The Near Response 1 and 2

Question 1

The Near Triad

Answer 1

convergence, accommodation and pupil myosis

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

Question 2

Subjective measurement

Answer 2

• Accommodation can be measured using the RAF rule or done in free space. This is known as the near point of accommodation and accommodative facility.
  Objective measurement- Done using the dynamic retinoscopy and autorefractors (Shin Nippon, PlusoptiX)

Question 3

Near point of accommodation

Answer 3

Maximum increase in optical power that an eye can achieve in adjusting its focus from far to near

Question 4

Calculation for emmetropes

Answer 4

Accom (D)= 1/ far point (m)- Accom (D)= 1/ near point

Question 5

Minus lens method

Answer 5

1. Tested monocularly
2. Patient fixates a small target at near or distance wearing refractive correction
3. Minus power lenses are introduced in 0.25D steps
4. Patient reports when letters become and remain blurred
   Near/distance not comparable
   (Momeni-Moghaddam et al 2013)

Question 6

Minus lens addes to induce…

Answer 6

Blur

Question 7

Minus lens added examples

Answer 7

-4.00 DS

-4-2.5= -6.5D
Minus lens amplitude= 6.5D
Testing distance 40cm/ 2.5 dioptres
1/0.4(m)
= 2.5 D

NOTE- Since the test is done at 40cm subtract working distance 2.5D from -4DS

Question 8

RAF rule instructions

Answer 8

Instruct patient to let you know when text starts to blur as this is the end point
Do RAF rule instructions matter?

Question 9

Goodall & Firth, 2003 findings

Answer 9

Found a clinically significant difference of 6.8cm between the point at which text blurs and the point at which it becomes indistinguishable in early presbyopia subjects.

Question 10

Recommendations of RAF

Answer 10

1) With target far from eyes and move forwards (Conventional method, clear to blur)
2) With target close to eyes and move back (Modified push-up method, blur to clear)

Question 11

What is the end point

Answer 11

NOTE- End point is when blur first noticed.

Question 12

RAF rule literature

Answer 12

Modified push up method
Better for young children as difficult to understand blur.
(Scheiman and Wick, 1994)

Easier to judge end point
(Esmail & Arblaster, 2016)

Question 13

Repeatability of RAF rule

Answer 13

Conventional method had poor test-retest in children 6 - 10 years. Variation of 3.1D found.
(Adler et al, 2013)
Conventional method gave significantly closer NPA (on average 0.73cm) in RE, LE and BEO but no clinically significant difference. Modified and Conventional push-up methods are not interchangeable.
(Esmail & Arblaster, 2016)
The 2 methods are similar in adults and children (but both different to minus lens method).
(Taub & Shallo-Hoffmann 2012)

Question 14

Accomodative facility

Answer 14

The ability to rapidly change accommodation to various stimuli.
Tested with flipper lenses.

Question 15

Accomodative facility method

Answer 15

Can be tested binocular (mostly) and monocular, near and distance.
Pt should wear refractive correction
Present +2.00DS lens
Allow patient time to clear target
Present -2.00DS lens
Allow patient time to clear target
Repeat for 1 minute
Record number of cycles in 1 minute

Question 16

Recording accommodative facility

Answer 16

Accomm facility +/-2DS 12cpm
Tested with +2 flipper lens and mostly tested binocular

Question 17

Accommodative facility norms 3 studies

Answer 17

Pandian et al (2006) in 1328 5-8 y/o:
– 7 cycles per min monocularly at near and in distance
– 5.5 cpm monocularly 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 7.3cpm to 10.4 cpm on 2nd test
– Recommendation: Should test binoc only
3 cycles more achieved on 2nd test monocularly in Horwood and Toor (2014)

Question 18

Dynamic RET methods

Answer 18

Monocular estimation method MEM- lens used
NOTT- RET distance moved

Question 19

MEM method

Answer 19

Patient fixates on target (at 40cm) attached to retinoscope
Lenses are used to neutralise reflex
Record dioptric value of lens at neutralisation

Question 20

MEM end result

Answer 20

End result:
+ve lens = lag of accomm (under accommodating)
-ve lens = lead of accomm (over accommodating)
Normal values are between +0.25 D and +1.00 D of accomm lag- accommodative lead is abnormal

Question 21

With V Against

Answer 21

With motion → plus lens
Against motion → minus lens

Question 22

Not retinoscopy

Answer 22

Patient fixates on target (often 40cm)
Distance of retinoscope moved to neutralisation point
With motion → move closer to the patient
Against motion → move further away from the patient

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

If target is 40cm and neutral point is 60cm there is… accommodative lag

Nott retinoscopy further
If target is at 40cm and neutral point is at 60cm, calculate the accommodative lag:
= 1/(0.4(𝑚)) - 1/(0.6(𝑚))
= 2.5D - 1.67D
= 0.83D

Is this normal?- Target is point of neutralisation

Question 23

Autorefractors

Answer 23

Measurement of refractive power change- accommodation is measured as myopic refractive change

Question 24

PROS AND CONS OF subjective methods and dynamic RET?

Answer 24

PROS- quick and engaging for children
CONS- poor fixation in nystagmus, high refractive error and can get damage

Question 25

Accommodation in research

Answer 25

1) Initial non-linear portion
2) Linear but showing a lag of accommodation
3) Response to stimulus reduces
4) No further accommodation as stimulus increased

• Accom response less than demand

Question 26

Response is less than demand in…

Answer 26

Hypo-accommodation seen in children, accommodative response is less than demand
More so in corrected hypermetropes (Horwood and Riddell 2011

Question 27

Main components to accommodation and convergence

Answer 27

Disparity

Question 28

Does accommodation drive convergence?

