This document provides information about various ophthalmic instruments including their parts, maintenance, troubleshooting, and proper use. It discusses direct ophthalmoscopes, indirect ophthalmoscopes, streak retinoscopes, keratometers, slit lamps, operating microscopes, and electricity as it relates to powering medical devices. Tips are provided for cleaning, replacing parts, checking for proper function, and storing the instruments to maximize their lifespan.

1. Ophthalmic Instruments
an introduction including some
tips for care and maintenance
Prof. V. Srinivasan M.A.,M.S. (Oregon USA)
Consultant, Instruments lab,
Aravind Eye Hospital. Madurai,
India

2. Direct Ophthalmoscope
A diagnostic instrument to look at
the fundus in the eye

3. Parts
• Handle
• Cells / Battery (use and throw,
rechargeable) / power supply
• On-off switch and brightness control
• Head
• Bulb
• Aperture, filter systems
• Lenses, reflectors, windows, shutter
• Disc lens + extra lenses
• Screws, springs, steel balls
• Shutter, pouch / box

4. Problem – No light or dim light – Level I
• Battery / cells not placed properly or rundown
- check their position, their voltage, recharge or
replace them (all cells)
• Power supply problems
- check input and output voltages, the switch,
connecting wires and the circuit and rectify
faults noticed
• Bulb fused or darkened - check and replace
• On off switch and brightness control not
functioning - check and clean rheostat & switch
• Head not mounted properly on the handle
- check and fix properly

5. Problem - No Light or dim light -
Level II – little more involved
• Reflector dislocated
• Window shutter stuck up
• Disc lens, aperture / filter system broken
or stuck up
• Lenses broken or dislocated
• Too much dust (particles of smoke) or
moisture inside the head
The remedy for all these is to open the head
clean and fix or replace the parts

6. Extra information for technicians
• The blue (red free) filter is used to cut out the red glare
of the retina
• Polarizing filter is used to cut out reflection from
cornea
• Small aperture is used for undialated (small) pupil
• Regular aperture is used otherwise
• Slit aperture is a used as in slit lamp
• The special aperture with concentric circles and the
plus sign is used to detect any bulge projection on the
surface of retina
• If the tiny steel balls in the instrument are lost one can
replace them with a steel balls used in the bearings of
bicycle
• Small springs can be wound using thin wires

7. Hints to be passed on to users
• Keep the instrument in the box / pouch when not in
use to avoid collection of dust on the instrument
• Make sure the on-off switch is fully turned off ( a
click sound will be heard) before placing the
instrument in the box / pouch.
• Recharge rechargeable cells at the end of each day
after work
• When the instruments is not likely to be used for a
few days remove the battery / cells keep them out of
the handle to avoid leakage
• Avoid smoking. Smoker’s breath carries fine smoke
particles into the instrument that reduce illumination

8. Bulb
Condensing lens
Image forming lens
Slit, filters apertures
Reflector
Optics of direct ophthalmoscope
• The bulb is filament type halogen bulb that gives more
light
• The reflector is a front silvered mirror (fully reflecting), or
a total reflecting prism except and in Welch Allyn
Ophthalmoscopes in which it is a partially reflecting
mirror
Total reflecting prism

9. Indirect Ophthalmoscope
A diagnostic instrument used to look at
the retina in the eye
Also used as therapeutic instrument to
deliver laser pulses at required spots in
the retina

10. Comparison
Indirect
• Binocular
• Stereoscopic (Three
dimensional image)
• Magnification is less (3X
with a 20 D lens)
• Field of view is more and
can be increased by using a
depressor
• Observer remains at a
distance from the patient
• Darkening of the room
required
• Inverted image
Direct
• Monocular
• Flat image ( Two
dimensional image)
• Magnification is more 15X
• Field of view is less
• Observer has to be close to
the patient
• Can be used in day light
• Erect image

11. Parts
• Head band / spectacle mounted
• Power supply, battery box, cable, switch
• Illumination system – bulb, lenses,
reflecting mirror, filters, apertures
• Viewing system – lenses, reflecting
prisms or front silvered mirrors, screws
• Teaching mirror
• 20D / 30 D lens
• Depressor

