Visual Field Changes in Glaucoma

VISUAL FIELD CHANGES IN GLAUCOMA

DR OLORUNDARE O. K.19/01/2011

OUTLINEINTRODUCTIONRELEVANT ANATOMYTHE NORMAL VISUAL FIELDVISUAL FIELD TESTINGVISUAL FIELD DEFECTSCONCLUSION

INTRODUCTIONGlaucoma

◦a group of conditions defined by a progressive optic neuropathy with accompanying visual field changes.

◦Raised IOP is classified as a risk factor.◦A leading cause of irreversible blindness◦Modalities of evaluating/monitoring

Intra-ocular pressure The optic disc appearance The visual field

RELEVANT ANATOMYOPTIC NERVE HEAD

◦Neuroretinal rim◦Cup◦Blood vessels

Neuroretinal rim◦the tissue between the outer edge of the cup and

the disc margin. ◦The normal healthy rim has an orange or pink

colour .◦Characteristic configuration.(ISNT)

RELEVANT ANATOMY

RELEVANT ANATOMYOptic Cup

◦the central portion of the disc that is not occupied by fibres.

◦The size of this cup is dependent on the size of the scleral opening the number of fibres passing through.

Cup-disc ratio◦the diameter of the cup expressed as a fraction of the

diameter of the disc◦measured in both vertical and horizontal meridians◦Most normal eyes have a vertical cup-disc ratio of 0.3 or

less:

RELEVANT ANATOMY

RELEVANT ANATOMYRetinal nerve fibre layer

◦nasal half of the retina srf and irf◦macular area papillomacular bundle◦temporal retina superior and inferior arcuate

fibres with a horizontal raphe in between

Within the optic nerve head◦from the peripheral part of the retina

Most peripheral (superficial) part of the optic disc.◦fibres originating closer to the nerve head

more central(deep) portion of the disc.

RELEVANT ANATOMYWithin the optic nerve head

◦Arcuate nerve fibres the superior and inferior temporal portions of

optic nerve head most sensitive to glaucomatous damage

◦Macular fibres most resistant to the glaucomatous damage retention of the central vision till end.

RELEVANT ANATOMYDistribution of

retinal nerve fibres

RELEVANT ANATOMY Arrangement of

nerve fibres within optic nerve head

THE NORMAL VISUAL FIELDThe field of vision

◦the area that is perceived simultaneously by a fixating eye.

◦a three-dimensional area of a subject’s surroundings.◦described as an island of vision in the sea of

darkness .◦the island of vision has a steep central peak that

corresponds to the fovea.◦The limits of the normal field of vision

60˚ superiorly 60˚ nasally 80˚ inferiorly 90˚ temporally The blind spot is located temporally between 10° and 20°.

THE NORMAL VISUAL FIELD

THE NORMAL VISUAL FIELDThe visual field can be divided into

◦Central field area from the fixation point to a circle 30° away. contains physiologic blind spot on the temporal

side

◦Peripheral field of vision The area beyond 30° to outer extent of the field

ofvision.

VISUAL FIELD TESTINGa.k.a as PerimetryDesigned to map a person’s visual field, to

document the level of peripheral vision.

Definition of Terms◦An isopter.

the contour lines on a map which enclose an area within which a target of a given size is visible

◦An absolute scotoma an area of total visual loss in which even the largest

and brightest target cannot be perceived.

VISUAL FIELD TESTINGDefinition of Terms

◦A relative scotoma area of partial visual loss within which brighter or

larger targets can be seen and smaller or dimmer ones can not.

◦Luminance the intensity or 'brightness' of a light stimulus.

measured in apostilb (asb).A decibel (dB) is a non-specific unit of luminance.

◦Visible threshold the luminance of a given stimulus at which it is

perceived 50% of the time when presented statically

VISUAL FIELD TESTINGTypes of perimetry

◦Kinetic perimetry.

the stimulus of known luminance is moved from periphery towards the centre to establish isopters.

Methods Confrontation method, Lister’s perimetry, Tangent screen scotometry Goldmann’s perimetry


◦Static perimetry. forms the basis of modern glaucoma

assessment. A stimulus is presented at a predetermined

position for a preset duration with varying luminance.

Methods

Automated perimetryFriedmann perimetry


◦Manual Perimetry Most of the kinetic methods of field testing are done

manually Methods

Confrontation Method Lister’s Perimeter Campimetry

◦Automated Perimetry computer assisted and test visual fields by a static method test suprathreshold and threshold stimuli and quantify

depth of field defect


◦Automated Perimetry Commonly used automated perimeters are:

Octopus Field Master Humphrey field analyser

◦Two basic testing strategies are used in automated static perimetry Suprathreshold testing.

uses targets that are well above the brightness that the patient should be able to see.

a screening procedure to detect gross defects.

VISUAL FIELD TESTING

Types of perimetry◦Testing strategies are used in automated static

perimetry Threshold testing.

