When only a slit lamp examination will do
In his fifth article on common eye complaints Dr Scott Fraser explains how to decide when referral for this examination is necessary
It is often felt the slit lamp allows the user to have supernatural powers of diagnosis when in fact, as in all medicine, it
merely allows confirmation of the diagnosis ascertained by taking a careful history.
This does mean that when a patient has certain symptoms they do need slit lamp examination for this confirmation and this article discusses these important symptoms.
Direct trauma to the eye, blunt or sharp, usually needs slit lamp examination, especially if there is a reduction of vision, a hyphaema, alteration in the shape of the pupil or any obvious corneal/scleral rupture.
Small abrasions and trauma associated with little force do not need examination unless the vision is reduced.
Trauma associated with potentially penetrating injuries such as hammer and chisel (the slit lamp is better at picking up intraocular foreign bodies then X-rays are) needs referral even if the patent is asymptomatic.
Superficial corneal foreign bodies can often be removed with a sterile needle
and a good light. Deeper debris and rust rings are more easily and safely removed at the slit lamp.
Chemical injuries, apart from the most mild, need examination for corneal damage. All incidents involving acids or alkalis need immediate referral.
Sudden decrease in vision
Sudden decrease in vision (within 24 hours) is obviously a potentially serious symptom and all these patients need referral for slit lamp examination.
Potential causes include:
l'Wet' age-related macular degeneration (for example sub-retinal neovascular membrane?
lAnterior ischaemic optic neuropathy
Flashes and floaters
Sudden onset of flashing light and increase in floaters is suggestive of changes in the vitreous and retina. Although the ophthalmoscope gives an excellent view of the fundus it is difficult to see beyond the equator of the eye, meaning retinal holes/ tears can be missed. Patients with these symptoms need slit lamp examination.
The symptom of pain – rather than irritation or itch – is an important one and can herald a number of eye diseases:
These conditions can be subtle and slit lamp examination is usually required. This is especially so if the vision is reduced, the patient has a previous history of these conditions or if they are photophobic.
Contact lens wearers should have regular examinations with their contact lens practitioner. If a contact lens wearer develops a painful photophobic eye they need immediate referral for slit lamp examination to rule out a bacterial keratitis.
Distortion of vision
This is a potentially important symptom in that it can indicate pathology at the macula. Fluid, blood or new vessels at the macula can distort its architecture, causing the patient to notice that straight lines become kinked or distorted.
The best way of examining this is using the binocular high power of the slit lamp combined with appropriate lenses that allow the fundus of the eye to be seen.
All patients who are within a month of intraocular surgery need slit lamp examination to rule out intraocular infection (endophthalmitis). Symptoms of this are reduced vision, pain and photophobia.
In fact ophthalmologists do come to rely a great deal on the slit lamp for diagnosis and treatment. Cataracts, glaucoma, macular degeneration, diabetic retinopathy and blepharitis/dry eye are most easily examined using it.
But once again, many of these conditions are diagnosed after taking an appropriate history and the slit lamp is merely a tool to confirm or refute the diagnosis.
Scott Fraser is consultant ophthalmologist at Sunderland Eye Infirmary and co-author of Eye Know How (BMJ Books, 2000)
Pros and cons of the slit lamp
A useful instrument for four main reasons
lIt aligns a good light source with the viewing pieces
lIt provides excellent magnification
of the eye
lIt has a short focal length so allowing procedures (for example foreign body removal)
to be performed on the eye
lIt allows a stereoscopic view
of the eye
Reasons it is not usually found outside specialist eye care
lIt is expensive
lIt takes up space
lIt requires a degree of practice to become proficient
l The slit lamp is a very useful and important piece of ophthalmic equipment
l It is not, however, necessary for all patients with an eye problem to be examined with it
l Certain symptoms such as pain, alteration in vision, significant trauma and photophobia are the commonest reasons that slit lamp examination is required
References and further information