Estimates based on data available in the World Health Organization up to 1990 suggest that approximately 35 million people in the world were blind at that time, with a visual acuity in the better eye of less than 3/60. The prevalence of blindness in industrialized countries is in the range 0.05 to 0.3 per cent, and in developing countries 0.5 to 2 per cent, while age/sex standardized rates show blindness to be at least 10 times more common in developing countries. This visual loss represents a massive public health and economic problem in many developing countries. The number of blind people is increasing because of population growth and longevity. It is estimated, however, that 70 to 80 per cent of all blindness is ‘avoidable’—that is, can be prevented or cured with resources which could reasonably be made available.

In this section, the discussion will emphasize the role of eye surgery in preventing blindness, particularly the situation as it applies to Asia and Africa. Reference will not be made to retinal detachment, vitreous surgery, and orbital exploration, which usually affect only one eye, or to squint, lacrimal, and plastic surgery which treat conditions that usually do not result in blindness.

Cataract is far and away the most common cause of blindness in the world, and cataract extraction is the most common operation on any eye service. It is only recently that the very large numbers of patients requiring cataract extraction have been appreciated.

The indications for cataract extraction have changed rapidly in the industrialized world with the widespread use of intraocular lenses, resulting in surgery at levels of only moderately reduced vision (6/12 - 6/36), but in most situations in developing countries the usual indication for surgery is a vision of less than 6/60 in the better eye. Examination includes a measurement of visual acuity, and if this is less than hand movements, the ability of the eye to perceive the direction from which a light is projected indicates that the peripheral retina is intact. A normal pupil light reflex is evidence that the optic nerve is functional. A second indication for cataract extraction is a swollen cataractous lens (Fig. 2) 2717, which may cause secondary glaucoma if not removed.

There are two main methods of cataract extraction, intracapsular cataract extraction when the lens is removed intact within its capsule, and extracapsular cataract extraction when the central part of the anterior capsule is removed, the nucleus expressed, and the cortex of the lens aspirated. In extracapsular cataract extraction, the posterior and peripheral parts of the capsule bag remain attached to the ciliary body by the zonules. Cataract extraction is most commonly performed under local anaesthetic.

Akinesia of the orbicularis oculi muscle is produced by injection of 4 to 5 ml of 2 per cent lignocaine or 0.5 per cent bupivicaine local anaesthetic near the main trunk of the facial nerve as it runs over the neck of the mandible, in front of the upper part of the ear lobe (O'Brien block) (Fig. 3) 2718. Alternatively, 5 ml may be injected from the lateral angle of the eye into the orbicularis muscle above and below the orbit (Van Lint block) (Fig. 4) 2719. The nerves running from the apex of the orbit to the globe (sensory) and the extraocular muscles (motor) are paralysed with a retrobulbar injection of 2 ml of the local anaesthetic (Fig. 5) 2720. Many surgeons prefer a needle of 3 cm in length, so that the point rests in the muscle cone not too close to the apex of the orbit. If the tip is slightly rounded the chances of penetrating an orbital vein are reduced. After the injection, pressure is applied to the eye for 10 min, in order to decompress the vitreous and reduce the intraocular pressure prior to operation.

Conventional intracapsular cataract extraction is still the most widely practised technique throughout the world. Some form of magnification (operating microscope or loupe) and good focused lighting is recommended. There are many different alternative methods possible at each stage. The following outline is one reliable approach. The illustrations of cataract operations are as viewed by the surgeon from the head of the bed.

1.Lids and fixation. The eyelids are retracted by a speculum or lid sutures. A retraction suture of 4/0 silk is usually inserted behind the insertion of the superior rectus muscle.

2.Corneoscleral section. The original von Graefe ab-interno incision with a cataract knife is quick and reliable in the hands of those trained to use it. A small limbus-based conjunctival flap is usually fashioned by the same incision. Alternatively an ab-externo incision using a razor blade fragment and/or corneal scissors may be used. The corneoscleral junction is first exposed by making a conjunctival flap based at the fornix or at the limbus.

3.Sutures. One to three sutures are usually placed before the corneoscleral incision is completed, or inserted immediately after the section is complete. Suture material is commonly 8/0 silk, but may be 9/0 or 10/0 monofilament nylon.

4.Peripheral iridectomy. One or two peripheral iridectomies are performed to prevent pupil block glaucoma due to the vitreous face coming forward after the removal of the lens. If there is any corneal opacity or adhesions of the iris to the lens, a complete sector iridectomy may be performed instead.

