Accommodation/Vergence/Oculomotor Function Flashcards
What is the MOST common type of oculomotor deviation?
Hyperphoria
Hypophoria
Esophoria
Exophoria
Exophoria
Explanation
By far the most common oculomotor deviations are exo in nature ( about 95%), however most do not pose a problem. The least common type of deviation is vertical.
While performing the Worth-4-dot test (red lens placed over right eye), your patient reports seeing 3 green circles to the left of two red circles. Based on the above findings, what is the correct extrapolation?
Hyperphoria
Hypophoria
Esophoria
Exophoria
Esophoria
Explanation
In the Worth-4-dot test, the red lens is generally placed in front of the right eye. Four dots are then projected onto the screen. The two horizontal circles are green, the top circle is white and the bottom circle is red (in most cases). Assuming the patient possesses simultaneous perception, the right eye alone views the bottom and the top circle as red and pink/red respectively. The left eye views three green circles. Combined, both eyes view four circles, two appear green, one lower appears red and the upper one appears red/green. Three green circles viewed to the right of two red circles indicate crossed diplopia (exophoria). The perception of three green circles viewed to the left of two red circles is indicative of uncrossed diplopia (esophoria). The perception of three green circles alone is indicative of right eye suppression. If the patient reports viewing two red circles, this indicates suppression of the left eye.
While performing the alternate cover test at near on a patient with esophoria, you ask the patient to note any target movement. Which of the following responses is this patient MOST likely to report?
The target appears to move in the same direction of the occluder movement
The target appears to move downwards
The target does not appear to move
The target appears to move in the opposite direction of the occluder movement
The target appears to move upwards
The target appears to move in the opposite direction of the occluder movement
Explanation
If a phoria is too small in magnitude to be observed while performing the alternate cover test, the clinician can ask the patient to fixate on the target and report any movement seen. Patients with esophoria will report that the target appears to become displaced in the opposite direction of the occluder movement. For example, when the occluder moves from the patient’s right eye to the left eye, the patient will note that the fixation target appeared to move from left to right or “against jump”. A patient with exophoria will report that the target is displaced in the same direction as the movement of the occluder or “with jump”.
Which of the following congenital extraocular muscle disorders occurs as a result of failure of innervation of the lateral rectus muscle by the sixth cranial nerve, accompanied by anomalous innervation of the lateral rectus by fibers from the third cranial nerve?
Congenital fibrosis of extraocular muscles Brown's syndrome Duane's retraction syndrome Mobius syndrome Marcus Gunn jaw-winking
Duane’s retraction syndrome
Explanation
Duane’s retraction syndrome occurs as a result of a developmental error in innervation of the lateral rectus muscle. The sixth cranial nerve fails to innervate the lateral rectus muscle, while at the same time fibers from the third cranial nerve inappropriately innervate the lateral rectus. It is common for this dysinnervation to affect both eyes; however, the involvement of one eye tends to be much more subtle.
The clinical signs leading to the diagnosis of this condition include the following extraocular motility defects of the affected eye:
- Restricted abduction, which may be partial or complete.
- Restricted adduction, which is usually partial.
- This occurs secondary to opposing muscles (lateral and medial recti) being innervated by the same nerve, limiting the eye’s ability to move.
- Retraction of the globe on adduction, which occurs as a result of co-contraction of the medial and lateral rectus muscles, leading to narrowing of the palpebral fissure; on abduction the globe will assume its natural position and the palpebral fissure will open.
- Up-shoots or down-shoots on attempted adduction can occur in some cases. This is thought to be caused by a tight lateral rectus muscle that can slip either over or under the globe, producing an anomalous vertical movement of the eye upon co-contraction of the medial and lateral recti.
- Convergence deficiency, in which the affected eye remains fixed in primary position while the contralateral eye converges.
Which of the following visual functions is present and continues to develop in a newborn infant?
Stereopsis
Horizontal saccadic eye movements
Vertical saccadic eye movements
Pursuits
Horizontal saccadic eye movements
Explanation
Horizontal saccadic eye movements first emerge at birth and continue to develop until roughly 24 months. Vertical saccades require a longer time to mature and emerge at around 2 months of age and continue to develop until about 24 months. Pursuits may be seen as early as 2 months but are more commonly evident at 4 months of age. Stereopsis is absent at birth and does not become apparent until 3-5 months of age (some sources quote 4-6 months), reaching adult levels at 5-7 years of age.
