Ophthalmic Instrumentsan 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

Direct Ophthalmoscope

A diagnostic instrument to look at the fundus in the eye

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

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

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 headThe remedy for all these is to open the head clean and fix or replace the parts

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

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

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

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

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

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

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

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

Optics of Indirect Ophthalmoscope

IPD

20D lens

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

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

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

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

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.

Keratometer

Used in measurement of the corneal power required in the calculation of IOL

power in cataract surgery

&

Used in contact lens fitting

Parts – Optical

• Bulb , bulb holder

• Switch and connecting cable

• Reflector

• The mire

• Telescope (objective and eye piece)

• The prisms

• Model cornea

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

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

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

What NOT to do

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

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

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

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)

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

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

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

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

Operating Microscope

Used in micro surgery of the eye

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)

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

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

Electricity

A good servant but a bad master

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 rod3. to get chillness – refrigerator, air conditioners, freezers4. to achieve movement – electric motors, fan, water pump, mixies, grinders,

locomotives5. 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 electroplating8. to get powerful electromagnet9. and so on and on……

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

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

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.

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

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.

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

Optics Cleaning

• Clean optics is needed for good vision.

• Optics get dirty due to dust and stain

Removal of dust

• By blowing air

• Using soft brush

• Using cotton swab and mild soap solution

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

Thank you.

One if the towers of the

temple in Madurai