5.Removal of lens. This is most commonly performed with a cryoprobe. Reliable results can be obtained with a disposable cryoprobe using Freon from a small cylinder. The probe is applied to the upper pole of the lens while the iris is retracted with a cellulose sponge or iris retractor. Alternative methods utilize lens capsule forceps or an erisophake to extract the lens.

6.Closure. Any iris tissue in the wound is reposited, the sutures already placed are tied, and additional sutures added to ensure that the wound is water-tight.

7.Anterior chamber. The anterior chamber may be reformed with fluid if necessary. Air has been used, but has the disadvantage that it may go behind the iris and cause a shallow anterior chamber with possible glaucoma.

8.Complications. The most common intraoperative complication is loss of the vitreous as the lens is removed. Using a vitrectomy machine if available, or a series of cellulose sponges and scissors, the anterior vitreous must be removed from the anterior chamber so that the iris falls back; any vitreous in the wound must be removed.

If the capsule breaks (accidental extracapsular extraction) during surgery, then the nucleus should be expressed and as much cortical lens material aspirated from the eye as is safely possible.

Early postoperative complications include rupture of a corneoscleral suture, with prolapse of iris. The repair consists of excision of the prolapsed iris and resuture of the wound. Other complications are endophthalmitis (infection), iritis (inflammation), hyphaema (bleeding), glaucoma (raised intraocular pressure), and striate keratitis (damage to corneal endothelium).

Late postoperative complications include cystoid macula oedema, retinal detachment, glaucoma, and corneal oedema.

Before operation the pupil must be well dilated with 1 per cent cyclopentolate and 5 per cent phenylephrine drops used with sufficient frequency to produce good mydriasis. In all the subsequent stages in the operation it is essential to protect the endothelium of the cornea from mechanical damage.

This operation ideally requires an operating microscope with coaxial illumination, but can be done with a 4.5 times magnification loupe with a light mounted on it.

1.Lids and fixation. If there is no movement in the extraocular muscles after local anaesthesia, many surgeons dispense with the superior rectus suture.

2.Section. A shelved incision with the first part of the section being angled posteriorly is preferred by many surgeons. This first part of the incision is made through 150°, a smaller circumference than 170 to 180° as in intracapsular cataract extraction, but the eye is not yet opened.

3.Capsulotomy. The tip and shaft of an insulin syringe needle are bent to make a cystotome, which is inserted through the section at one point. The anterior chamber is maintained, if necessary, by fluid in the insulin syringe. The centre of the anterior capsule is perforated in a circle in the ‘can opener’ technique, or the tip of the needle may be used to tear the capsule under direct vision to make a smooth edge (‘capsulorrhexis’).

4.The corneoscleral section is now completed. The incision bevelled downwards, is completed with the blade or corneal scissors through 150°.

5.A viscoelastic substance (hydroxypropylmethylcellulose or Healon) is injected into the anterior chamber. The anterior capsule is removed with fine non-toothed forceps.

6.Expression of the nucleus. The nucleus may be separated by hydrodissection—balanced salt solution injected from a fine cannula to separate the layers of the cortex. The lens is expressed by pressure on the lower limbus and counter pressure on the upper edge of the corneoscleral incision.

7.Irrigation—aspiration. The lens fibres of the cortex are carefully removed under direct vision using a two-way cannula, irrigating with a suitable solution (such as Hartmann's or Ringer's solution). The opening of the cannula must remain facing the operator and care must be taken not to catch the posterior capsule.

8.Suturing. 10/0 monofilament nylon can be used, and the knots buried by turning them into the wound. The sutures must be tied evenly and not tightly if astigmatism is to be avoided.

9.Complications. The early complications are similar to those of intracapsular cataract extraction. The most common long-term complication is thickening of the posterior capsule, which is more likely if lens fibres have been left on the posterior capsule. This can be anticipated with a capsulotomy at the time of surgery or treated with a Nd-YAG laser capsulotomy later. Cystoid macula oedema and retinal detachment are reported to occur less frequently with extracapsular cataract extraction than with intracapsular cataract extraction.

This technique was introduced in the late 1960s to break down the nucleus of a cataractous lens by means of ultrasonic vibration applied to a needle, at 40 kHz frequency. It is popular in industrialized countries because it enables a smaller incision (3 mm) to be used and therefore reduces the chance of postoperative astigmatism and reduces the need for hospital admission. The cost of the phakoemulsifier, the difficulty of the procedure, and maintenance of the machine restricts its suitability in developing countries at the present time.

Optical correction of aphakia after cataract extraction

When the lens has been removed, the eye is referred to as being aphakic. In order to obtain good vision the aphakia must be corrected optically. There are three principal methods. The advantages and disadvantages are outlined in Table 3 656. In Western countries, most ophthalmologists perform an extracapsular extraction with posterior chamber implantation of an intraocular lens. In many developing countries there is a trend towards this type of surgery although at present more patients in Africa and Asia receive an intracapsular extraction with spectacle correction.

