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Accommodation and Convergence

• To have efficient single binocular vision (SBV), well-focused retinal images on both eyes are needed.
• Images need to be of similar size and shape for each eye (OU).
• Placed and maintained on each fovea for each eye (OU).
• Accommodation and convergence are needed to keep near targets clear and stable and require binocular vision and image focus.
• These are linked neurologically through CN III, therefore coordination is needed for clear vision and stereopsis.
• Patients without single binocular vision may have amblyopia, strabismus, or nystagmus that affects their ability to focus correctly.

Amplitude of Accommodation

• Amplitude, facility, and accommodative response need individual clinical tests to determine a patient's capacity to accommodate
• Amplitude is measured in diopters, and AOA (accommodative amplitude) or NPA (near point of accommodation) measures it
• Facility is how much accommodation can be stimulated and how easily it can be exerted and relaxed as a problem if either is missing
• Accommodative Response defines how accurate the accommodative response is to a given stimulus; less accurate means "buny", and more accurate means overexerting, leading to asthenopia or headaches.

Accommodation

• Accommodation is a change in focal length of the optical system in response to a stimulus.
• Mediation by the ciliary muscle and crystalline lens occurs during the accommodative process, however rigidity of lens can be a source of issues.
• Accommodation is specified in accommodative stimulus and response to near stimulus
• Resting state of accommodation, lag and lead of accommodation are all factors
• Clinical methods of measuring accommodative response are dynamic retinoscopy and binocular crossed cylinder (BCC, BEC, FCC) tests.

Accommodative Stimulus

• Accommodation is stimulated by placing an object closer than infinity (6m or 20ft), or by placing an object at 20ft and using negative lenses.
• Both methods result in increased vergence of light rays reaching the eye. Positive value is reported because accommodation response is positive
• Accommodative stimulus is expressed in diopters, and the diopter always has no sign.

Stimulus of Accommodation Examples

• At 1m distance, a test object stimulates 1.00D of accommodation (1M = 1/1 = 1.00D).
• For an emmetrope (-2.00DS lens @ spectacle plane) fixating at a test object at 1m, the stimulus of accommodation can be determined

Stimulus of Accommodation Example Problem

• A -2.00D myope, uncorrected, using a -4.00D lens at the spectacle plane with a test object at 1m will have this stimulus of accommodation:
• Stimulus of accommodation from object at 1m = 1D
• From lens at spectacle plane = 2.00D
• 1 + 2 = 3.00D

Accommodative Response

• Accommodative response involves the accommodative system responding when the eye changes fixation from one point in space to another.
• The accommodative response should match the accommodative stimulus.
• Measuring occurs with a haploscope, dynamic retinoscopy (MEM, Nott, Bell), or fused crossed cylinder (FCC).

Accommodative Response: Dynamic Retinoscopy

• Dynamic retinoscopy (near retinoscopy) determines the accommodative response to an accommodative stimulus at near.
• Measurement of Lead or Lag of Accommodation is involved
• Nott, Bell, and MEM are different methods
• Fused Crossed Cylinder (FCC) or Binocular Cross Cylinder (BCC): subjective testing; performed at 40cm.
• Patient describes when both sets of lines are equally distinct, while adding + lenses

Lag vs Lead of Accommodation

• Lag occurs where the accommodative response is less than required.
• Lead occurs where the accommodative response is more than required.
• Expected results using dynamic retinoscopy and BCC are +0.25D-+0.75D ±0.50D of lag for young patients; these tests estimate the required near addition for presbyopes.

