Basic principles and procedures for eye surgery
Ocular tissues are delicate, and eye surgery requires careful operative procedures with maximum precision. Good lighting is essential for safe surgery, and magnification by means of an operating loupe (X 2 or more) is always advisable.
When the patient is admitted to hospital, carefully examine the eye and test visual acuity. Look for infection in the eye, including the lacrimal sac, and treat this as necessary. Check for raised intraocular pressure. Avoid elective surgery if the patient has hypertension or severe diabetes, or is undergoing long-term treatment with anticoagulants or steroids.
Twenty-four hours before surgery, wash the patient’s eye and start treatment with antibiotic eye drops. On the day of the operation, carefully irrigate the eye with fresh sterile saline and, if intraocular surgery is planned, cut the lashes. Clean the eyelids and surrounding skin with soap or cetrimide. Properly mark the eye to be operated on, and recheck this just before surgery.
Use of eye ointment and eye drops
Eye medication may be required both before and after surgery. Eye ointment gives a more prolonged action than do eye drops and can be used, for example, after surgery on the eyelid. Avoid steroid-containing antibiotic preparations and restrict the use of preparations containing steroids in combination with other eye medications unless they have been prescribed by an ophthalmologist.
Measurement of intraocular pressure
If you suspect a rise in the patient’s intraocular pressure either before or after surgery, measure the pressure by means of a Schii:itz tonometer. With the patient prone, instil anaesthetic drops in both eyes. Instruct the patient to look up, keeping the eyes steady. With your free hand gently separate the lids without pressing the eyeball, and apply the tonometer at right angles to the cornea.
Note the reading on the scale and obtain the corresponding value in millimetres of mercury or kilopascals from a conversion table. Verify readings at the upper end of the scale by repeating the measurement using the additional weights supplied in the instrument set. Repeat the procedure for the other eye. An intraocular pressure above 25 mmHg (3.33 kPa) is above normal but not necessarily diagnostic.
Values above 30 mmHg (4.00 kPa) indicate probable glaucoma, for which the patient will need immediate referral or treatment followed by referral. It is very important that the tonometer be regularly cleaned and maintained, to avoid false readings.
Care of instruments
Most instruments used for eye surgery are delicate and should therefore be handled with special care. Clean all instruments after surgery and sterilize them before re-use. Sterilize sharp instruments using appropriate chemical solutions such as chlorhexidine and glutaral; sterilize other instruments using an autoclave or dry heat. In an emergency, instruments may be sterilized by immersion in 70% ethanol for 1 hour.
General anaesthesia is normally recommended for major intraocular surgery, for example for enucleation of the eye, and for children. Always instil anaesthetic eye drops, for example tetracaine 0.5% (5 g/litre), before surgery.
To produce facial block for intraocular surgery, inject Novocaine into the area 2 cm in front of and below the tragus of the ear. As an alternative, infiltrate the supraorbital and infraorbital branches of the facial nerve by injection along the orbital margins.
The purpose of retrobulbar block is to anaesthetize the eye and also to prevent its movement. Use this block only for major intraocular surgery, and only if general anaesthesia is not available and the patient is already in grave danger of going blind. Always be aware of the possible complications of this technique. Retrobulbar block is to be particularly avoided if the patient has perforating injuries of the eye, as it can cause a dangerous increase in the volume of orbital contents, which may cause tissues to extrude from the eye.
Retrobulbar block is effected by injecting 2. 5 ml of 2% (20 g/litre) Novocaine into the cone formed by the rectus muscles. With the patient supine, palpate the orbit of the eye to locate the lower outer border. Introduce a 23-gauge, 2.8 cm needle vertically at this point.
Penetrate the skin and then the orbital septum; resistance will be encountered as the needle passes through each of these two layers. Once the tip of the needle is lying below and behind the globe, angle the needle in the direction of the junction between the roof and the medial wall of the orbit.
Introduce it further and penetrate the muscle layer, which will be indicated by a slight resistance. Draw back the plunger of the syringe (to make sure that the tip of the needle is not in a vein) and inject the local anaesthetic. It should flow freely. Resistance may mean that the tip of the needle is lodged in the sclera, in which case move the tip of the needle slightly from side to side until it is disengaged.
If the needle has accidentally entered a vein, resulting in haemorrhage and a rapid swelling of the orbit, abandon the procedure. Delay the operation for at least 1 week, after which it can be performed with the patient under either a repeat retrobulbar block or, preferably, general anaesthesia.
Postoperative care for the patient who has undergone extraocular surgery is quite simple: change the dressing the day after surgery and apply tetracycline 1 % eye ointment daily for about 1 to 2 weeks. Remove sutures as indicated, after about 5-14 days.
After intraocular surgery, the patient should remain in hospital for at least 5 days. Strict immobilization is usually unnecessary, but the patient should avoid physical strain during the week following surgery. Dress the eye daily and apply appropriate topical medication. Remove conjunctival sutures after a week and corneoscleral sutures after about 3 weeks.