Worldwide, glaucoma is the third cause of blindness, being responsible for approximately 15 per cent of all blindness (i.e. five million people), although in some parts of West Africa and south-east Asia this proportion is higher.

Definition and classification

Glaucoma is a broad term used to describe a group of different pathophysiological processes which have in common an optic nerve damage as demonstrated by pathological cupping of the optic disc and characteristic visual field loss. The intraocular pressure is usually high, but may be within normal limits. It is classified as shown below.

1.Primary angle-closure glaucoma;

2.Primary open-angle glaucoma (chronic simple glaucoma);

3.Secondary glaucomas

(a)closed angle

(b)open angle;

4.Congenital glaucoma (buphthalmos).

This is a very common form of glaucoma worldwide. It is especially prevalent in Mongolian races. The proportion of primary angle-closure to open-angle glaucoma is 1 : 10 in the United Kingdom, 1 : 1 in India, and 4 : 1 in Burma.

The predisposing factors are a shallow anterior chamber (Fig. 11) 2732, a smaller corneal diameter, and, to a lesser extent, a shorter axial length. These parameters are partially determined genetically. The precipitating factors include a gradual increase in the size of the lens with age, causing the anterior chamber to become shallow and producing partial pupillary block. The acute attack may also be precipitated in a dark room where the pupil is partially dilated. The iris root is bowed forward to touch the back of the cornea, thus preventing the aqueous from having access to drainage through the trabecular meshwork.

The patient may present either with an acute attack with pain, or as a chronic form with gradual loss of vision. In an acute congestive attack there is typically sudden reduction of vision and severe pain in one eye. This may be accompanied by nausea and vomiting. The eye is red, with dilated ciliary vessels around the limbus. The cornea is hazy, the anterior chamber shallow, and the pupil semidilated and non-reactive. The intraocular pressure is very high, feeling stony hard to the fingers. There may be a history of previous transient prodromal attacks of blurred vision and discomfort.

The traditional treatment has been frequent pilocarpine 2 per cent drops every 5 min for the first hour, then hourly. However, this is now questioned, as it is argued that the pilocarpine increases accommodation, and increases lens thickness, allowing it to move forwards, thus increasing the relative pupillary block.

First, intraocular pressure must be quickly reduced, to limit damage to the optic nerve. Second, it is necessary to separate the iris from the corneal periphery by miosis so that permanent adhesions (synechiae) are not formed. These two aims are achieved by the following actions.

1.(a)Laying the patient on his back to allow the lens to fall back.

(b)Giving acetazolamide 500 mg by intramuscular or very slow intravenous injection and then 250 mg 4 times per day orally.

(c)Giving topical &bgr;-blocker drops such as timolol 0.5 per cent twice daily.

(d)If the previous treatment does not lower the intraocular pressure adequately giving oral glycerol or intravenous mannitol in severe cases, to withdraw fluid from the eye by osmosis.

2.Then give pilocarpine 0.5 to 2 per cent, one or two drops, four times per day to induce miosis.

1Incision. In the past a corneoscleral incision was usually performed under a conjunctival flap which could be either limbus- or fornix-based. Nowadays a corneal section is more common.

2The incision is made in two stages. The first incision is angled backwards, the width is 3 to 4 mm, and it is situated on the cornea 1 mm from the limbus. The second part of the incision is bevelled forwards. The posterior lip is then depressed so that the iris prolapses. If the iris does not present in the wound, the iris may be picked up close to its root with fine-toothed forceps, taking care not to touch the anterior lens capsule.

3Iridectomy. The iris is drawn slightly out of the wound and a full thickness piece excised by De Wecker's scissors.

4Reposition of the iris. The iris can be replaced by stroking the lips of the wound with an iris repositor. A full thickness iridectomy should now be visible.

5Wound closure. The two-stage corneal wound is usually self sealing. If on touching with a cellulose swab there is a visible leak, one or two corneal sutures of fine (10/0) suture material can be inserted, and the knots buried.

In units with appropriate facilities it is common to make an iridotomy with either an argon or Nd-YAG laser. A portable Nd-YAG laser is now available which can be used in rural situations.

The second eye of a patient treated for an acute angle-closure attack should be given either a prophylactic peripheral iridectomy or an iridotomy before the patient is discharged. It is often difficult to persuade a patient to have an operation on an eye which has shown no symptoms, or to persuade a patient with incipient angle-closure, who has had no symptoms in either eye, to undergo such a procedure. However, with the laser iridotomy it is more likely to be accepted than with a formal operation.