Lead or Lag Results

• LAG is indicated If the result is > +0.75D, there might be under-corrected hyperopia, over-corrected myopia, accommodative dysfunction, near esophoria or presbyopia
• LEAD is indicated If the result is +0.25D , there might be under-corrected myope, spasm of accommodation or near exophoria

Monocular Estimation Method (MEM)

• This test is performed binocularly under normal illumination.
• The patient's Harmon WD is set to reading level, and no phoropter is used
• Perform retinoscopy on each eye as the patient reads letters. Apply quick plus/minus lenses in front of the eye to neutralize the reflex.
• The reflex should be measured in both horizontal and vertical axes. Expected values is +0.25D to +0.75D

Lag vs Lead of Accommodation Control

• Lag depends on depth of focus of the eye or the depth of field.
• FCC: use dim light to avoid pupil constriction as depth of focus varies with pupil size and object size; room isn't totally dark however and computer screen and VA projector screen should be turned off
• Lead: fogging lenses minimize accommodation (young patients tend to accommodate even at 20ft.).
• Overaccommodation leads to latent hyperopia and pseudomyopia, therefore dry and wet refractions are compared and streak retinoscopy is fogged or uses the R lens.
• Cycloplegic agents in case of excess accommodative response could be: Cyclopentolate, Atropine, Homatropine, Scopalamine, Tropicamide

Amplitude of Accommodation Tests

• Donder's Push-up tests require habitual SRx, target one line above BVA tested eye, and full illumination
• Target held in one hand at patient's spectacle plane while occluding other eye. Moving target starting at 50-30cm to the patient.
• Report the first blur, attempt to clear it, and then resume until the endpoint when target cannot clear.
• The distance is recorded and reported. Repeat on the other eye and complete with Hofstetter's formula to compare

Donder's Disadvantages

• Results tend to be overestimations.
• Target subtends a greater angle as it gets closer (relative size magnification).
• Results in a large difference in diopters
• Must wear their prescription for near and subtract the NPA from your findings to prevent further issues
• For example: a presbyope w/ +2.50D reports target blurry at 25cm while wearing spectacles; and an AoA calculation would be AoA= 4.00-(+2.50) = 1.50D,

Sheard's/ Minus to Blur Lens Assessment

• Assessment is performed monocularly with the target remaining still.
• MPMBVA SRx, is used one line above BVA in 40cm distance at near rod under full illumination
• Must use a accommodated result, already requiring a 2.50D
• Patient asked to keep the letters clear and blink to clear them
• -0.25D lenses are added until reach sustained blur, and the other eye is rechecked to ensure a blurred result
• The result is calculated using: (-diopters obtained) + (-2.50D)= | diopters |; without sign.

Expected Amplitude of Accommodation Values

• Hofstetter's Formula estimates amplitude and is measured:
• Minimum expected: 15 -0.25 (Age)
• Average expected: 18.5 -0.30 (Age)
• Maximum expected: 25 -0.40 (Age)

AoA Testing Errors

• Factors that introduce incorrect results included Depth of focus, reaction time, and patient delay
• Measurement discrepancies, instrumentation issues, practitioner bias and errors in dynamic retinoscopy can also occur

Sheard's and Donder's Interpretation

• Young patients have lower values with disorders
• Patients over 40 should keep clear comfy vision, needing no more than half accommodative results in sustained reading or close work
• Ex: emmetrope 40cm requires 2.50 DA, it would be 5.00 DA for a comfy rule in Donders table would result in AoA of 4.50 DA thus NPA is accounted
• Emmetrope with 3.50D of AoA uses 1.75D of their accommodative amplitude for sustained near work.
• Patients should reserve for sustained reading or close work, which is 3.50D/2 = 1.75, and is consistent working at 40cm (which requires 2.50D) needs an extra 0.75D.