Answer 28

Accommodation does not drive vergence, neither does vergence drive accommodation, but both are driven by a combination of cues from the outside world

Question 29

Which factors causing accommodation can be isolated

Answer 29

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

Question 30

Open loop mechanism

Answer 30

Feedback loop broken
Allows individual parts of accomm function to be measured
i.e. Unable to tell if target becomes blurred so eliminates accomm due to blur

Opening the loop causes blur
Gabor/ Difference of Gaussian
-No stimulus for accomm, Eliminates blur
Pinhole (0.5mm)
-Dist target, Eliminates blur
Ganzfeld field
-Illuminated empty field with no focusable contours, Eliminates blur

Question 31

Proximal accommodation

Answer 31

• Rosenfield et al (1991) show that proximally induced accommodation occurs for targets up to 3m away
• 3D accommodation at 20cm
• Graph: Mean open loop
  accommodative response drops off after 3m, plotted against target position

Question 32

Blur driven accommodation

Answer 32

“Blur is the subjective awareness that the edges of a high contrast image are indistinct.” (Horwood, 2022) +ve and –ve retinal image blur is identical

Question 33

Chromatic effects

Answer 33

Fincham and Walton (1957) suggested chromatic aberrations give a cue as to direction of accommodation adjustment necessary.
* Retinal images have subtle colour fringes, not visible on a conscious level.
* This is due to the spectrum of foci of a retinal image.
* Short wavelengths (e.g. blue 400nm) focus much further forward in the eye than long wavelengths (e.g. red 700nm).
* Red fringe retinal image: focus behind the retina
(under-accommodation).
* Blue fringe retinal image: focus in front of the retina
(over-accommodation).
* Monochromatic light (chromatic aberration neutralised) showed: accommodation was less accurate.
* Reduced sensitivity to blur (Kruger and Pola 1986)

Question 34

Two pilots both have excellent visual acuity in the examining room. However, at night one can consistently detect and identify targets faster than the other…
WHY?

Answer 34

Darkness reduces other cues

Question 35

Tonic accommodation TA

Answer 35

When visual stimulus is poor e.g. at night, the eyes adjust involuntarily for a distance determined by the individual amount of ‘tonic accommodation’.
Distance is usually intermediate and varies widely between individuals.

TA aka
* ‘resting focus’
* ‘tonus state’
* ‘dark focus’

Question 36

Leibowitz and Owens (1978) findings

Answer 36

Reported distribution of dark-focus values for 220 emmetropic/fully corrected college students. All measures were taken with a laser optometer in total darkness. There is a wide range. Average = 1.5 diopters, This corresponds to a focal distance of 67 cm. 1/1.5 = 0.67 m
Convert to cm 67 cm.

Question 37

Convergence accommodation

Answer 37

The amount of accommodation resulting directly from convergence of the eyes.
CA/C ratio assesses if a known amount of convergence results in excessive or defective convergence accommodation.

Question 38

Convergence us initiated with…

Answer 38

a base out prism

Question 39

CA/C ratio in region of

Answer 39

0.1D : 1PD
(Hirani and Firth, 2009 – their mean 0.13±0.04)
For every 10 PD of forced convergence, around 1D of convergence accommodation occurs and must be inhibited to maintain clear vision (relative negative accommodation).

Question 40

AC/A Ratio value

Answer 40

Its the amount of accommodative convergence
(measured in prism dioptres (PD)) occurring per dioptre of accommodation
4:1 or LESS
So for every 1D of accomm, there is 4PD of accommodative convergence

Question 41

Response AC/A Ratio

Answer 41

Response AC/A ratio measures the response and uses this in formula.
Response AC/A was higher than stimulus AC/A ratio:
x 1.08 (Alpern et al, 1959) – 4 subjects
x 1.23 (Gratton and Firth, 2010) – 16 orthoptic students
x 1.41*(Miyata et al, 2006) – 63 strabismic patients, 79% exo deviations

– mean was 1.41 higher, but large range (Miyata et al, 2006)

Strabismic patients:
46 patients with intermittent exotropia, 4 with exophoria, 8 with esophoria, and 5 with esotropia

Question 41

Stimulus AC/A Ratio assumption

Answer 41

assumes the change in accommodation (i.e. the response) which occurs when viewing a target through a minus lens is equivalent to the power of the lens used (i.e the stimulus). Response = stimulus.
e.g. assume 3D accomm for -3D lens

Often a lag of accommodation (response < stimulus)
e.g. 2.5D accomm for -3D lens
When plus lenses used for near often lead of accommodation as incomplete relaxation of accommodation (response > stimulus)
e.g. 4D accomm for -3D lens

Question 42

Cognitive accommodation; effort increases the level of accommodation

Answer 42

Francis et al (2003):
‘Effort-to-see’ affects vergence and accommodation levels
Instructions to concentrate vs space-out

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

Question 43

Asymmetrical accommodation

Answer 43

Accommodation was thought to be symmetrical between eyes, however this is not always the case. 23% Anisometropic amblyopic children studied had very asymmetrical or even inverse responses in amblyopic eye. Accommodated more in distance and relaxed accommodation for near.