Visual field

In glaucoma, visual field defects result from damage to the retinal nerve fiber layer. Field defects are seen mainly in primary open angle glaucoma. Because of the unique anatomy of the RNFL, many noticeable patterns are seen in the visual field. Most of the early glaucomatous changes are seen within the central visual field, mainly in Bjerrum's area, 10°-20° from fixation.[10]

Following are the common glaucomatous field defects:

Bjerrum's area and types of scotomas on the visual field

• Generalized depression: Generalized depression is seen in early stages of glaucoma and many other conditions. Mild constriction of the central and peripheral visual field due to isopter contraction comes under generalized depression. If all the isopters show similar depression to the same point, it is called a contraction of the visual field. Relative paracentral scotomas are the areas where smaller and dimmer targets are not detected by the patient.[10] Larger and brighter targets can be seen. Small paracentral depressions, mainly superonasal, occur in normal-tension glaucoma (NTG).[11] The generalized depression of the entire field may occur in cataract also.[9]
• Baring of blind spot: Baring of the blind spot means the exclusion of the blind spot from the central field due to inward curve of the outer boundary of the 30° central field.[12] It is only an early, non-specific visual field change, without much diagnostic value in glaucoma.[12]
• Small wing-shaped Paracentral scotoma: Small wing-shaped Paracentral scotoma within Bjerrum's area is the earliest clinically significant field defect seen in glaucoma. It may also be associated with nasal steps. Scotoma may be seen above or below the blind spot.[12]
• Siedel's sickle-shaped scotoma: Paracentral scotoma joins with the blind spot to form Siedel's sickle-shaped scotoma.
• Arcuate or Bjerrum's scotoma: This kind of scotoma is formed at later stages of glaucoma by extension of Seidel's scotoma in an area either above or below the fixation point to reach the horizontal line. Peripheral breakthrough may occur due to damage of nerve fibers.[12]
• Ring or Double arcuate scotoma: Two arcuate scotomas join to form a Ring or Double arcuate scotoma. This defect is seen in advanced stages of glaucoma.
• Roenne's central nasal step: It is created when two arcuate scotomas run in different arcs to form a right angled defect. This is also seen in advanced stages of glaucoma.
• Peripheral field defects: Peripheral field defects may occur in early or late stages of glaucoma. Roenne's peripheral nasal steps occur due to contraction of peripheral isopter.[12]
• Tubular vision: Since macular fibers are the most resistant to glaucomatous damage, central vision remains unaffected until the end stages of glaucoma. It results in Tubular vision, or Tunnel vision, by the loss of peripheral vision with retention of central vision, resulting in a constricted circular tunnel-like field of vision. Retinitis pigmentosa, is another disease that causes tubular vision.[13]
• Temporal island of vision: It is also seen in end stages of glaucoma. The temporal islands lie outside of the central 24 to 30° visual field,[14] so it may not be visible with standard central field measurements done in glaucoma.

The macula of the retina is the central area in the visual field of about 10 to 17 deg diameter (in visual angle). It is responsible for high-resolution vision in good light, in particular for reading. Many diseases affecting the macula may cause defects in the central field of vision, among them Metamorphopsia and central scotomas.

Visual pathway lesions
From top to bottom:
1. Complete loss of vision in the right eye
2. Bitemporal hemianopia
3. Homonymous hemianopia
4. Quadrantanopia
5.& 6. Quadrantanopia with macular sparing

The visual pathway consists of structures that carry visual information from the retina to the brain. Lesions in the pathway cause a variety of visual field defects. The type of field defect can help localize where the lesion is located (see figure).

• A lesion in the optic nerve of one eye causes partial or complete loss of vision in the same eye, with an intact field of vision in other eye.
• A lesion at the proximal part of optic nerve of one eye cause, central field defect in one eye and temporal half-field defect in the other eye (not shown in the figure).[15]
• A lesion in the center of the optic chiasma causes bitemporal hemianopia[15]
• A lesion to the optic tract, or involving the complete optic radiation causes homonymous hemianopia
• When part of the optic radiation in the parietal lobe is affected, the resulting field defect may be inferior quadrant hemianopia[15]

• Cerebral palsy: Field loss due to cerebral palsy may be hemianopic affecting even upper or lower half, central scotoma, peripheral scotoma, or islands of vision.[16]
• Epilepsy: Although field defects are rarely associated with epilepsy,[17] defects may occur after temporal lobe surgery for epilepsy.[18]
• Periventricular leukomalacia (PVL): Bilateral inferior visual field defects may occur due to damage of the optic radiations[19]

• Generalized depression is seen in cataract
• Central visual field loss is seen in Optic neuritis,[20] Leber hereditary optic neuropathy,[21] Macular hole,[22] Cone dystrophy,[23] Branch retinal artery occlusion[24] etc.
• Peripheral visual field loss including tunnel vision is seen in Retinal detachment, Retinitis pigmentosa,[25] Branch retinal vein occlusion[24] etc.
• Hemianopia and quadrantanopia are seen in patients with stroke, traumatic brain injury, tumor etc.[26]
• Altitudinal visual field defect is seen anterior ischemic optic neuropathy, compressive neuropathy (due to a tumor or aneurysm),[26] Branch retinal artery occlusion, Branch retinal vein occlusion, Coloboma, Papilloedema, lesions in visual cortex etc.[27]