The Near Response Flashcards
What is the Near Triad/Near Synkinesis?
- Convergence
- Accommodation
- Pupil Miosis
(As each of the responses can occur independently of the others, the term ‘synkinesis’ preferred opposed to ‘reflex’)
What is a subjective measurement of accommodation?
- Near point of accommodation
- Amplitude of accommodation
- Accommodative Facility
What is a objective measurement of accommodation?
- Dynamic Retinoscopy
- Autorefractors (Shin Nippon, PlusoptiX)
What is the Amplitude of Accommodation?
Maximum increase in optical power that an eye can achieve in adjusting its focus from far to near
Aka. Near point of accommodation (in the literature)
How do we calculate amplitude of accommodation in emmetropes/fully corrected eyes?
Near point = 6cm
Accommodation (D) = 1/near point (m)
e.g. if near point was 6cm
1/0.06 - 16.7 (D)
How do you calculate amplitude of accommodation when not at optical infinity?
1/far point (m) = Accommodation (D)
MINUS
1/near point (m) = Accommodation (D)
What did Momeni-Moghaddam et al (2013) find in minus lens method?
Near/distance not comparable according to research (amplitude at distance lower than at near)
What is the calculation in the minus lens method?
Minus lens added – (1/testing distance) = minus lens amplitude (ignore the – sign)
How do we test the minus lens method?
- Tested monocularly
- Patient fixates a small target at near or distance wearing refractive correction
- Minus power lenses are introduced in 0.25D steps
- Patient reports when letters become and remain blurred
What does the minus lens method test?
Way of measuring amplitude of accommodation
What is not comparable when using the minus lens method?
Near/distance not comparable according to research (amplitude at distance lower than at near)
(Momeni-Moghaddam et al, 2013)
What is the minus lens amplitude when the minus lenses added to induce blur was a -4DS lens and testing distance was 40cm?
Minus lens added – (1/testing distance) = minus lens amplitude (ignore the – sign)
(-4D) - (1/0.4)
(-4D) - (2.5D) = -6.5D
Minus Lens Amplitude = 6.5D
What did Goodall & Firth (2003) find about the RAF rule?
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 presbyopic subjects.
= End point is when blur is first noticed
When would we use the modified push-up method?
- Better for young children as difficult to understand blur.
(Scheiman & Wick, 1994) - Easier to judge end point
(Esmail & Arblaster, 2016)
What did Scheiman & Wick (1994) find out about the modified push-up method?
Better for young children as difficult to understand blur.
(Scheiman & Wick, 1994)
What did Esmail & Arblaster (2016) find out about the modified push-up method?
Easier to judge end point
What do we know about the repeatability of the RAF?
- 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)
What did Adler et al. (2013) find out about the repeatability of the RAF rule?
Conventional method had poor test-retest in children 6 - 10 years. Variation of 3.1D found.
What did Esmail & Arblaster (2016) find out about the repeatability of the RAF rule?
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.
What did Taub & Shallo-Hoffman (2012) find out about the repeatability of the RAF rule?
The 2 methods are similar in adults and children (but both different to minus lens method).
What is Accommodative Facility and what do we use to measure it?
The ability to rapidly change accommodation to various stimuli.
Tested with flipper lenses.
What is the method for testing accommodative facility?
- Can be tested binocular 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
What is 1 cycle of in accommodative facility?
- Present +2.00DS lens
- Allow patient time to clear target
- Present -2.00DS lens
- Allow patient time to clear target
How do we record accommodative facility?
Recording:
E.g.
Accomm facility+/-2DS 12cpm
What did Pandian et al. (2006) find out about accommodative facility norms?
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
What did Adler et al. (2018) find out about accommodative facility norms?
In 136 4-12 y/o:
- Binocular (11.6cpm) lower than monoc (12.7cpm)
- Prone to practice effects in younger children
What did Horwood & Toor (2014) find out about accommodative facility norms?
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
Should you test accommodative facility binocularly or monocularly?
Recommendation: Should test binoc only
What are the two methods of dynamic retinoscopy for testing Accommodative lag?
- Monocular Estimate Method (MEM) retinoscopy
(lenses used) - Nott retinoscopy
(ret distance moved)
How do we do the monocular estimate method (MEM)?
- Patient fixates on target (at 40cm) attached to retinoscope
- Lenses are used to neutralise reflex
- Record dioptric value of lens at neutralisation
With motion → plus lens
Against motion → minus lens
What does it mean if you have a plus lens in the Monocular Estimate Method?
