Examination of the eyes is a popular OSCE station in many medical schools but one that is often taught haphazardly on Ophthalmology placements. The examination of the ocular structures and function need not frighten the medical student and is similar in structure to examination of other systems of the body. The student or junior doctor should bear in mind that the eye is the only organ that can be examined from both inside and outside and so detection of ocular problems need not be onerous.
Assessment of the eyes and vision consists of two main components: history taking (covered in the article on Ocular History Taking) and anatomical/functional testing. Following these steps will ensure that the eyes are examined in a systematic and thorough manner. As with all examinations, not all these tests are needed and history taking will be the guide as to what ocular functions need to be assessed. This list is not meant to be exhaustive but should help guide you in terms of directing your differential diagnosis of common ocular problems that present in general practice and eye casualty.
The examination of ocular function can be broadly categorised into four parts:
For this you will need:
Visual acuity is tested by use of the Snellen chart. This is a board that consists of high contrast letters, decreasing in size as one reads the letters to the bottom. Depending on which Snellen chart is used, the patient will be positioned at 3 or 6 metres. Each row is denoted a number from 6 to 60 and corresponds to the distance from which a normal eye, i.e. one without refractive errors, could read that row of letters e.g. a row denoted 12, means that a normal eye can read that row at 12 metres.
To examine a patient, test each eye separately by asking the patient to cover one eye with their hand or by using a hand-held occluder. If a patient wears spectacles, then these should be worn. Ask the patient to read down to the lowest row of letters that they can see clearly. Then test each eye again with the pinhole. The use of the pinhole should give a more accurate reading of their visual acuity, as any true refractive errors not corrected by the patients spectacles will be eliminated by the pinhole. Visual acuity is recorded as the distance at which the patient is positioned from the chart (numerator) over the number of the lowest line read (denominator). For example, if a patient read to line 12 and was positioned at 6 metres, their visual acuity is recorded as 6/12.
Normal visual acuity is defined as 6/6. Sometimes if a patient reads a row but gets one or two letters incorrect, the visual acuity can be recorded with a negative value; for example, if a patient reads to the line 12 but reads two letters incorrectly, their visual acuity is recorded as 6/12-2. For anymore than two letters misread, the the previous line read correctly should be recorded as the true visual acuity.
If a person cannot read any lines, counting fingers (CF) can be tried by asking the patient to see how many fingers they can see you holding at 1 metre. If this is unsuccessful, proceed to elicit whether the patient can percieve hand movements (HM). If this also proves to be unsuccessful, test light perception by use of a pen torch. If the patient sees nothing at all, then the visual acuity should be recorded as NPL (no perception of light).
Other tests of visual acuity
For patientswho are illiterate, a Snellen chart of randomly arranged capital letter 'E' can be used. Like the normal Snellen chart, these are arranged in decreasing order of size and in different directions. The patient is asked which direction the letter 'E' is facing.
For paediatric patients, there are a variety of assessment tools to test visual acuity:
Confrontational visual field testing is a relatively simple method and relies on comparing the patient's visual fields with your own. Sit in front of the patient about 1 metre away. Ask the patient to cover one eye with their hand. If the patient covers their left eye, cover your own left eye i.e. the contralateral eye, with your hand as well. Ask the patient to focus on your face and not move their eyes anywhere else, otherwise the test is void. Placing your arm to the outside, maintain an equidistance between yourself and the patient. Hold a random number of fingers and ask the patient how many fingers you are holding. Do this another two times in each quadrant.
N.B. this will involve you swapping your hands to keep the same eye covered.
A more accurate way of doing this is by use of a white hat pin. If a visual defect is present, work towards the centre to see if the defect passes away. Repeat the test again for the other eye.
Testing pupillary reactions requires a dimly light room, to avoid interference from daylight. The patient should focus on a target, so as to eliminate the accommodation reflex. A pen torch is used and should be positioned from just below, to prevent causing any discomfort to the patient by suddenly shining a bright light directly onto their eyes.
Direct light response
First check pupillary response to light by slowly introducing the light from the pen torch onto that eye (direct light response). Normal response is constriction of the pupil. Failure for this to happen is known as an afferent pupillary defect and indicates a pathology with the corresponding optic nerve. Check the response of the other eye (to assess the consensual response).
Swinging flashlight response
Shine light onto one eye for about 3 seconds and then rapidly alternate to the other eye and back. A normal response should be brisk constriction of each pupil as light is shone onto the eye, with a consensual response seen in the other eye i.e. constriction. An abnormal response can be seen when light is shone onto the diseased eye - a dilation process ensues. This is known as a relative afferent pupillary defect (Marcus Gunn Pupil) and indicates that the sensory (afferent) stimulus sent to the midbrain is impaired.
