Mohamed Abdelzaher

InterpretationOf

Perimetry

When is Perimetry Called For?• most conclusive and concrete means of

establishing a diagnosis of chronic open-angle glaucoma

• great value in diagnosing neurological diseases but When it comes to managing neurological disease, field testing is not as crucial a technique as it is in glaucoma management; neuroimaging can often replace perimetry.

• direct observation of the fundus through ophthalmoscopy is usually of greater value in retinal diagnosis

GLAUCOMA

NEUROLOGICAL DISEASES

RETINAL DISEASES

Ordering a test

Choosing a Test1) Central vs Peripheral test2) Stimulus size3) Test strategy4) Follow-up test5) Testing for special conditions

Central vs Peripheral testing- Central 30-2 or 24-2

- Central 30-2 or 24-2, Exception: small central scotoma is suspected in a patient

who has normal or near-normal visual acuity but a history that suggests acute optic neuritis - central 10-2

- Peripheral e.g. to rule out retinal detachments, or to differentiate between

detachment and retinoschisis in eyes that cannot be well visualized ophthalmoscopically

GLAUCOMA

NEUROLOGICAL DISEASES

RETINAL DISEASES

Stimulus size• Standard size is

Goldmann size III• Small enough (0.43 degrees in

diameter) to be used even in fairly detailed examinations, and large enough to be visible when the patient’s refractive correction is not quite perfect

The typical blind spot is roughly 5 by 7 degrees.

About two hundred size III stimuli or 12 size V stimuli

fit inside the area of a typical blind spot.

• Advanced glaucoma: use size V stimulus which is 4 times size III

stimulus, WHY?• Testing with size V stimuli will result in sensitivity levels

that are 5 to 10 decibels higher than those found using size III, often extending the available sensitivity range and making it possible to follow such patients.

• NB. When the size V stimulus is used, one no longer has access to several of the analytical follow-up tools available for the standard size III tests

Exce

ption

30-2 test using a size III stimulus does not contain

enough data for good follow-up

Same patient tested with size V stimulus and to the 10-2 pattern

resulted in enough data for meaningful long term follow-up

Test strategy

Threshold

•More diagnostic in glaucoma testing•SITA Thresholding: standard - fast

Suprathreshold

•Screening in glaucoma•Not sensitive to early glaucomatous changes•Sensitive to neurologically based field loss

Switching from the older Full Threshold strategy to SITA

Standard cuts test time almost in half for glaucoma patients.

Modern threshold perimetry can be very time efficient. Normal

subjects can be tested in about 4 minutes; glaucoma patients will

take somewhat longer.

The SITA strategies have clear advantages over the older strategies and should be

used whenever available

Follow-up test• SITA Standard or SITA Fast• 30-2 or 24-2 programs for both glaucoma

detection and follow-upThe standard

test

Exceptions

* central vision loss: e.g. macular degenerationPatient fixates in the center of a large diamond pattern

* very late stages of glaucoma:SITA Standard or SITA Fast 10-2 test use larger stimulus,size V (not with SITA)

NB- Changing test programs in follow-up also makes comparisons with earlier tests more difficult and less exact.- When switching from the earlier standard Humphrey threshold tests, Full Threshold, to the corresponding newer, faster SITA Standard or SITA Fast, the most relevant comparisons can be made by focussing on probability plots.

Testing for special conditions

• Goal: rule out profound visual dysfunction• Use: stimulus Goldmann III 4e (10dB)

suprathreshold testing

Disability Driving Blepharoptosis

Drug induced maculopathies

e.g. chloroquine, hydroxychloroquine10-2 test pattern, standard size III white

stimulus, SITA standard or SITA fast

• When perimetric test is needed

using a size III white stimulus is the best choice in most cases

30-2 SITA Standard threshold test

24-2 SITA Standard threshold test OR

Glaucomatousvisual field loss

RNFL & ONH Anatomy

• Arcuate path of axons• Superior & Inferior temporal axons do not mix, respect the

horizontal raphe• Retinotopic organization of axons in optic disc

1) Generalized depression:- Can be an early sign of glaucoma- Non specific, also occurs with aging, miosis,

or hazy media- Generalized depression can increase the

physician’s suspicion that glaucomatous damage has occurred, especially if it is:

… unilateral or …. more pronounced in the eye with the

higher pressure or larger cup/disc ratio- If the patient has generalized field loss, the