Torsional eye movements account for the maintenance of an upright image when a person tilts his or her head to either side. Upon head tilt to the right, which of the following torsional movements occur in the right and left eye, respectively?
Intorsion, intorsion
Extorsion, extorsion
Intorsion, extorsion
Extorsion, intorsion
Intorsion, extorsion
Explanation
Also known as righting reflexes, torsional eye movements occur in order to maintain upright images when a person tilts his or her head either right or left. In the case of right head tilt, the superior limbus of each eye will rotate to the left. This causes intorsion of the right eye and extorsion of the left eye. The opposite will occur when the head is tilted to the left.
Which 3 tests directly examine the accommodative system? (Select 3)
Positive fusional convergence ranges (PFC)
Monocular estimation method (MEM)
Monocular amplitudes
Second-degree fusion
Monocular facility testing with +/- 2.00 D lenses
Stereopsis
Monocular estimation method (MEM)
Monocular amplitudes
Monocular facility testing with +/- 2.00 D lenses
Explanation
MEM measures the accuracy of the accommodative response to a given target. Monocular amplitudes and monocular facility also evaluate the performance of the accommodative system.
PFC measures the interaction between the accommodative and the vergence system.
Stereopsis is a product of binocular retinal disparity. Stereopsis is not a measure of accommodation but serves to evaluate the capability of the eyes to work in unison. Although accommodation must be accounted for when performing this test, stereopsis will not quantify any type of accommodative dysfunction. Stereopsis as a cue to depth works best if the objects are not too far away. In order for stereopsis to occur, the retinal disparity must be within a certain limit to result in a perception of depth.
Second-degree fusion is the ability to superimpose like objects (not necessarily identical objects), with the end result being the perception of a single object that is a composition of the two separate images. The Worth 4 dot is an example of a test that evaluates second-degree fusion. Second-degree fusion evaluates if the eyes are capable of working together and does not measure accommodative capability.
An object is located 50 cm from the corneal plane of an eye with 2.00 D of myopia. What degree of accommodation is required to achieve a clear retinal image of the object with no corrective lens in place?
-2.00 D \+1.50 D 0.00 D \+2.00 D \+1.00 D
0.00 D
Explanation
A 2.00 D myope has a far point of 50 cm (1/2.00 D= 0.50 m or 50.0 cm). Because the object is located at the far point of the eye, no accommodation is required to bring the image into focus.
The near phoria at 40 cm for a patient wearing their spectacle lenses is 6 exophoria. +1.00 D is then placed over the patient’s spectacles and the resulting phoria at 40 cm is measured as 9 exophoria. Based upon these clinical findings, what is the gradient AC/A ratio?
6/1
4/1
3/1
9/1
3/1
Explanation
The gradient AC/A ratio allows for the determination of the magnitude of change in the ocular deviation as a result of stimulation or relaxation of the accommodative system by the introduction of ophthalmic lenses. The patient is asked to view a target at near (typically 40 cm) through the lenses that achieve the best corrected visual acuity, and the phoria is measured. +1.00 or -1.00 is then placed in front of the ophthalmic corrective lenses and the resultant phoria is re-measured (some clinicians use a +3.00 D lens). Plus-powered lenses relax the accommodative system, resulting in a decrease in accommodative convergence, while minus-powered lenses stimulate the accommodative system, thereby causing increased accommodative convergence and an increased eso deviation or a decreased exo deviation. The resulting AC/A ratio is then determined via the following formula: gradient AC/A= (deviation-deviation with lens)/power of lens in diopters. For the above question, the gradient AC/A is calculated as follows: (6-9)/1=-3/1. Conventionally, a minus sign indicates an increase in exodeviation or a decrease in esodeviation. Typically, AC/A ratios are given in absolute values.
While performing the bichrome test with the left eye occluded, the patient initially reports that the letters on the red side appear bolder, blacker and sharper. -0.25 D is then placed before the right eye and the patient reports that the letters on the green side now appear clearer. Which of the following is the MOST appropriate next step?