Light-near dissociation reflex
This test is performed in a well lit room and tests for the accommodation reflex. This is done by asking the patient to focus on an object or a wall in the distance. Inform the patient that you will soon bring a hat pin/tip of a pen into their visual field but not to look at this unless told to do so. Introduce this object into their line of vision and ask the patient to now focus on the object, observing their pupils. A normal response is pupillary constriction as the eye accommodates to focus. Failure to do this is termed light-near dissociation.
More information on pupillary disorders can be found in the article on Pupillary Abnormalities.
To perform this test, you should know which nerves innervate which eye and how each extraocular muscle works:
Each eye is connected to six different extraocular muscles. The functions of each muscle are:
A simple and well known mnemonic to remember the innervations of the extraocular muscles is "SO-4, LR-6, everything else-3" (Superior Oblique - cranial nerve 4, Lateral rectus - cranial nerve 6, all other muscles - cranial nerve 3).
Sit up close, in front of the patient. Tell the patient that you are going to stabilise their head, by gently place your hand underneath their chin. With the other hand, ask the patient to focus on your index finger and follow it with their eyes only. You should trace an imaginary 'H' shape and look at how both eyes move. Check for any nystagmus or inability of one eye to move in accordance with your finger (palsy). Ask the patient if there was any diplopia when looking in any particular way.
Specific information on nerve palsies can be found in the article on Extraocular nerve palsies.
Testing for pathology at the level of the optic nerve can only be done after tests for visual acuity and RAPD have been carried out. The main way to assess optic nerve function is to test for colour impairment/ This is primarily done by use of the Ishihara colour plates, which test primarily for red-green colour defects. The Ishihara test conists of using a book of plates with a circle of dots with varying size and colour. Within the circle is a seprate entity of dots that form a random number or alphabet. These figures will be visible to those with normal colour vision but not to those with red-green defect. There are usually 15 plates in total and th examiner will flick through each plate, giving a 5 second delay between each plate. A colour defect will become apparent after the use of a few plates. A score of 13+/15 is considered normal.
If there is no access to the Ishihara colour plates or the patient is illiterate, a brightly coloured object (red) can be used. If the patient says that the colour appears washed out, this should alert the examiner to optic nerve pathology.
The examination of the eyes should be methodical so as to not miss out any areas of potential pathology. For this reason, most doctors in eye casualty examine the eyes "front to back" - i.e. from lids to optic nerve.
This ideally should be performed with the use of a slit lamp. Examine both upper and lower eyelids, making sure to compare one with the other. Note the position of the eyelids for drooping (unilateral or bilateral? Complete or incomplete?). Are the eyelids unusually everted or inverted? Are the eyelashes normal (presence of crusting or aberrant eyelashes)? Is there any presence of swelling or erythema? Has the patient sustained a laceration (consider if the cornea is involved)? Any unusual lumps or bumps? If you suspect that a foreign body is under the eyelids, you will need to evert these to gain as much access possible. It is good practice to do this with the use of a local anaesthetic but this is not always necessary. Gain consent first from the patient and warn them that you will fold back their eyelids for a few seconds to examine inside. To do this, ask the patient to look down. With the base of your thumb and index finger, grab hold of the edge of the eyelid, folding it over a cotton bud to expose the tarsus and fornix. Clean out any foreign body that is not embedded too deeply.
Things to consider:
Examining the lacrimal system begins with inspecting the eyelids as mentioned above. Check for whether entropion and ectropion are present, as these interfere with drainage through the puncta (minute orifices from which the canaliculi begin). Entropion particularly poses a problem as the eyelid is everted, causing the lower punctum to be turned away from the ocular surface and hence lead to epiphora (overspill of tears). Examine the punctum under the slit lamp to check for any stenosis caused by scarring or papillomas. The medial canthus should be examined in detail for any unusual erythematous swellings and discharge (dacrocystitis). Patients who complain of sore-gritty eyes with a foreign body sensation should be checked for dry eyes. To do this, the eyes should be stained by fluorescein eye drops by asking the patient to look up and inserting a drop into the lower fornix. The patient then blinks to spread the fluorescein across the ocular surface. Slit lamp settings are then adjustered to cobalt blue light and the patient's eyes are examined with this light shining on them to give a luminous green appearance. Dry eyes may reveal mucin strands and punctate epithelial erosions on the cornea. The tear film should be assessed by asking the patient to blink with the fluorescein and measuring how long the film takes to break - normal timing is at least 10 seconds.