MD has a negative sign

Common glaucomatous field defects and their anatomical correlates

Mild: MD < -6 dBModerate: MD < -12 dB

Severe: MD > -12 dB

2) Irregularity of the visual field:- lack of uniformity in the visual field- variation of decibel level among contiguous points that is greater than that

anticipated in normal patients of the same age- These areas of loss appear non-uniformly throughout the field- This variation is expressed statistically as the standard deviation of the

deviations found in the, Humphrey uses the term pattern standard deviation(PSD),

3) Nasal step: • Limited field loss adjacent to the nasal horizontal meridian with at least one

abnormal point (p < 5%) at or outside 15 degrees on the meridian. Cannot include more than two significant points (on either plot) in the nerve fiber bundle region on the temporal side

• Anatomy: widespread involvement of fibers in the optic disc will seldom be entirely symmetrical, but usually will involve a larger percentage of lost fibers in either the inferior or superior half of the optic disc. As a result, differential light sensitivity in the opposite visual field halves will not be the same

• Occurs early in glaucoma and may persist to last stages of the disease

4) Isolated Paracentral scotomata:

• A relatively small visual field abnormality (a cluster or a single point) in the nerve fiber bundle region that is generally not contiguous with the blind spot or the nasal meridian.

• In particular, it does not involve points outside 15 degrees that are adjacent to the nasal meridian.

• NB: Scotomata smaller than 6° may be missed in 30-2 field. This is particularly critical in the paracentral region where even very small scotomata can be visually symptomatic. Spacing the test spots closer than 6° (for example 3° apart) increases the chances of identifying such scotomata but also increases the test time to an impractical level. If one is concerned about identifying or monitoring a paracentral scotoma, use the central 10-2 test.

notch is partial, that is, it involves only a portion of the

axons in the affected area of the optic disc

5) Arcuate defect (Bjerrum scotoma) begins at the blind spot, arcs around point of fixation, in the nerve

fiber bundle region, end abruptly in at least one point outside 15

degrees adjacent to the nasal horizontal meridian (corresponding to temporal raphe)

Anatomy: focal notch in ONH reaching the edge of the disc NB: double arcuate defectRepresents middle to late stage glaucoma

6) Temporal step:A small visual field defect that is temporal

to the blind spotmay develop as an isolated finding or in

conjunction with other glaucomatous defects

more commonly found as a component of late-stage disease

Anatomy: erosion of the nasal aspect of the optic disc

7) Enlargement of the blind spot:

• Nonspecific changes for glaucoma• If the blind spot enlarges in an

arcuate manner, it is called a Seidel’s scotoma and may be seen in early glaucoma

8) End stage defects (central and temporal islands):

small central island and a larger temporal crescent remaining

Anatomy: most of the axons at the superior and inferior poles of the disc are destroyed, leaving only the papillomacular bundle and some nasal fibers

Reversal of visual field defects

Fluctuation

Increasing familiarity with the test

Patients following therapy for glaucoma

• The narrower normal limits of SITA mean that statistically and clinically significant defects can be identified in probability plots even before they are clearly visible in grayscale representations.

• This happens regularly in patients who are developing early glaucomatous visual field loss, and it is therefore important to focus on probability plots rather than grayscale representations.

Pitfalls

• A large percentage of glaucoma patients have coexisting media opacities, complicating follow-up analysis of their visual fields. These problems can be largely avoided by using analyses based on pattern deviation.

Large, sudden visual field changes are not typical in glaucoma. Such changes often occur for reasons other than progression of the glaucomatous disease process, e.g., arterial or venous occlusions in the retina or neurological disease. If a large change is seen and part of the field loss seems hemianopic or occurs in the other eye as well, neurological causes are generally the rule.

Glaucomatous field defects may not correspond well to the amount of cupping of the nerve head. During the acute phase of angle-closure glaucoma in patients with high IOP, corneal edema and retinal ischemia can produce bizarre field defects that have little clinical value for following disease progression.After the pressure has been normalized, field defects may remain and may sometimes be extensive if ischemic atrophy of the nerve has occurred. In such cases, pallor of the nerve may be more severe than cupping.

