Editing Visual field (section)

==Visual field loss==
Visual field loss may occur due to many disease or disorders of the [[human eye|eye]], [[optic nerve]], or [[brain]]. For the eye, e.g., Glaucoma causes peripheral field defects. [[Macular degeneration]] and other diseases affecting the macula cause central field defects. Lesions of the visual pathway cause characteristic forms of visual disturbances, including homonymous [[hemianopsia]], [[quadrantanopsia]], and scotomata.

The main classification of visual field defects is into
#Lesions to the eye's retina (heteronymous field defects in Glaucoma and AMD)
#Lesions of the optic nerve (heteronymous field defects)
#Lesions in the chiasm (e.g. Bitemporal hemianopia, loss of vision at the sides)
#Lesions after the chiasm (homonymous field defects like homonymous [[hemianopia]], [[Quadrantanopia]], homonymous [[scotoma]]ta)

Other characterisations are:
#Altitudinal field defects, loss of vision above or below the horizontal meridian – associated with ocular abnormalities
#[[Central scotoma]], loss of central vision
#Peripheral field loss including [[tunnel vision]]
#Generalized depression of the entire field of vision <ref name="Eyerounds" />

===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.

===Field defects in macular degeneration (AMD)=== 
{{main|Macular degeneration}}

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 [[scotoma]]s.

===Field defects in visual pathway lesions=== 
{{main|Visual pathway lesions}}
{{See also|Visual system}}
[[File:Hemianopsia en.jpg|thumb|350px|right|'''Visual pathway lesions''' <br>
From top to bottom: <br> 1. Complete loss of vision in the right eye <br> 2. Bitemporal hemianopia <br> 3. Homonymous hemianopia <br> 4. Quadrantanopia <br> 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 scotoma|central field defect]] in one eye  and temporal half-field defect in the other eye (not shown in the figure).<ref name="Khurana-NO">{{cite book |last1=Khurana |title=Comprehensive ophthalmology |publisher=Jaypee, The Health Sciences Publisher |isbn=978-93-5152-657-5 |pages=314–315 |edition=6th |chapter=Neuro-ophthalmology|date=31 August 2015 }}</ref>
*A lesion in the center of the [[optic chiasma]] causes [[bitemporal hemianopia]]<ref name="Khurana-NO" /> 
*A lesion to the [[optic tract]], or involving the complete [[optic radiation]] causes [[Homonymous hemianopsia|homonymous hemianopia]]
*When part of the optic radiation in the [[parietal lobe]] is affected, the resulting field defect may be inferior [[Quadrantanopia|quadrant hemianopia]]<ref name="Khurana-NO" />

===Neurological causes of visual field defects===
* '''[[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.<ref>{{cite web |title=Cerebral Palsy and Children with Vision and Hearing Loss |url=http://www.tsbvi.edu/seehear/fall98/cpvh.htm |website=www.tsbvi.edu}}</ref>
* '''[[Epilepsy]]''': Although field defects are rarely associated with epilepsy,<ref>{{cite journal |last1=G |first1=Valli |last2=S |first2=Zago |last3=A |first3=Cappellari |last4=A |first4=Bersano |s2cid=22141996 |title=Transitory and Permanent Visual Field Defects Induced by Occipital Lobe Seizures |journal=Italian Journal of Neurological Sciences |language=en |date=1999|volume=20 |issue=5 |pages=321–5 |doi=10.1007/s100720050048 |pmid=10933442 }}</ref> defects may occur after temporal lobe surgery for epilepsy.<ref>{{cite journal |last1=Manji |first1=H. |last2=Plant |first2=G. T. |title=Epilepsy surgery, visual fields, and driving: a study of the visual field criteria for driving in patients after temporal lobe epilepsy surgery with a comparison of Goldmann and Esterman perimetry |journal=Journal of Neurology, Neurosurgery & Psychiatry |date=1 January 2000 |volume=68 |issue=1 |pages=80–82 |doi=10.1136/jnnp.68.1.80 |pmid=10601407 |pmc=1760599 |language=en |issn=0022-3050|doi-access=free }}</ref> 
* '''[[Periventricular leukomalacia]]''' (PVL): Bilateral inferior visual field defects may occur due to damage of the [[optic radiation]]s.<ref>{{cite journal |last1=Kozeis |first1=N |title=Brain visual impairment in childhood: mini review |journal=Hippokratia |date=2010 |volume=14 |issue=4 |pages=249–251 |pmid=21311632 |pmc=3031318 |issn=1108-4189}}</ref>

