Neurophysiology
What extraocular muscle is innervated by cranial nerve 6?
Lateral rectus
What is the primary stimulus for accommodation?
Blur at the fovea
What is the functional goal of vergence?
Single vision
Is push-up amplitude of accommodation tested monocularly or binocularly? Why?
Monocularly, to eliminate the influence of vergence and get a true measure of absolute accommodative amplitude.
Is near point of convergence (NPC) performed monocularly or binocularly?
Binocularly
Which near test requires the target be only dimly illuminated?
Crossed Cylinder (fused or unfused)
What is the prism orientation used to neutralize an esophoria on ACT?
BO
What are Worth's Levels of Sensory Fusion?
Simultaneous perception, superimposition, flat fusion, stereopsis
Which aspect of the autonomic nervous system is responsible for an increase in accommodation?
What factor allows a target to be perceived as clear despite an accommodative response that is not equal to the accommodative stimulus?
Depth of focus
Crossed or Exo
Given Hofstetter's minimum amplitude norm, what is the expected accommodative amplitude for a 12 year old?
15 - (0.25 x 12) = 12 D
Positive relative vergence (PRV) uses _______ (BO or BI) prism and stimulates _______ (convergence or divergence).
BO, convergence
What is the target for the PRA test?
20/30 letter(s)
What type of phoria would be expected for a patient that has an objective break on NPC at 20cm?
Exophoria due to poor convergence ability
What are 3 advantages of having two eyes?
stereopsis, expanded field, "spare" eye, safety, binocular summation, spatial localization, egocentric reference point, visuomotor performance
What muscle is responsible for accommodation?
Ciliary body
What is the effect on the vergence system when the accommodative system is engaged?
Convergence increases due to accommodative convergence
What aspect of the vergence system (tonic, accommodative, fusional, proximal) contributes about 2/3 of vergence change?
Accommodative convergence
What is the expected finding for MEM at 40cm?
+0.37 D to +0.75 D (small LAG of accommodation)
When performing a near cover test you see no movement on the UCT and outward movement on the ACT. What is this patient's finding?
Esophoria
What aperture setting should be in place during the BCC test?
+/0.50 D over each eye
When performing a near cover test you see no movement on the first UCT, inward movement on the ACT, and inward movement on the second UCT What is this patient's finding?
Intermittent exotropia
Given the following findings, what is the AC/A ratio?
habitual phoria: 2 EP
phoria through +2.00: 2 XP
2:1
What is Sherrington's Law?
Innervation to a muscle is accompanied by a simultaneous and proportional relaxation of its antagonist
What element of the visual system influences depth of focus?
Pupil diameter
Name three ways to dissociate (turn off) the vergence system.
Occlusion, red/green, prism, blur, Maddox rod, septum, polarization
If binocular accommodative facility is low, but monocular accommodative facility is normal, which system is likely deficient?
Vergence system is limiting accommodation
When performing NRV at near, a patient reports no diplopia but observes the image moving to their left. What does this finding indicate?
Suppression of right eye
What is the lens in place for the NPA (push up) test?
Habitual near Rx (or habitual distance Rx for non-presbyopes)
Why are patients instructed to keep the target clear during dissociated phoria tests, such as the von Graefe?
Controls accommodation to reduce testing variability
Why is NRA reduced in a patient with high exophoria at near?
Relaxation of accommodation is limited by divergence
What are the 4 extraocular muscles innervated by cranial nerve 3
medial rectus, superior rectus, inferior rectus, inferior oblique
What are the only two ways to change the accommodative stimulus?
Change target distance and/or lens in place
What is the clinical term for a misalignment of the eyes under associated conditions?
Strabismus, heterotropia, tropia
What may a high NRA finding (e.g., +5.00 D) indicate?
Distance refraction is under-plussed or over-minused
What does a blur point on distance negative relative vergence (NRV) indicate?
What does an MEM finding of -1.00D indicate?
1.00D accommodative LEAD, i.e., accommodative response is 1.00 more than accommodative stimulus
What is the target for the NPC test and what purpose does this target serve?
Good accommodative target (bead, 20/20 letter); stimulate accommodation to provide additional accommodative convergence
The near point stress model predicts an increase in which type of phoria.
Eso