Other Accommodative Testing

• Other accommodative tests includes
• Negative and Positive Relative Accommodation (NRA and PRA)
• Fused Cross Cylinder Test (FCC)
• Facility of Accommodation (flippers) both Monocular and binocular for disorders without strabismus
• Binocular vision is important to evaluate because patients low in AoA can suffer Accommodative or Convergence Insufficiency

Negative Relative Accommodation (NRA)

• NRA measures ability to relax accommodation while keeping clear, binocular vision
• Near card 40cm, ask BCVA one above line. Add plus lensOU; until fuzzy letters stop, ex: 2.25-2.50, High values over minus indicates hyperopia

Positive Relative Accommodation (PRA)

• PRA measures ability to stimulate accommodation while keeping clear, binocular vision
• Objective Rx (MPMBVA) at 40 cm view one line above BCVA on near card. Add (-) lens until gets blurry, 1.50 D to -2.00 D values

Flipper Bar Procedure: Test for Accommodative Facility Assessment

• This procedure is designed for accommodative facility measurement, and is very important when children 7+ complain of distant blur problems, but normal tests
• Flippers, usually -2.00/+2.00. Distant Rx full illumination to near card40 cm, BVA line above
• Fixate target change lens with clear letters: done using mono or bino vision for both accommodation and vergence
• Assessed lens one to other, one is a cycle, done one minutes in cycles per minutes, and take time to clear lenses if longer than usual *test vergence functions

Flipper Bar Procedure: Interpretation

• Tests failures indicate monocular or binocular problems
• Monocular: accommodative excess (Fails (+) cannot relax), accommodative excess stimulation (Fails (-)), infacility
• Binocular, fails when passed mono result: + fail: divergence problem, - fail convergence: or FUsional decline functions

Accommodation Test: BCC and FCC

• Use the cross grid from Roto near char at 40cm with distance SRx, use tentative add for presbyotic individuals
• Overhead needs be dim target at 2 feet and use either JCC or auxiliary +/- 0.50DC lens for best vision
• Introduce JCC in eye front, if they don't click, use red dots at, axis in oppostie side(red dots at vertical90 degree).
• Target observe needs a report with sharpness. Dark and sharpness of lines will be different
• Add lenses, same orientation.

Test for Lead or Lag of Accommodation

• Phoropter is used to add plus lenses, only if horizontal lines are darker
• Phoropter is used to add minus lenses, only if vertical lines are darker
• Measures in both circumstances.

BCC Interpretation

• Correct accommodation is clear two horizontal clear or equals to target position
• Can find hidden hyperopes. Find lag as dyanmic tests, careful with overminused Used also in presbyopes, is convenient to determing. +1.00 D: is is a normal result, needs to be equal

Anomalies of Accommodation

• Anomalities are:
  • Presbyopia
  • Spasm of accommodation
  • Lag of accommodation
  • Insufficiency of accommodation
  • Fatigue of accommodation
  • Paralysis of accommodation (CN III palsy or medications).

Anomalies of Accommodation: Presbyopia

• This is a universal condition associated with aging.
• Crystalline lens changes as fiber compress in outer cortex, loses elasticity as the ciliary muscle contracts
• With age the muscle loses power
• Accommodation amplitude decreases as aging progresses, so the patient uses thumb to see better.

Presbyopia: Determine Add Power

• Add determined tables, make additions to hold materials, add tentaitive add. then TF with tentaitive is 1.00, also make a BCC + (Near-PRA(/2

Accommodative Problems: Insufficiency

• Occurs when the eye gio pthais 10 . is over11.25 but minimum (High BCCC_
• The patient fails stimulating the accommidation and must be stimulated plus lenses with accommidations and dont like that, nor minus leases for relx

Problems with Accommodative Infacility

• The patient mentions same issue when close to nearto distant and harder elear and same effect
• Children hate writing from front and easy, difficult to simulat

Accommodative Spasm

• Occurs more with the vision but relax not much, also hyper accomidations, as the patient exerts is an exaggerated result as with pain is consistent with accem
• Etiology: unconverted by stresss, etc Associated with convergencies, asthenopia, is very important to check this out to better support and understand.

Pseudomyopia

• Results from spasm cillary muscle is the definition of reversible myopia
• Is excessive for the reason. will be cyoplegied with drops, and you will see the change and can understand better.

Myopia Vs Pseudomyopia

• Both cause distance blurring,.Pseudomiyopia fluctuations with headaches but the rest is unlikeness.