Eccentric Fixation

1. Eccentric Fixation
A failure of an eye in monocular
vision to take up fixation with the
fovea, but with some other point.
This hardly occurs except in clinical
conditions as the patient is generally
not fixing with that eye anyway.
It is only shown when the better eye
is covered (Exception = microtropia
with identity)

2. X
F l
F r
O
P
In visual cortex
Fl = X and Fr = O,
Therefore results in confusion

Fl and P both see the X but
In Fl, X = Central
In P, X = In Temporal field,
Therefore results in diplopia

3. Four Theories as to the cause of
Eccentric Fixation
lSuppression Theory (Worth, 1906,
Bangerter,1953)
lAnomalous correspondence theory
(Chavasse, 1939, Cuppers, 1956)
lMotor theory (Schor, 1978)
lPickwell (1981)

4. Worth (1906)/Bangerter (1953) –
Suppression Theory:
loccurs when central acuity has dropped to a
level below that of the surrounding area, so
that better acuity results.
lnow thought to be unlikely as foveal VA
still seems to be better than in the rest of the
retina.

5. Duke-Elder (1973)/ Chavasse
(1939)/Cuppers (1956):
la change in the central area of localisation
resulting from a central scotoma in the
amblyopic eye
lEF secondary to the development of ARC
lMajor problem with this theory is that the
angle of anomaly is usually much greater
than angle of EF

6. Schor (1978) :
lfailure of the EOM to relax from the
deviation (in strabismus) = MUSCLE
POTENTIATION. This is a likely cause as
habitual strabismic deviation causes an
adaptive after-effect which modifies the
subsequent monocular localisation

7. Pickwell (1981) :
l a sequel to an enlargement of Panums
fusional area following decompensated
heterophoria at an early age – eventually
leads to microtropia – a loss of accurate
correspondence
lAlso a sensorimotor theory by Cuiffreda,
Levi and Selenow (1991)
NB One or more of these theories may apply
to any one patient

8. 0.1
1
10
-15 -10 -5 0 5 10 15
Hess and Jacobs (1979)
Minimum Angle of Resolution (mins of arc)
Eccentricity (deg)
Temp Nasal
Blue = normal
Green = ambyope 1
Red = amblyope 2

9. Relative Localisation
lBased on each retinal receptor having its
own “local sign”, which determines the
direction of objects in visual space.
lRefers to localisation with reference to each
eye separately.

10. In EF the relative localisation
may be as follows:
-Normal or abnormal at
eccentrically fixing retinal point
- Normal or abnormal at the
fovea of the same eye
lUsually if the eccentric point continues to be
localised eccentrically and the fovea
centrally then patients describe objects as
being slightly to one side = ECCENTRIC
VIEWING.
lThis has a better prognosis for treatment
than if localisation is abnormal.

11. Investigation of EF
l is best to use two methods.
l EF is nearly always present in strabismic
amblyopia

12. Ophthalmoscopic Methods
lA target is projected and focussed onto the retina and is seen by both
the Px and the practitioner.
lPx is asked to look at the centre of the target and the position of the
fovea is noted.
lPosition is then recorded in diagram – also record if steady/unsteady
- usually EF is slightly nasal in SOT
- can calibrate using the size of the optic disc in the graticule Disc = 5
deg x 7 deg
NB accommodation is usually induced using this method – change
focus or cycloplegia

14. Visuscope

16. In amblyopia –
lreduced VA by one Snellen line per 0.5
degree of eccentricity (very rough guide)

17. Past Pointing Test
lrelated to localisation
lcarry out test initially with good eye (checks normal ability
and increases confidence)
locclude amblyopic eye, hold pen 25cm in front and ask
patient to touch pen with the tip of their finger
lrepeat with the non-amblyopic eye occluded.
lIf finger goes a few cm to the side then past pointing has
been demonstrated (do not repeat too many times as PX
adapt)
lthis result indicates that fixation does not coincide with the
centre of localisation

18. Corneal Reflex Test
lcompare reflex position in each eye in turn
(other eye occluded). The relative
displacement of the reflex by 1mm =
approx. 11degrees or 20 PD
leccentricity is not usually this great however
making EF difficult to detect by this
method.

