Eye injuries and infections
The visual acuity of all patients with an ocular injury must be measured using a Snellen chart, and recorded. Eye injuries caused by an accident or personal violence are often the subject of litigation. The visual acuity on presentation can then be of importance, especially if there is a delay in reaching specialist care.
Visual acuity testing
The Snellen chart consists of rows of letters of decreasing size. The number on each line shows the distance at which a person with normal sight should be able to read the line.
- Stand the patient 6 m from the chart with the palm of the left hand covering the left eye, but not pressing on the eye.
- Instruct the patient to read the letters on the chart from the top down. Each line is numbered. The number represents the distance in meters at which a person with normal sight can read the line.
- The last line the patient reads is recorded: e.g. 6/18. The top line represents the distance from the chart, and the bottom line the distance from the chart at which a person with normal sight would read that line. Thus 6/18 is not a fraction; the patient reads at 6 m the line a normal person would read at 18 m. The patient now covers the right eye and repeats the test.
- If no letters on the chart can be seen, bring the chart closer until the top letter can be identified. If this occurs at 2 m the acuity is recorded as 2/60 (the top letter on the chart can be seen by a person with normal sight at 60 m).
- If the top letter cannot be identified at any distance, then wave a hand in front of the eye (with the other eye covered). If the movement is perceived, it is recorded as HM (Hand Movements).
- If hand movements cannot be seen, shine a light into the eye. If it is seen, this is recorded as LP (light perception). Shine the light into the eye from different directions and instruct the patient to point to the light. If this is performed accurately, the acuity is recorded as “LP with accurate projection.”
- If a bright light cannot be seen, the acuity is recorded as NLP (no light perception).
Eye injuries may be caused by a concussive blow, by perforation of the eye, and by chemical or thermal damage.
Always identify the causative mechanism as this has predictive value in determining both investigations and treatment. For example, an eye with visual loss from an accident using a hammer and cold chisel may harbour a retained intra-ocular foreign body, and indicate the need for a CT scan.
History and examination
Take a careful history of the cause of the injury, and then examine the eye.
Always use the same routine in examining an eye.
Face - note any abnormality in the lids or eyes in relation to the rest of the face
Lids - check lid movement
Conjunctiva and sclera - the white of the eye should be white
Cornea - the cornea should be clear
Pupil - should be black and moving
Eye movements - up to the right and left, down to the right and left, and from side to side.
Injuries such as a punch or a blow by a tennis ball may produce a peri-orbital haematoma (black eye), which requires no specific treatment provided that intra-ocular derangement has been excluded. Check the visual acuity.
Blow-out fracture of the orbit
An object larger than the orbital opening will compress the orbital contents and may produce a blow-out fracture of the orbital floor into the maxillary antrum or, less commonly, of the medial wall into the ethmoidal air cells. These are the thinnest of the orbital walls and are most likely to be damaged.
The patient will complain of diplopia owing to entrapment of the fascia around the inferior rectus muscle in the fracture in the floor of the orbit. (See (A) This patient has a blow-out fracture of the right orbit, and shows absent elevation in that eye. (B) CAT scan of the orbit reveals the blow-out of the floor of the orbit.) Because of damage to the infra-orbital nerve in the floor of the orbit the upper teeth and part of the gum and cheek will be anaesthetic. Because of prolapse of orbital fat into the antrum, the eye will be enophthalmic, as it sinks back into the orbit.
The treatment is surgical with release of the entrapped tissues from the fracture site.
A hyphaema is a haemorrhage into the anterior chamber of the eye (between the cornea and iris).
The visual acuity will be decreased. The pupil will usually not respond to light. Check the intra-ocular pressure by gently palpating the eye as one would to assess fluctuance. Compare with your own eye.
When blood completely fills the anterior chamber, the pressure may rise acutely to a level sufficient to occlude the central retinal artery, and cause permanent blindness. Immediately commence treatment with Acetazolamide 500 mg initially, and 250 mg three times a day. The patient must be referred immediately for specialist treatment.
Where the hyphaema occupies less than three quarters of the anterior chamber, treat with bed rest and sedation; the blood will absorb in a day or two. A hyphaema may be complicated by intra-ocular damage, which will not be apparent on presentation. Therefore refer for specialist examination to exclude intra-ocular damage
Following a blow on the eye, the iris muscles may be paralysed, producing a fixed dilated pupil, which may recover within a few days. Small tears in the lid margin may involve the sphincter and cause permanent pupil dilatation.
