Low vision patient have serious visual problems that have caused serious visual loss. 1. Contrast sensitivity testing and visual field testing 2. subjective testing of patients with media loss # potential acuity meter # interferometry # photostress recovery test # glare test # color vision test # dark adaptometry 3. objective testing of retinal loss # USG ERG/EOG

2. Low vision patients have serious visual problems that
have caused their vision loss.
The underlying cause of the vision loss is not easily
determined.
Electrodiagnostic & psychophysicalvtestsvmay provide
invaluable information concerning the diagnosis.
The doctor may want to provide prognostic information
for problems, such as the potential for cataract surgery
in patients with both age reksted maculopathy &
cataracts or in patients who are multiply impaired.
Color vision testing also important.

3. 1. Contrast sensitivity testing & visual field testing
2. Subjective testing of patients with media & retinal loss
▪ Potential acuity meter (PAM)
▪ Interferometry
▪ Photostress recovery test (PRT)
▪ Glare test (BAT)
▪ Color vision testing (Ishihara)
▪ Dark adaptometry (DA)
3. Objective testing of retinal functioning
▪ B- scan ultrasonography (USG)
▪ Electrodiagnostic testing (ERG /EOG)

4. CONTRAST
SENSITIVITY –

5. Assessment of CS should be performed routinely when the
patient’s performance does not match the expected results.
For ex - when a Pt reports that he or she is having greater
difficulty seeing in the rain & fog & measurement of remains
consistent from visit to visit, loss of CS should be suspected.
Similar problem, he or she is no longer able to read the
newspaper with his or her present microscope.
Problems going up & down stairs, seeing objects in din
illumination, finding food on their plate, or stepping off a curb.
Significant loss of CS is common along low vision patients.
Advanced diabetic retinopathy & glaucoma strongly associated
with significantly reduced CS.

6. ▪A reduction in CS provides information to the practitioner that a
patient may benefit from one or more of the following:
A lighting evaluation.
Environmental conditions, to help a pt with daily living activities.
Orientation & mobility services
CCTV, display to enhance contrast of letters when reading.
A typoscope, to reduce glare
Filters, to reduce glare & enhance contrast.
Greater magnification.

7. MR.HAPPY CONTRAST SENSITIVITY CHART
HIDING HEIDI CHART
LEA SYMBOLS CS CHARTS
PREFERNTIAL LOOKING CS CHARTS
CANBRIDGE LOW CONTRAST GRATINGS
PELLI- ROBSON CS CHART

8. This charts consists of letters that subtend an angle of 3° at z
dustance of 1m.
The chart is printed on both sides.
The two sides have pdufferent letter sequence.
The Lester’s on chart are irganisedvas triplets, there being triplets in
each line.
The contrast decreases from one triplet to to the next.
The log CS varies from 0.00 to 2.25.
To perform the test, the chart is hung on the wall, so that it’s centre is
approx at tge kevel of the subjects eye.

9. The chart is illuminated as uniformly as possible, so tgatvthe
luminance of the white areas is b/the acceptable range of 60
& 120 cd/m.
While recording, the subject sits durectly in front of the chart
at a distance of 1 m.
The subject is made to name or utlineveach letter on the
chart, statingvfrom the upper left corner& reading
horizantally across the line.
Subject is madevto guess, even when he or she believes that
the kettersvare invisible.
The test is concluded when the subject guess two of the
three letters of the triplet incorrectly.
The subjects sensitivity is indicated by the finest triplet for
which two of the three letters are named correctly.

12. CONCLUSION -
Loss of high spatial frequency contrast usually indicates
problems with near point & reading tasks. A oatient may
require increased magnification, increased contrast of
materials, increased illumination.
Loss of low spatial frequency contrast usually indicates
problems with mobility & night time travel. A patient may
require orientation & mobility services & perhaps a flash
light for night time travel.
If normally sighted binocular patients, binocular CS is
higher than monocular sentivity across all spatial frequency.
This is called binocular summation.

13. VISUAL FIELD
TESTING –

14. Visual fueld testing for low vision Patients is used for the
following reasons:
▪ Determining legal blindness.
▪ Determining eligibility for privileges such as driving.
▪ Calculating compensation for functional loss.
One important aspect of field testing, if a field defect is the
principal cause of a patient’s inability to achieve a particular goal.
There are two visual field regions that are typically tested during
a low vision evaluation;
1. The central field as tested by the AMSLER’S GRID.
2. The peripheral field testing by CONFRONTATION
METHOD OR HVFA PERIMETER.

15. AMSLER’S GRID –
It indicates 7 different charts to test the quality of Central
vision within a field of 20°.
The chart is held 13 inch from the patient is wearing the
appropriate addition.
The standard chart consists of a central white horizantal &
vertical grid, with each line 0.5mm apart.
The karge square grid is 20cm on each side of the fixation
target.
The patient occludes one eye, stares at the centre of the grid,
& is asked if he/she can see all four corners of the square.
The patient is then asked if any of the vertical /horizantal
lines are missing or distorted.

