3. “
It is a box containing
different types of spherical
& cylindrical lenses, prisms,
trial frame, cross cylinder,
maddox rod, stenopeic slit,
pin hole, occluder, red and
green filters, etc.
2
4. Contents of the trial set :
1. Spectacle trial frame
2. Spherical lenses
3. Cylindrical lenses
4. Prisms
5. Occluder
6. Pin hole
7. Plano lenses
8. Red & green filters
9. Maddox rod
10. Stenopeic slit
11. Jackson cross cylinder
3
5. Trial frame
● It is made up of metallic or plastic
frame.
● It is light weight with comfortable nose
rest.
● It has usually three compartments one
each for spherical lenses, cylindrical
lenses and occluder.
● Compartment of cylindrical lens has
smooth & accurate rotation.
● Nose bridge and temple are adjustable
according to patient face. 4
8. Full aperture lenses
Approximately 38mm
diameter.
Biconvex or biconcave
form.
Trial lens
Reduced aperture lenses
Lenses of 20mm
diameter mounted in the
metal rim of 38mm
diameter.
Planoconcave or
planoconvex form.
7
During refraction the practitioner utilize a
set of known lenses called as trial lenses.
USES : - For hand neutralization and to
check refractive error.
9. Spherical lenses
Present in plus (convex) & minus
(concave) form.
Range: + & - 0.12 to + & - 20.00D
Variations:
0.25 to 4.00 in increment of 0.25D
4.00 to 6.00 in increment of 0.50D
6.00 to 14.00 in increment of 1.00D
14.00 to 20.00 in increment of 2.00D
Cylindrical lenses
Present in plus (convex) & minus
(concave) form.
Range: + & - 0.25 to + & - 6.00D
Variations:
0.25 to 4.00 in increment of 0.25
4.00 to 6.00 in increment of 0.50
88
10. Prisms
● A prism is a refractive medium having
two surfaces inclined at an angle.
● Prism displace the image towards apex.
● Prisms are arranged by base apex
notation.
● USES : - To measure small squint
- To prescribe prisms in spectacles
- Convergence relaxation and
reducing diplopia
9
11. Occluder
● It is a black opaque disc made up
of plastic or metallic rim.
● It is used for uniocular testing and
to intercept the light reaching to
the eye.
● Used to relax accommodation and
occlude one eye while the other
eye can be tested for visual acuity.
10
12. Pin hole
● Opaque disc with a pin hole of 1-2mm
diameter in its centre.
● Allows only a pencil of light to pass
through the cornea.
● Helps to determine whether the eye has
refractive or pathological error.
● Pinhole of 1.32mm diameter is more
effective.
● Usually available pinhole is 1mm in trial
set. 11
13. Stenopeic slit
It is made up of black opaque disc
with slit aperture.
The slit is usually 1mm in wide.
It allows the rays of light to pass
through only one meridian.
It is used to find the axis of the
cylinder.
Plano lens
Zero power lens, used to satisfy
and identify malingering patient.
1212
14. ● Red before the RE and Green before the
LE.
● Used for colour dissociation, to find out
suppression of eyes, diplopia, to
measure fusion and squint.
● Used in WORTH FOUR DOT TEST and
FRIEND TEST.
● Some trial lens also contain yellow
filters.
13
Red & Green filters
13
15. Maddox rod
● The maddox rod is a handheld instrument
composed of red parallel plano convex
cylinder lens, which refracts light rays so that a
point source of light is seen as a line or streak
of light. Due to the optical properties the streak
of light is seen perpendicular to the axis of
cylinder.
● The maddox rod is usually coloured red or
green.
● It is used to find out the presence of
heterophoria or heterotropia.
14
16. ● It is a combination of two cylinders of
equal strength but opposite signs placed
with there axis at 90° to each other and
mounted in a handle.
● Usually the cross cylinder are of + & - 0.25
or + & - 0.50.
● Spherical equivalent is zero.
● Used to determine both cylindrical power
and axis.
1515
18. “
It is commonly used by eye
care professionals during an
eye examination, and
contains different lenses
used for refraction of the eye
during eye testing, to
measure individual’s
refractive error.
17
20. Manual phoropter
• It is operated manually by the
practitioner.
• Not all the refractors are same,
but they all have the essential
features i.e. controls to adjust
sphere, cylinder axis, cylinder
power, and an occluder.
19
21. Controls of the manual phoropter :
1. Rotation adjustment knob 12. Cylinder power knob
2. Mounting bracket 13. Cross cylinder unit
3. Mounting adjustment knob 14. JCC
4. Forehead rest knob 15. Cyl power scale
5. Spirit level 16. Cyl axis reference scale
6. PD knob 17. Cyl axis indicator
7. Vergence lever 18. Weak sphere dial
8. Auxiliary lens scale 19. Sphere power scale
9. Auxiliary lens knob 20. Strong Sphere control
10. Rotary prism unit 21. PD scale
11. Cylinder axis knob 22. Reading rod clamp screw
2020
23. Auto phoropter
• This machine is divided into main
body and keyboard.
• Has some principle of operation
like manual phoropter.
• Easier to operate, one button to
start the test.
• Contains memory system i.e. it
stores all the testing process.
• Simple and convenient.
22
24. Advantages
• More comfortable for patients.
• Lenses do not become dirty or
scratched.
• Axis of any cylindrical
correction can be read off
from the refractor.
• Additive errors can be reduced.
Disadvantages
• Examiner depends upon
subjective response.
• Refracting unit hides the
patients face.
• Corrects only lower
aberrations.
• If head is tilted during
refraction, the cylindrical axis
will be prescribed off axis.
823
25. Difference between Trial set & Phoropter
Trial Set Phoropter
A box containing arranged lenses, a trial
frame and other devices used in
testing vision.
An instrument containing different lenses
and other devices as whole one unit.
Time consuming and basic technique for
eye testing.
It is advanced, modified and faster
technique to use.
Can’t measure IPD. Can measure IPD.
Has 32 pairs of spherical lenses, 20 pairs
of cylindrical, 10 prisms and other
accessories.
It has all the accessories same as trial set
& it also contain spirit level and digital
viewing system.
26. Separated accessories are difficult
to use.
All accessories are attached
in it.
It is portable. It is not portable.
It is cheap to buy. It is expensive.
Patient can move freely and feel more
comfortable.
Can’t move freely and feel
uncomfortable.
Lenses are open and separated. All the lenses are inside the instrument.
Can be sterilized easily. Difficult to sterilize.
27. 8
Spirit level indicator is absent. Spirit level indicator is present.
Chances to lose accessories. No accessories can be lost.
Doesn’t hide patient’s face so easy to
interact with the patient.
It hides patient’s face so difficult to
interact with the patient.
Easy to perform retinoscopy.
Difficulties arises while doing
retinoscopy.
Large field of vision. Restricted field of vision.
Maintenance is cheaper. Requires expensive maintenance.