Re-explain the goal of the test, as the patient is likely unclear as to the test instructions
Add an additional -0.25 D over the right eye
Leave the findings in the phoropter, occlude the right eye and proceed to the left eye
Add +0.25 D over the right eye
Add +0.25 D over the right eye
Explanation
The bichrome test is performed by occluding one eye and projecting letters on a red and green background. The patient is initially fogged by roughly + 0.50 D. Fogging over-plusses the patient and shifts the chromatic interval forwards (causing objects projected on a background with longer wavelengths (red) to be bolder) such that the patient should report that the letters are blacker and bolder on the red side of the chart. The addition of minus lenses should equate the two sides such that the letters appear equally black and bold on the red and green sides. If the patient initially reports that the letters on the green side are bolder, then either plus lenses need to be added or minus powered lenses need to be reduced to shift the chromatic interval forwards. If the patient does not report equal boldness/blackness/sharpness of the letters on the green and red sides of the chart but instead instantly reports reversal upon switching lenses, the majority of clinicians will leave the power of the lens in the phoropter at the setting where the patient last reported that the letters on the red side of the chart appeared bolder/blacker to minimize the chances of over-minussing the patient.
Nerve fibers from the abducens nucleus innervate which of the following extraocular muscles?
Contralateral superior oblique Contralateral lateral rectus Contralateral medial rectus Ipsilateral superior oblique Ipsilateral medial rectus Ipsilateral lateral rectus
Ipsilateral lateral rectus
Explanation
The nucleus of the abducens nerve (cranial nerve VI) is located in the dorsal lower portion of the pons. Motor neuron axons from the abducens nerve course from this location to the ipsilateral lateral rectus muscle via the cavernous sinus and superior orbital fissure. Additionally, interneurons also traverse from the abducens nucleus to the opposite medial longitudinal fasciculus (MLF) and terminate at the oculomotor nucleus, thus coordinating horizontal gaze movements of both eyes.
The trochlear nucleus innervates the contralateral superior oblique muscle.
The oculomotor nucleus innervates the ipsilateral medial rectus, inferior rectus, and inferior oblique, as well as the contralateral superior rectus.
Which of the following extraocular muscles is considered the synergistic pairing to the left superior oblique?
Left inferior rectus
Right inferior oblique
Right inferior rectus
Left superior rectus
Left inferior rectus
Explanation
Synergistic extraocular muscles pairs are those muscles of the same eye which, when contracted, act to move the eye in the same direction. In this question, one of the actions of the left superior oblique is to depress the left eye. Additionally, in the left eye, the left inferior rectus also acts to depress the eye. Therefore, the muscle that acts synergistically with the left superior oblique is the left inferior rectus.
Which of the following extraocular muscles has its insertion point FURTHEST from the limbus?
Superior rectus
Inferior rectus
Lateral rectus
Medial rectus
Superior rectus
Explanation
The spiral of Tillaux is an imaginary line that joins the insertion points of the four recti muscles. As their insertions get further away from the limbus, a spiral pattern is created, starting with the medial rectus. The insertion point for the medial rectus is the closest to the limbus (5.3mm), followed by the inferior rectus (6.8mm), lateral rectus (6.9mm), and finally the superior rectus, which inserts the furthest from the limbus (7.9mm).
While performing the unilateral cover test, the right eye assumes an exo position when covered. If the right eye were to maintain an exo position when the occluder is removed where would the target’s image fall on the retina in relation to the fovea?
The target’s image would be nasal to the fovea
The target’s image would be temporal to the fovea
The target’s image would be superior to the fovea
The target’s image would be inferior to the fovea
The target’s image would be temporal to the fovea
Explanation
An exo position places the fovea of the right eye nasal to the image projected from the object of regard. This is due to the outward rotation of the eye which rotates the fovea nasally relative to the object. This places the target’s image temporal to the fovea.
Using the Von Graefe method to determine the amount of phoria present at near on your patient he reports that the targets are lined up horizontally with 5 base up prism before the left eye. What conclusion can you deduce from the above results?
Left hyper deviation or right hypo deviation
Right hyper deviation or left hypo deviation
Esophoria of 5 prism diopters
Exophoria of 5 prism diopters
Right hyper deviation or left hypo deviation
Explanation
When performing the Von Graefe method, a 4 base up dissociating prism is placed before the left eye and an 18 base in prism (biasing prism) is placed before the right eye. A single letter or target is projected at far (or near). The patient should initially perceive two targets with one being up and to the right and the other down and to the left . The 4 base up prism is then slowly reduced (either via intermittent occlusion or no occlusion) until the patient reports that the two targets are directly beside one another lined up horizontally. When the targets are aligned horizontally, the amount of prism before the left eye is recorded. If there is base up prism in front of the left eye then the deviation is described as either right hyperphoria or left hypophoria in the amount equal to the neutralizing prism before the left eye.
