Visual System Flashcards
Differentiate between Argyll-Robertson Pupil and Holmes-Aide Pupil.
Which structures are involved?
Argyll-Robertson Pupil - result of syphilis infection. Clinically, the pupils are unreactive to light, but constrict during accommodation. This is probably due to the destruction of the pretectum, which is important in the light reflex, but not in accommodation.
Holmes-Aide Pupil - tonic (Adie) pupil is a benign condition, which may be due to a lesion of the ciliary ganglion; Initially, the tonic pupil does not appear to react to convergence. However, if convergence is maintained for several seconds, the pupil will slowly constrict; eventually, the affected pupil may be smaller than the normal pupil.
Describe how you are to test and interpret the visual fields.
ALWAYS test with ONE eye closed!
- Lesions of the visual system are ALWAYS described in terms of their visual field deficits
- Visual field deficits are described from the perspective of the patient’s right or left
Differentiate between the visual and retinal fields.
Visual Field - An irregular, oval shape. The binocular field is that part of the visual field, which is seen by both eyes; that part seen only by one eye is the monocular field. The macular field is usually binocular and focused on the macula. The absence of receptors at the optic disc presents a normal scotoma (blind spot) in the visual field
Retinal Field - divided into 2 halves: the nasal and temporal hemiretinas. It may also be divided into four quadrants: the upper and lower temporal retinal quadrants, and the upper and lower nasal retinal quadrants.
Describe Retinotopic Projection.
Describe the Rule of “L’s”
Fibers from the Temporal Hemiretina DO NOT CROSS @ the Optic Chiasm, only the fibers from the Nasal Hemiretina CROSS @ the Optic Chiasm
Rule of L’s:
- Information from the Lower hemiretina projects to the Lateral part of the Lateral geniculate body, the Loop of Meyer (portion that projects forward from the lateral geniculate body), and the Lingual gyrus.
Describe the relationship between the Visual and Retinal Fields.
Visual field projects an INVERTED and REVERSED image onto the retina!
Only Nasal Hemiretina will CROSS @ the OPTIC CHIASM
Differentiate between homonymous and heteronymous visual fields.
- *Homonymous** - Same Colors (Temporal Hemiretina in right eye and Nasal Hemiretina in the left eye)
- EVERYTHING POSTERIOR to the OPTIC CHIASM
- *Heteronymous** - Different Colors (Both Temporal Hemiretinas from right and left eyes)
- Travel in Optic NERVE
Differentiate between voluntary and nonvolitional eye movements.
Voluntary Eye Movements - controlled by the frontal eye fields in the posterior portion of the middle frontal gyrus
Nonvolitional Eye Movements - occipital eye fields in the visual association cortex project corticotectal fibers to the superior colliculus, which controls unconscious (nonvolitional) eye movements
What is hemianopia?
A blindness (-anopia or -anopsia) of one-half of the visual field.
In clinical terms, a nasal hemianopia of the left eye indicates a lesion of the temporal hemiretina of the left eye, or somewhere along the length of the retinogeniculocalcarine pathway, which conveys that specific information.
Describe the lesion in the optic pathway:
Monocular Blindness
Monocular Blindness - Unilateral Lesion of the Optic Nerve
Describe the lesion in the optic pathway:
Binasal Hemianopia
Which structure is involved in this lesion?
Binasal Hemianopia - bilateral lesion of the lateral aspect of the optic chiasma that results in a heteronymous blindness in the nasal fields of each eye. It may also be only unilateral, since it is frequently due to atherosclerosis of the internal carotid arteries.
Describe the lesion in the optic pathway:
Unilateral Lesion of the Lateral Aspect of the Optic Chiasm
Unilateral lesion of the lateral aspect of the optic chiasm - results in a nasal hemianopia of the ipsilateral eye. Below is an example of a lesion of the temporal retina of the left eye that would result in a (right) nasal hemianopia of the left eye.
Describe the lesion in the Optic Pathway:
Bitemporal Hemianopia
What other symptoms does this lesion also present with?
1 MOST COMMON TEST QUESTION ON BOARDS!!!!!
Bitemporal hemianopia - may be due to a midline lesion of the medial portion of the optic chiasma. This heteronymous deficit is usually caused by pituitary tumors.
**** Going to also have HORMONAL ABORMALITIES (pituitary gland) and RECENT MEMORY IMPAIRMENT (mamillary bodies)
Describe the lesion in the Optic Pathway:
Contralateral homonymous hemianopia
Contralateral homonymous hemianopia - Unilateral lesions of the lateral geniculate body, complete optic radiations or visual cortex result in a contralateral homonymous hemianopsia. Below is an example of a left homonymous hemianopia, which would indicate a lesion on right visual pathway, i.e., optic tract, lateral geniculate body or complete optic radiations.
Describe the lesion of the Optic Pathway:
Contralateral superior quadrantanopia
Where is the tumor going to be present in order to cause this lesion pattern?
Contralateral superior quadrantanopia - Unilateral lesions of the loop of Meyer usually result in this homonymous deficit. It may be caused by a tumor or infarction in the posterior temporal lobe. Below is an example of a left superior quadrantanopia, which would indicate a lesion of the right loop of Meyer.
Describe the lesion in the Optic Pathway:
Incongruent contralateral homonymous hemianopia with macular sparing
Which structure is going to be obstructed in order to cause this lesion pattern?
Incongruent contralateral homonymous hemianopia with macular sparing - indicative of a unilateral lesion of the visual cortex. It may be due to obstruction of the posterior cerebral artery (PCA). Lesions of the visual cortex are usually incongruous (asymmetrical) whereas lesions of the LGB or optic radiations are congruous (BILATERAL) in their visual field deficits. Below is an example of a left incongruent homonymous hemianopia with macular sparing, which would indicate a lesion of the right primary visual cortex.
- D
- B
- E
- A
- D
