Near Vision Assessment

1
Near Vision Assessment

• Assigned readings
• Zadnik Chapter 5
• Accommodation

2
Always be looking at Complaints involving

• Near point asthenopic symptoms
• Eyestrain
• Headache
• Burning, tearing, redness
• Diplopia
• Skipping lines
• Disinterest in material
• Etc

3
Always be evaluating

• Cover test
• Near Point of Convergence
• Amplitude of Accommodation
• Stereopsis
• Binocular Crossed Cylinder
• Phorias/Vergences
• Facility

4
Near Point of Convergence

• Maximum convergence
• Reduced NPC may correlate with near point
  findings such as
• Diplopia
• Frontal headaches
• Decreased reading comprehension, fatigue

5
NPC

• Expected range is from 6 to 10 cm
• When it is closer than 6cm the patient may be
  displaying signs of Convergence Excess (tend to
  over-converge)
• Intuitively when the NPC is receded beyond 10cm,
  the patient may be manifesting signs of
  Convergence Insufficiency

6
Accommodation

• Accommodation is the dioptric adjustment of the
  crystalline lens of the eye to obtain clear
  vision for a given target.
• This is done thanks to the contraction of the
  ciliary muscle
• A persons Amplitude of accommodation refers to
  the maximum amount of accommodation a person can
  achieve.

7
Anatomy of Accommodation

• Purkinje images III and IV (anterior and
  posterior lens)
• Per Helmholtz demonstrated the anterior pole of
  the lens moves forward
• The posterior pole remains stationary

8
Innervations

• Ciliary muscle is innervated by the
  parasympathetic and sympathetic nervous system
• Parasympathetic from Visual cortex to ciliary
  ganglion where they synapse, to ciliary muscle
• Sympathetic fibers from cervical trunk and
  synapse at the cervical ganglion

9
Uncorrected Refractive error

• Emmetropic Eye has 60D of power
• What is accommodative demand of an object at
  50cm?
• Emmetropic Eye exerts 2D, total power 62
• Hyperope with 58D to start with must exert 4D to
  get to 62 total
• Myope with 62D initially will not accommodate at
  all to see this target, b/c it is already at the
  far point

10
Common Symptoms

• When someone does not have enough accommodative
  reserves they exhibit characteristic symptoms
• Fatigue during near tasks
• Blurring of near vision
• Inability to read in dim illumination

11
convergence

• 4 Types
• Tonic physiologic position of rest of the ocular
  muscles (distance finding)
• Proximal- convergence that arises because of
  psychological awareness of objects
• Accommodative- convergence that occurs with a
  change in accommodation (in the triad
  (accommodation, convergence and pupil miosis)
• Fusional- responds to keep object of regard single

12
accommodation

• Blur Driven
• Convergent
• Tonic
• Proximal

13
Accommodation

• Tonic Accommodation
• absence of visual stimuli
• Intermediate dioptric position on the order of
  0.50 to 1.00 D
• Dark accommodation/dark focus
• Night myopia
• Infrared autorefractor used
• Mohindra retinoscopy (total darkness) pt views
  the retinoscope beam monocularly (probably
  doesnt work well)

14
tonic

• Most accurate method using a DOG target
• Low center spatial frequency
• Difference of Gaussian Grating (DOG)
• Not precise as proximal accommodation stimulated
• No blur driven or convergent accommodation

15
expected

• Children and young adults between 0.50 and 1.00 D
• DOG results slightly higher
• Tonic declines with age and development of
  presbyopia

16
Proximal Accommodation

• Varies between people
• Awareness of closeness of objects in space
• To evaluate how much it contributes, you need to
  eliminate the other accommodations
• Monocular DOG target
• Dog target close, Sheard dynamic retinoscopy
• NORM 0.45DS per Rosenfield et al. declines w/age

