

• how much extra convergence can the patient use while maintaining single binocular vision?

negative relative convergence

• How much extra divergence can the patient use while maintaining single binocular vision?

measures fusional vergences

• measure in blur/break/recovery

• Blur = target first becomes blurry

• Break = target becomes double / fusion is lost

• Recovery = you reduce the prism, and the patient reports the target is single again

ex. BO 10/16/10

would you do BI or BO first for NRC/PRC? Which one is which>

NRC (Base IN) should be first

then PRC (BO)

what is vergence facility? do the flippers use equal prisms? Why or why not

How quickly and efficiently can the vergence system change to uptake a convergence or divergence response on demand?

• no (Prism facility/flippers (12^ Base out & 3^ Base in))

• MORE base out (12) because our convergence ability is much better than our divergence ability

Minimum expected PRC/NRC measurements (near and distance): are expected PRC/NRC measurements lower at distance or near? WHY

PRC values > NRC values (eyes are better at converging than diverging)

PRC minimum expected

• Near: 10/16/10 BO

• Dist: 10/16/10

NRC minimum expected

• Near: 10/16/10 BO

• Dist: -/6/4

• much lower in the distance! When we are looking distant we can’t really diverge much further

normal posture/phoria values (near and distance)

near: 3 exo ± 3^

dist: 1 exo ± 1^

normal vergence facility values

near: 15 cpm

vergence dysfunctions and characteristic signs (just give one for each)

Dysfunction	Characteristic signs
Convergence insufficiency / CI	Near exo > distance exo; reduced PRC and BO facility; receded NPC
Convergence excess / CE	Near eso > distance eso; reduced NRC and BI facility
Divergence insufficiency / DI	Distance eso > near eso; reduced NRC at distance; distance blur/diplopia
Divergence excess / DE	Distance exo > near exo; reduced PRC at distance
Basic esophoria	Distance = near esophoria
Basic exophoria	Distance = near exophoria
Vergence infacility	Reduced BI/BO facility

what could explain this case?

A 45 yo woman presents with symptoms of intermittent diplopia and blur after reading more than 15 minutes when reading in bed • It doesn’t go away unless she stops and gets some rest

Vergence dysfunction?

Decompensated heterophoria?

Refractive error?

what must you test before testing accommodation and vergence? Why?

Binocularity! (e.g. cover test, stereopsis, VA difference)

What is AC/A and how is it used clinically?

AC/A = accommodative convergence / accommodation

How much convergence changes for each dioptre of accommodation.

• units Δ/D

does accommodative-convergence (AC/A) increase or decrease with age

AC/A = accommodative convergence / accommodation

• Accommodative-convergence increases with age (the amount of convergence generated per diopter of accommodation)

• This is likely due to the fact that our accommodation reduces with age and as a result the convergence response increases to compensate – so AC/A should increase as we get older

how does the AC/A test work? What are the steps?

We alter the amount of accommodation and measure vergence changes as a result of that change on pretence card (ex. relax + or stress -)

• prentice card (6 base down infront of eye)

• establish near reading

• repeat with +2, +1, -1, -2 flippers and document responses

in AC/A, would you expect more eso or exo readings with plus and minus lenses?

• + = relax accom, more exo

• - = strain accom, more eso

when accommodative demand increases (minus lens), what happens to the AC/A ratio and the amount of convergence that is created

• AC/A increases

• convergence increases with increased accommodative effort

what is PRA/NRA? what does it measure? how does it work

range/amplitude of accommodation

PRA - positive relative accommodation

• add minus lenses until the target becomes blurry

• measuring the amount of accommodation that can be EXERTED while maintaining binocular single vision, without changing the vergence

NRA - negative relative accommodation

• add plus lenses until the target becomes blurry

• The amount of accommodation that can be RELAXED while maintaining binocular single vision, without changing vergence

colour vision: opia vs anomaly

opia = missing cone photopigment

anomaly = anomalous cone photopigment

What are the main congenital colour vision deficiency types? (3 categories → 6 types)

Protan defects

• long-wavelength / “red” cone system

• protanopia = missing red cone photopigment

• protanomaly = anomalous red cone photopigment

Deutan defects

• medium-wavelength / “green” cone system

• deuteranopia = missing green cone photopigment

• deuteranomaly = anomalous green cone photopigment

Tritan defects

• short-wavelength / “blue” cone system

• tritanopia = missing blue cone photopigment

• tritanomaly = anomalous blue cone photopigment

what is the prevalence of congenital CVD?

