Accommodation Anomalies Flashcards
1
Q
What D power does lens have and what is lens held by? How many D of accomm needed at 25cm?
A
- Lens makes up 15D refractive power of eye
- Lens is held in place by zonules/suspensory ligaments
- Zonules are attached to ciliary muscle
- Ciliary body supplied by IIIrd nerve – parasympathetic system
- Dioptres of accomm = 1/fixation distance in metres
o How many dioptres of accomm needed at 25cm? 1/0.25 = 4D
Fixing up close but not accommodating blurred as behind eye
2
Q
Describe accomm and age?
A
- Normal aging process
- Onset usually between 40-50years old
- Onset can be premature
- Nutritional
- Environmental
- Disease related
- At about 60 yrs – lost all accomm
3
Q
What are the components of accommodation?
A
- Blur driven:
o Chromatic aberration gives cue as to direction of adjustment needed
o Pupil size can also increase depth of focus & reduce blur - Proximal:
o Occurs for targets up to 3m away
o Aware that something is closer to use – not because of blur but where it is - Cognitive:
o Mental effort increases level of accomm - Tonic:
o Resting point of accomm (dark accomm) - Convergence Accommodation:
o Produced as eyes converge
o For every 10^ forced converge about 1D accomm occurs – counteract with relative -ve accomm
4
Q
What aspects of accomm can be measured in clinic?
A
- Near point of accomm/amplitude of accomm (terms interchangeable)
- Accomm facility
- Accomm response
5
Q
How do you measure near point of accomm?
A
- Performed using RAF rule
- Refraction worn
- N series type used as target
- Pushed towards px and px says when text becomes blurred – recorded
o Do this method when in exams – just to when it is blurry - Drum then moved back to when px can recognise text being clear – this can be recorded instead (modified)
- Binocularly and then monocularly.
- Repeated x3 to watch for fatigue – look for accomm problem or insufficiency
- Recording:
o cgls BEO to 10cms, 12cms, 15cms c N5
o RE to 12cms, 12cms, 14cms c N5
o LE to 12cms, 14cms, 18cms c N5 - Record in dioptres (rotate RAF rule to see D)
6
Q
Why is it important to measure accomm?
A
- Assess if amplitude is same in both eyes
- Assess if its normal for patient’s age
- Assess if amplitude is sufficient for px’s needs – does px have enough or do they become fatigued?
- Amplitude of accomm reduces with age – 0 by ~60yrs old
7
Q
Describe AC/A ratio?
A
- Accommodative convergence/Accommodation Ratio
- Normal if 4:1 / 5:1 or less
- Gradient method
- Measuring amount of convergence for 1 unit of accomm
- Convergence excess SOT – they over converge for amount that they accommodate – high AC/A ratio – so SOT at near than distance
- Intermittent XOT – high AC/A ratio
8
Q
What is accommodation facility and how do you measure it?
A
- Measure of eyes ability to change accommodation status
o How quickly they can exert accomm then how quickly they can relax accomm
This is automatic in normals
o Pre-presbyope can start to complain of problems changing focus
Eventually make a blurred image clear - Reduced accommodation facility may create near vision problems – even if amplitude is normal (for their age)
- Training accomm facility can result in an improvement
- Measuring:
o Flipper lenses are used +2.00 lenses and -2.00 lenses
o Introducing these lenses in front of eyes will relax accomm (+2.00DS) & stimulate accomm (-2.00DS)
o Measure binocularly first
o If this is abnormal, measure monocularly
o If binocular accomm is abnormal but monocular is normal = other BV anomaly - Procedure:
o Full distance Rx corrected
o Given px reading chart to hold at 40cm
o Determine smallest text they can read clearly
o Ask px to fix on word this size
o Give clear instructions
“There will be a lens put in front of eye that may blur the word, try and focus to make it clear and say “clear” as soon as it happens. I will continue to repeat this process for 1 minute.”
o Target: focusing something at 40cm
o Start time for 1 minute the second you place first lens (+2.00DS) in front of eyes
o As soon as px says “clear” flip lens to -2.00 lens
o One clear of +2.00DS & one clear of -2.00DS = one complete cycle
o Repeat - Results:
o Count no of cycles completed in one minute
o Young adult: 10-12 cycles per minute is considered normal (using +2.00DS flippers)
If presbyopic and a bit lower than this no. then probably not accomm problem (not normally done in presbyope)
If <10-12 cycles in young adult then know there is an issue with facility
9
Q
Describe the accommodation response and what is means?
A
- Accomm response to a near target can- at times- not match exactly with accommodation stimulus.
- If accommodation response is less than the stimulus: Accommodation Lag.
- A target at 40cm should elicit at 2.50DS response but may only elicit a 2.00DS response. Therefore lag of 0.50D
- A lead of accommodation is when the response exceeds the stimulus.
