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Archive for the ‘Ophthalmoscope and auroscope’ Category

OPHTHALMOSCOPES AND AUROSCOPES.

The ophthalmoscope is an instrument for looking into the eye, and the auroscope is for looking into the ear. It may be called an Otoscope.
The instruments that I am referring to in the description are the basic ones made by KEELER of the UK.

The Auroscope.
This is the most simple of the two.
First there is the handle which holds the batteries, this pushes into the black plastic part which houses the rheostat that controls the brightness of the bulb.
Then into this screws the head, the head contains the bulb, it may have a lens on the back, it may have a tubing adapter for testing the timpanic membrane, and will hold the specula, the specula is the conical shaped object, of which there are 5 sizes, which goes into the ear.
The tubing adapter which sticks out of the side and is used for testing the timpanic membrane is used like this;
The lens is put on the rear of the head and makes an air tight seal, a piece of tubing with an inflation bulb, such as is used on a blood pressure machine, is attached to the adapter.
When the operator looks through the auroscope into the ear the can see the membrane and by gently pumping the bulb can watch the membrane move in and out and thus see how elastic it is.
So the head should be reasonably air tight, test this by putting your finger over the end of the specula and gently inflating the bulb, it will be quite obvious if there is a leak.
The leak will either be around the lens or around the specula, some times you will find that there is a crack in the glass of the lens, or that the specula has become deformed.
If the glass is broken there are a number of ways around it.

a. Is to fit an official replacement, (if you are lucky enough to have one).

b. Find a lens from something else and grind it to fit.

c. Fit a piece of thin ordinary glass, obviously not ideal because you have lost the magnifying part, but better than nothing.
The lens can be glued in with some epoxy glue.
The problem of the batteries being corroded into the handle was written about in the section on Laryngoscopes so if you have that problem you will know what to do.
With these handles there is a hole in the base, you may be able to put a punch in and punch out the corroded batteries.

The bulb will not light this is a favourite complaint.

a. Check the batteries,

b. Check the bulb,

c. Check the contacts at each end of the batteries are clean.

d. Check the wire in the bulb holder, I must say that I don’t think that I have ever had this wire go, so the chances are that it will be all right.

If the batteries have been allowed to corrode badly you will some times find that it has also damaged the plastic part where the rheostat goes, and unless you have an approved spare there will not be much that you can do about it, apart from perhaps using epoxy glue to hold together any cracks.
It is always worth keeping any old parts from instruments that have been scrapped off to use for spare parts to keep others going.
Sometimes the rheostat wires will have been attacked by corrosion from the batteries, all you can do is to take out the rheostat and find some very thin wire, perhaps out of an old transformer or an old car ignition coil, and try to rewire it, I can’t say that I have ever done it, but I can’t see why you shouldn’t, do scrape off the insulating layer where the arm of the rheostat touches the wire, otherwise you will re-assemble the whole thing only to find that it won’t work and a fault like that will not readily spring to mind and you will spend a lot of time wondering where the fault could be.
When you look at many of the problems that you will find in these instruments, they are in the main caused by one thing and that is allowing the batteries to corrode in the handle, if you can cut this out then I think that you will get rid of most of your problems.

Ophthalmoscope.
The battery handle will often be the same one as is used for the auroscope, you buy one handle and the two heads, there are different size handles available, so all that we have said about the handles previously applies in this section.
The head however is quite different, and is much more complicated inside and thus needs much greater care when taking it apart.
I must repeat again that I am referring to the Keeler Practitioner in this section, other Keeler types will be slightly different, and other makes completely different, but this one is a good basic one to describe.
NOTE>>>>>>>>When you are taking these apart take great care, inside there are a number of very small ball bearings and springs, these are used to line up the lenses in the correct positions.
As you remove parts do it slowly and watch because these balls and springs will jump out and are capable of going great distances when you do not have any spares.
You will probably have some difficulty in locating them in the correct position when you come to re-assemble the instrument, the secret is that behind the spring will be a small grub screw that increases or decreases the tension on the spring.
This can be found on the other side of the instrument often hidden under a sticker or plate.
If you can find this then it is easier to re-assemble the lenses and put the ball and spring in afterwards, and adjusting the tension correctly.
There is a bulb in the bottom of the head, which has a locating pin in the side of it, this shines up through a series of lenses in the body and the light beam is then turned through 90 degrees and out through one of the lenses of the may wheel.
The light path through the Keeler Practitioner ophthalmoscope is as follows:

a. From the bulb it passes through a set of three lenses in a tube.

b. Through one of three openings which may be used, (others models and makes may have more, see a list at the end of the section).

c. Through another set of three lenses in a tube.

d. Off the mirror and through 90 degrees.

e. Through the may wheel, this is the ring of lenses that alter the magnification available. There are 19 lenses and one empty hole.

f. Lastly, through one of three lenses or a hole, these are to allow for people who wear glasses.

