The bichrome method is based on the same principle, and is done in an analogous way, as that explained for refining the sphere in the chapter on the subjective exam from distances. Important: The refraction of DV must be correct Keep the bichromatic test of NV at the patient’s habitual reading distance. Good lighting. It can be done monocularly or binocularly. Given that the person is presbyope, he/she is always expected to indicate better vision on the green background. After that, positive lenses are added until achieving clear and similar vision on both backgrounds. Test lastly, as has been indicated before, functioning, clear vision.
The cross-cylinder method from near consists in putting a cross-cylinder in front of the eyes that provokes formation of Sturn’s conoid. After that, the necessary positive lenses are put in front as well in order to situate the circle of least confusion on the retina. Important: The refraction of DV must be correct Situate the grid test at 5 arms at the person’s habitual work distance. The illumination during the test must be dim (around 20 lux). It can be done monocularly or binocularly. Put the cross-cylinder with the negative axis at 90º in front of the person. Given that the person is appropriately compensated for DV, this will provoke Sturn’s conoid with less focal distance for the image of the horizontal lines. Since this person is presbyope this image will form behind the retina. The objective is to put the necessary positive lenses in front of the person in order to supplant the conoid and situate the circle of least confusion on the retina. In this moment, the subject will indicate that he/she sees the vertical and horizontal lines equally clearly. Test lastly, just as mentioned before, functioning clarity of vision.
Gauri S. Shrestha, M.Optom, FIACLE
Institute of Medicine
Dipak Sah, B.optom final Year
Age normal amplitude of accommodation
Range of Accommodation
Gradual decrease in amplitude of accommodation
as expected with age
The onset is usually anticipated by age 40 years or
amplitude of accommodation tends to drop below
Old aged eye (आँखा बुढो भयो)
Age Functional effect
Hyperopia Additional accommodative demand
Occupation Near vision demands
Gender Earlier onset in females (short stature, menopause)
Systemic disease Diabetes mellitus, multiple sclerosis, cardiovascular
Drugs alcohol, chlorpromazine, hydrochlorothiazide,
antianxiety agents, antidepressants
Proximity to the equator (higher average annual
temperatures, greater exposure to ultraviolet
Iatrogenic factors laser photocoagulation; intraocular surgery
◦Beginning stage of presbyopia when
symptoms or difficulty are first encountered
in near vision.
◦Patient will have more difficulty in dim
illumination while can do well in bright
◦Presbyopia occuring at an earlier age than
expected for normal population.
◦Usually associated with ocular diseases,
nutritional deficiencies or ingestion of certain
◦ Presbyopia with some amplitude of
◦ Presbyopia with amplitude of accommodation
“My arms are not long enough to see up close anymore”
Blurring of near vision
Drowsiness after a short period of near work.
Half in reserve for
distance greater than
One third in reserve
for working distance
less than 40 cm
Addition based on amplitude of accommodation.
Tentative addition based on age.
Plus build-up method.
Relative accommodation method.
Dynamic Retinoscopy method.
Amplitude of accommodation decreases with
◦ Presbyopia is reported when NPA exceeds 8 inches
(22cm) ie AA = 4.50D (Donders)
Presbyopia exists when amplitude of
accommodation is less than 5D (Morgan).
Working distance (WD)= 40cm
RAF (Amp accommodation) = 2.00D
What should be the near addition ???
Accommodation required for WD = 2.50 D
Accommodation in Reserve = 1.00D
Amount of accommodation left = 1.00D
Amount of Near addition = (2.50 –1.00)
Working distance (WD) = 25 cm
RAF (Amp accommodation) = 1.50D
What should be the near addition ???
Accommodation needed at WD = 4.00D
Amplitude held in reserve = 0.50D
Amplitude of accommodation left = 1.00D
Amount of near addition = (4.00-1.00)
Amplitude of accommodation to age
◦ Maximum = 25.0 – 0.4 (age)
◦ Probable = 18.5 – 0.3 (age)
◦ Minimum = 15.0 – 0.25 (age)
◦ Amount of near add calculated by holding certain
amount of accommodation in reserve
Rule of 4s (४ को िनयम)= 4*4-age/4
Age of Range
Range of Near Add
in Diopter for 40 cm.
40 to 44 5.00 to 4.00 +0.75 to +1.00
45 to 49 3.75 to 2.75 +1.00 to +1.50
50 to 54 2.50 to 1.50 +1.50 to +2.00
55 to 59 1.25 to 0.25 +2.00 to +2.25
60 and over 0 +2.25 to +2.50
Can be done binocularly or monocularly
Plus lenses are increased in steps of 0.25D to the
amount necessary to read the desired letters at a
customary working distance.
Monocular build-up usually lands in more amount of
In presbyopic patients red
& green are focused behind
the retina with red farther
Green appears clear.
Plus lenses are added until
both red & green appear
Can be combined this
technique with tentative add
method/amplitude method etc
◦ Patient with Rx for DV,
◦ Bichrome test at habitual distance in
◦ Ask patient which background
letters are more clear
Green-add plus, Red-remove plus
until he/she sees letters equally
clear in both
A near point grid is
presented to the patient
at their customary
Illumination on the
target should be diffuse.
Plus lenses are added
until patient sees the
Crossed cylinder (±0.50D)
with their minus axes
vertical are placed before
the patient’s eyes.
Patient is asked to report
which sets of lines running
across or up & down
appear clearer, sharper,
Cross cylinder creates artificial astigmatism
with an interval of sturm of 1D
If patient accommodates exactly for the target,
both sets of lines should be equally clear.
If patient under-accommodates, the horizontal
lines will appear clear.
Add positive lenses until verticle and
horizontal lines are seen equally clearly
◦ Can be done monocularly or binocularly
Measure of lenses to blur letters of N6.
Patient is provided with plus lenses determined by
bichrome method/add based on age/Amplitude
◦ Minus lens to blur (PRA)
◦ Plus lens to blur (NRA)
Near add = NRA+PRA/2
The addition is 1.00 (say)
We add minus lenses until blur and the value be (1-
0.5)= +0.50 D
We add plus lenses and the value be +2.00 D= (1+1)
Then the final add is (+0.50+2.0)/2=
Determine lag of accommodation (dynamic
Reduce amount of lag by +0.50 to +0.75D
Prescribe remaining as addition for near
Method Procedure Advantage
40 cm fused
Compare manifest refraction to plus
value on 40 cm fused cross-cylinder,
add is the plus over the manifest
In older patient with limited
accommodative amplitude and
Accommodative amplitude determined
from PRA, add based on allowing the
patient to use only one-half of available
amplitude at the desired reading
Good for early presbyopia with
slightly reduced amplitude of
accommodation account for
the patient’s desired reading
PRA/NRA Plus add is the value that puts the total
near power in the middle of the
PRA/NRA blur points.
Add is the middle of the
Accommodative range from
PRA to NRA