This is a form of glaucoma where the angle gradually becomes closed off by creeping adhesions of the iris root to the peripheral cornea. The slow onset means that this form does not have acute symptoms but presents late, similar to a chronic open-angle glaucoma. Because aqueous drainage is occluded by permanent iris synechiae, trabeculectomy is indicated as for chronic open-angle glaucoma.

Chronic simple glaucoma is the most common form of glaucoma in European and African populations. It starts at an earlier age in black populations and appears to be more aggressive. High prevalences have been reported in some Caribbean islands.

The aqueous circulates through the pupil and has access to the drainage mechanism of the trabecular meshwork of the angle as normal, but the rate of drainage is reduced. There is a gradual rise in intraocular pressure, without acute symptoms. The raised intraocular pressure predisposes to loss of visual field with characteristic ‘cupping’ of the optic nerve head (Fig. 14) 2735. Central visual loss is only noticed in the advanced stages when the optic nerve has already been severely damaged. Emphasis is therefore placed on early detection of raised intraocular pressure by tonometry and abnormal or asymmetrical optic disc cupping by ophthalmoscopy.

Diagnosis is confirmed by finding the characteristic defects (‘scotomas’) on testing the visual fields.

The trend is to operate rather than to start life-long medical treatment. Certainly in the African situation most patients do not continue medical treatment on a long-term basis, even if the drugs are available and can be afforded. Surgery is therefore the first line of treatment.

Trabeculectomy is a drainage operation in which a rectangular segment of the corneoscleral tissue is excised. This is performed under a partial thickness scleral flap. The stages of trabeculectomy are as follows.

1.Lids and fixation. As for cataract extraction.

2.Conjunctival flap. To form a fornix-based flap the conjunctiva is incised at the limbus. A limbus based conjunctival flap may also be used. The Tenon's capsule is cleared away from over the sclera in the area in which the scleral flap will be raised.

3.Superficial scleral flap. A limbus-based flap of superficial sclera is now fashioned. It is usually half thickness and approximately 5 mm wide at the limbus. The position is marked out on the sclera with a knife or razor-blade fragment. Main blood vessels running through the sclera should be avoided or coagulated. The margins of the flap are incised to half the thickness of the sclera. One corner is picked up and the section carried forward with the blade or a Tooke's knife until it is past the limbus into 1 mm of clear cornea. At this point the tissue beneath the scleral flap changes from white to blue/grey opalescent in appearance.

4.Excision of trabecular tissue. While the superficial scleral flap is held back by an assistant, a small rectangular block of the deep corneal - scleral tissue is now excised. This should be approximately 3 mm wide in the line of the limbus and 2 mm in radial depth. The area is marked out and incised with a sharp knife, and the removal of the block completed with small scissors.

5.Iridectomy. The iris either prolapses spontaneously through the trabeculectomy opening, or can be gently grasped with fine forceps so that a small piece can be excised with De Wecker's scissors as in a routine peripheral iridectomy. On stroking of the cornea with an iris repositor, the sphincter should constrict and the iris be repositioned within the anterior chamber.

6.Closure. For closure, the scleral flap is sutured at each posterior corner with fine nylon or virgin silk. The conjunctival flap is then sutured firmly in position at the limbus with two sutures of similar material, or if a limbus-based conjunctival flap was used, a running suture is used to close the conjunctiva.

7.Postoperative treatment. Steroid drops and antibiotic drops are used three times a day for 5 to 7 days (i.e. while in hospital). Cyclopentolate 1 per cent or tropicamide 1 per cent twice daily for 1 week is recommended to prevent adherence of the iris to the lens.

8.Complications. The most common early complication encountered is a delay in reforming of the anterior chamber. This is usually because of excessive drainage, either due to a leak beneath the conjunctiva, demonstrated by the flow of aqueous after fluorescein is placed into the conjunctival sac (the Seidel test), or due to the scleral flap being too thin or loose. Occasionally a shallow anterior chamber is due to a choroidal detachment. The anterior chamber will usually reform over several days with conservative management; if not, revision of the flap with additional conjunctival or scleral sutures usually solves the problem. Iritis is common in pigmented eyes, but can usually be controlled by topical steroids and mydriatics.

The causative organism of trachoma is Chlamydia trachomatis, serotypes A, B, and C. The organism infects the conjunctiva, particularly of young children, and produces a mucopurulent discharge which is spread within the family by children's fingers, by contaminated bed clothes and rags, and by flies. The inflammation is made more severe by repeated infection with Chlamydia and superinfection by bacteria. Trachoma becomes a disease of blinding severity under conditions of poverty where there is lack of water for keeping the face clean and lack of sanitation so that the breeding of flies is encouraged.