Provides more precise results preferred by most clinicians, takes more time and the equipment often costs more.

VISUAL FIELD TESTINGEvaluation of Humphrey single-field print-

out◦Uses a software called Statpac printout◦Can be studied in parts or zones

1. Patient data and test parametersPatients data (name, date of birth, eye (right/left) pupil size visual acuity).

Test parameters (test name, strategy, stimulus used, background)

◦


out2. Reliability indices

examination is considered unreliable if ≥ 3 of the following reliability indices have below mentioned values

Fixation losses ≥ 20%, False positive error ≥ 33%, False negative error ≥ 33%, Short-term fluctuations ≥ 4.0 dB, Total questions ≥ 400.

◦


out3. Gray scale

provides the field defects at a glance The darker the printout, the worse is the field.

4. Total deviation plots provide the deviation of patient’s threshold values from that of age corrected normal data.

Numeric value plot and the probability plot An indicator of the general depression and cannot reveal hidden scotomas

◦


out5. Pattern deviation plots.

adjusted for any generalized depression in the overall field which might be caused by factors such as lens opacities or miosis.

6. Global indices provide overall guidelines to assess the field results as a whole rather than on point-to-point basis

used to monitor progression of glaucomatous damage rather than for initial diagnosis

◦

VISUAL FIELD TESTINGMean deviation (MD)

◦the mean difference between the normative data for that age compared with that of collected data

◦Worse than normal value is indicated by a negative value

Pattern standard deviation (PSD).◦a measure of variability within the field◦points out towards localized field loss ◦most useful in identifying early defects.

VISUAL FIELD TESTINGCorrected pattern standard deviation (CPSD).

◦indicates the variability between adjacent points that may be due to disease rather than due to intra-test variability.

7. Glaucoma hemifield test (GHT)◦compares identical 5 clusters of points in the

upper field (above the horizontal midline) with the 5 in the lower field

8. Probability Values indicates the significance of the defects


8. Probability Values indicates the significance of the defects shown as < 5%, < 2%, < 1% and < 0.5% The lower the P value the greater its clinical

signiflcance

VISUAL FIELD TESTINGHumphrey Display


VISUAL FIELD TESTINGSources of error

◦Miosis s threshold sensitivity of the peripheral field Pupils less than 3mm in diameter should be dilated prior

to perimetry.◦Lens opacities◦Uncorrected refractive error

cause a significant decrease of central sensitivity.◦Spectacles

Can cause rim scotomas if small aperture lenses are used◦Ptosis

can result in suppression of the superior visual field◦Inadequate retinal adaptation

VISUAL FIELD DEFECTS Visual field defect

◦Any clinically or statistically significant deviation from the normal shape of the hill of vision

◦Defects can either be diffuse depressions of the visual field localized defects that conform to nerve fiber bundle

patterns

Visual field defects in glaucoma are initially observed in Bjerrum’s area (10-25˚ from fixation)

VISUAL FIELD DEFECTS The natural history of the progressive

glaucomatous field loss

◦Isopter contraction mild generalised constriction of central as well

as peripheral field the earliest visual field defect occurring in

glaucoma. of limited diagnostic value.

VISUAL FIELD DEFECTS ◦Baring of blind spot.

exclusion of the blind spot from the central field due to inward curve of the outer boundary of 30° central field

very non-specific of limited diagnostic value

◦Paracentral scotoma the earliest clinically significant field defect. may appear either below or above the blind spot in

Bjerrum's area

VISUAL FIELD DEFECTS A. Baring of blind

spot; B. Superior

paracentral scotoma; C. Seidel's scotoma; D. Bjerrum's scotoma; E. double arcuate

scotoma andRoenne's central

nasal step

VISUAL FIELD DEFECTS ◦Arcuate or Bjerrum’s scotoma

formed by the extension of Seidel’s scotoma in an area either above or below the fixation point

reaches the horizontal line

◦Ring or double arcuate scotoma Develops when the two arcuate scotomas join together

◦Roenne's central nasal step created when two arcuate scotomas run in different arcs

meet to form a sharp right-angled defect atthe horizontal meridian

VISUAL FIELD DEFECTS Advanced

glaucomatous field defects◦ only a small island of

central vision (tubular vision) and an accompanying temporal island are left

◦ The temporal island of the vision is more resistant and is lost last NPL

REFERENCES

Jack J Kanski, Ocular Examination techniques, Clinical Ophthalmology, A Systematic Approach, ch. 26

A. K. Khurana, Glaucoma, Comprehensive Ophthalmology, p216 – 220

Jeffrey Henderer, Understanding Visual Field Testing

Visual Fields in Glaucoma, ppt presentation

Dr Caroline Cobb, Glaucoma Evaluation Tutorial; 2010, optic-disc.org.

THANK YOU

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Visual Field Changes in Glaucoma