16. Distortions of the Amsler grid reflect the presence of
metamorphopsia, caused by macular elevations or
depressions.
The patient should also he asked if the actual white
grid seems to have any colour or tints.
If so, this effect may be due to fresh hemorrhaging or
exudate mechanism.

18. PERIMETER –
It indicates peripheral visual field more than 20 °.
In Confrontation method, this is a tough but rapid and
extremely simple method of estimating the peripheral VF.
The pt is seated facing the examiner at s distance of 1 m.
While testing left eye, the pr covers his right eye and looks into
the examiners right eye.
The examiner occludes his left eye & moves his hand in from
periphery keeping it midway from b/w patient & himself.
The pt & the examiner ought to see the hands simultaneously,
for tge Patients field to be considered normal.
The hand is moved similarly from above, below, & left to right.

20. SUBJECTIVETESTING
OF PATIENTSWITH
MEDIA & RETINAL
LOSS –

21. ▪ When evaluating low vision patients , doctors must
consider the effects of medical abnormalities on overall
vision loss.
▪ When cataracts, Corneal scars or vitreal opacities make it
difficult or impossible to perform a fundus examination.
▪So, testing for retinal functioning & pathology can proceed
through other means.
▪The instrumentation & tests described in this section
enable the practitioner to perform subjective testing to
determine retinal functioning.

22. POTENTIAL
ACUITY
METER (PAM) –

23. It measures the retinal VA behind mild to moderate opacities
such as cataracts.
The PAM was manufactured by Mentor, & introduced by
Guyton & Minkowski.
It is a small device that mounts on a slit lamp & projects an image
of a Snellen visual acuity chart, using a 0.15 mm diameter
aperture, through clear areas in the lens on to retina.
PAM unit is designed to be brighter than the standard Snellens
chart.
It has black letters or numbers set against a white background.
The chart can test VA from 20/20 to 20/400 .
The instrument can be focused to compensate for a patient’s
refractive error b/w +13.00 D to -10.00 D.

24. The test is best performed with the pupil dilated
The patient should also wear his or her best
spectacle correction, or trial lens adjustment.
The patient should be placed comfortably at the slit
lamp in a dim light room.
The beam of light is directed through the clearer
areas of the cataract & the patient is asked to read
thevchart.
If the patient should be able to read a small line, than
macula is normal.

26. INTERFERO-
METRY –

27. Interferometry refers to the technique of the estimation of
visual acuity through mild to moderate ocular media
opacities e.g. Cataract & Corneal opacity by projecting a
resolution target ditectly on the macula.
The device used to perform this test is termed the
interferometer.
It works on the principle of optical interference fringes b/w
two beams of light & is less affected by a patient’s refractive
error.
TYPES –
1. Laser interferometers
2. White light interferometers

28. In laser interferometer, exploit the coherent naturevof laser
light.
The two point light source come from a safe, low power He-Ne
laser.
Laser light, being coherent & of one pure colour, can come to a
very fine point focus & produce vivid interference patterns.
The He-Ne laser light, being red is also scattered less than other
visible wavelengths & thus penetrates the opaque media more
clearly.
In white light interferometer, uses polychromatic white light
incandescent bulb as a source of light.
It works similar to laser except that the contrast of the gratings
may be reduced by chromtic aberrations.

29. In working optics, the maxima refers, which both beams
are in phase & are seen as bright white bars.
The minima, which both beams are out of phase, & are
seen as black bars.
This is a fringe pattern, & increasing the separation
produces a finer fringe pattern which requires greater
Macular resolution.
The space b/w the fringes is repeatedly adjusted by the
examiner till the patient can no longer detect their
orientation.
The last repeatedly perceived grating value recorded in
decimal system is converted to Snellen potential acuity.

30. Technique-
▪ Explanation to the patient, before starting this procedure, the oatient
should be explained that partial patterns (scotomas) may be seen &
that the patient should look only for band pattern direction, ignoring
the scotomas.
▪ Instrument & patient adjustment, the patient is made to sit in front of
slit lamp, with the chin resting on the chin rest & forehead supposed
to the forehead rest & room is darkened &. Slit lamp is switched on.
▪ Measuring visual acuity, using retro illumination technique, the
region of the highest transparency in the patient’s crystalline kens is
identified & the instruments bmbeam is detected here.
▪ When the patient visualize of pattern lines, one of the knob us
adjusted to allow an entrance pupil of 1.5 mm.
▪ Testing is started, the fringe pitch is increased in steps of 0.1 by
others knob.
▪ The pt is asked to indicate the durection of fringes (horizantal,
vertical, oblique).

31. ▪ The orientation can be changed
by the examiner using the third
knob.
▪The end point is usually indicated
by slower patient response.
▪ Four consecutive correct
responses are needed for final
potential acuity reading.
▪ With low media transparency,
helpful to increase the voltage
from initial 5-7.5 V.
▪ The pt end point fring pitch
decimal reading is read off from
one of the knobs & converted to
Snellen equivalent.

