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HOW TO UNDERSTAND IT How to interpret visual fields

How to interpret visual fieldsSui H Wong,1,2 Gordon T Plant1,2,31 Department of Neuro-ophthalmology, Moorfields EyeHospital, London, UK2 Medical Eye Unit, St Thomas Hospital, London, UK3 National Hospital for Neurologyand Neurosurgery, London, UKCorrespondence toDr Sui H Wong, Consultant inNeuro-ophthalmology,Moorfields Eye Hospital,162 City Road, LondonEC1V 2PD, 31 May 2015 Published Online First3 July 2015To cite:Wong SH, Plant ;15:374 you are assessing a patient withvisual difficulties or optic disc a bedside visual field examinationwith waggling fingers and even a redhatpin, you decide that there is an abnor-mality. After requesting quantified visualfield tests, the patient returns with ablack and white printout with numbers(eg, Humphrey fields ) or coloured lineson a sheet (eg, Goldmann fields ).

May 31, 2015 · apply to results from Octopus machines. It is beyond the scope of this paper to cover the neuroanatomical localisation of visual field defects. Instead we recom-mend two excellent recent reviews.12 Skilled interpretation of visual field tests requires a good grasp and application of this prior knowledge. Useful aspects of eye anatomy 1.

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Transcription of HOW TO UNDERSTAND IT How to interpret visual fields

1 How to interpret visual fieldsSui H Wong,1,2 Gordon T Plant1,2,31 Department of Neuro-ophthalmology, Moorfields EyeHospital, London, UK2 Medical Eye Unit, St Thomas Hospital, London, UK3 National Hospital for Neurologyand Neurosurgery, London, UKCorrespondence toDr Sui H Wong, Consultant inNeuro-ophthalmology,Moorfields Eye Hospital,162 City Road, LondonEC1V 2PD, 31 May 2015 Published Online First3 July 2015To cite:Wong SH, Plant ;15:374 you are assessing a patient withvisual difficulties or optic disc a bedside visual field examinationwith waggling fingers and even a redhatpin, you decide that there is an abnor-mality. After requesting quantified visualfield tests, the patient returns with ablack and white printout with numbers(eg, Humphrey fields ) or coloured lineson a sheet (eg, Goldmann fields ).

2 Whereis the report you ask? There is none!Static perimetryuses flashing stationarylights. This can be automated (eg, evenlyspaced points on a grid) or manual (eg,as a small part of Goldmann test: detailedlater). The Humphrey field analyser is byfar the most commonly used for auto-mated static perimetry, although there arealso other machines such as Octopus andHenson. Later, we describe in detail theinterpretation of Humphrey perimetryuses a moving illumi-nated target and is done either manually(eg, Goldmann) or on an automatedmachine (eg, Octopus). Goldmannmachines are no longer manufactured,being slowly replaced by Octopusmachines.

3 Nevertheless, Goldmannremains the most commonly used kineticperimetry, and so we use this here to illus-trate interpretation of kinetic fields . Theprinciples for interpreting Goldmann alsoapply to results from Octopus is beyond the scope of this paper tocover the neuroanatomical localisation ofvisual field defects. Instead we recom-mend two excellent recent interpretation of visual field testsrequires a good grasp and application ofthis prior aspects of eye anatomy1. The fovea is the area of greatest visual sen-sitivity, where the cone photoreceptordensity is at its highest. The visual sensitiv-ity slopes off further from the fovea.

