the near response

Question 1

what is the near train / near synkinesis

Answer 1

Each of the responses can occur independent of the others and hence term ‘synkinesis’ preferred rather than ‘reflex’

Convergence

Accommodation

Pupil miosis

Question 2

how is accommodation investigated

Answer 2

Subjective
Near point of accommodation (amplitude of accommodation)
Accommodative facility

Objective
Dynamic retinoscopy
Autorefractors (Shin Nippon, PlusoptiX)

Question 3

what is the amplitude of accomodation

Answer 3

Max accommodative ability of the eye
Near point of accommodation
(literature – called amplitude)

Range of accomm from far point to near point

Question 4

how to calculate amplitude of accomodation

Answer 4

Simple to calculate in emmetropes (or if wearing full refractive correction)
1/near point (m) e.g. 6cm = 1/0.06 = 16.7D
(Otherwise… amplitude accomm = 1/far point (m) – 1/near point (m))

Question 5

how are - lenses used for amplitude of accomodation

Answer 5

Some use minus lenses only
Target at near or distance
Lenses in 0.5D steps
Until notice blur
If done at near, take off working distance e.g. 40cm = 2.5D
Near/distance not comparable (Momeni-Moghaddam et al 2013)

Question 6

what are the limitations of the Raf rule

Answer 6

Blur or not able to read?
Goodall & Firth, 2003
Difference in end point if different instructions given?
Mean difference 6.8cm in early presbyopic subjects
Recommend end point is when blur first noticed

Modified push-up (or push down) method
Start with target close to eyes and move away until clear
Suggested in young children as difficult to understand blur (Scheiman and Wick 1994)

Question 7

repeatability and the Raf rule?

Answer 7

The 2 methods are similar in adults and children (but both different to minus lens method) (Taub & Shallo-Hoffmann 2012)
Conventional method poor test-retest in children
Aged 8.1 ±2.1 years
Variation 3.1D
Adler et al, 2013
Modified and Conventional push-up methods are not interchangeable (Esmail & Arblaster, 2016)
Conventional NPA significantly closer RE, LE and BEO
But clinically not significant – on average 0.73cm

Question 8

what is accommodative facility

Answer 8

Ability to rapidly change accomm to various stimuli

‘Flippers’
+2.00DS/-2.00DS
Alternated ensuring that target is cleared before change
Number of cycles in 1 minute

Recording:
Accomm facility+/-2DS 12cpm

Question 9

what is the normal range for accommodation facility

Answer 9

Pandian et al (2006) in 1328 5-8 y/o:
7 cycles per min monocularly at near and in distance
5.5 cpm monoculalry in myopes in distance
Greater cpm with increasing age
Adler et al (2018) in 136 4-12 y/o:
Binocular (11.6cpm) lower than monoc (12.7cpm)
Prone to practice effects in younger children
Horwood and Toor (2014) in 156 young adults:
Binoc accomm facility 9cpm
Monoc accomm facility prone to practice effects
Improved from 7.3 to 10.4 cpm on 2nd test
Should test binoc only

Question 10

what are the 2 methods of dynamic retinoscopy

Answer 10

Monocular Estimate Method (MEM) retinoscopy
(lenses)

Nott retinoscopy
(distance)

Question 11

what is mem retinoscopy

Answer 11

Lenses used to neutralise reflex when patient fixes on retinoscope (target attached)

Record dioptric value of lens

+ve lens = lag of accomm (under accommodating)

-ve lens = lead of accomm (over accommodating)

Question 12

what is not retinoscopy

Answer 12

Distance of retinoscope moved
to neutralisation point

Distance from target
calculated to give lead or lag
Neutral point behind target = lag accomm
Neutral point in front of target = lead accomm

E.g. target at 40cm and neutral point at 60cm
Accomm lag = 1/0.4m – 1/0.6m = 2.5D – 1.67D = 0.83D
Is this normal?

Question 13

what do autorefactors do

Answer 13

Measurement of refractive power change
Accommodation measured as myopic refractive change
Shin Nippon
PlusoptiX

Question 14

what is accommodative stimulus and response function

Answer 14

When presenting an accommodative stimulus to a participant how much do they actually accommodate?

Initial non linear portion

2 Linear but showing a lag of accommodation

3 Response to stimulus reduces

4 No further accommodation as stimulus increased

Question 15

what are component of accomodation

Answer 15

Proximal

Tonic

Blur

Disparity

Cognitive

Question 16

what are the main cues for convergence

Answer 16

Horwood and Riddell (2008, 2009)
Blur, disparity, proximity
Disparity is the main cue

Question 17

what is the main cue to accomodation

Answer 17

Blur, disparity, proximity
Disparity is the main cue
Not blur

Question 18

how is accomodation measured in laboratory conditions

Answer 18

Closed Loop
Normal conditions
Feedback mechanism
i.e. Know when something is blurred

Open Loop
Feedback loop broken
Allows individual parts of accomm function to be measured
i.e. Unable to tell if target becomes
blurred