Lenses B, E and F are selected by the doctor to suit his needs.
The others are fixed and should not be moved unless you really feel that you have to.
Some parts of the lens system need to be looked after from time to time, the lenses may be cleaned with methylated spirit and a soft cloth.
The only problem that you might get here is that the green filter may come unstuck and fall out, the same may happen to the black circle and cross, all you do is to glue them back in as neatly as possible.
If the mirror is cracked it can be replaced by undoing the screw on the side of the head and tapping it out, when you put the new one in, its position is quite important and you will have to move it in and out a tiny bit until you get a nice clean round circle of light, then tighten up the screw again.
If you haven’t got a new mirror then you will have to use the one you have because you are unlikely to be able to make your own, as the glass is very thin.
Unless the crack is very big it will probably be still usable.
If the May wheel falls apart and all the lenses spill out, which does sometimes happen, replacing them all in the correct order can be difficult and time consuming, but don’t give up as it is quite possible, even without the correct instruments to do it.

Old may wheels were made in two parts, two circular disks held together with small screws, ┬áthe lenses were held in between. Modern may wheels are all in one with the lenses moulded into the ring, you can’t take them apart.

Clean them by first blowing each side of the lens with a puff of air then brush with a camel hair brush of the sort used to clean camera lenses and such like. Complete the job and take a cotton bud, dip it in methylated spirits or pure isopropyl alcohol and carefully clean each side.
First find all the lost lenses and put them in under a glass cover to keep off the dust.
Next you will need to sort them into the correct order and replace them in the holder.
It will help you, in the long run, if you can make a disc with the correct number of depressions cut out so that you can put the lenses in after sorting out, it can also be used if you find that you have to deliberately take them out for cleaning or something.

Now sorting them out is a difficult job unless you have the right equipment, what you need is a lens meter, the Japanese firm of TOPCON make one, with this you can hold the lenses in front of an eyepiece focus an image and read off a scale what the strength of the lens is, it is then easy to get them in the correct order in the wheel.
The chances are that you won’t have one of these and will have to resort to the sun, what you do is hold the lens in front of a piece of white paper and allow the sun to shine through it and project a disc of light on to the piece of paper.
The size of the disc of light will vary depending on the strength of the lens, obviously you will have to make a holder to make sure that the lenses are held at the same distance from the paper each time.
Providing the sun is shining this works quite well, if the sun is in then a strong lamp will probably do just as well, only sitting in the sun is more pleasant.
I’m not suggesting that this method is easy, but with care it does work.
If a lens is broken there is not much that you can do about it, you will have to do without that lens, sometime you will get an ophthalmoscope head that looks as if it has been has been run over by a bus and will be able to salvage the lens you need out of that.
It’s always worth keeping things that are broken beyond repair so that you can scavenge parts as need be. (I think I said this before).
The two sets of lenses in the tubes should not be touched as I said before; these are there to concentrate the light.
If you should ever have to take them out, do note their position in the body and the way each lens sits in the tube.
When all has been repaired and cleaned it should be tested.
Turn it on and look at something closely like a wristwatch and see that the lenses are in the correct order, and that the projected images are there, and that the circle of light, when shone on a piece of white paper, is round and even in brightness and that there are no dust spots to be seen, if there are any then you will have to start to clean again.
Different makes of ophthalmoscope will be made differently and the means of repair will be different but there are things that will be similar.
Here are some of the aperture/ graticule applications you may find and what they are for. I do not pretend to understand some of the deeper medical terms, so consult your medical dictionary or ask someone who does.

a. Large round circle of light. This is a wide-angle beam and illuminates the largest area possible.

b. Middle sized circle of light. Allows easier access through an un-dilated and in the peripheral examination. Good for children.

c. Small round circle of light or macular beam.
This is designed to look at the macula, (a small area lying slightly to the side of the centre of the retina of the eye and is the region of best vision). Being a small area of light it causes less pupil reaction and less discomfort for the patient.

d. A thin vertical slit. Used to determine retinal elevations and depressions, but may also be used to assess anterior (front) chamber depth.

e. Fixation star or cross. Projects an image on to the retina to assess the degree and direction of eccentric fixation as a result of, for example, macula degeneration.

f. Glaucoma. Projects an image on to the retina to assess the optic cup/disc ratio as an aid to glaucoma diagnosis.
Glaucoma is a disease of the eye causing increased pressure within the eyeball which can damage the retina and result in loss of sight.

g. Red free. This green filter is used to examine the blood vessels of the eye in detail, by filtering out the red. The blood vessels are shown as black against a dark green background.

h. Cobalt blue. Used with Fluorescein dye for the detection of corneal scars and scratches.

 

 

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