• Visual field artifacts:1) Perimetric learning:• a large minority, probably 10% to 20%, of

patients with a normal visual field do not produce an entirely normal test result on their first test

• Typically, such fields show depression of sensitivity in the mid-peripheral area 20 to 30 degrees from fixation, while the very central field is normal

• How to avoid?- Use shorter SITA test- Use 24-2 test point pattern- Do not rely entirely on the 1st test result,

repeat

2) Eyelid artifacts:• patients with somewhat droopy eyelids will often produce grayscale results that

look relatively dark superiorly• this type of pattern is common and normal is obvious from the probability plots,

where it usually does not result in readings indicating high statistical significance

3) Correction lens artifacts:• Strong positive correction lenses --- concentrically contracted field• Misaligned lenses or their rims may create artifactual patterns

4) The cloverleaf field:

- very characteristic artifactual pattern- threshold values are normal or near

normal at and sometimes around the four primary points where the test begins in all Humphrey threshold programs, but they are much reduced at other locations where the threshold is measured later in the test

- occurs when the patient has responded more or less appropriately during the first part of the test, and then given up

• You have to instruct and supervise patients

5) The “Trigger-Happy” field:• The patient presses the response

button as often as possible, resulting in large numbers of false responses given when, in fact, the patient has not seen the stimulus.

• This will push up measured threshold values at some points to levels that no human can see.

• The result is a classical “trigger-happy”field, characterized by patches of abnormally light or even entirely white tones in the grayscale presentation.

- High false +ve- GHT: “Abnormally High Sensitivity”

• Other diseases may cause arcuate nerve fiber bundle visual field defects that may be confused with glaucomatous damage:

1) Chorioretinitis2) Myopic retinal degeneration3) Refractive scotomata4) Trauma5) Retinal laser damage6) Optic nerve ischemia7) Optic nerve compressive lesions8) Optic neuritis9) Drusen of optic nerve head

G l a u c o m a i s a j i g s a w p u z z l e i n w h i c h a l l t h e‘ p i e c e s ’ o f t h e d i s e a s e s h o u l d fi t . I f a p i e c e

D o e s n o t fi t p r o p e r l y, t h e p hy s i c i a n s h o u l d b eS u s p i c i o u s t h a t i t m ay b e l o n g to s o m e o t h e r

P u z z l e ( d i s e a s e ) .

Neurologicalvisual field loss

• In the era of CT and MRI, perimetry remains simple and cost-effective method of making neurological diagnoses because the visual system occupies or passes through so much of the brain.

• SITA Standard has been found to be at least as good as the older Full Threshold test in detecting optic neuropathies and hemianopias.

Optic nerve diseases

Central scotoma

Altitudinal defect

Enlargement of blind spot

Optic neuritis: e.g.

Toxic,Compressive

AIONOptic discswelling

Arcuate defect

Drusen,Ischemia

Centrocecal scotoma

Optic chiasm lesions- e.g. pituitary adenomas, craniopharyngiomas, suprasellar

meningiomas, aneurysms coming from the arterial circle of Willis

Pituitary adenoma craniopharyngioma

Bitemporalhemianopia

Post chiasmal lesions- Respect the vertical meridian- More posterior More congrouos “extent, pattern”- Extensive defect: Homonymous hemianopia

Congrouos hemianopiaIncongrouos hemianopia

• LGB lesion:Homonymous SectoranopiaHomonymous Quadrable sectoranopia

• Optic radiation and visual cortex lesion:

Visual pathways: correlation of lesion site and field defect

various causes of visual loss according to lesion site within the afferent visual pathway

Visual field lossIn retinal diseases

• Most retinal lesions are visible on ophthalmoscopy• Importance of field:- field defects found accidentally- to determine whether encountered field loss is caused by one

disease or the other e.g. in glaucoma follow-up

ARMD

• central scotoma• More evident with 10-2

test• Patient tested with the

large diamond fixation target

CSR• central scotoma• VA is moderately

reduced• Resulting field loss may

be discrete and visible only on probability plots

Retinochoroiditis• arcuate or wedge-like

defects (DD, glaucomatous field defect)

• Field defects:- deep and have sharp

borders- show much less variability

from test to test than glaucomatous lesions

Diabetic retinopathy• relative and multifocal

“mottled” defects• Visible in moderate and

more advanced stages

RD and retinoschises• usually located in the

peripheral field• RD: relative defects,• Retinoschises: absolute

defects

Retinitis pigmentosa• Typical field loss is circular

and initially located in the midperiphery,

• progress to tunnel vision• Suprathreshold test that

includes the peripheral field is preferable, because field defects are often deep and easily identified

Retinal vascular occlusions• Important when following patients with glaucoma• Arterial occlusions typically result in absolute field defects• Venous occlusions produce highly variable field loss