17
Anomalies of Accommodation

• Problems arise when demand and response are
  different
• Can fail to

Zadnik, pg.111
18
Anomalies, contd

• 5 categories
• 1. Fatigue of Accommodation
• 2. Failure of Accommodation
• 3. Accommodative Inertia
• 4. Paralysis of accommodation
• 5. Accommodative Excess

per, Duke-Elder and Abrams
19
Contd

• Fatigue Accommodative fatigue has been defined
  as the inability of the ciliary muscle to
  maintain contraction while viewing a near object,
  with a resultant decrease in the accommodative
  response. (Zadnik, pg.112)

20
Contd

• Failure of accommodation Inability to produce
  or maintain an appropriate accommodative
  response. (Zadnik p.112)
• Subdivided category

21
Contd

• Accommodative Inertia
• Person has problems changing their accommodation.
  (usually 1 second)
• Work induced myopia

22
Contd

• Paralysis of accommodation
• Unilateral, bilateral, sudden onset
• Pupil mydriasis
• Paralysis is extreme insufficiency

23
Contd

• Accommodative Excess
• Spasm
• Pseudomyopia
• Hyperaccommodation, High Lead (greater than
  .40D)
• a condition in which a greater accommodative
  response than is considered normal is observed
  for a given accommodative stimulus. (Suchoff and
  Petito)

24
Contd

• Symptoms ocular fatigue, headaches, blurred
  vision, diplopia,
• Causes mostly functional, possibly organic

25
and so on

• Cycloplegic examinations
• Ret more than subjective
• High lag
• Esophoric
• Prevalence (per Hokoda) 16.8 in urban optometry
  clinics

26
organic

• Trauma
• Inflammatory
• Toxic
• Metabolic
• Degenerative
• Neoplastic
• Vascular
• Psychogenic
• Iatrogenic/pharmacologic

27
Donders Table (Wold, RM, Am J Optom
196744642-664)
Age (yr) Amp (D) Age (yr) Amp (D)
10 14 35 5.5
15 12 40 4.5
20 10 45 3.5
25 8.5 50 2.5
30 7 55 1.75
28
Duanes Table (Wold, RM, Am J Optom
196744642-664)
Age (yr) Amp (D) Age (yr) Amp (D)
10 11.00 35 6.50
15 10.25 40 5.50
20 9.50 45 3.50
25 8.50 60 1.25
30 7.50 70 1.00
29
Hofstetters Formulae

• Calculate Maximum, Average, and Minimum
  amplitudes of accommodation based on age
• Maximum 25- .4(age)
• Average 18.5 - .3(age)
• Minimum 15.5- .25(age)

(Hofstetter HW. Penn Optom 194775-8)
30
Calculate

• Example a 29 yo
• Maximum 25-0.4(29) 13.4 D
• Median 18.5 0.3(29) 9.8 D
• Minimum 15.0 0.25(29) 7.75 D

31
Clinical Testing

• Push Up/Pull Away(Donders)
• Record as dioptric equivalent of distance
• Minus to Blur (Minus lens amps)
• Both are done monocularly
• Binocular testing of accommodation may mask a
  unilateral problem, or one complicated by the
  vergence system

32
Push Up Technique

• Want to identify the near point of accommodation,
  that means you want the Maximum amount the
  patient can accommodate (accommodative response)
• Bring target to the first sustained blur
• Use appropriate target size

33
Did you know,

• We never accommodate exactly the correct amount?
• The response is dependent on the position of the
  target
• For distant targets we tend to over-accommodate
  (lead)
• For close near point objects the response is
  slightly less than the stimulus (lag)

34
Then how do we see clearly?

• Depth of focus of the eye!
• Allows this slop to still be clear
• The patient will not report blur until the slop
  exceeds one half of the depth of focus

35
Of Note

• Donders results may be higher due to the angular
  subtense of the letter increasing throughout
  testing.
• Contrary to Donders push up, minus lens
  amplitude testing will decrease the target size
  as you increase the minus lens, making this value
  slightly lower