===Other causes of field defects===
* Generalized depression is seen in [[cataract]]
* Central visual field loss is seen in [[Optic neuritis]],<ref>{{cite web |author1=Benjamin Osborne |author2=Laura J Balcer |title=Optic neuritis: Pathophysiology, clinical features, and diagnosis |url=https://www.uptodate.com/contents/optic-neuritis-pathophysiology-clinical-features-and-diagnosis#:~:text=The%20visual%20field%20defect%20in,%2C%20hemianopic%2C%20and%20cecocentral%20defects. |website=www.uptodate.com}}</ref> [[Leber hereditary optic neuropathy]],<ref>{{cite web |title=Leber Hereditary Optic Neuropathy |url=https://rarediseases.org/rare-diseases/leber-hereditary-optic-neuropathy/ |website=NORD (National Organization for Rare Disorders)}}</ref> [[Macular hole]],<ref>{{cite web |title=Macular Hole - The American Society of Retina Specialists |url=https://www.asrs.org/patients/retinal-diseases/4/macular-holepucker |website=www.asrs.org}}</ref> Cone dystrophy,<ref>{{cite web |title=Cone Dystrophy |url=https://rarediseases.org/rare-diseases/cone-dystrophy/#:~:text=Cone%20dystrophy%20can%20variably%20cause,broad%20groups%20%2D%20stationary%20and%20progressive. |website=NORD (National Organization for Rare Disorders)}}</ref> [[Branch retinal artery occlusion]]<ref name="AAV-ES" /> etc.
* Peripheral visual field loss including tunnel vision is seen in [[Retinal detachment]], [[Retinitis pigmentosa]],<ref>{{cite web |title=Retinitis Pigmentosa Symptoms |url=https://www.aao.org/eye-health/diseases/retinitis-pigmentosa-symptoms |website=American Academy of Ophthalmology |language=en |date=30 October 2019}}</ref> [[Branch retinal vein occlusion]]<ref name="AAV-ES">{{cite web |title=Eye Occlusions, Blockages or Eye Strokes |url=https://www.allaboutvision.com/conditions/eye-occlusions.htm |website=All About Vision |language=en}}</ref> etc.
* Hemianopia and quadrantanopia are seen in patients with [[stroke]], [[traumatic brain injury]], [[Brain tumor|tumor]] etc.<ref name="ncbi.nlm.nih.gov">{{cite journal |last1=Elgin |first1=Jennifer |last2=McGwin |first2=Gerald |last3=Wood |first3=Joanne M. |last4=Vaphiades |first4=Michael S. |last5=Braswell |first5=Ronald A. |last6=DeCarlo |first6=Dawn K. |last7=Kline |first7=Lanning B. |last8=Owsley |first8=Cynthia |title=Evaluation of On-Road Driving in Persons with Hemianopia and Quadrantanopia |journal=The American Journal of Occupational Therapy |date=2010 |volume=64 |issue=2 |pages=268–278 |doi=10.5014/ajot.64.2.268 |pmid=20437914 |pmc=2964938 |issn=0272-9490}}</ref>
* Altitudinal visual field defect is seen [[anterior ischemic optic neuropathy]], compressive neuropathy (due to a tumor or aneurysm),<ref name="ncbi.nlm.nih.gov"/> Branch retinal artery occlusion, Branch retinal vein occlusion, [[Coloboma of optic nerve|Coloboma]], [[Papilloedema]], lesions in [[visual cortex]] etc.<ref>{{cite journal |author1=Akash Raj |title=ALTITUDINAL VISUAL FIELD DEFECT |journal=Journal of the Bombay Ophthalmologists' Association |volume=11 |page=127 |url=http://www.boamumbai.com/journalpdfs/oct-dec01/altitudfielddefect.PDF}}</ref>