N.B. The Schirmer's test is no longer used in most ophthalmic departments.
Be sure to examine both the upper and lower fornices in both eyes. This is done by everting the eyelids as described previously. Assess the colour of the conjunctiva. Check for any follicles or papillae. Be also sure to check for any foreign bodies that may be stuck in the folds of the conjunctiva.
Things to consider:
It is best to check corneal sensation before instilling any fluorescein drops, which contain local anaesthetic. This can be done by assessing sensation on both sides by lightly touching the surface with a wisp of cotton. A brisk blink reflex should follow. Then fluorescein can instilled and the cornea examined under blue light to see if any epithelial loss (ulcer or abrasion) is present. Penetrating injuries should be carefully ruled out by the Seidel test: application of 10% fluorescein to the suspected site of injury will change the fluorescein from a brownish to a light orange colour due to dilution with aqueous.
Things to consider:
The presence of pus in the anterior chamber (hypopyon) can indicate inflammation i.e. uveitis or something more sinister such as endophthalmitis. Uveitis can be confirmed by angling the slit lamp light at 30 degrees to the cornea. Flare (cloudiness - like a beam of light passing through a smokey room) is usually indicative. Blood settling in the inferior aspect of the chamber (hyphaema) is usually caused by trauma. The iris should also be assessed for discrepancy in colour (heterochromia) and any suspicious lesions such as iris melanomas. In glaucoma suspects, gonioscopy is performed to view the iridocorneal angle by use of a "three way mirror" or goniolens, but this is outside the scope of this article. Pupil sizes should be noted for discrepancy (anisocoria). The size may also be distorted in acute angle aclosure glaucoma (oval) or anterior synechiae (general shape distortion).
The lens should ideally be examined in a dilated patient. Depending on the patient, you may see eyes with normal lens (phakic) or artificial lens (pseudophakic). Patients may be aphakic due to a number of conditions. Early signs of cataracts can be spotted with experience. Usually a dimming of the red reflex when the ophthalmoscope is held around arm's length from the patient's eye is a give away, especially in the elderly patient. Slit lamp examination can reveal which type of cataract has formed. Sometimes the lens maybe displaced in a number of congenital conditions. Examining the red reflex in young children and infants can be difficult and should be attempted with the parent holding the child in place and encouraging them to look towards the light of the ophthalmoscope. In some cases, the paediatric ophthalmologist will opt for the use of cyclopentolate 0.5% (a mydriatic and cycloplegic) to help dilate the pupil. Any paediatric patient with a 'white pupil' (leukocoria) should be referred immediately for further investigations.
Things to consider:
The examination of the fundus can be carried out in the primary care setting with the use of a direct ophthalmoscope. More detailed examinations will need the use of a slit lamp or an indirect ophthalmoscope; where a light source is attached to a head-set worn by the ophthalmologist, who holds a lens piece to focus into the eye. The indirect method is useful because it gives a wider view of inside the eye, all the way to the ora serrata (periphery of the retina).
Examination with the direct ophthalmoscope should be be started off by warning the patient that you will get very close to them and that they should stare into the distance, unless otherwise told. The red reflex should be attained first by standing at a distance. Then examining with your right eye, advance on the right side of patient, coming up close to their face until you can see the retina and the blood vessels. It is best practice to divide the retina into four quadrants and examine the blood vessels as they come out of the optic disc. To visualise the macula, ask the patient to look directly into the light (making sure that the source is not too bright for them). The macula is two disc diameters to the temporal side. With the slit lamp, a handheld lens (usually 97 diopters) is used to look into the fundus. The image produced will be inverted e.g. a lesion noted through the slit lamp on the inferior side is in reality located in the superior edge. The patient can look in different directions for the ophthalmologist to see different areas of the retina.
Things to consider:
1. James B, Chew C, Bron A. Lecture notes on Ophthalmology. Blackwell publishing: Oxford. 2004
2. Olver J, Cassidy L. Ophthalmology at a Glance. Blackwell publishing: Oxford. 2005
Images used from:
Kay pictures: http://biomed.science.ulster.ac.uk/vision/-Recognition-Visual-acuity-.html
Snellen chart: http://www.ndrs.scot.nhs.uk/Train/Handbook/drh-21.htm
Ishihara plates: http://www.rpfightingblindness.org.uk/index.php?pageid=237&tln=aboutrp
Slit lamp: http://mosaik.wordpress.com/2006/06/12/safety-reminder/
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