A simplified grading scheme was introduced by the World Health Organization in 1987 that gives good reproducibility between observers in field studies, and which can be taught to and used by community health workers.

Active infection (TF or TI) is treated with 1 per cent tetracycline ointment instilled twice daily for 6 weeks or possibly with systemic chemotherapeutic agents. Repeated reinfection can be prevented by regular face washing and community action to improve sanitation and reduce fly density. The actual blinding process is due to vascularization and scarring of the cornea as a result of trichiasis, secondary infection, and corneal ulceration.

A large number of operations have been devised for the correction of trichiasis and entropion as a result of trachoma. There are two main principles: (1) to evert the lid margin so that the eye lashes are directed outwards, and (2) to correct any shortening of the upper lid. Recently some of these operations have been the subject of a randomized control trial. Bilamellar tarsal rotation was the most successful operation regardless of previous surgery. It was devised by Ballen in 1964, and is itself a modification of the earlier procedure described by Weis.

1.Apply topical anaesthetic drops to the conjunctiva. Inject 3 ml of local anaesthetic into the upper eyelid between skin and tarsal plate above the eyelashes of the upper eyelid and massage the local anaesthetic into the tissues for 1 min.

2.Place haemostat forceps vertically at the lateral end of the upper eyelid (5 mm on to the eyelid) and at the medial end, just lateral to the lacrimal punctum.

3.Incise through the skin and muscle of the upper eyelid between the two haemostats 3 mm above the eyelash margin.

4.Evert the eyelid, and using a scalpel, make an incision 2 mm from the lid margin cutting through the tarsal plate to join up with the skin incision. Complete the division of the tarsal plate medially and laterally with scissors.

5.Place three mattress sutures using double-armed needles in the eyelid to rotate the distal lid margin outwardly. The suture starts from the inner conjunctival surface of the proximal tarsal plate margin. The needle on each arm of the suture is passed through the proximal tarsal plate and is then rotated and passed through the muscle and skin of the distal eyelid margin anterior to the tarsal plate. The three mattress sutures are tied above the eyelash line.

6.The skin is closed with interrupted silk sutures.

7.Topical antibiotic is applied three times daily for 7 days.

8.All sutures are removed after 7 days.

The advantage of bilamellar tarsal rotation is its relative simplicity. It takes approximately 10 min to perform on one eye, and is a procedure which can be taught to ophthalmic assistants and nurses and performed under field conditions in communities where trichiasis is prevalent. Its disadvantage is the potential for shortening of the upper eyelid. For this reason in young patients (under 25 years), or in patients with severe shortening of the upper eyelid, the more difficult buccal mucous membrane graft is considered preferable.

Leprosy is a chronic bacterial disease of low grade infectivity, due to Mycobacterium leprae. The disease is distributed mainly in developing countries. It is thought to be spread by droplets from the upper respiratory tract; such a mechanism is encouraged by conditions of poverty and crowding. In most people, infection heals spontaneously without producing clinically recognizable disease. Established infections may produce a spectrum of disease from multibacillary leprosy, in which the cellular immunity is low and there are many leprosy bacilli in the tissues, through borderline to paucibacillary leprosy with high cellular immunity and correspondingly low bacterial counts.

Most complications are caused by either a massive bacterial load in the patients and secondary atrophy of tissues, or by sudden changes in the patient's immune response to the organism. Type I reaction (reversal reaction) occurs in all types of borderline leprosy and is associated with an increase in cell-mediated activity. Type II reaction (erythema nodosum leprosum) occurs in multibacillary leprosy. Type I reaction can lead to paralysis of the ophthalmic branch of the trigeminal nerve and the facial nerve. Type II reaction can lead to acute iritis.

Lagophthalmos may occur as a result of a Type I reaction. If of recent onset (6 months or less), treat vigorously with oral prednisone 30 mg per day, decreasing over 6 months, together with blinking exercises and protective spectacles. If a long-standing lagophthalmos causes exposure keratitis, then surgical treatment is indicated. This is usually by lateral tarsorrhaphy. Experience with temporalis muscle transfer surgery has given disappointing recovery of spontaneous regular blinking.

Corneal anaesthesia, due to involvement of the Vth nerve in Type I reactions, may occur in combination with lagophthalmos. Partial loss of corneal sensation, resulting in an itch, can be especially dangerous if the eye is rubbed with insensitive, deformed hands. In severe cases tarsorrhaphy is indicated if corneal clarity is threatened.

Acute iritis is treated with atropine 1 per cent and steroid eye drops. If it occurs in combination with scleritis, topical treatment has to be combined with systemic treatment for erythema nodosum leprosum (Type II reaction).

