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Walker HK, hall WD, Hurst JW, editors. Clinical Methods: The History, Physical, and also Laboratory Examinations. 3rd edition. Boston: Butterworths; 1990.


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Definition

The field of vision is that portion of room in i beg your pardon objects space visible in ~ the very same moment during steady permanent of gaze in one direction. The monocular intuitive field consists of main vision, which has the within 30 degrees of vision and main fixation, and the peripheral visual field, which extends 100 levels laterally, 60 levels medially, 60 degrees upward, and 75 levels downward (Figure 116.1) A vertical heat bisects central fixation and also divides the visual ar into a nasal and temporal hemifield. Situated in the temporal hemifield is the normal blind spot about 12 come 17 levels from fixation and also 1.5 degrees below the horizontal meridian. The blindspot is represented on a visual field chart by an absolute scotoma and also corresponds anatomically to the scleral canal v which the retinal nerve fibers leaving the eye at the optic disk.


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Figure 116.1

Normal intuitive field. I-4e is a bigger target 보다 I-2e.


A normal visual field is an island the vision measuring 90 levels temporally to main Fixation, 50 degrees superiorly and also nasally, and 60 degrees inferiorly. Intuitive acuity rises from activity discrimination in the extreme peripheral vision to much better than 20/20 in the center of vision. Depression or absence of vision all over in the island of vision is abnormal.


Technique

A perimetrist is a human being who actions the visual ar with a machine called a perimeter. Various perimetric techniques and also apparatus room available. In each kind of testing, however, including confrontation ar testing, patients need to be continuous urged to keep steady fixation right ahead if objects of varying size, color, or luminosity transcend their visual threshold. V kinetic perimetry, objects are moved from external the border of visual perception toward fixation. When the patience perceives the details test object, a set of visual threshold points are plotted by the perimetrist. The line the connects these comparable visual thresholds is dubbed an isopter. In figure 116.1, the huge oval circle indicates that the target I-4e was checked out at every these point out of the intuitive field during steady gaze on main fixation. A smaller sized target (I-2e) subtends a smaller sized amount of intuitive field. A Goldmann perimeter utilizes different-type targets that have the right to be varied according to size and also light intensity. The larger or brighter objects are perceived in the periphery while smaller targets outline boundaries and defects the the main visual field. Depression the the visual field, defined as an inward shift of a specific isopter, is depicted in figure 116.2. If all the isopters show similar depression to the very same point, the is then referred to as a convulsion of intuitive field. In neighborhood contraction, only component of the ar including the periphery is restricted; however in concentric contraction, the whole peripheral vision is attenuated.


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Figure 116.2

(A) Depression the the upper nasal isopters. (B) contraction of the temporal field.


There is a great variety in both the methods and also apparatus supplied for examining fields the vision. Quantified visual field experimentation with one of two people a Goldmann perimeter or a tangent screen is ideal yet may it is in impractical or impossible in a an excellent many situations. Patients may be too ill to be relocated to the device and experimentation rooms, and also children and aphasic or demented subjects certainly cannot comply with the examiner"s complicated directions. For these situations, the is necessary to understand the approaches of confrontation visual field testing.

Each eye should be tested individually in four steps:


Ask the patient to look at her nose and count fingers organized briefly in the area of central fixation.
Move and flash her fingers in each of the four quadrants the vision, simultaneously encouraging the patience to maintain fixation on your nose. That is best to flash only one, two, or all five fingers since three and also four finger are complicated to distinguish.
To depict dual simultaneous sensory stimulation, hold your hands around 18 inches (45 cm) apart and flash fingers concurrently in the nasal and temporal hemifields. Again, the patience must keep fixation. A variety of permutations should be tried. Because that instance, with the patient"s ideal eye fixing, raise one finger through your left hand and two fingers through your appropriate hand; then organize up two fingers through your left hand and one ~ above the right. If the patient an initial sees only one finger and also then in the second component of the test sees only the hand with two fingers, you may suspect a nasal ar defect that the appropriate eye.
Hold both hands in the hemifield under suspicion (in this case, the nasal ar of the ideal eye) and also flash the fingers above and listed below the horizontal meridian, thereby trial and error the upper and lower parts of the impacted field of vision.

The techniques used to explore visual ar defects in younger patients are comparable to those used in adults who room dysphasic, illiterate, or obtunded. The human challenge is wonderful fixational target. Among our most primitive visual reflexes is to carry interesting fixational targets into main fixation. This fixational reflex may be put to usage by observing an individual"s eye activities as the examiner"s challenge enters the visual ar along different meridians.

Color perception is a an ext refined and much more sensitive parameter of visual field function. The relative lack of shade perception in one eye or in one-half the the visual ar may it is in the important manifestation of an active or resolved intra-cranial lesion. On the wards or in an emergency room, a qualitative assessment of color vision may be acquired by asking the patient to to compare the wealth or brightness that a primary shade shown very first to the ideal eye and also then to the left. A patient through a main or cecocentral scotoma, as result of an optic nerve lesion, will typically report that the fancy objects show up dimmer, duller, or not as bright in the affected eye.

