3.1.5 Investigates the visual fields of patients with all standards of acuity and analyses and interprets the results.

Question 1

What patients require VF assessment?

Answer 1

• FH of Glaucoma
• If patient reports field loss
• Recent onset HAs
• Assessing progression/severity of condition e.g. Glaucoma
• Localisation e.g. patient has stroke and you find neurological defect corresponding to certain portion of visual pathway
• Acquired colour vision changes/anything neurological
• Certain medications e.g. quinine
• DVLA driving assessment

Question 2

Normal Visual field

Answer 2

 Superior 60 degrees
 Inferior 70 degrees
 Nasally 60 degrees
 Temporally 100 degrees
 Central VF subtends 30 degrees
 Blind spot = 15 degrees temporally
 VF defect = departure from the topography of the hill of vision normal limits
 Static
o Measures the sensivity of retinal points
o Stimulus is stationary, luminance changes
o 3D hill of vision
 Kinetic
o Measures the extent of the VF by plotting isopters
o Stimulus moves from a non-seeing to seeing area
o 2D measurement of hill of vision
o Only done with a Goldmann visual field

Question 3

Causes of VF defect

Answer 3

• Medication
  
  • Chloroquine (anti-malarial) - central &/or ring scotoma
  • Alcohol or Vitamin deficiency - bilateral central, paracentral or centrocecal defect
  • Vigabatrin (anti-epileptic) - concentric constriction with binasal predominance
• Retinal Lesion
  
  • RP - ring scotoma
  • Artery or Vein occlusion
  • Retinal detachment - focal defect in affected area
• Optic Nerve
  
  • Glaucoma - arcuate, nasal step, paracentral
  • Coloboma
  • Optic disc drusen - arcuate, enlargement of blindspot
  • Optic pit
  • Papilloedema
  • Optic neuritis - altitudinal, central, peripheral
  • Ischeamic optic neuropathy - respect H midline

Question 4

Amsler Chart

Answer 4

• Flat book, central 10° from fixation, 30cm distance; 1° squares.
• For assessing macular function.
• Asked to report any areas missing (scotomas e.g. in geographic atrophy) or distorted (metamorphopsia).
• Learn of different types of Amsler charts

Question 5

Gross perimetry/Confrontation

Answer 5

• True confrontation when examiner compares visual field wiht patients,
• Facial outline or hand perimeter arc technique, arc at 33cm from patient
• Supra-threshold comparison test, four quadrants and patient asked whether appears brighter, dimmer or difference in any position

Question 6

HFA III

Answer 6

Bowl, 90º from fixation, 30cm distance. Background luminance 31.5 asb. Various screening and threshold strategies available.
SATPA compares results to age normal and glaucoma databases.
SITA alters the program during the test depending on the result.

Question 7

Visual field pathway and understand the field defects that the patient would perceive if the pathway was cut at various points along the visual field pathway?

Answer 7

 Fibres from the nasal retina account for the temporal area of the VF (and vice versa)
 Nasal fibres cross at the optic chiasm, temporal fibres remain at the same side
 Optic chiasm is 10mm above the pituitary gland
 Most common lesion here bitemporal hemianopia caused by pituitary gland tumour
 From the chiasm, optic tract then projects to LGN
 LGN projects to the visual cortex via optic radiations

 Progressing further down the pathway – results in increase congruity i.e., the defects in each eye become more similar i.e., homonymous hemianopia
 Any post-chiasmal lesion will result in defect at the contralateral side i.e., left optic radiation lesion = right homonymous hemianopia

Question 8

Can you discuss the affected part of the visual field pathway and associated visual field defects for:

Answer 8

 Optic neuritis – enlarged blind spot
 Pituitary tumour – compression of nasal fibres at chiasm = bitemporal hemianopia
 Right carotid aneurysm (early and late) – R nasal defect with compression of temporal fibres / binasal defect in later stage
 Pie in the sky – lesion at temporal lobe / Meyers loop causing right homonymous superior quadrantopia
 Pie on the floor – lesion at parietal lobe causing left homonymous inferior quadrantopia
 Altitudinal defect – superior / inferior hemianopia – caused by AAION
 Retinal detachment can present as any defect

Question 9

Anterior and posterior knee of Willebrand?

Answer 9

 Located at the optic chiasm is the knee of Von Willebrand
 This is where inferior nasal retinal fibres cross the chiasm – but course 4mm anteriorly into the contralateral ON before running posteriorly
 A lesion here would result in a junctional scotoma
o i.e. posterior L optic nerve & involvement on inferior nasal crossing fibres of the fellow eye = vision loss in LE, superior temporal defect RE
 Superior nasal fibres dip into the posterior knee of Willebrand

Question 10

Vertical & horizontal midline

Answer 10

 Retinal lesions will respect horizontal midline due to the distribution of the RNFL layer – with the horizontal raphe dividing the retina into superior and inferior sections
 Neurological defects respect vertical midline due to arrangement of nasal / temporal fibres in pathway

Question 11

What are the classical glaucomatous field defects and how do these relate to optic disc changes? You should be able to name 6