12. Problems – No light
• Check on-off switch - rectify defects if any
• Check power supply voltage (input /
output) and rectify defects if any
• Check battery pack voltage - recharge if
necessary
• Check connecting wires for continuity or
short circuit - replace if necessary
• Check the fuse - if blown out replace
• Check the bulb - if fused or blackened
replace

13. Other problems and tasks
• Spot of light not in focus – lenses, filters,
reflector, aperture in the illumination system
disturbed - check and rectify
• Diplopia (Double image) – mirrors / prisms and
lenses in the viewing system disturbed. – check
and align them properly looking at an object at
a distance of a meter
• Head band problems – cleanliness, padding,
fitting screws and connecting wire should all be
checked cleaned often and defects removed
• Keep the 20D lens clean

14. Optics of Indirect Ophthalmoscope
IPD
20D lens

15. Streak Retinoscope
Along with the lenses in a trial set
it is used in objective refraction for
the measurement of spectacle
power and for fixing the axis of
astigmatism if present

16. Parts
• Handle
• Cells / Battery (use and throw,
rechargeable / power supply)
• On-off switch and illumination control
• Head
• Bulb
• Beam width adjustment
• Beam orientation adjustment
• Lenses, reflector and window

17. Problem – no light
• Battery / cells not properly placed or run down
- check and replace battery / cells
• Power supply problems - check input output
voltages, switch & connecting wires and the
circuit
• Bulb fused or darkened - check and replace
• Head not mounted properly on the handle
- check and fix properly
• Lenses disturbed - check and correct
• Reflector disturbed - check and correct

18. Other Problems
• Light flickering - loose electrical contact at
the bulb holder and illumination control -
check and clean
• Beam width adjustment problem - check,
clean and gently lubricate shaft movement
in the head
• Beam orientation adjustment problem -
check, clean and lubricate the turning
knob
• Dust on reflector, window - clean

19. Additional Information
• Keep the retinoscope in the box when not in use
• While turning it off turn the switch all the way till a
click sound is heard
• If the retinoscope is not likely to be used for a
few days keep the battery / cells outside. This will
avoid leakage of battery / cells
• The handle of streak retinoscope and direct
ophthalmoscope are the same. Some
manufacturers supply the two heads with a single
handle for economy and convenience in carrying
them in a single box
• The bulbs of direct ophthalmoscope and streak
retinoscope are not the same. Retinoscope bulbs
have a straight filament.

20. Keratometer
Used in measurement of the corneal
power required in the calculation of IOL
power in cataract surgery
&
Used in contact lens fitting

21. Parts – Optical
• Bulb , bulb holder
• Switch and connecting cable
• Reflector
• The mire
• Telescope (objective and eye piece)
• The prisms
• Model cornea

22. Parts - Mechanical
• Base
• Up - down movement screw
• Left - right rotation with a lock for fixing
• Forward - backward movement (focusing) screw
• Power reading drums - horizontal / vertical
• Circular scale to measure the axes for
astigmatism
• The chin and head rest

23. Maintenance tasks
• Keeping the instrument covered when not
in use
• Cleaning the body & the optics (removal of
dust)
• Periodic lubrication of all moving parts
• Replacement of bulb when required
• Checking the on-off switch and the power
cable replacing them when necessary

24. Calibration check
• Check the calibration every day before
using the instrument using the model
cornea. If the calibration is disturbed
correct it immediately
• Correct power of IOL to be used in a
cataract surgery depends on the power of
the cornea. Correct Keratometer readings
are very important

25. What NOT to do
• While cleaning do not disturb the optics
especially the two prisms inside used to
get the extra images

26. Slit Lamp
An instrument used to examine all parts
of the eye
Also used to deliver laser pulses into the
eye for treatment
Convenient instrument for
photographing different parts of the eye

27. Types
• Bulb located at the top
– tilting type
– Uses a front silvered
mirror to reflect light
in the direction of
the patient
• Bulb located at the
bottom – fixed type
– Uses a total
reflecting prism to
reflect light in the
direction of the
patient
• Inclined optics
– consists of two
objectives looking at
an angle.
Magnification
change achieved
by changing the
objective
• Parallel optics
– Single objective lets
two beams of light
into the instrument
at an angle. Has 3
or 5 step
magnification using
Galilean set-up