A comparison of brightness or wealth of color can likewise be supplied to assess sleep versus temporal field perception. Every eye is experiment individually. In order to discover the opportunity of an hemianopic defect, two an in similar way colored objects are held prior to the patient with one in the nasal and the other in the temporal zone that vision. The patient, instructed to keep fixation ~ above the examiner"s nose, speak whether the two objects watch the exact same or even if it is one appears brighter or duller than the other. The object in an undamaged hemifield will usually be described as brighter or richer in hue; perception of a darker or duller thing presents a potential zone that defective vision that should be more explored by moving the target indigenous the area of relatively poor saturation right into the brighter area. Together this is done, the patient is inquiry to determine the exact allude at i beg your pardon the relocating object becomes as bright together the companion stimulus. The point of shift is very closely noted. If that lines up through an imaginary line attracted through the suggest of fixation, it is extremely probable that the area of shade desaturation represents a ethereal hemianopic ar defect. Locations of dull perception should always be explored by moving the test stimulus slowly into area of brighter experience. In this manner, a careful and also patient clinician may detect little hemianopic, quadrantic, and even cecocentral ar defects.

The tangent display is a black felt display on which radial lines and 5-degree concentric circles are inconspicuously marked. It is provided to examine the main field in ~ 30 levels from fixation and to recognize the dimension of the blind spot. Due to the fact that the papillomacular bundle forms 90% of all the optic nerve axons, and also subserves the main 30 levels of vision, the tangent display is wonderful tool for evaluating neurologic-type field defects. The examiner stand in former of the patient to watch fixation and works from every side that the screen in turn. White or colored targets room fitted top top wands, i beg your pardon are progressively moved from outside visual perception towards fixation. Although an excellent versatility is a component of this technique, a distinct disadvantage is additionally obvious: The examiner"s arm and also body can be a distraction come a patient that is trying come concentrate and also maintain continuous on a tiny white target.

The hemispheric estimate perimeter (Goldmann perimeter) is a specific and popular instrument for trial and error both the peripheral and main portions of intuitive field. It affords a amazing speed of operation for kinetic perimetry and also luminence of the hemispheric background deserve to be retained precisely controlled to keep retinal light adaptation constant. Permanent is maintained by the perimetrist through a telescope i beg your pardon is a an ext accurate technique than provided with the tangent screen. Projected point out of continuous size and also fixed contrast are relocated from the periphery in towards the center.


Topical Localization that Visual ar Defects

To translate the results of perimetry accurately, the reader need to firmly recognize some an easy neuroanatomy the the visual pathway. The major visual sensory pathway in humans is composed of the retina, optic nerves, chiasm, and also optic tract, along with the lateral geniculate bodies, geniculo-calcarine radiations, and also the occipital cortex. Secondary complex nerve fiber systems affix the occipital striate cortex through the ipsilateral and also contralateral intuitive association areas.

The retina is a well-differentiated stratified sensory membrane. Occurrence light eventually stimulates the ganglion cell layer that the retina and axons from ganglion cell course toward the optic disc in three an easy patterns: a papillomacular bundle, which occurs from the macula or main point the the retina, superior and also inferior arcuate bundle, which comes from the temporal retina, and also radial fibers from the sleep retina (Figure 116.3). An imagine vertical and horizontal line through the macular anatomically divides the retina right into nasal/temporal, superior/inferior halves, respectively. Nasal axons subserve the temporal fifty percent of vision, temporal axons the nasal hemifield, remarkable axons the reduced visual field, and also inferior axons the premium visual field.


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Figure 116.3

Retinal nerve Fibers: M, papillomacular bundle; 1,4 superior and inferior arcuate bundles; 2,3 superior and also inferior sleep fibers.


The papillomacular bundle represents an ext than 90% of all the retinal nerve fibers in the optic nerve. It projects pictures from the macula and functions to maintain sharp emphasis of central fixation. Lesions that interrupt the papillomacular bundle produce main or cecocentral scotomas (Figure 116.4). A scotoma is an area of poor vision surrounded on every sides through relatively far better vision. The arcuate fibers surround the papillomacular bundle, originating above, below, and also temporal to it. Lesions the the arcuate bundle create arcuate or cuneate-shaped scotomas (Figure 116.5). Damage to the premium arcuate bundle, because that instance, in glaucoma, manifests together an worse arcuate scotoma.


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Lesions of nasal retinal axons cause temporal ar defects. If the sleep axons nearest the macula room spared, the resulting field defect mirrors sparing the the parafixational temporal hemifield (Figure 116.6). Yet if the nasal fiber components of the papillomacular and also arcuate fibers are involved, a temporal hemianopia is noted. All of the affiliated temporal field is affected; hence, the ar defect abuts up against the vertical meridian (Figure 116.6B). Intracranial lesions that the optic chiasm and retrochiasmal visual pathway create hemianopia, that is, visual field defects i beg your pardon "respect" the vertical meridian.