Cataract may occur secondary to iritis, but is usually incidental age-related cataract. Routine cataract extraction can be performed without special precautions if the patient is under treatment or has been released from treatment and has not recently experienced any reaction.

Prevention includes early systemic multidrug treatment, prompt treatment of Type I reactions with systemic steroids, early treatment of any eye complications, and provision of cataract surgical services for leprosy patients with cataracts.

A temporary tarsorrhaphy is indicated for corneal protection when a VIIth nerve palsy is expected to recover, or to assist healing of an indolent corneal ulcer. A permanent tarsorrhaphy is required for established VIIth nerve palsy and when there is severe loss of corneal sensation.

This can be carried out medially, centrally, or laterally along the eyelids. The length is marked out on the margins of the upper and lower lids and an incision 2 mm deep is made in the ‘grey line’ in the middle of the eyelid margin, between the orifices of the meibomian glands behind, and the eyelash follicles in front. The marginal epithelium of the lid margins is then excised. The upper and lower eyelids are apposed and sutured together in two layers. The raw surfaces of the tarsal plates of the upper and lower lids are approximated with 6/0 absorbable sutures, making sure that these do not go through on the conjunctival surface when they might abrade the cornea. Double-armed 6/0 or 4/0 non-absorbable mattress sutures are inserted through ‘buttons’ (cut from a rubber or plastic cannula), through the skin well back from the lid margin of the upper lid, out through the grey line in the raw area, into the corresponding position of the lower lid, and through the skin of the lower lid to be tied over a similar ‘button’ or ‘bolster’. The mattress sutures are removed after 2 to 3 weeks.

The eyelids are overlapped with excision of a margin of soft tissue from the eyelid margins, to produce a more permanent adhesion that will not undergo retraction. This is most frequently done at the lateral canthus. After the lateral ends of the lids have been split into their two lamellae, a triangle of skin and orbicularis muscle (the anterior lamella) is excised from the lower lid, and a corresponding triangle of tarsal plate and conjunctiva (the posterior lamella) from the upper lid. The upper edge of the tarsoconjunctival lamella of the lower lid may be sutured with fine catgut to the cut edge of the conjunctiva of the upper lid to strengthen the future union. A mattress suture is then brought forward from the conjunctival surface of the lower lid, and through the prepared triangle of the upper lid to be tied finally over a bolster on the skin surface. If a vertical incision is now made at the medial end of the upper lid triangle, a flap is created which can be pulled down to cover the raw tarsal triangle of the lower lid.

The major cause of blindness from bilateral corneal opacity is trachoma. Other important causes are suppurative keratitis (although usually unilateral), vitamin A deficiency, climatic keratopathy, and exposure due to the lagophthalmos in leprosy. Excimer laser may prove to be the treatment of choice for climatic keratopathy. Pterygium only rarely crosses the pupil to impair vision.

Occasionally a patient blind from corneal scarring may obtain useful travel vision by the creation of an artificial pupil (optical iridectomy). This is only indicated in a patient who is bilaterally blind and who has a central scar (leucoma) with clear peripheral cornea. Ideally, the optical iridectomy is made inferonasally to be most useful for vision. The incision is made under a conjunctival flap at the limbus. The iris is prolapsed and gently eased out through the wound. An iridectomy from the iris root to the pupil margin is performed with scissors. The limbal incision is closed with sutures.

Corneal grafting, either full thickness or lamellar, is the definitive treatment for opacities due to corneal dystrophies, corneal scar of various causes, and distortion due to keratoconus. With gradual evolution of technical improvements over the last 30 years (operating microscope, fine sutures, microsurgical instruments, and topical local steroids), the prognosis for survival of corneal grafts is now good for many conditions. Heavily vascularized corneas, absence of lacrimal secretion, or distortion of the eyelid margins all, however, decrease the chance for successful grafting.

Corneal storage has also improved. The method which has been used for many years is to store the whole eye in a sterile container in a refrigerator at 4°C. Under these conditions the cornea should be used for transplantation as soon as possible to avoid extensive endothelial cell death; the limit is usually regarded as 48 h after death. Short-term storage in tissue culture media, such as the McCarey - Kaufman solution, now allows storage for up to 4 days. Corneal organ culture allows the donor tissue to be used for up to 30 days after death.

Allograft rejection is substantially reduced by the use of fine monofilament sutures which reduce the inflammatory reaction. 10/0 nylon sutures are most often used, either interrupted or continuous. An operating microscope and high quality microsurgical instruments are required to be able to suture the donated cornea into the recipient satisfactorily. The suture knots are buried in the corneal stroma.

