Visual Pathway.pdf

Visual Pathway: great majority of VF defects begin in the central visual field, which is within 30 degrees of central fixation A single eye’s visual field has a normal range of 130 to 145 degrees Each eye has a physiological blind spot corresponding to the optic nerve (falls temporal to the eye we’r...

Visual Pathway: great majority of VF defects begin in the central visual field, which is within 30 degrees of central fixation A single eye’s visual field has a normal range of 130 to 145 degrees Each eye has a physiological blind spot corresponding to the optic nerve (falls temporal to the eye we’re evaluating) ○ 15 degrees temporal and 5 degrees inferior from central fixation Central VF: central 30 degrees; highly developed area of the retina responsible for detailed vision Reading, color vision, details, recognition Peripheral VF: specialized in the detection of motion signals Driving, enables safe navigation around our environment VF Dimensions: Temporal (100-110 degrees) Inferior (60-80 degrees) Nasal (60 degrees) Superior (50-60 degrees) VF eval.: VF loss or defect may be the only or most obvious sign that there is a lesion present in the visual pathway. All basic eye exams should include some form of VF evaluation VF defects may be present due to: ocular, systemic, or neurological disease or medications Glaucoma: used for diagnostic decisions and monitoring progression ○ Cannot be diagnosed w/o VF and OCT Choroid or retinal conditions: even though most are seen in ophthalmoscopy Practitioner can perform Confrontation Visual Fields (CVF)/Finger Counting Fields (FCF) ○ 8 VF locations: S, SN, N, IN, I, IT, T, ST ○ Recording: FCF/CVF: Full to Finger Counting (FTFC) FCF/CVF: Full Fields to Four Quadrants (FFFQ) FCF/CVF: Full OD/OS If not full, report areas are restricted OD: FTFC, OS: temporal restriction Drawings of constrictions ○ Expected findings: full VF in OD and OS If suspected of having a VFD or need to perform a more detailed VF evaluation: tangent screens, automated perimetry Perimetry: measurement of the VF where the eye is located at the center of a curved instrument and the targets are projected in an automated form Humphrey Automated VF Campimetry: measurement of the VF where the eye is located from a flat instrument and targets are presented Tangent Screen VF Defects Terminology Congruous (symmetric): the VFD is of the same size and shape in both eyes Incongruous (asymmetric): the VFD is not of the same size and/or shape in both eyes Quadrantanopia: loss of ¼ VF of one or both eyes Altitudinal defects: above or below the horizontal meridian ○ Associated with ocular abnormalities Homonymous: corresponding VF of the two eyes are affected ○ Affects the same half (either left or right) of the VF in each eye ○ Homonymous Incongruous Defect ○ Homonymous Congruous Defect Left or Right: in respect to the vertical meridian Superior or Inferior: in respect to the horizontal meridian Congruous Right Quadrantopia (“pie in the sky”) Left Homonymous Congruent Hemianopia Congruous Inferior Altitudinal Defect Incongruous (anterior lesion - optic tract or LGN) Depression/Constriction: a general reduction in overall sensitivity of the VF Can be described when evaluating with confrontation VF Generalized depression can be described when evaluating with a quantitive method such as Humphrey ○ Can be an early sign of glaucoma, but may also occur with aging, miosis or hazy media Automated VF compares the results with the population of the same age and will provide the mean deviation from the normal population Constriction Depression Scotoma: A VFD contained in an area within the boundaries of the overall VF; area of depressed vision in the VF, surrounded by an area of less depressed or normal vision Shallow or Relative: marks an area of the retina that is not sensitive to relatively dim stimuli but is sensitive to brighter/lighter stimuli ○ Patient has reduced sensitivity ○ The area is perceived as blurry by the patient ○ Deep or Absolute: no response to a stimuli regardless of brightness or size (definite absence of processing from this area) ○ Refers to a defective retinal area that cannot see (ex: physiologic optic nerve) ○ Hemianopic Scotoma: half of the central VF is depressed or lost Annular (ring) scotoma: circular area of depressed vision surrounding the point of fixation ○ Trial lens ring ○ Central scotoma: an area of depressed vision corresponding with the point of fixation and interfering with central vision Ceco-central scotoma: a horizontal oval defect in the field of vision situated between and embracing both the point of fixation and the blind spot ○ Peripheral scotoma: visual field defect distance from the fixation point Paracentral scotoma: VF defect around or near the central vision ○ ARMD, exudates, early glaucomatous VFD ○ Peri-central scotoma: a ring scotoma surrounding a normal fovea ○ Plaquenil toxicity can cause this scotoma ○ VF Defects: any visual field loss is related to the anatomy of the visual pathway Visual pathway lesion anterior to the optic chiasm (prechiasm) will produce a monocular ipsilateral defect Ex: macular hole, retinal detachments, glaucomatous changes, optic atrophy or optic neuropathy If OS optic nerve lesion = VFD in the OS only Chiasm lesions: if the lesion is in the center of the chiasm (mid-optic chiasm) will produce a bitemporal hemianopsia Close to the chiasm lies the pituitary gland and there is significant vasculature surrounding it if a patient presents with a bitemporal hemianopsia, rule out: tumor compressing pituitary gland (most common adenoma) or aneurysm of the anterior communicating artery Post-chiasm defects: the visual loss will present on the opposite side of the lesion (contralateral) due to the fiber crossing at the chiasm Any damage to the visual pathway behind the optic chiasm most often produces VFD in the left or right side of vision which affects both eyes Right complete homonymous hemianopsia: it affects the right side of both VF (homonymous); it is a complete loss of half of the VF (hemianopsia) Most common cause is a stroke in the left side of the brain ○ Right-sided defect, left-sided lesion VF defects continued: defects identified as superior, or inferior are referred to as altitudinal defects Pre-chiasmal altitudinal defects generally respect the horizontal meridian Post-chiasmal altitudinal defects generally respect the vertical meridian VF defects location: 1. ON lesion will cause partial or total loss of vision and VFD of that eye (monocular-ipsilateral) 2. Lesion to the proximal fibers of an ON and the nasal fibers of the opposite eye (before central chiasm), will cause a central VFD in one eye and a partial temporal VFD in the opposite eye (junctional scotoma) 3. Lesion in the center of the chiasm will cause a bitemporal hemianopsia 4. Lesion to the optic tract or a lesion that involves the complete optic radiations will cause a homonymous hemianopsia 5. Optic radiation lesions: a. Parietal lobe will cause an inferior quadrantanopsia (pie in the floor) b. Temporal lobe will cause a superior quadrantanopsia (pie in the sky) Generalized depression is seen in cataracts, early glaucoma. Central VFD is seen in optic neuritis, macular hole, cone dystrophy, BRAO, BRVO Peripheral VFD can be seen in retinitis pigmentosa, BRVO, BRAO, hysterical amblyopia, Streff Syndrome Hemianopia and quadrantanopia can be seen with strokes (CVA), traumatic brain injury (TBI), intracranial mass Altitudinal VFD can be seen in anterior ischemic optic neuropathy (AION), compressive neuropathy (due to a tumor or aneurysm), BRAO, BRVO, papilledema, disc edema