The retina at the posterior pole of the eye may become oedematous and pale, with decreased acuity due to macular involvement. Recovery will take several days and may be incomplete.
Rupture of the choroid occurs in an arc concentric with the optic nerve. It results in disruption of the overlying nerve fibers and hence produces a permanent visual field defect. If the rupture occurs between the disc and the macula the central vision is permanently lost.
Contusion deformity of the chamber angle
The intra-ocular pressure is controlled by a balance between the rate of formation of aqueous humour, and its rate of removal from the eye via the trabecular meshwork in the angle between the cornea and the iris. Damage to this structure can cause glaucoma up to 10 years after the injury.
Perforating injures are caused by laceration of the cornea or sclera - commonly by glass in motor vehicle accidents, by knives, and in industrial accidents such as the shattering of a tool when using a capstan lathe.
Where the suspicion of a perforating injury exists, examine the eye carefully, after the instillation of two or three drops of local anaesthetic. Ask the patient to open the eyes. If this is not possible, assist by pressing on the brow and cheek and gently pulling the lids apart, taking care to apply no force to the eye. If the lids are swollen and they cannot be easily pulled apart, use a retractor made from a bent paper clip which may be hooked under the lid margins and the lids pulled apart, or examine the eye under a general anaesthetic.
Examine the cornea with a good light. A small perforation is often overlooked, but can be detected by examining the pupil - the iris is usually trapped in the perforation as the aqueous humour gushes from the eye through the wound, and this will distort the pupil into a pear shape pointing at the wound.
Transporting the patient
Instill chloramphenicol eye drops, and apply an eye pad - using two strips of transparent tape passing from the forehead on the opposite side to the cheek on the same side. Apply a protective cone over the pad, held with transparent tape. (see Protective cone)
Instruct the patient to keep the head above the level of the heart during transport to specialist care, to prevent increase in intra-ocular pressure with subsequent loss of intra-ocular contents.
There may be air inside a perforated eye and expansion of the air at altitude may cause internal derangement of the eye. Therefore aerial evacuation of a patient with a perforating ocular wound may exacerbate the injury when the intra-ocular air expands.
Principles of treatment
- Replace the layers of the eye in their normal relationship to each other. Administer antibiotics locally and systemically to control infection.
- Administer steroids topically to control the reparative process and prevent intra-ocular fibrosis. Microsurgical techniques are used to repair the eye, and good results are often obtained.
This complication of perforating injury is rare nowadays, thanks to improvements in the surgical repair of perforating wounds. The exact aetiology of the condition is unknown, but is usually regarded as an autoimmune reaction to uveal pigment or antigen or both. Today, repeated retinal surgery causes more sympathetic ophthalmitis than do penetrating injuries. The antigen is thought to be retinal in origin. It causes a low-grade uveitis in the perforated or exciting eye, and also in the healthy sympathising eye. It develops about 2 weeks after the injury but may occur up to 30 years later. It can be completely avoided by removing a perforated eye during the first week after injury, if by then it does not have the capacity for useful sight.
The disease is treated with systemic and topical steroids and many cases recover with aggressive treatment.
Both acids and alkalies produce serious damage to the eye. Both penetrate readily into the eye, resulting in corneal opacification, inflammation, and cataract. Long-term complications include retinal detachment and glaucoma. Acids and alkalis also cause thrombosis of the circum-corneal blood vessels which supply nutrients to the cornea, resulting in corneal ischaemia and opacification.
The most important aspect of treatment is first aid, both at the site of injury and in hospital.
Irrigate the eye immediately by holding the victim's head in a stream of water from a tap or a hose. The victim should then be transported to specialist care rapidly.
On arrival at a hospital instill local anaesthetic drops into the eye. Then insert a giving set into a flask of normal saline. Hold the eyelids open with a speculum and wash the eye and conjunctival sac for 20 minutes. Instill more local anaesthetics as required. Evert the upper and lower lids to ensure that no solid matter is retained behind the lids.
Patients with chemical injuries are usually admitted to hospital for intensive treatment with antibiotics and steroids.
Chemical injuries have a poor prognosis. The cornea is always damaged, and may require corneal grafting to restore sight. Because of ischaemia of surrounding tissues corneal grafting is often unsuccessful.