In certain circumstances a localized central opacity can be treated with a rotation autograft, when an eccentric corneal graft of the patient's own cornea rotates the opacity out of the optic axis towards the limbus. In rare circumstances, a corneal exchange can be undertaken between an eye with a clear cornea and total blindness due to posterior segment disease, and the other eye of the same individual who has corneal opacity but an otherwise healthy eye. There is no possibility of graft rejection with such an autograft. Both these techniques are readily applicable in a developing world situation where the supply of donor allograft material may be very limited.

This is a very common condition. The interaction of different causes is not fully understood. Pterygium very seldom causes blindness.

Many different operations have been devised to remove the pterygium and try to prevent a recurrence. A simple technique is to excise the conjunctiva at the base of the pterygium after the head is removed from the cornea, leaving the sclera bare. If the pterygium recurs, it can be treated with a free rotational conjunctival graft after a second excision.

An estimated 1.5 million children in the world are blind. At least 50 per cent of this blindness is due to vitamin A deficiency.

Each year some 250 000 children are needlessly blinded because of the effects of deficiency of vitamin A in their diet. Another 250 000 children are left with lesser degrees of permanent visual impairment due to corneal damage. The conditions under which vitamin A deficiency and xerophthalmia occur are poverty, high incidence of precipitating infections (measles and gastroenteritis) in pre-school age children, and lack of maternal education (Fig. 35) 2758. Illness and death from measles, lower respiratory tract infections, and diarrhoea have all been reported as being more common in young children with a low vitamin A status. Conversely, these infections themselves worsen the vitamin A status, thus precipitating blindness.

The older child may complain of night blindness. Signs include dryness of the conjunctiva (xerosis) due to a decrease in the goblet cells and keratinization of the epithelium. Bitot spots are white, foamy, raised areas usually on the temporal conjunctiva (Fig. 36) 2759. The most dangerous signs are dryness of the cornea, ulceration, and then a sudden melting of the cornea, keratomalacia, leading to perforation and often loss of the eye. The exact reason for the sudden melting of the cornea under these conditions is not fully understood. The end-stage of blinding malnutrition is corneal scarring, which may be a leucoma, impairing vision but allowing the structure of the anterior chamber to remain, or there may be anterior staphyloma (bulging forward of the cornea) or phthisis bulbi (a small shrunken globe).

Corneal involvement is a medical emergency. Three doses of vitamin A in the form of high dose capsules are given on day 1, day 2, and 1 to 4 weeks later. The dose is 200 000 IU for children aged 1 to 6 years, and 100 000 IU under the age of 1 year. Topical antibiotic ointment is also used. A joint WHO/UNICEF statement has now recommended that this high dosage of vitamin A should be given to all children with measles in communities where measles has a mortality of 1 per cent or more.

Occasionally a blind child or adult with central leucomas may be helped by an optical iridectomy. Because of iris adhesions to the cornea, keratoplasty is usually disappointing. Evisceration of the globe may be indicated for a painful or unsightly staphyloma.

In the long run, this must consist of improved dietary habits and improved availability of vitamin A containing foods. Short-term measures include vitamin A supplementation through capsule distribution or food fortification.

This is the most common cause of treatable childhood blindness after vitamin A deficiency. The major underlying causes are heredity and congenital acquired rubella syndrome.

Long-term visual loss can occur because of amblyopia, and early surgery is essential with immediate postoperative aphakic correction if reasonable visual results are going to be obtained. In general, the visual results are much better in bilateral congenital cataract than in unilateral. The most widely practised surgical technique is aspiration and irrigation, as for extracapsular cataract extraction in an adult. Since the nucleus is less hard than in an adult and more easily aspirated, a small incision can be made. A posterior capsulotomy may be performed at the end of the procedure. Some surgeons now advocate lensectomy and anterior vitrectomy through the anterior chamber, in order to avoid the problem of secondary capsular opacification which may impede vision and make accurate refraction and optical correction of the aphakia difficult.

Congenital glaucoma or bulphthalmos usually presents in early childhood with an enlarged cloudy cornea and photophobia. Assessment, including ophthalmoscopy, tonometry, and gonioscopy (if possible), is performed under general anaesthetic. If a membrane of tissue is present (as described by Barkan), then goniotomy is the treatment of choice. This requires a surgical gonioscopic lens, and an irrigating goniotomy knife so that the membrane can be incised under direct vision.

In cases due to other structural abnormalities and where the cloudiness of the cornea prevents a clear view of the angle, a filtration procedure such as trabeculectomy is the management of choice.