8% in men (1/12), 0.5% in women

what is the most common colour vision defect (CVD) subtype

deuteranomaly (5%)

How does testing differ for congenital vs acquired colour vision defects? important

Congenital CVD

• binocular

• often stable

Acquired CVD

• may be monocular/asymmetric

• arises from damage along colour vision pathway

what colour vision test category is Ishihara?

Pseudoisochromatic plates

name three colour vision test categories (there are more but 3 should be fine)

1. pseudoisochromatic plates

• ishihara

• HRR

• F2

2. Arrangement tests

• D15, Adams, Lanthony, H16

• FM100

3. Anomaloscopy (colour matching)

4. Computerised testing

• CAD

• Konan CCT-HD

Occupational specific testing (testing to see if someone can do specific task)

• lanterns

• Wire tests

what test category gives us a definitive diagnosis?

Anomaloscopy

How are pseudoisochromatic plates designed? Are they good for detection or grading?

use colour camouflage

• designed using colour confusion lines

• lines along which someone with that particular deficiency will see the same colour

  • good for detection, not very reliable for grading

What are the 6 types of plates in the 24 plate edition? what do they see

• introduction plate

  • seen by all observers

  • checks VA sufficient

  • detects malingerers

• transformation

  • normal sees one figure, CVD sees different figure

• vanishing

  • CVD sees nothing

• hidden

  • CVD sees a figure, normal may not

• classification

  • attempts protan/deutan classification

    • Protans confuse red and grey- say “6” or (2) 6 • Deutans confuse purple and grey- say “2” or 2(6)

• tracing

  • for kids - trace with cotton bud

Pros and cons of Ishihara

pros:

• high sensitivity and specificity, not sensitive to luminance changes

  • sensitivity 1.0, specificity 0.98

cons:

• red/green testing only, no tritan plates

• Does not test severity - number of errors is not an index of severity

• diagnosis by type is not reliable

• some ppl combine dots when they shouldn’t’ but not necessarily indication of CVD

describe the HRR test. What is it useful for

Test Tritan defects, and diagnostic plates examines severity

like Ishihara but only symbols. Similar sensitivity and specificity

• may detect Tritan defects

• includes screening plates to test P, D and T

  • if a pass is obtained CV id normal

• 14 diagnostic plates provide type and extent (mild, moderate or severe) of defect

  • not perfect

What is the F2 plate used for? What would result indicate?

F2 plate may detect tritan defects.

Normal colour vision:

• sees 2 squares in correct location

• green clearer/more defined than blue

Possible tritan error:

• only sees blue, or blue is clearer

Not tritan error:

• only sees green

What is the Farnsworth D15 determine? What category is it?

D15: hue discrimination / arrangement test

Used to:

• separate mild CVD from moderate/severe CVD

• classify type by orientation of crossing errors

in D15, what will the patient place next to eachother if they have a CVD? what will this look ilike on the recording

colours lying on their confusion loci will be placed next to eachother

look like a crossing

How does D15 work? Principle and fail rate

• hue discrimination

• Principle: patients will place colours lying on confusion loci are placed next to each other.

• order of colours as arranged by the patient is recorded on a circular diagram

Fail:

• generally 2 or more diametrical crossings

Not significant:

• minor transposition error

• especially around colour 7

Compare D15, Lanthony, and H16, Adams

All use confusion-line principles at different saturation levels.

D15

• standard saturation

• moderate/severe screening

Desaturated = Adams and Lanthony

More saturated = H16

• more saturated

• only red-green

• fail = 3+ errors

What is the Farnsworth-Munsell 100 Hue test used for? What is it interpreted by? What type of CVD would it be good for

FM100 = hue discrimination / arrangement test

• patient arranges 85 closely spaced coloured caps in hue order

• interpreted by:

  • total error score (severity)

  • distribution of errors around the hue circuit (type P, D T)

• mild deficiencies may go undetected

what is the normal values for FM100? What is FM100 useful for?

take square root of total error score

• normative values change with age!

• useful for acquired CVD

what test is a coloured cap mixed in with neutral greys? What does this test provide indication of?

Mollon Reffin Minimalist

• Coloured cap mixed in with neutral greys and patient needs to identify it

• good for kids

Provides an indication of severity along protan, deutan and tritan axis

what is the gold standard test for diagnosis? What is

anomaloscopy

how does Anomaloscopy work? What are the 2 equations

Anomaloscopy - colour matching test by additive colour mixing w/ spectral colours.