Plus lens = lag of accomm (under accommodating)
What does it mean if you have a minus lens in the Monocular Estimate Method?
Minus lens = lead of accomm (over accommodating)
What are the normal values of accommodative lag?
Normal values are between +0.25 D and +1.00 D of accomm lag
How do we do Nott Retinoscopy?
- Patient fixates on target (often 40cm)
- Distance of retinoscope moved to neutralisation point
With motion (under-accommodating) → move further away from the patient
Against motion (over-accommodating) → move closer to the patient
How do we get Nott Retinoscopy to calculate lead or lag?
- 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 a target is at 40cm and neutral point is at 60cm is there accom lead or accom lag?
1/0.4(m) - 1/0.6(m)
2.5D - 1.67D
= 0.83D
= Normal
What are the advantages and disadvantages of autorefractors?
Adv:
- Quick
- Non-Verbal/Understanding - Portable
Disadv:
- Not as accurate – it’s an estimation
- Need to be looking /fixation
- Blinking and alignment an issue
- Nystagmus an issue
- Struggles with high refractive error
When presenting an accommodative stimulus to a participant how much do they actually accommodate?
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
What did Horwood & Riddell (2011) find out about accommodative stimulus/response function?
Hypo-accommodation seen in children, accommodative response is less than demand
More so in corrected hypermetropes
What are the components of accommodation?
- Proximal
- Tonic
- Blur
- Disparity
- Cognitive
What is the main cue to convergence and the main cue to accommodation?
Disparity (compared to blur and proximity - Horwood & Riddell, 2008)
What is a closed loop measurement under lab conditions of accommodation?
Closed Loop
- Normal conditions
- Feedback mechanism
- i.e. Know when something is blurred
What is an open loop measurement under lab conditions of accommodation?
Open Loop
- 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
This is to isolate factors causing accommodation
What are the methods for opening the loop (blur) when testing accommodation?
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
These manipulate proximal and disparity cues too
What did Rosenfield et al (1991) find out about proximal accommodation?
Rosenfield et al (1991) show that proximally induced accommodation occurs for targets up to 3m away
3 dioptres (D) accommodation at 20cm
Graph: Mean open loop
accommodative response
plotted against target position.
When is Blur driven in Accommodation?
“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
What did Fincham & Walton (1957) find out about chromatic effects in accommodation?
Fincham & 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).
What does the red fringe retinal image suggest in accommodation (Fincham & Walton, 1957)?
Focus behind the retina
(under-accommodation).
What does the blue fringe retinal image suggest in accommodation (Fincham & Walton, 1957)?
Blue fringe retinal image: focus in front of the retina
(over-accommodation).
What did Kruger & Pola (1986) find out about monochromatic light and accommodation?
Monochromatic light (chromatic aberration neutralised) showed: accommodation was less accurate.
Reduced sensitivity to blur.
(Kruger & Pola, 1986)
Why might someone have excellent VA but be less able to detect and identify targets at night?
Tonic Accommodation might be reduced
What is Tonic Accommodation?
Tonic accommodation is the accommodation amount caused by the tonus of the ciliary muscle, It is described as resting (when in the dark and without a stimulus) or active when a stimulus is missing
Tonic accommodation (TA) isthe resting position of the eye’s lens when there’s no visual stimulus.It’s characterized by the lens adopting an intermediate position of approximately 1 dioptre (D).
How do the eyes adjust involuntarily for distance determined by the individual when a visual stimulus is poor?
When visual stimulus is poor e.g. at night, the eyes adjust involuntarily for a distance determined by the individual amount of ‘tonic accommodation’.
This distance is usually intermediate and varies widely between individuals.
What is ‘tonic accommodation’ also referred to as?
- ‘Resting focus’
- ‘Tonus state’
- ‘Dark focus’
What did Leibowitz & Owens (1978) find about tonic accommodation?
Reported distribution of dark-focus values for 220 emmetropic/fully corrected college students.
All measures were taken with a laser optometer in total darkness.
Wide range.
Average = 1.5 dioptres,
This corresponds to a focal distance of only 67cm
What is Convergence Accommodation?
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.
Convergence is initiated with a base out prism.
What did Hirani & Firth (2009) find about Convergence Accommodation?