Thermal injuries cause burns to the eyelids. The management of the skin burn follows the usual principles, but particular care must be exercised to protect the cornea.
Shrinkage of the eyelids in the healing phase puts the cornea at risk from exposure and drying.
Care of the eye
Protect the cornea by the instillation of antibiotic ointment (chloramphenicol) every hour to provide a layer of grease, which would delay the evaporation of tears. If this is insufficient to prevent corneal drying, the eyelids must be sutured together (tarsorrhaphy).
Alternatively, cover the eye with transparent plastic film. A piece large enough to cover the orbit reaching from the forehead to the cheek is held in position by applying a layer of Vaseline to the skin around the orbit to which the plastic film adheres.
Corneal foreign body
The commonest eye injury is probably a foreign body on the cornea. The patient complains of a scratching sensation in the eye, and with a good light and magnification, the foreign body can usually be seen easily.
If it is not immediately obvious, stain the cornea with fluorescein - moisten a fluorescein strip with local anaesthetic and touch the inner surface of the lower eyelid. Ask the patient to blink to spread the dye, and then illuminate with the blue filter in the ophthalmoscope. The site of the foreign body will glow bright green.
The foreign body may be adhering to the deep surface of the upper lid - a sub-tarsal foreign body. Evert the upper lid and wipe off the foreign body. (see Tarsal eversion)
Corneal foreign body removal
- Lie the patient down
- Instill local anaesthetic drops - two drops every minute for three minutes
- Use a focused bright light to illuminate the eye
- Lift off the foreign body with a cotton-tipped applicator or needle
- Instill antibiotic drops and apply an eye pad. It is helpful to use a magnifying lens to facilitate foreign body removal.
Instill antibiotic drops (chloramphenicol) every 2 hours until the cornea heals and the eye is comfortable.
If the foreign body is hot and for example was from using a grindstone, a rust ring may be left in the cornea after its removal. Instill chloramphenicol ointment in the eye four times a day for 2 or 3 days. The rust ring can then be lifted off with a fine needle.
The main defence mechanisms against infection in the eye are the tears, which contain lysozyme, and the corneal epithelium. Once these are breached, an infection can be established and will progress rapidly.
Acute conjunctivitis is common, usually due to a staphylococcus and responds rapidly to the instillation of eye drops every 2 hours. The most commonly used antibiotic is chloramphenicol. Even untreated, most acute conjunctivitis resolves in about 3 days.
Of more concern in rural and underdeveloped communities is trachoma. This recurrent conjunctivitis is caused by the organism Chlamydia trachomatis. The organism replicates intra-cellularly in the conjunctival epithelium. It is a mild infection but after each attack, scarring occurs at the site of the follicles in which the organism replicated. After probably 30 or 40 attacks the scarring becomes serious and causes inversion of eye lashes and subsequent damage to the cornea, causing blindness.
The control of trachoma requires attention to the following:
- Surgery to the inverted eye lids
- Antibiotic treatment with azothromycin
- Fly eradication - the commonest vector
- Environmental upgrade.
This is the SAFE strategy devised by the World Health Organization.
When trachoma is diagnosed all members of the family are treated with a single dose of azithromycin. Children and young mothers are most commonly infected.
The management of intra-ocular infection follows the principles of management of any infection:
- Identify the organism
- Treat it with the appropriate antibiotic.
If the infection is a corneal abscess (Corneal abscess. The pathological process is visible because of the transparency of ocular structures.), the scrapings should be taken from the surface of the ulcer for culture, and smeared on a slide for Gram staining, and sent to the laboratory for culture and investigating the sensitivities.
If the organism is Gram-negative, commence treatment with gentamycin drops; if Gram-positive, commence treatment with cephalosporin drops. These are not available commercially as they have a short shelf life of a few days only, but can be prepared in a pharmacy by adding the antibiotic to artificial tear drops to produce a 5% solution.
If no organism can be seen on Gram staining, use both antibiotics. When the results of culture and sensitivities are available the treatment may be modified.
The commonest organisms causing ocular infection are:
- Staphylococcus epidermidis
- Staphylococcus aureus
- Pseudomonas pyocyaneus
The treatment regime is important, and topical treatment must continue around the clock, combined with systemic antibiotics:
- Hour 1: 2 drops every 15 minutes.
- Next 4 hours: 2 drops every 30 minutes.
- Then: 2 drops every hour, day and night.
- If both antibiotics are being used, alternate them.