19. Bjerrum Screen Method
lIn normal subjects the blind spot is the same
angular distance from fixation in both eyes.
lPlot the blind spot carefully in both eyes and
compare positions
lDegree of eccentricity can be measured by
the difference in angular distance of blind
spot from fixation in each eye
lRequires good co-operation

20. Amsler Chart
l5mm square in a 10 cm square, printed in
white or red and black
lamblyopes often have small foveal scotoma
which shows up as a disturbance on Amsler
loccurs centrally if central localisation
leccentrically if EF
lthis is not a very convincing test

21. After-image Transfer Test
lAfter images are transferred to normally corresponding points in the
other eye.
lphotography flashgun that is masked to provide a very bright strip of
light
locclude amblyopic eye and PX fixates the centre of the strip
lflash then produces a central after-image
loccluder is then changed to the good eye and PX looks at a small
fixation target (eg Snellen letter)
lthe after image then appears after a few seconds (transferred at cortical
level)
lPx is then asked to locate position of after-image in relation to the
fixation point.
lIf it appears at one side of the letter = EF

22. Haidingers Brushes
lan entoptic phenomenon due to characteristics of the
central fovea area
lseen with a brightly illuminated blue polarised field when
the direction of the polarisation is rotated
llooks like two darkened and opposing sections rotating in
the central field
lin EF they are not seen at the point of fixation but
somewhere to the side or not at all if VA < 6/30
lalso Maxwell’s spot

24. Acuity Measurement
lCrowding phenomena : difference of 1 line
can be normal but more indicates
amblyopia, especially with EF

25. Neutral density Filters
lIf a ND filter is added and no reduction in
VA occurs then EF is likely to be present

26. Speed of Accommodation
lMuch slower in EF (?also in other
amblyopes)

27. Assessment of Fixation
lCentricity of Fixation (central vs eccentric)
lMagnitude
lQuality of fixation (steady vs unsteady)
lPattern of fixation (drifts, saccades, nystagmus)
lPercent foveation (30second visuoscopy)
lDirectional bias (nasal, temporal etc)
lSubjective localisation of primary visual direction
lZero retinomotor point

28. Treatment of EF
lAs in amblyopia, have to encourage foveal
fixation
lDirect Occlusion alone may improve
fixation but often a slight eccentricity
remains
lPleoptic Treatment – desensitises
eccentrically fixing area
lAfter image transfer – use to locate foveal
fixation
lNB Established EF is hard to remove.
Remember in amblyopia treatment VA will
not improve beyond that expected for
eccentrically fixating point

29. Treatment of EF
lCuiffreda, Levi and Selenow (1991)
l2 types of treatment strategy
lPatient A - direct patching - break down inhibition of
dominant eye
lPatient B - break down the EF - fine fixation tasks
under controlled conditions
Patient A Patient B
Fixation Status 2 degrees nasal 2 degrees nasal
Pretherapy VA 20/200 20/50
Expected acuity based on retinal
eccentricity
20/50 20/50
Percent of VA loss due to EF <30% Approx 100%

30. Haidinger’s Brushes
l brain to look to side to make centre at
fixation point
lNot usually very successful and can not be
done at home.

31. Microtropia
(Microsquint, microstrabismus)
la misalignment of the eyes with an angle
deviation so small (less than 5 degrees) that
it would usually be controlled except on
dissociation of the eyes in which case in
becomes a phoria.

32. Certain characteristic features
lFrequently presents between ages 2-3 years but may be
overlooked until later life where it is found on routine
check as VA is slightly low.
lOften made evident by the crowding phenomenon.
lAmsler charts are useful for demonstrating the abnormal
fixation pattern
lPresence of HARC in small angle squint is associated with
eccentric fixation and amblyopia
lIs invariably eso, exo is rare
lVery subtle tests are required to discover microtropia

33. General Characteristics
lSmall angle (<6 )
∆
lAnisometropia
lAmblyopia
lEccentric Fixation
lHarmonious ARC
lPeripheral Fusion
lMonfixation syndrome
lStereopsis

34. Anisometropia
l usually 1.50D or more. Occassionally the
patient has equal refractive errors.

35. Amblyopia
lusually VA is reduced by 1 or 2 lines only
(6/9 – 6/12)

36. Eccentric Fixation
l always occurs in microtropia.
lANGLE OF ECCENTRICITY = ANGLE OF SQUINT -
lno movement is detected on the CT (the area of the retina
where the image falls in binocular conditions is the same as
the eccentrically fixing area)
lOccasionally the degree of EF < angle of squint and a very
small CT movement can be seen (small relative or absolute
scotoma at the fovea)

37. Harmonious ARC
l the retinal area where the image falls in
Pxs habitual vision = anomalously
corresponding area = area used for
monocular fixation = MICROTROPIA
WITH IDENTITY
lMost microtropia’s are of this type.
lthis is a fully adapted strabismus in terms of
both motor and sensory aspects.