Optic Chiasm

All the sleep retinal yarn decussate in the optic chiasm (Figure 116.7). However the inferior sleep fibers rotate rostrally into the the contrary optic nerve prior to projecting earlier into opposing optic tract. This anterior elbow of inferior nasal axons right into the opposite optic nerve is dubbed Von Wille-brand"s knee. Lesions of the posterior optic nerve whereby it joins with the optic chiasm will develop impaired vision in the ipsilateral eye and also an top temporal ar loss in the contralateral eye (Figure 116.8), a syndrome described as a junctional scotoma.


Figure 116.7

Note anterior angulation of crossing inferior sleep fields before they project posteriorly to form optic tract. Superior nasal yarn cross directly to opposite side and also align v uncrossed superior and also inferior temporal retinal fibers.


Damage to the human body of the optic chiasm chin produces bitemporal hemianopia (Figure 116.9). Lesions of the optic tract produce homonymous hemianopia; specifically, incongruous homonymous hemianopia (Figure 116.10). Incongruity refers to asymmetry that the visual field defects. Within the optic tract the crossing nasal fibers and also the uncrossed temporal yarn are relatively separated anatomically. Hence, corresponding points of the visual ar from every eye are not carefully aligned. Visual ar loss from lesions of the optic street or the lateral geniculate body impact each eye differently (Figure 116.10), causing asymmetric ar loss in each eye. Retrogeniculate homonymous ar defects are virtually always congruous or specifically alike because the nasal and also temporal yarn from corresponding points in the visual ar are carefully opposed.


Optic Tract

Optic street fibers synapse at the lateral geniculate body and project backward as the geniculo-calcarine radiations. Every the retrogeniculate fibers move laterally and also inferiorly roughly the temporal horn that the lateral ventricle. The most anterior-inferior fibers kind Meyer"s loop, which consists of projections of the worse retinal fibers. Hence, lesions the Meyer"s loop, situated primarily in the temporal lobe, create congruous, exceptional homonymous quadrantanopias (Figure 116.11); more superiorly situated parietal lobe lesions create the train station defects, inferior homonymous hemianopias or quadrantanopias.


Visual Cortex

The striate or major visual cortex of human beings occupies the medial and also posterolateral surfaces of the occipital lobe. Striate cortex can be discovered above, below, and also even within the walls and also floor of the calcarine fissure itself. Topographically, the central or parafixational zone of every hemifield is subserved by retinal axons that ultimately terminate at the many posterior pole that the intuitive cortex. A lesion below will create a homonymous, paracentral hemianopic scotoma. Such defects involve the central 5 to 10 degrees of vision and may preventive the remainder of visual field if the remainder that the striate cortex is forgive (Figure 116.12). The opposite-type ar defect, a homonymous hemianopia "with macular sparing," occurs through occipital lesions the spare the posterolateral striate cortex (Figure 116.13).


The peripheral section of each hemifield, which contains the temporal monocular crescent, jobs to the anterior lip of the calcarine fissure. Lesions that spare the anterior cortex will cause homonymous hemianopias with sparing the the peripheral hemifield or temporal crescent. The temporal crescent is a 30-degree segment the temporal field that starts 60 levels from fixation. It is totally unshared and monocular (i.e., checked out by one eye only). This nasal retinal axons decussate in the optic chiasm and terminate in ~ the many anterior occipital cortex. Focal damages here could theoretically create a monocular visual field defect the only requires the temporal crescent that the contralateral eye. Sparing the the temporal crescent, ~ above the various other hand, in the visibility of a congruous homonymous hemianopia permits exact localization of the website of the lesion to the contralateral posterior occipital cortex.

Bilateral homonymous hemianopsias result from bilateral, commonly ischemic lesions that the intuitive cortices. If every homonymous field defect involves the parafixational zone, the merged defects lead to a central scotoma and also loss of main vision. Cortical blindness is identified by (1) symmetric ns of intuitive acuity, (2) relatively normal pupils and fundal structures, (3) refusal of blindness, and also (4) bilateral occipital–cortical lesions.

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Accurate visual ar testing and an intelligent interpretation of the outcomes can administer the wary examiner through extremely helpful information about the site and also sometimes the specific histologic kind of lesion. Because the visual sensory pathway of human beings spans the brain from front come back, visual ar abnormalities are current in a wide selection of CNS and orbital disorders. Some of these incorporate orbital and parasellar tumors, the amenorrhea-galactorrhea syndromes, diabetes insipidus, multiple sclerosis, starvation, administration of details drugs (e.g., ethambutol), cerebrovascular disease, and many more. The reader must be maybe to use these principles now come the day-to-day review of neurologic and ophthalmologic problems.