Editing Visual field (section)

===Visual field defects in glaucoma===
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.<ref name="Parson-GL">{{cite book |title=Parsons' diseases of the eye |publisher=Elsevier |isbn=978-81-312-3818-9 |pages=288–295 |edition=22 |chapter=Glaucoma|date=15 July 2015 }}</ref>

Following are the common glaucomatous field defects:
[[File:Bjerrums area and types of scotomas on the visual field.png|thumb|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 [[wikt:isopter|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.<ref name="Parson-GL" /> Larger and brighter targets can be seen.  Small paracentral depressions, mainly superonasal, occur in normal-tension glaucoma (NTG).<ref name="Kanski-GL">{{cite book |last1=John F |first1=Salmon |title=Kanski's Clinical ophthalmology |publisher=Elsevier |edition=9 |chapter=Glaucoma|pages=362–365}}</ref> The generalized depression of the entire field may occur in cataract also.<ref name="Eyerounds">{{cite web |author1=Joy N. Carroll |author2=Chris A. Johnson |title=Visual Field Testing: From One Medical Student to Another |url=https://eyerounds.org/tutorials/VF-testing/ |date=2013-08-22}}</ref>
* '''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.<ref name="Khurana-GL">{{cite book |last1=Khurana |title=Comprehensive ophthalmology |publisher=Jaypee, The Health Sciences Publisher |isbn=978-93-5152-657-5 |pages=223–224 |edition=6th |chapter=Glaucoma|date=31 August 2015 }}</ref> It is only an early, non-specific visual field change, without much diagnostic value in glaucoma.<ref name="Khurana-GL"/>
* '''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.<ref name="Khurana-GL"/>
* '''Siedel's sickle-shaped scotoma''': Paracentral scotoma joins with the [[Blind spot (vision)|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.<ref name="Khurana-GL"/>
* '''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.<ref name="Khurana-GL"/>
* '''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.<ref>{{Cite web|title = Retinitis pigmentosa|url = http://ghr.nlm.nih.gov/condition/retinitis-pigmentosa|website = Genetics Home Reference}}</ref>
* '''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,<ref>{{cite web |last1=Themes |first1=U. F. O. |title=Visual Fields in Glaucoma |url=https://entokey.com/visual-fields-in-glaucoma/#:~:text=The%20typical%20visual%20field%20in,24%20to%2030%C2%B0%C2%B0 |website=Ento Key |date=11 July 2016}}</ref> so it may not be visible with standard central field measurements done in glaucoma.