Answer 11

 Nasal step - damage at the temporal disc with corresponding loss of RNFL; defect is nasal (opposite side from blind spot), can be inferior or superior but will respect midline
 Temporal wedge – defect is at same side as blind spot (less common than nasal step)
 Paracentral (more common in NTG)
 Arcuate scotoma – defect arcs towards disc (RNFL distribution pattern)
 Tunnel vision – end stage with central sparring
 Enlarged blind spot, soft sign

Question 12

Suprathreshold vs Full threshold

Answer 12

 Threshold = minimum brightness required to evoke a visual response
 Threshold are determined at all stimulus locations using staircase method
 This is more sensitive than suprathreshold
 Enables statistical analysis of visual field because values can be compared with database
 More usual for monitoring progression closely
 Can pick up subtle changes more readily
 Full threshold should be used in glaucoma – more sensitive and with oculus it goes slightly wider

Suprathreshold
 Target is set at a moderate brightness, above expected threshold (based on patients age)
 Recorded as either seen / or note seen
 Does not quantify threshold seen at each point and is less sensitive
 More useful for screening / gross defects

Question 13

Different tests / grid size

Answer 13

 24-2
o 24 degrees from fixation (in 3 directions, 30 degrees nasally)
o 58 locations over central 25 degrees, extends 30 degrees nasally, pts are 3 degrees apart
o 2 = at each side of horizontal, no points on horizontal midline
o Slightly quicker than 30-2 (reduces test time by 25%)
 30-2
o 30 degrees from fixation (in 4 directions)
o 76 locations over central 30 degrees, pts are 6 degrees apart
o Glaucoma, cataract, neurological
 10-2
o 10 degrees from fixation
o 69 points, 2 degrees apart
o Useful for macular investigation
 C40
o Central 40 points
 FF81

Question 14

Reliability indices

Answer 14

 If >20% the test should be repeated as it is not reliable
 Fixation loses - assessed by presenting suprathreshold targets in the blind spot
 False positive- indicate a trigger-happy patient, responding to the sound of the perimeter when no target is presented
 False negative - patient fails to respond to a suprathreshold target at any given location; associated with fatigue/inattention
 Gaze-tracking – displayed as a chart at the bottom of the page, upward deflections indicate upwards eye movements, downward deflections are recorded when the position of the eye cannot be determined or there is a blink

Question 15

Single field analysis.. greyscale, total deviation, pattern deviation, GHT

Answer 15

 Threshold values at each point
 Grey scale – represents raw decibel sensitivity; darker areas indicating reduced sensitivity
 Total deviation = compares to aged-matched norms for each point
 Pattern deviation = highlights localized loss after correcting for any overall change in the hill of vision i.e., by a cataract
 Glaucoma hemifield test (GHT) analyses the relative symmetry of five pre-defined areas in the superior field to five mirror areas in the inferior field, judging the overall sensitivity
o Classified as being within normal limits, outside normal limits, borderline, abnormally high sensitivity, general reduction of sensitivity
 Oculus also includes a defect curve

Question 16

Global indices

Answer 16

 Data reduction statistics designed to describe the characteristics of a field plot
 MD (mean deviation) = mean difference in decibels between the normal expected hill of vision and the patients hill of vision
o If deviation out with norm a p value will be given
 PSD (Pattern standard deviation) = takes into account generalised loss i.e., overall depression
 SF = measure of intra-test variance, little clinical significance

Question 17

Sometimes we refer to Goldmann bowl perimetry - kinetic perimetry technique - what is this and what’s the difference to static perimetry?

Answer 17

 Kinetic Perimetry – Stimulus presented from non-seeing to seeing (light or physical target)
 Optimal stimulus speed 4 degrees per sec
 Points of equal sensitivity form together to make an isopter, different isopters are measured using different stimulus sizes or light intensities or both
 Map contour of hill of vision – smaller targets toward the peak, larger target edge of hill of vision
 Instrumentation – Goldmann Perimeter, Bjerrum Screen, Confrontation Test

Question 18

Esterman

Answer 18

 Binocular assessment for drivers
 Expresses the VF as a percentage of seen targets, presented a suprathreshold level of 10dB
 Binocular Esterman uses 120 pts & favours the inferior visual field
 Available on the HFA
 Patient aligned in the centre – nose lined up with fixation rather than eye
 Habitual driving correction should be worn
 Group 2 – 4 extra pts in the periphery

Question 19

Common errors

Answer 19

 Inappropriate correcting lens
 Poor alignment
 Poor instructions
 Failing to encourage patient
 Cloverleaf defect – fatigue after initial 4 areas are examined, px performs better at beginning of test and becomes inattentive with time
 Mask defect – steam
 High + can give edge scotoma

Question 20

Amsler

Answer 20

 Evaluates the central 10 degrees of vision from a focal point (which overall evaluates the central 20 degrees)
 WD 30cm (patient holds)
 +3.25 near add for absolute presbyopes
 Room lights should be on
 Test should be performed monocularly
 Chart 1:
 Patient should be asked if they can see central white dot
 Ask patient to keep looking at dot for remainder of test
 Ask patient if they can see all four sides and corners of the large square
 Ask patient if any of the small squares with the grid are missing or blurred
 Ask patient if any of the lines appear wavy or distorted
 Record – amsler chart: central fields full R and L