- An accommodation lag of 1D or more may be an indication of the following:
o Presbyopia.
o Uncorrected or under corrected hypermetropia.
o Reduced amplitude of accommodation. - Accommodation lead may represent:
o Accommodative Spasm (accomm too much)
Pseudo myopia due to accomm spasm – accomm too much that when look in distance it’s blurred
10
Q
Describe the Monocular Estimation Method (MEM) and Nott method of dynamic retinoscopy?
A
- Accomm lag or lead can be identified & measured by dynamic ret
- 2 methods:
o Monocular estimation method (MEM) – more common method
o Nott method - MEM:
o Px wears full distance prescription.
Want to just be looking at accomm – image needs to be falling on retina
o A near chart is attached to the front of the retinoscope.
o Measure patients habitual working distance.
o Dim room lights.
o Px fixes on suitable sized letter on near chart.
o Don’t fog an eye and don’t dilate
o Perform ret at habitual working distance with vertical alignment.
o Observe light reflex: against, with or neutral.
If with or against, place lens in front of the eye until neutral achieved.
o Observe this for a little while to assure no change!
They can start to lag as fatigue
o Repeat with the other eye.
o Record neutralising lens for each eye.
o Positive lenses= Lag
o Negative lenses= Lead - Nott Method:
o Px wears full distance prescription.
o Measure px’s habitual working distance.
o Place near chart at px’s habitual working distance. (not at ret this time)
o Px fixes on word of suitable size.
o Dim room lights
o Perform ret from 10cm behind the near chart with streak vertical.
o If reflex isn’t neutral: Change position.
Reflex is with: (move) Further away.
Reflex is against: (move) Closer
o Measure distance from your retinoscope from the patient when the reflex is neutral.
o Neutral point behind target=Lag
o Neutral point in front of target= Lead
o The dioptric distance between the near chart and the neutral point is a measure of the lag or lead.
Near chart position: 40cm (2.50D)
Neutral position: 50cm (2.00D)
2.50-2.00: Lag= 0.50DS
11
Q
What is accommodation insufficiency?
A
- Px has a reduced amplitude of accommodation compared to their age-matched normal.
- This can be sub categorised:
o Ill-sustained accommodation- accommodation response cannot be sustained (fatigue).
o Paralysis- ability to accommodate is totally absent.
o Paresis- markedly reduced.
o Unequal: amplitude is 0.50DS more different between the eyes. - May be associated with convergence insufficiency
o Likely to have accomm insufficiency and vice versa (due to near triad) - Symptoms:
o Usually bilateral
o Blurred vision for near
o Asthenopic symptoms
12
Q
What is accommodation paralysis?
A
- Px has lost ability to exert accommodation completely – cant accomm at all
- May come hand in hand with convergence paralysis.
- Symptoms
o Blurred near vision
o Diplopia if associated with convergence paralysis
o May have dilated pupil- so photophobia. - Aetiology:
o Drugs (recreational)
o Trauma to the eye – e.g. if something happened to lens
o Closed head injury / whiplash
o IIIrd CNP – likely unilateral – bilateral would be v specific part of brainstem
o Midbrain disorders (rostral area)
Pineal tumour
o Conditions affecting CNS
Alcoholism, encephalitis
13
Q
What is accommodation infacility/inertia?
A
- The patient has difficulty focusing from distance to near (or opposite)
o But then when looking at the particular distance for a while then becomes clear - The dynamics of accommodation are slowed down.
- Symptoms:
o Blurred vision when changing fixation
o Accommodation is reduced for age- facility and amplitude
14
Q
What is accommodation spasm?
A
- Contraction of the ciliary muscles: excessive accommodation.
- Distance vision is blurred: pseudo myopia.
- Usually associated with convergence spasm.
- Lack of 20-20-20 rule – accommodating all time to study/read etc
- Aetiology:
o May happen in young, uncorrected hypermetropes. (they are already over accommodating at all tmes – usually when correct this is fine and can relax the eyes
o Functional response
o Lack of relaxation after close work
o Nystagmus blocking syndrome- manipulation of accommodation
o Closed head trauma
o Rostral midbrain lesion
o Increased ICP
o Drugs
o Para sympathomimetics
o Anticholinesterase agents - Resolves with cycloplegia – should stop spasm – relax accomm
15
Q
What is accommodation anomaly in pxs with Down Syndrome?
A
- Accommodation deficit in patients with down syndrome 55-76%
- Accommodation response assessed.
o Assess accomm response first by doing dynamic ret
o If 1D accomm lag then give bifocals of +1D to make up for lag they have - Accomm lag – struggle to accom up close
- Bifocal use incorporated – use long-term as never been able to accomm properly