Question 19

how to induce blur (open the loop)

Answer 19

Closed Loop
Normal conditions
Feedback mechanism
i.e. Know when something is blurred

Open Loop
Feedback loop broken
Allows individual parts of accomm function to be measured
i.e. Unable to tell if target becomes
blurred

Question 20

what is blur driven accomodation

Answer 20

+ve and –ve blur of retinal image identical – how do we know if too close or too far away?
Stimuli = chromatic aberration – gives cue as to direction of adjustment necessary
Fincham and Walton (1957)
Sense if higher contrast of a blue fringe or red fringe to determine if over or under accomm (not visible on conscious level)
If use monochromatic light (chromatic aberration neutralised) accomm less accurate
Reduced sensitivity to blur (Kruger and Pola 1986)

Question 21

what is proximal accomodation

Answer 21

Rosenfield et al (1991) show that proximally induced accommodation occurs for targets up to 3m away

3D at 20cm

Graph: Mean open loop
accommodative response
plotted against target
position.

Question 22

what is tonic accomodation

Answer 22

Dark focus/accomm

Resting point of accomm

Mean 0.9 to 1.2 D

Rosenfield et al (1993)
Tonic accomm in 220 students, measured with laser optometer, found mean 1.52D

Question 23

what is convergence accomodation

Answer 23

Produced as the eyes converge

Value in region of 0.1D/Δ
(for review see Hirani and Firth, 2009 – their mean 0.13±0.04 D/Δ)

Thus for every 10Δ of forced convergence, around 1D of accommodation occurs and must be inhibited to maintain clear vision (relative negative accommodation).

Question 24

what is the act ratio

Answer 24

Stimulus AC/A ratio: Assumes response is equal to stimulus (e.g. 3D lens, assume 3D accomm)

Response AC/A ratio: Measures response and uses this in formula

Response AC/A higher
x 1.08 (Alpern et al, 1959) – 4 subjects
x 1.23 (Gratton and Firth, 2010) – 16 orthoptic students
Strabismics – mean x 1.41 higher, but large range (Miyata et al, 2006)

Question 25

what is cognitive accomodation

Answer 25

Recognised that mental effort increases the level of accommodation

Francis et al (2003):
‘Effort-to-see’ affects vergence and accommodation level….Instructions to concentrate v space-out

Horwood and Toor (2014); Horwood et al (2014):
Compared accomm in various exercise groups
‘Effort’ had most significant improvement on accomm (and convergence)

Question 26

what is asymmetrical accomodation

Answer 26

Asymmetrical accommodation is a condition where the two eyes are not properly aligned when focusing on an object, resulting in different levels of accommodation in each eye. In other words, one eye focuses more than the other eye, causing a difference in the clarity of the image between the two eyes. This can lead to discomfort, eye strain, and blurred vision, and can occur in people with certain eye conditions such as strabismus (eye turn) or anisometropia (unequal refractive error).

Question 27

what are the two pathways of the light reflex

Answer 27

Afferent pathway
Pupillary fibres travel with visual fibres but leave them before the LGN to go to pretectal area, synapse here and fibres then go to Edinger-Wesphal nucleus

Efferent pathway
From Edinger-Westphal nucleus fibres travel with 3rd nerve to ciliary ganglion and then enter eye by short ciliary nerves.

Question 28

describe the afferent pathway of pupillary constriction

Answer 28

Retina

optic nerve

optic chiasma

optic tract

prectectal nucleus

parasympathetic oculomotor nucleus

Question 29

describe the efferent pathway of pupillary constriction

Answer 29

oculomotor nerve - nerve to inferior oblique , cillera ganglion, short cillary nerve , sphincter papillae and cillaris muscle

Question 30

what is the afferent pathway of the near reflex/ synkinesis

Answer 30

Afferent pathway
Probably follows the visual pathway to the striate cortex from where information is relayed to the frontal eye fields, then to the oculomotor nucleus and the Edinger Westphal nucleus, bypassing the pretectal nuclei.

Efferent pathway
As per light reflex

Question 31

how to test pupils for near reflex

Answer 31

For near reflex
Observe constriction of pupil on stimulus approach
Should be symm and equal, and occur whether or not either eye covered.

Question 32

how to test pupils for light reflex

Answer 32

For light reflex
Patient fixes dist target. Light introduced
Direct: Constriction observed in eye into which light shone
Consensual: Constriction of fellow eye should be equal
PERL

Question 33

what is the swinging list test

Answer 33

Used to detect relative afferent pupillary defect (RAPD)
Light swung from one eye to other and held there for approx 3 secs
Initial constriction should be seen followed by very slight dilation (pupillary escape)
RAPD – pupils dilate when light swung from unaffected eye to affected eye

Question 34

what does a +ve rapd on a swinging light test indicate

Answer 34

+ve RAPD - differences between the eyes in the afferent pathway
E.g. due to retinal or optic nerve disease

If the light used is sufficiently bright, even a dense cataract or corneal scar will not give a RAPD as long as the retina and optic nerve are healthy