Retinoblastoma classically presents as a white pupil, or occasionally as a squint. There may be a family history. Patientsare often brought late in the course of disease in developing countries with secondary glaucoma or proptosis. The prognosis for the child's life under these circumstances is poor. Usually, enucleation is the only treatment possible in developing countries because of the advanced state of the tumour and the limited resources available. The emphasis when training physicians and nurses must therefore be on early detection and immediate referral and treatment.

The enucleated eye should be examined histologically for extension through the cut end of the optic nerve, or extension outside the sclera. In these circumstances, and in the event of orbital recurrence, radiotherapy and adjuvant chemotherapy are indicated if available. Screening of the second eye may allow conservative treatment to be undertaken with preservation of the eye should the disease prove to be bilateral. Depending on the size of the tumour when discovered, this may be external radiotherapy or radioactive scleral plaques for retinoblastomas up to 10 mm in diameter. Cryotherapy with a retinal cryoprobe, with a triple cycle of freezing and thawing, may be used for tumours up to 7 mm in diameter. Photocoagulation with a xenon light coagulator for tumours up to 5 mm is also possible; the light is not applied directly to the tumour but to the surrounding retina to cut off the blood supply.

Surgical removal of the entire globe is called enucleation. It is indicated when there is a painful blind eye (especially from severe trauma), and malignant tumours if other treatment is not possible. Removal of the anterior part of the globe and the contents, leaving only the scleral coat and optic nerve is referred to as evisceration. Evisceration usually gives better cosmetic results and ocular mobility. It is indicated when there is suppurative endophthalmitis or painful or unsightly staphyloma. Evisceration is an easier procedure than enucleation and may be performed by a non-specialist for a blind, painful, non-malignant eye.

1.Anaesthesia. A general anaesthetic is preferred, but the procedure can be done with lid akinesia and retrobulbar local anaesthetic.

2.Conjunctiva. The conjunctiva is incised 360° around the limbus and Tenon's capsule is incised and undermined well back into each quadrant.

3.Extraocular muscles. Each rectus muscle is identified and isolated with a muscle hook. 5 - 0 chromic catgut sutures are passed through each muscle, near its insertion, at least twice, and are locked in place. The rectus muscle is then divided on the globe side of the suture. The oblique muscles are usually divided near their insertions to the globe without inserting sutures. The remaining fascial sheath is dissected from the globe.

4.Optic nerve. Curved enucleation scissors are inserted along the lateral orbital wall, and opened to feel the tough rubbery optic nerve between the blades. The optic nerve is cut, in the case of a malignant tumour as close to the apex of the orbit as possible. The globe is removed, and the orbit immediately packed with gauze, under pressure from the surgeon's hand, until bleeding stops.

5.Implant. Many different types of implant are now available. Most commonly, a silicone or plastic sphere of appropriate size is inserted into the muscle cone. The opposing rectus muscles are tied to each other in front of the implant by means of the absorbable retention sutures already attached. An implant allows some degree of movement of the future artificial eye. Some implants have grooves or slots through which the retention sutures on the rectus muscles can be passed, to improve movement.

6.Closure. Tenon's capsule and conjunctiva are each closed separately with a 5 - 0 continuous absorbable suture. Antibiotic ointment is applied to the conjunctiva, a plastic conformer inserted into the socket, and a pressure bandage applied for 2 days.

When the conjunctiva is healed, the conformer can be replaced with an artificial eye which matches the patient's remaining eye as closely as possible.

1.Anaesthesia. General anaesthesia is preferable, but if not available the procedure can be performed under local anaesthetic.

2.Excision of cornea. The conjunctiva and Tenon's capsule are divided all round the limbus and dissected back anterior to the rectus muscle insertions. A knife is passed through the cornea at the limbus. The corneal circumference is cut with corneal scissors and the cornea removed.

3.Intraocular contents. A curved scoop or ‘evisceration spoon’ is introduced between the ciliary body and the sclera, and all the contents are scraped from the scleral coat. A dry swab held in forceps removes any remaining choroidal tissue, particularly at the exit of the vortex veins and the optic nerve.

4.Dressing. The inside of the sclera is filled with topical antibiotic. A tulle gras dressing may be inserted for 48 h. The sclera and conjunctiva may be loosely sutured in two layers with absorbable catgut, but in the case of endophthalmitis it may be better to leave the wound open. A pressure bandage is applied for 48 h. Systemic antibiotics are advisable for 5 days if endophthalmitis was present.

5.Implant. If the evisceration is for a cause other than infection, a ball implant can be inserted which is small enough for the scleral edges to be brought loosely together. The conjunctiva is closed with interrupted sutures. As the sclera shrinks down, the resulting fibrous scar may allow good movement of a later artificial eye.

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