4 Thisdrop in sensitivity can be visualised as ahill, with the fovea is at the peak (figure 1).Conventional perimetry is carried outunder photopic (well lit) conditions, andtherefore, rod photoreceptors do not con-tribute to the The normal field of vision extends toapproximately 60 nasally, 90 temporally,60 superiorly and 70 The blind spot indicates the location ofthe optic nerve head an area with nophotoreceptors in the temporal part ofthe visual Anything obstructing the travel of lighttowards the retina may affect the field tests,for example, lens opacity (cataract), ptosis(if not taped away from the pupil) or therim of a correcting lens (test artefact)

5 Goldmann field testDuring a Goldmann field test, the patientpositions their eye opposite the centre of awhite hemispherical bowl (figure 2). Thepatient fixates upon the central target33 cm away, while the examiner sitsopposite viewing through an eyepiece toensure good fixation throughout the examiner moves an illuminated whitetarget from the periphery towards thecentre, and the patient presses a buzzer toindicate when they first see the is repeated from different directions allowing the examiner to plot thepatient s field of vision using targetsvarying in size and brightness. The exam-iner plots the blind spot and the edges ofscotomas in a similar way, with the patientpressing the buzzer to indicate when theyfirst see the light target moving from ablind to a seeing area.

6 The examiner alsoperforms static testing involving thebrief appearance of the stationary lighttarget in the four quadrants within thecentral 20 or so, marking a tick on thechart when the patient sees the target anda cross if they do target sizes are labelled with threealphanumeric digits, for example, V4e .1. The first digit is a Roman numeral (I V),indicating the size of the target, for example,V is equivalent to a target diameter mm. With every drop in number (eg,from V to IV) the diameter The second digit is an Arabic number(1 4), indicating the brightness of theEditor s choiceScan to access morefree contentHOW TO UNDERSTAND IT374 Wong SH, Plant ;15:374 381.

7 On August 4, 2022 by guest. Protected by Neurol: first published as on 3 July 2015. Downloaded from on August 4, 2022 by guest. Protected by Neurol: first published as on 3 July 2015. Downloaded from on August 4, 2022 by guest. Protected by Neurol: first published as on 3 July 2015. Downloaded from stimulus: the larger the number the higher The third digit is a letter (a e), indicating a finer calibrationof luminance. 4e is equivalent to 10-decibel (dB) bright-ness; each consecutive drop in number represents a 5 dBchange and each drop in letter represents a 1 dB convention, the examiner maps three isopters:lines of equal sensitivity to targets of a specified sizeand luminance.

8 The first isopter, mapping the farthestperipheral vision, requires the largest and brightesttarget V4e . Another isopter is mapped in the central30 of vision, and a third isopter is intermediatebetween these two. The isopter lines therefore showthe margins of different visual sensitivity, analogous tothe contour lines of a map marking different eleva-tions. This allows us to visualise the hill of vision. Thebase of the hill represents the area at the peripherywith least visual sensitivity, detecting only the largestand brightest target. As we move up towards the peakof the hill, the visual sensitivity increases and thepatient sees smaller and dimmer field testThe same principles apply to the Humphrey test as tothe Goldmann test, but instead with static light stimula-tion.

9 The machine can also be programmed to performkinetic tests though we have no experience with illuminated targets appear for 200 ms at prede-termined locations on a grid. Humphrey tests arewidely used in glaucoma clinics, the most common setup being to test the central 24 ( 24-2 setting). Someexaminers test smaller or wider visual angles;however, the wider the visual angle tested, the morecoarse the grid, and hence the greater the likelihoodof missing small scotomas. The 24-2 assesses thecentral 24 with a 54-point grid; 10-2 assesses thecentral 10 with a 68-point grid; and 30-2 assesses thecentral 30 with a 76-point examiner plots the hill of vision based uponthe threshold for detecting different target luminance;as visual sensitivity improves towards the fovea, so thedetection threshold for the target decreases.

10 UnlikeGoldmann, the target size stays the same during thetest, with a default size equivalent to Goldmann sizeIII targets. It is rare to need a different default Swedish interactive threshold algorithm (SITA)is the most commonly used test algorithm,3designedto reduce the time to complete a test; a short test dur-ation limits the likelihood of errors from patientfatigue. SITA starts by determining the visual stimula-tion thresholds at the four quadrants. If the patientsees the initial stimulus, the examiner reduces itsbrightness to the level where it is no longer , if the patient does not see the stimulus, itsbrightness is increased to find this threshold.


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