Contrast sensitivity, Clinical assessment of intra-ocular light scatter, recovery from glare (macular photo stress test)Presentation Transcript
Contrast sensitivity, Clinical
assessment of intra-ocular
light scatter, Dark adaptation,
recovery from glare (macular
photo stress test)
Mohammad Arman Bin Aziz
March 20, 2014
• The ratio of the difference of maximum luminance and
minimum luminance to the sum of max and min luminance
• Contrast /modulation = L max – L min
L max + L min
• E.g. White stimulus in white background, contrast= 0%
• Black in white background = 100 %
• Expressed in percentage
Luminance - The intensity of light per unit area of its source
• Object with the lowest contrast that a patient can recognize
• The minimum contrast required to be able to see a target.
• Contrast sensitivity : reciprocal of contrast threshold
• CS = 1 / CT
• Increase in CT = Decrease in CS
• An object with the lowest contrast that a patient can recognize.
• Expressed as percentage.
• CS= reciprocal of CT
• Maximum CT = 100%
• CT depends on size of object
Ability to perceive slight
change in luminance
between regions which
are not separated by
Photopic system is more
sensitivity to contrast than
the scotopic system
• Snellen VA measures patients
high frequency cut-off.
• Normal high frequency cut off
= 60 cycles/degree.
• Snellen letter - not represent
visual function in reality.
• Refractive errors – decrease
visual performance at mid &
Contrast in VA letters
•CS measurement for
•To detect abnormal visual performance
•To diagnose ocular disease & monitor its states
•To predict performance on specific visual tasks
•VA normal but CS of low & medium SF decrease in
•Amblyopia, astigmatic error, cataract, diabetes,
glaucoma, keratoconus, multiple sclerosis, ocular
hypertension, optic neuritis & papilledema.
Why to measure CS?
Contrast Sensitivity Function (CSF)
• Identical Snellen acuities can yield substantially different visual
• Predicts the outcome of ophthalmic aids. e.g. the final reading
speed with a magnifying device (Leat & Woodhouse)
• Monitors the course of ocular disorders that result in contrast
sensitivity reduction, such as cataracts or ARM
• Monitors a variety of conditions that result in visual impairment
• E.g. Multiple sclerosis
- Snellen acuity within normal range, hidden losses in the mid
and low spatial frequency domains (Pace & Woo, 1984)
Contrast sensitivity of
the human eye
Modulation transfer function for a
human eye at various pupil diameters.
Curves for 2.0 and 2.8mm pupils cross over at about 27c/d.
• 6 rows
• 3 inch diameter sine wave
• Each row a sample grating and a
• series of test grating fixed
• frequency but varying contrast.
• S.F 1, 2,4,8,16,24 c/d
• Vertical ,slanted 15 deg to R, 15
deg to L
Melbourne edge test
•Use of boundary between
light and dark background
•20 circular stimuli each
2.5mm in diameter
•Subject shown a key card
vertically, horizontally and
Addressing Reduced contrast
Needs adequate magnification
good lighting on object or print
bold lined paper
Types of contrast sensitivity loss
CS loss at high frequency
Normal at low frequency
E.g. early cataract, ARMD
CS loss at all spatial
High frequency CS normal
Reduced CS at low frequency
e.g. optic neuritis
(Leguire and Regan 1991)
CS measurement for………..
• To detect abnormal visual performance
• To predict performance on specific visual task
good/ disable reading capacity
• Contrast provides critical information about
variations in brightness
VA normal but CS of low & medium SF decrease
o Astigmatic error
o Multiple sclerosis
o Ocular hypertension
o optic neuritis
o Contact lens wearing Patient
Factors Affecting CS
To diagnose ocular disease & monitorTo diagnose ocular disease & monitor
its statesits states
• Predicts the outcome of ophthalmic aids.
e.g. the final reading speed with a
(Leat & Woodhouse)
• Monitors the course of ocular disorders
that result in contrast sensitivity reduction
Adjustable illumination, contrast
& magnification system
• Refers to the presence of one or more
areas in the field of vision that are of
sufficient brightness to cause
discomfort in vision.
• Visual perception created by external
• Glare source : Axial / Peripheral
• Reduces the quality of the image
• an unpleasant sensation
• a temporary blurring of vision
• a feeling of ocular fatigue
• Veiling or disability glare
• Discomfort glare
• Specular reflection glare
Veiling or disability glare
Arises from stray light falling on the retina, usually from
scatter by the media of the eye.
Scattered light falls as a patch of veiling illuminance on the
fovea and reduces the contrast of the retinal image.
Reduces the contrast of the retinal image.
Reduces visibility and visual performance.
E.g. sky, sand, brightly illuminated walls etc.- the reflected
images are large in angular sub tense leading to reduction in
contrast observed in the visual field.
Glare in Cataract
Occurs when the illumination in a part of the visual field is
much greater than the level of illumination for which the
retina is adapted.
Occurs when the ratio between the highest level of
illumination in the visual field and background illumination
exceeds a ratio of 3 to 1.
An extreme case of glare often occurs during night driving-
causes extreme discomfort.
Specular reflection glare
Occurs when patches of bright light are reflected form
smooth, shiny surface into the eye.
Typical reflecting surfaces include expanses of water,
snowfields, roadways etc.
Reflections are not only annoying but interfere with
visibility, at times seriously.
Can be well controlled by using polaroid glasses.
• Objective :
• quantify the deleterious effects of light scatter on visual
• Reduce the effect on impairment of vision
• Corneal opacities
• Corneal dystrophies/ Degeneration
• A glare source when
introduced in an eye with
media opacity causes some
degree of visual disability.
• Current glare testing
devices gives this extent of
disability in the form of
sensitivity or visual acuity.
• Brightness Acuity Tester (BAT)
• Optec 1500 Glare Tester
• Miller-Nadler Glare Tester
• Terry Vision Analyzer (TVA)
Assessment of Glare
Brightness Acuity Tester Miller-Nadler Glare Tester
• Clinical procedure of Primary Eye Care
• Clinical Procedure of Optometry