Equations:

• Rayleigh equation match = red-green diagnosis

  • red/green mixture until it appears yellow

  • abnormal mixture of green/red: more green = DA, more red = PA

• Moreland equation match = blue-yellow diagnosis

Process:

• rough match

• bracket upper/lower limits

• plot matching range

What does the Medmont C-100 do?

Main function: differentiate protan vs deutan.

Patient views yellowish flickering light from alternating red/green LEDs and adjusts until flicker disappears/minimises.

Useful because:

• quick: 1–2 minutes

• inexpensive

• good sensitivity/specificity

• may detect female carriers of protan/protanomalous genes

IMPORTANT - in clinic, how would you screen/detect, assess severity, and diagnose

1. Detect = Ishihara, HRR, tritan plate test

• pass = normal CV

• fail = abnormal CV

1. Assess severity: Farnsworth D15 (pass = mild, fail = moderate to severe)

• pass = desaturated test

• fail = H-16 saturated test

1. Anomaloscopy or medmont c-100

• confirm protan, deutan, tritan

vergence system: define posture and give 2 clinical tests that can measure this

Posture: the resting alignment of the eyes relative to the visual target when fusion is disrupted. Ex. how accurately the eyes are pointing when they’re allowed to drift

• cover test

• Prentice card

• Von Grafe

• Maddox rod

vergence system: define amplitude and give a clinical tests that can measure this

amplitude: the maximum amount of convergence or divergence the system can do while maintaining single vision

• NPC

vergence system: define facility and give a clinical tests that can measure this (be specific)

facility: how quickly and efficiently can the vergence system switch between convergence and divergence demands. It reflects the speed of the vergence response.

• 12 base out and 3 base in flippers

vergence system: define reserves and give 2 clinical tests that can measure this

reserves: how much spare capacity of fusional vergence available beyond the patient’s habitual posture while maintaining clear and single vision.

• PFV/NFV

• BO (PRC) and BI (NRC) ranges at distance and near, measured in prism dioptres with blur/break/recovery

what is the normal range for AC/A test? How to calculate?

normal range = AC/A = 4prismD /D ± 2 (i.e. 2-6 prism diopters/D)

AC/A ratio = (phoria with additional minus lenses - baseline phoria) / power of additional minus lenses

accommodation posture: what it means and tests to measure

posture: Accuracy of the accommodative response: is the patient focusing on, behind (lag), or in front (lead) of the near target

• binocular cross-cylinder

• MEM retinoscopy

accommodation amplitude: what it means and tests to measure

amplitude: Maximum amount of accommodation the patient can generate

• NPA

accommodation reserves: what it means and tests to measure

reserves: spare capacity of the accommodative response. How much can accommodation be relaxed or stimulated while still maintaining a single and clear target?

• NRA/PRA

PRA - positive relative accommodation

• add minus lenses until the target becomes blurry

• measuring the amount of accommodation that can be EXERTED while maintaining binocular single vision, without changing the vergence

NRA - negative relative accommodation

• add plus lenses until the target becomes blurry

• The amount of accommodation that can be RELAXED while maintaining binocular single vision, without changing vergence

accommodative facility: what it means and how to measure

facility: how quickly and efficiently accommodation can change back and forth (when strained and relaxed)

• measured with ± 2 DS flippers first (if can’t clear then go to 1)_

NRA/PRA normal value

Normal range: +2.00 ±0.50 D

• similar for negative I think

normal binocular X cyl result

+0.5 ± 0.5

normal near and distance phoria values

near: 3 ExoP ± 3

distance 1 exo ± 1

normal near and distance NRC/PRC value (and what prisms do u use)

NRC

• measured in blur/break/recovery

near: 10/16/10 BI

distance: -/6/4 BI

PRC

• measured in blur/break/recovery

near: 10/16/10 BO

dist: 10/16/10 BO

normal vergence facility values

12BO/3BI

near: 15cpm

normal accommodation facility (monocular and binocular)

mono

• 11cpm ± 5SD (8cpm for adults)

bino

• 10 cpm ± 5 SD (8cpm for adults)

normal AC/A range?

2-6 prism diopters

what will happen to the AC/A ratio as we INCREASE negative lenses

AC/A ratio increases

• * Increases as we strain accom and with age

normal NRA/PRA values

PRA: -2.5 D (and higher)

NRA: +2.5D (and higher)