CA/C ratio in region of 0.1D : 1PD
So…
For every 10 PD of forced convergence, around 1D of convergence accommodation occurs and must be inhibited to maintain clear vision (relative negative accommodation).
What is the AC/A Ratio?
The amount of accommodative convergence
(measured in prism dioptres (PD))
which occurs per dioptre of accommodation
Typically 4:1 or less
So for every 1D of accomm, there is 4PD of accommodative convergence
What is stimulus AC/A Ratio?
Stimulus AC/A ratio 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
What’s an issue with Stimulus AC/A Ratio?
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
What is Response AC/A Ratio?
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 & Firth, 2010) – 16 orthoptic students
x 1.41*(Miyata et al, 2006) – 63 strabismic patients, 79% exo deviations
What is Cognitive Accommodation?
Effort increases the level of accommodation
What did Francis et al. (2003) find out about Cognitive Accommodation?
- ‘Effort-to-see’ affects vergence and accommodation levels
- Instructions to concentrate vs space-out
What did Horwood & Toor (2014) find out about Cognitive Accommodation?
- Compared accomm in various exercise groups
- ‘Effort’ had significant improvement on accomm (and convergence)
What did Toor et al. (2017) find out about Asymmetrical Accommodation?
23% Anisometropic amblyopic children studied had very asymmetrical or even inverse responses in amblyopic eye.
Accommodated more in distance and relaxed accommodation for near.
What is the Near Reflex?
- Convergence of visual axis
- Increased accommodation & associated constriction of both pupils
What is the Light Reflex?
- Refers to the simultaneous and equal constriction of both pupils in response to stimulation of one eye.
- Present even in low light intensities.
How does the near reflex occur? (Explain the pathway)
- Afferent pathway
1) Light stimulates the retinal ganglionic cells
2) Action potential travels to optic nerve (CN II)
3) Then bilaterally to right and leftlateral geniculate bodies
4) Axons synapse at right and left pre-tectal nuclei in midbrain
5) Then projects to Edinger-Westphal nucleus of oculomotor nerve (CN III) via interneurons
- Efferent pathway
6) Action potential passes to the right and left ciliary ganglions via inferior division of oculomotor nerve
7) Enters eye by short ciliary nerves
8) Sphincter pupillae and cillaris muscle contract
How does the light reflex occur? (Explain the pathway)
The pretectal nucleus supplies the right and left Edinger-Westphal nuclei
So, shining light in one eye causes ipsilateral and contralateral pupil constriction
This is known as the consensual light reflex.
Afferent pathway
Retina –> LGN –> Visual cortex –> Frontal eye field –> oculomotor nuclear –> Edinger Westphal nucleus
(bypasses pretectal nuclei)
Efferent pathway
Parasympathetic fibres
Edinger Westphal nucleus –> oculomotor nerve –> right and left ciliary ganglions –> short ciliary nerve –> iris sphincter
How do we test the Near Reflex?
- Observe constriction of pupil on stimulus approach
- Should be symmetrical and equal
- Should occur when BEO or one eye occluded
i.e. Both pupils constrict equally on convergence
- Patient fixes distance target & light is introduced
- Look for direct and consensual reflex
Record as PERL / PEARL (pupils equal & reactive to light)
What is the swinging light test for?
- Detects relative afferent pupillary defect (RAPD)
- Efferent pathway intact
How do we do the Swinging Light Test?
- Patient fixates in distance
- 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
What is a +ve RAPD on the swinging light test indicative of?
+ve RAPD – due differences between afferent pathways of the eyes
Pathology is before the optic chiasm e.g. due to retinal or optic nerve disease
Indicative of:
- Large retinal detachment
- Central retinal artery or Ischaemic central retinal vein occlusion
- Optic nerve ischaemia, optic neuritis, compression, asymmetric glaucoma
What wouldn’t give an RAPD response on the swinging light test?
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 (Broadway, 2012)
What is Holmes Adie (Tonic) Pupil?
- Damage
- Signs
- Direct Light Reflex
- Consensual Light Reflex
- Near Reflex
- Accommodation
- Aetiology
- Damage: efferent pathway, ciliary ganglion or short ciliary nerves (unilateral)
- Signs: dilated pupil
- Direct light reflex: absent
- Consensual light reflex: absent
- Near reflex: present but slow
- Accommodation: reduced
- Aetiology: unknown (most common in women aged 20-40 yrs), Viral (e.g. herpes zoster), bacterial or inflammatory