28. Parts
• Illumination system
– Bulb, condensing lens, slit, slit width adjustment, slit height
adjustment, slit orientation adjustment, filters, power supply
illumination control and power card
• Magnification system
– Stereo compound microscope. With a prism arrangement
that lets adjustment of eye pieces separation to suit the IPD
of the observer. The final image is erect without left right
inversion
• Mechanical system
– Table movement up / down (manual / electrical)
– Joystick movement up / down, forward / backward, left /
right
– Chin and head rest movement up / down
– Illumination system tilting arrangement / slit adjustments
(width, height and orientation with respect to the vertical)

29. Maintenance tasks
• Keep the instrument covered when not in
use
• Replace bulb when necessary
• Remove of dust and stain
• Lubricate and check all mechanical
movements periodically
• Check electrical parts

30. Trouble shooting
• No light
– Check power at the socket, check the switch, check
whether the slit is open, check bulb, check slit width /
height / orientation adjustments (they may be stuck
up) rectify the defect noticed
• Diplopia – double image
– Eye pieces disturbed – check and restore it to proper
position
• Hard movement
– Clean relevant parts and lubricate gently
– The spherical surface in the joy stick set
up may be worn out. Replace it

31. Suggested maintenance schedule
• Optics cleaning as and when found
necessary – at least once a week
• Stripping, cleaning and assembling of
illumination system – once in three
months
• Stripping, cleaning and assembling of
mechanical systems once in a year
• If the location is in a monsoon area a
thorough cleaning is very important soon
after the monsoon is over

32. Other instruments used with Slit
Lamp
• 78D / 90D lens to look at the fundus
• Gonio lens to look at the angle of the eye
• Applanation tonometer to measure the
IOP
• Micromanipulator to used to deliver the
laser beam at required spots
• Camera

33. Operating Microscope
Used in micro surgery of the eye

34. Parts
• Objective lens
• Eye pieces
• Magnification changer mechanical 5 step
arrangement or motorized (zoom) system
• Illumination system – bulb, fiber optic cable, the
axial illumination arrangement power unit, cooling
fan
• Attachments – Beam splitter, assistant scope,
recording systems (camera / video)
• The vertical stand, rotating arm, the base wheels
and locking arrangement (Ceiling mounted and
table mounted microscopes are also in use)

35. Maintenance tasks
• Keep the optics covered when the instrument is not in use
• Clean optics (external surfaces) every day after use
• Do not open the microscope head or eye pieces assembly.
They are usually airtight. Open and clean only if any dust or
foreign body is noticed inside
• A full cleaning of all optical parts may be needed in monsoon
areas soon after monsoon to avoid the growth of fungus. In
such regions keep silica gel pockets in the vicinity of the optics
to keep the region dry this will prevent fungus growth. Also
keep the region around the microscope warm with an electric
bulb hanging just above the microscope this will also help to
reduce fungus formation
• Remove the microscope out of the OT when the OT is washed
or cleaned and keep it outside till the OT is dry
• Check the wheels and lubricate it for easy movement, check
the locking system, repair it if it is not working
• Check the electrical parts. At the commencement all the bulbs
should be in good condition
• Check that the optic fiber is not bent sharply nor twisted tight

36. Some tips for the users
• Remove all extra attachments, beam splitters,
recording systems, assistant scopes when not in use.
They tend to reduce the brightness of the final image
• Greater magnification implies lesser brightness of the
image and lesser field of view
• Longer working distance also reduces the field of view
• Keep the brightness low unless it is needed this will
ensure a longer life for the bulb
• Avoid movement of the microscope when the bulb is
on
• Microscope head can be moved up or down during the
surgery with the help of foot switch control. When such
movement is necessary at the start of the surgery
position the microscope such that there is enough
movement. It is always better to test this in advance

37. Electricity
A good servant but a bad master

38. What is it and what are the uses?
It is energy – readily available and very clean
Uses:
1. to get light – bulb, fluorescent tube light, discharge lamps, the LED (light
emitting diodes)
2. to get heat – ovens, sterilizers, soldering rod
3. to get chillness – refrigerator, air conditioners, freezers
4. to achieve movement – electric motors, fan, water pump, mixies, grinders,
locomotives
5. in communication and entertainment – telephone, radar, audio, radio, TV,
video ans some musical instruments, toys
6. in electronic instruments – computers, instruments used in health care
Diagnostic instruments : X-ray machine, CT, NMR and other scan
machines, ECG, ERG and similar recording devices
Therapeutic instruments: Electro surgical instruments, phaco machine used
in eye care
7. in electroplating
8. to get powerful electromagnet
9. and so on and on……

