Semester 2, Skill 3 Part A: The Eye 1. Testing your distance visual acuity with the Snellen Chart 1. Stand 6 meters away from the chart. (For this purpose, a Snellen chart is displayed on the wall and a line is marked on the floor with a tape at a distance of 6 meters from it.) 2. Close one eye and read the lines on the chart from the top until you can no longer read the letters clearly. 3. Read off the visual acuity number on the side of the chart. Record this as a fraction, the first number being the distance from the chart in meters or feet e.g. 6/9 or 20/30 4. Repeat for the other eye, then for both eyes open together Left eye Right eye Both eyes Fraction in feet Fraction in meters 2. Using The Ophthalmoscope The ophthalmoscope is a lighted instrument used to examine the interior of the eye, including the lens, retina and optic nerve. It consists of a concave mirror and a battery- powered light (contained within the handle). The operator looks through a single monocular eyepiece into the patient's eye. The ophthalmoscope is equipped with a rotating disc of lenses to permit the eye to be examined at different depths and magnifications. This may be enhanced by drugs that dilate the pupil and enlarge the opening into the structures within the eye. Brow rest Practitioner side of the ophthalmoscope Diopter dial Viewing window Dioptre power display On/off switch GEEKYMEDICS.COM 1. Familiarise yourself with the ophthalmoscope. Check that you know how to switch it on and that the light is working. Set the value to 0 to begin (stronger lenses will be needed to inspect other parts of the eye). Use the head model with diagnostic eye trainer to practice using the ophthalmoscope. 2. Gently place your free hand on the model's head. Use your right eye to examine their right eye, and your left eye to examine their left eye. Look towards the subject's face through the aperture of the ophthalmoscope, steadying it against the side of your nose. Move the instrument around until the spot of light falls on the eye. Move your head with the ophthalmoscope (as a single unit) sideways until you see a red glow (the red reflex) from the pupil of the eye. Gradually move towards the subject until the fundus is seen (you will need to be close to the subject). You can then try to see other features by moving the dial to change focus. 3. Make observations using the head model provided. Aim to identify key features of the normal eye, then change the view to observe some different disease conditions (by changing the number on the model's controls) and make observations of notable differences. 3. If you feel comfortable using the Ophthalmoscope, practice on a real human eye. Ask your partner to sit comfortably and stare at a distant object behind you, keeping their eye open. Stand or sit in front of your partner and try to examine their eye in the same way as you did on the model trainer. Make a note of any features you manage to see. Examination of the Fundus The fundus consists of the optic disc, retina, retina vessels, maculae lutea. You may need a weak diverging lens (-2D to -4D) to focus on the optic disc and macula. Examination of other parts of the eye You will need to use converging (+ve) lenses to focus on structures anterior to the fundus. e.g. vitreous humour +4D - +8D Lens +10D Iris +15D Aqueous humour +14D+18D fovea optic nerve Cornea +20D Human retina Part B: The Ear 1. Audiometry An Audiometer is an electrical instrument used for measuring a subjects hearing. Auditory responses are monitored at different frequencies over a range of amplitudes. You will be using a screening audiometer to measure threshold in decibels at different frequencies. To produce an audiogram: a) Connect the left (blue) and right (red) jack plugs to the headphones and the jack plug (black) of the persons response button into the corresponding coloured and labelled sockets (4, 5, & 6) on the back of the panel. b) Connect the power cable to the mains input (2) on the back of the panel and to the mains supply. Turn the switch ON at the socket. The green ON indicator should light up on the front panel. Press the Right/Yes button. c) Sit the subject with his/her back to the audiometer. The subject should be told to press the response button upon hearing the tone and release it when the tone is no longer heard. d) The headset should be fitted with the RED earpiece on the RIGHT ear e) Select the "LEFT" ear position first on the earphone selector. Select 1 kHz (1000Hz) on the frequency selector and select 30 dB on the attenuator level. f) Press the "PRESENT” button for 2 secs, the green "present" button will light up. If the tone is heard, the subject should respond by pressing the response button (if there is a hearing impairment, the tone will not be heard). The attenuator level should be increased in steps of 5 dB until the tone is heard. Always release the “PRESENT” button before changing frequency or attenuation g) Once the initial threshold has been established, the attenuator level should be decreased in 10 dB steps until the tone is no longer heard and then increased in 5dB steps for the hearing threshold level to be checked h) The threshold of hearing is the lowest level at which a subject can identify the tone when it is re-introduced. Thresholds should be measure in sequences of 500Hz, 250Hz, 1, 2, 4, 6 and 8 kHz) i) Plot the threshold dB on the audiogram chart provided, for left ear thresholds mark using a small cross and for right ear use a small circle j) Repeat for the other ear 2. Parts of the ear Observe the model of the ear and try to identify the structures in the diagram below. Then, look at your partner's ear and try to identify the same structures. Finally, use the model to examine the structure of the inner ear before proceeding to the next section. Make note of your observations for your skills report. Triangular fossa Crus of helix Tragus Helix Scaphoid fossa -Crura of antihelix Concha cava Antihelix Lobule Antitragus 3. Observations with Otoscope An otoscope is an instrument which is used to look into the ear canal. The ear speculum (a cone-shaped viewing piece of the otoscope) is slowly inserted into the ear canal while looking into the otoscope. A light beam extends beyond the viewing tip of the speculum. The otoscope is gently moved to different angles to view the canal walls and eardrum. The normal eardrum appears pinkish-grey in colour and is approximately circular in shape. The first of the three small bones that transmit sound vibrations to the hearing mechanism (the cochlea) lies against the far side of the drum and can be seen through it in the upper part, like the clock handles in approximately the 12 o'clock position. Otoscope Eardrum Michael Saunders FRCS You will be called in small groups to view your own eardrum with the otoscope attached to a camera/imager. 4. Observation with Ear Diagnostic Trainer Familiarise yourself with the otoscope using the model head trainer. To safely use the otoscope: a) Gently lift the pinna (lobe) of the subject's ear upwards and backwards b) Hold the otoscope between the thumb and forefinger (like a pencil) with the back of the hand resting gently but firmly against the subject's cheek. This prevents you from pushing the otoscope too far in and harming the ear. c) The otoscope should then move in unison with the subjects head if moved. The whole tympanic membrane cannot be seen one time so the examiner will need to adjust his/her line of vision and the position of the speculum to observe a view of the whole membrane d) Observe the healthy eardrum first, then change the number on the model head to make observations of some other conditions If you feel confident to do so, look at your partner's ear with the otoscope. You should both be seated to do this. USE A CLEAN SPECULUM FOR EACH EXAMINATION. 5. Observe the Models of the teeth. A model of the teeth and mouth has been provided. Examine the model and make observations for your written lab report.