36
Minus Lens Technique

• Target is fixed (40cm) and minus lenses are
  introduced until the patient cannot clear the
  target anymore
• The total amplitude is the total amount of minus
  lenses introduced plus the demand at 40cm (2.50D)
• Monocular test

37
Comparing the Tests

• Minus Lens Fixed target, proximal stimulus
  remains constant, minification from the minus
  lenses
• Push Up angular subtense of the letters keep
  increasing as it is brought closer in, more
  natural

38
Binocular Measurements

• We are measuring amplitude of accommodation when
  we test monoc, but what about when we test
  binocularly?
• Now patient is forced to keep fusion as well as
  clarity
• Need to have accurate accommodative and vergence
  responses

39
Binocular Push Up

• NPC, measure distance and take the inverse

40
Dynamic Crossed Cylinder

• Aka FCC, BCC
• Theory patient views a set of vertical and a set
  of horizontal lines through crossed cylinders
  (/- 0.50D, which are incorporated in the
  phoropters)
• This creates a situation where the patient has
  mixed astigmatism and the foci are equidistant in
  front of and behind the retina

41
BCC contd

• The patient is asked to view the crossed lines
  and report which set is darker and clearer, or
  are they equal.
• Equal the patient is focusing perfectly in the
  plane of the target and the two sets of lines are
  equidistant from the retina therefore equally
  clear

42
Contd

• Horizontal lines are clearer Indicates that the
  patient was initially underaccommodating and
  therefore there is a LAG of accommodation.

43
Contd

• Vertical Lines are clearer The patient was
  initially over accommodating exhibiting a LEAD of
  accommodation, therefore the vertical lines
  appear clearer to the patient

44
Contd

• What to do
• LAG shown add plus lenses until both horizontal
  and vertical lines are equally clear
• LEAD shown minus lenses are added until the two
  sets are equally clear

45
Interpretation

• The lenses that make the patient report that both
  sets of lines are equally clear provides a
  measurement of their accommodative system
• Horizontal lines clearer, add 0.50DS, now they
  are equal
• The patient had an accommodative lag of 0.50

46
Addnl info

• This test is performed in very dim illumination
  (but patient must see target)
• Minimizes the depth of focus of the eye (larger
  pupil)
• This test can be performed 3 ways
• Monocular
• Binocular fused
• Binocular unfused

47
Addnl info

• Young people with active accommodative systems
  can manipulate the test
• Can introduce a 1.00DS fogging lens before
  introducing the target, to stabilize the
  accommodative response somewhat
• Some patients just relax by 1D and still have
  the same problem

48
Contd

• Some patients react very poorly to this test
• Introduction of the plus lens will lessen the
  blur driven accommodative response

49
Accommodative Facility

• Ability of patient to alternate focus near to far
• Classroom setting
• Tested monocular and binocular with /- flipper.
  (2.00DS)

50
procedure

• Patient views fine print (20/25 or 20/30) at a
  distance of 40cm
• Introduce flipper lenses
• If using 2.00 DS, this makes the accommodative
  demand 0.50Dand 4.50D alternatively
• The flippers are flipped when patient reports
  the letters are clear

51
Contd

• Need to have a watch (either digital or one with
  a second hand for this procedure)
• Recorded as the number of cycles (clearing both
  sides plus and minus lenses) per minute
• Should do test for full minute
• Note which side patient has more difficulty with
• Record both monocular and binocular findings

52
Contd

• Monocular accommodative
• Binocular - varying accommodative response while
  keeping vergence response stable
• Suppression tests needed with binocular testing

53
Norms

• Monocular clinical pass rate is 11 cpm, cycles
  per minute
• Binocular is 8 cpm
• Per Hoffman and Rouse studies
• 2 cpm difference between the two eyes is also
  considered significiant and can be related to
  visual asthenopias

54
interpretation

• Problems with difficulty relaxing
  accommodation, possible spasms of accommodation
  and pseudomyopia
• Problems with - difficulty accommodating,
  possible accommodative insuffiency
• Problems switching back and forth accommodative
  infacility