39. Some terms used in electricity
• Volt – a measure of the strength of electricity
• Ampere (current) – a measure of flow of
electricity
• Watt (power) – product of volt and ampere
– 1000 watt bulb glowing under 200 volt will require
take 4 ampere of current
• KWH (kilo watt hour, also known as the unit) –
is a measure of electrical energy consumed
– A 1000 watt bulb glowing for an hour consumes a
unit of electrical energy

40. AC / DC
• Electricity is available as DC (current flowing in one
direction only) or AC (with the direction of flow
alternating). The frequency of alternation is 50Hz in
most countries and 60Hz in some countries in
American continent
• With AC, voltage can be stepped up or down easily
using a transformer. This property is very useful in
transport of electricity with minimum loss in
transmission. Higher the voltage lower is the current
for the same amount of energy and hence lower the
heat loss in transmission
• Almost all electronic instruments require DC. The first
unit in any electronic instrument is a power unit that
converts (rectifies) AC into DC

41. Caution
• The mains voltage is 220 V in most countries. However it is 110V in certain
countries in the American Continent. An instrument designed for 110V if
connected to a 220V supply will ‘burn off’. Suitable voltage transformer is
required
• Some instruments have a facility for choosing the voltage. Set the correct
voltage before using the machine. This may require change in the protective
fuse. A 110V instrument that has a 200 mA fuse will be equally safe only
with a 100 mA fuse while working on 220V.
• These days instrument that work on a range of voltages 110 to 220 are
available. Such instruments however are not protected against accidental
higher voltages like 240 that one may get in some locations. It is safer to use
such instruments with a 220-110 step down voltage transformer than to
expect a steady voltage of 220V all the time.
• Instruments that use the frequency of AC in any aspect of its function like
the TV working in America, the NTS system working on 60 Hz will not work
in other countries that have the PAL system working on 50 Hz
• Some instruments that have electric motors and designed for use with 60Hz
may work in 50 Hz but the motor may get heated more
• The voltage and frequency ratings on instruments are always indicated on
the instrument. They must be noted before use.

42. Problems
• Power cut – solved using stand by
generator, inverter, UPS
• Voltage fluctuation – solved using voltage
regulator, stabilizers (relay or servo)
• Surge – sudden increase in voltage due to
natural (lightning) or man made causes –
solved using surge protector

43. Safety factors
• Insulation – of the cable and of all electrical
accessories (switches, plugs sockets etc.) is
important. Insulation tape is only a temporary
solution
• Ground (earth) connection ensures protection
when there is any leakage of electricity in the
instrument or in the building. Ground connection
should be used where ever provided. Periodic
inspection of the grounding (earthing) installation
of the building is necessary
• Fuse / Cutout – these are safety devices used in
the building and in individual instrument to
protect against high current (consequent over
heating and fire) that may arise due to some
accident or overloading of the instrument. The
fuse rating should be strictly adhered to.

44. Some tips
• Always wear foot ware while working on
electrical instruments / installations
• Keep the working area dry. Moist surfaces
provide easy flow (leakage) of electricity
• Don’t take any risk with electricity
• Check the instrument / installation using a line
tester or a multimeter and ensure there is no
voltage before you start working
• Even in instrument that are turned off
components like capacitors may retain electricity
and can cause harm
• Remember electricity can do lot of work for us
(like a good servant) but if you make a mistake it
will punish you (like a bad master) even if it is
your first mistake

45. Optics Cleaning
• Clean optics is needed for good vision.
• Optics get dirty due to dust and stain

46. Removal of dust
• By blowing air
• Using soft brush
• Using cotton swab and mild soap solution

47. Removal of stain
• Using cotton swab and distilled water
• Using cotton swab and mild soap solution
• For hard stain use cotton swab and
acetone.
• Don't use acetone on plastic optics. You
may use alcohol

48. Thank you.
One if the towers of the
temple in Madurai