38. Peripheral Fusion
l peripheral vision provides fusional
impulses that help maintain the eyes in their
straight position.
lCan be measured like prism vergences.

39. Monfixation syndrome
l in many cases the angle of deviation increases on
alternating CT or if one eye is covered longer than
usual.
lAn SOP is seen superimposed on the microtropia.
lThis is also called a monofixational heterophoria
(due to the eye moving from its adapted position to
the full angle of squint under the cover)

40. Stereopsis
l a low grade stereopsis has been reported.

41. Investigation and Diagnosis

42. Visual Acuity
lthe presence of amblyopia in one eye is
usually the first clue that microtropia may
be found.
lCrowding phenomenon present and letters
may be missed due to the central scotoma.

43. Fixation
lThe presence of eccentric fixation should be checked for
using an ophthalmoscope, visuscope.
lThe EF may be associated with ARC in the microtropia.
lTwo types:
»Eccentric fixation = angle of anomaly (no shift on CT)
»Eccentric fixation does not equal the angle of anomaly
(shift on CT).

44. Cover Test
lNot usually a strabismic movement but may
find esophoria in monofixational syndrome.
lThis could result in microstrabismus being
missed.

45. 4-Dioptre Prism Test
l4 base out prism is placed before the dominant eye
lthe image moves across the retina and the eye moves to take up
fixation.
lThe non-dominant eye moves laterally in the same direction (Herings
Law of equal innervation) as it is not fixing – VERSIONAL movement
is seen.
lThe prism is then removed and a recovery versional movement is seen.
lThe prism is then place before the amblyopic eye.
lThis time the image is moved across the retina within the suppression
area: no movement of either eye.
AMBLYOPIA + NO CT MOVEMENT + POSITIVE 4 TEST =
∆
MICROTROPIA

48. Bagolini Lens Test
lShould get HARC – streak passes through
the spot, with or without a suppression gap.

49. Amsler Charts
lScotoma may be demonstrated due to the
eccentric fixation.

50. Classification of Microtropia
lPrimary – remains constant throughout life
and is rare.
lA primary microtropia which becomes
decompensated particularly between 1 –3
years as a result of an accommodative
element or superimposed phoria
lSecondary – follows optical or surgical
correction of a concomitant squint

51. Lang – 3 types of microtropia
(reference to fixation)
lCentral Fixation
lEccentric Fixation with ARC, where the
angle of anomaly is greater than the
degree of eccentricity
lEccentric Fixation with ARC where these
angles are the same
On CT 1 and 2 will give positive results
whilst 3 gives a negative CT
Also 3 gives a sensory adaptation to the
deviation envisaged by Cuppers in his
correspondence theory for the development
of eccentric fixation

52. Development
lThe mechanism is not fully understood.
lIt is likely that the condition arises as a response to a
scotoma that occurs in the foveal area of one eye, usually
due to a blurred retinal image caused by uncorrected
anisometropia.
lFixation is therefore established at the edge of the scotoma
in an area of the retina that is not suppressed.
lThis implies that it develops on the basis of eccentric
viewing.
lIt is natural that the onset of EF should be followed by the
development of HARC.

53. Heterophoria Theory:
lSOP causes an expansion of Panums areas with an
alteration of visual direction
lthis results in ARC that in turn causes the development of
eccentric fixation because of deep suppression at the fovea.
lProblems with this theory
lDifficult to explain why this does not happen in all patients
with esophoria (unless some additional abnormality is
present)
lDoes not explain microtropia in the absence of SOP.
lFamilial Studies – Lang claims ARC is inherited as primary
congenital defect

54. Treatment
lRefractive Error Correction, especially in high anisometropia.
lAniseikonia is often a problem.
lContact lenses correction may help.
lTreat underlying amblyopia by occlusion of non-squinting eye (if
patient <6 years old).
lFull time occlusion of the fixing eye will occasionally produce a
complete cure of the esotropia with restoration of normal visual and
stereo acuity.
lRegular review – improvement must be seen within 4 months or
discontinue.

55. Treatment
lOrthoptics are not appropriate.
lIn patients >6 years – correct refractive error, otherwise do not treat the
microtropia.
lIn most cases correction of the refractive error, if necessary, is the only
profitable action.
lSurgery is not appropriate