32. PHOTOSTRESS
RECOVERY
TEST (PRT) –

33. It can help to diagnose disruption of normal macular physiology
from early optic nerve disease.
Early optic nerve disease will show normal recovery whereas slow
recovery from a bright light may mean Macular pathology.
During testing, the pt is dark adapted for 1 minute, then is
instructed to stare at a bright light for 10 seconds with only one
eye.
The light is then turned off & the practitioner measures the time it
takes until the patient can read one line less than his / her best VA.
This procedure is subsequently repeated with the other eye.
If the recovery time is substantially longer, or a large difference is
recovery time b/w two eyes, Macular disease, most probable
cause.
Recovery time, may also be decreased by the age of the pt, poor
visual acuity & dense media opacities.

34. GLARE
TESTING –

35. The brightness acuity test (BAT) is useful in measuring the reduction
of visual acuity in the presence of glare, when a cataract or corneal
opacity is present.
Glare can be caused by intraocular light scattering.
Glare testing , evaluating anterior segment media opacities.
To perform this test, the patient is instructed to wear his/her best
spectacle correction.
The BAT encloses the unoccluded eye in a small sphere with an exit
hole along the visual axis.
The VA is measured in non illuminated conditions.
If there is a decrease of two or more lines of VA, then media opacities
or other ocular pathology may be seen.
The effect of absorptive filters on improving the glare problem may
be tested by placing tinted lenses b/w the BAT & the patient’s eye.

36. COLORVISION
TESTING –

37. Color vision testing can be extremely valuable in
making the correct diagnosis concerning the cause of
a patient’s decreased vision.
Color vision testing can help monitor the progression
of a disease or difficulty of patient may have in
performing tasks such as daily living activities.
The most commonly used color vision tests are –
Ishihara test,pseudoisochromatic or Dvorine color
plates, color arrangements tests such as the Fransworth
dichotomous test .
Most commly used ISHIHARA COLOR VISION PLATES.

38. DARK
ADAPTOMETRY –

39. Patients with night blindness or some form of temporetinal
degeneration will commonly complain Decreased senstivity
when in dimly light environment.
Dark adaptometry allows the doctor to quantify the classic
complaints of these patients concerning their adaptation
When going from a light to a dark environment.
Dark adaptometer, uses a bowl into which the patients
views.
Within the bowl are lights for bleaching the patient’s retina &
a dim red fixation light & a flashlight white test light.
The pt is first light adapted for 5 min, which essentially
bleaches the retina.
Immediately, after these bright lights are extinguished, the pt
views a superiority located red fixation light & taps on the
examination table when he/she detects flashing stimulus
light.

40. For each measurement, the doctor increases the intensity
until reaching the patient’s threshold.
This Measurement is repeated as often as possible in the
first few minutes & every minute thereafter.
The test proceeds for approximately 45 minutes.
The recording sheet plots time versus senstivity.
Patients who are visually normal usually have a 5 log unit
change in sensitivity over the course of the test.
After 5-10min, the pt rod system will become more sensitive
than his/her cone system & thereafter, vice versa.
Patients with moderately advanced retinitis pigmentosa
usually display no more than a 2 log unit change in
sensitivity.

41. OBJECTIVE TESTING
OF RETINAL
FUNCTIONING –

42. Objective testing of visual system is
theoretically less biased than subjective
testing.
Objective tests, although excellent for
diagnosis, are sometimes poor
prognosticators of low vision management.

43. B-SCAN
ULTRA-
SONOGRAPHY –

44. If a media opacity is present & prevents satisfactory views of
the fundus, then diagnostic ultrasound can be a benefit in
detecting changes in structure of the retina.
B scan ultrasonography may help detect retinal detachment,
retinoschisis, staphyloma, buried drusen or retinal tumours.
The technique is accomplished by using a handheld probe,
which both transmits ultrasonic energy & receives the
reflections of this energy from the ocular structures.
The probe is held against the pt’s closed kids & produces an
image of a section through the ocular structures.
The orientation of the probe is changed to investigate the
entire globe & orbit.

45. The image is stored in a computer & displayed
on a video monitor.
A final Polaroid picture or high resolution print
of the B scan ultrasound is produced for the
record.
Sample results from two patients,one with a
long standing retinal detachment & another
with a posterior staphyloma.

46. ELECTRO-
DIAGNOSTIC
TESTING –

47. Electroretino graphy (ERG) & visual evoked potential
(VEP) are the most valuable electrodiagnostic tests used
in assessing the electrical processing of the ocular
structures in low vision patients.
These two tests measure the function of different
anatomic structure.
ERG is most important in case of family history of
temporetinal degeneration in which there are observable
pigmentary or other suspicious retinal findings,vor when
the patient has unexplained loss of field or prolonged
dark adaptation.
VEP testing is most valuable in cases of unexplained
visual acuity loss, pallor or other suspicious changes in
the appearance of the optic nerve, or as a rough gauge of
VA in patients who are unable to co-operate for
standardized tests.

48. Patients who require these tests will need
further monitoring of their condition.
Fundus photographs taken near the time of
the electrodiagnostic tests can be quite
valuable when evaluating these patients in the
future.

49. ANY
QUERIES…..