toxins (A to G) produced by the anaerobic bacterium Clostridium botulinum. The toxin is a two-chain polypeptide, with a heavy chain joined by a disulphide bond to a light chain. The heavy chain adheres to axonal terminals and the toxin is brought into the terminal by endocytosis [24]. The light chain then leaves the endocytic vesicle to enter the cytoplasm. The light chain is a protease enzyme which selectively degrades SNAP-25, a SNARE protein which is a fusion protein at the neuromuscular junction necessary for docking neurosecretory vesicles [31].

Failure of the vesicles to dock on the axonal synapse plasma membrane prevents release of their acetylcholine content. The lack of acetylcholine dampens the nerve impulse, leading to flaccid paralysis. This is overcome and neuromuscular function returns by new axonal sproutings; the process of recovery begins within days and takes some weeks to be functionally effective [56].

For over two decades botulinum toxin has enjoyed widely accepted use, initially off label, for many other pathological conditions [12]. In ophthalmology this includes entropion, blepharospasm and the induction of a temporary ptosis for corneal protection [15, 17, 29, 42, 67]. Although taping the entropic lower lid outwards is a useful temporising measure, it requires some patient dexterity and the tape can be irritating to the skin. Botulinum toxin does not involve the patient in continued management. It is effective in overcoming the overriding orbicularis of entropion while waiting, for whatever reason, to proceed to formal surgical correction. Occasionally, the effect of the toxin is prolonged as the cycle of spasm, secondary to pain from corneal trauma due to in-turned lashes, is broken. The toxin is injected without the need for local anaesthetic. An injection of 5–7 U Botox (approximately 20–28 U of Dysport) will effectively dampen the orbicularis override and reverse the entropion. It should be injected above the inferolateral orbital rim in the preseptal fibres of the orbicularis, over 5 mm below the lid margin so as to avoid the pre tarsal fibres as these are needed for lid closure. The needle (30 gauge) is inserted into the muscle fibres for direct delivery of the toxin.

As with any toxin injection, it takes a few days to take effect and wears off on average some 8–12 weeks later. Complications are unusual and include inadvertent bruising and spreading of the toxin inferiorly into cheek muscles with resultant temporary loss of movement. These signs resolve with time.

1.3 Lower Lid Ectropion

1.3.1 Introduction

The term ectropion comes from the Greek words ec (away from) and tropein (to turn). As for entropion, the commonest cause of ectropion is involutional. Less common categories are paralytic, cicatricial and mechanical. The outward displacement of a lid margin from ageing changes is predominantly due to horizontal laxity of its components (lateral canthal tendon, tarsus, and medial canthal tendon) and less commonly from laxity/loss of the lower lid retractors resulting in total tarsal ectropion [32, 58, 71, 6, 68]. Initially, the latter leads to loss of the lower skin crease but can, in severe cases, produce total tarsal eversion. Surgical procedures are well established, the lateral tarsal strip and a full thickness pentagon excision being the standard operations for laxity of the lateral canthal tendon and tarsus respectively [1, 13]. Several operations are available to correct medial laxity but its repair is more complicated than its lateral counterpart, as anatomically it has two limbs, anterior and posterior (Fig. 1.5). The amount of lid laxity due to medial canthal tendon depends on which limb is affected. The severity of the laxity is assessed by seeing how far laterally the punctum can be dragged across the globe [7].

Punctal ectropion alone can be addressed by excising a small tarso-conjunctival diamond from the posterior lamella, the so-called medial spindle, ensuring the lower lid retractors are picked up in the single stitch that closes the wound; if the punctual ectropion is associated with mild to moderate medial laxity of the lid tissues, where the punctum can be dragged laterally but no further than the level of the medial corneal limbus, various surgical interventions are available including the so-called Lazy-T procedure and medial canthal anterior limb plication [54, 66].

If the punctum can be pulled laterally beyond the medial corneal limbus, and laxity may be severe enough for the punctum to reach the mid-pupillary line, this is seen as evidence of loss of the posterior limb of the medial canthal tendon. Those procedures which only address the anterior limb would be ineffective. The posterior limb can be recreated by horizontally resecting part of the lid medially thus shortening it, marsupialising the cut canaliculus and reattaching the newly shortened medial end of the tarsus to the

posterior lacrimal crest. Although less complex operations have been proposed [39], durable long term results have been shown with this resection procedure [22, 69]. This open surgical procedure may not be suitable in elderly or frail patients. A less invasive procedure involves reattaching the medial end of the tarsus without shortening the lid, by the use of a suspensory non-dissolving suture, the Royce Johnson suture [43].

1.3.2 The Royce Johnson Suture

The medial lower lid is injected with vasoconstrictive local anaesthetic, as is the upper lid medially. The bolus is then massaged down so as to reach the deeper tissues. A small horizontal incision is made with a D15 blade, inferolateral to the lower punctum, at the level of the medial edge of the tarsal plate. Orbicularis fibres are divided by blunt dissection to expose the medial edge of the tarsus. The tip of a blunt ended instrument, such as an artery clip, is placed just behind the plica semilunaris and pushed posteriorly to identify the posterior lacrimal crest by palpation, thus giving the surgeon an indication of its position. A double armed 4/0 Prolene stitch is then passed through the exposed tarsal

edge and the needles passed “blind”, one needle at a time, medial to the globe and lateral to the lacrimal sac, pointing backwards, upwards and medially through the connective tissue towards the superior end of the posterior lacrimal crest. The needle tips pick up periosteum before continuing a short distance upwards to tent the skin of the upper lid superomedially. A D15 blade is used to cut down on this tenting to allow the needle out. The second needle is passed in the same way, and exits through the skin opening fashioned by the first one (Fig. 1.6). The stitches are then gently pulled upwards to judge how far up the medial end of the lower lid needs to be elevated. They are then tied and the knot buried close to periosteum, well under orbicularis which is closed with an absorbable stitch such as 6/0 vicryl, as is the skin. Only one or two interrupted sutures are required for each layer.

1.3.3 The Pillar Tarsorrhaphy

Strengthening a weak muscle is easier than compensating for a paralysed one, and managing paralytic ectropion is no exception. In this clinical setting, there is descent as well as forward displacement of the lid margin. This is due to loss of orbicularis muscle tone

as a result of damage of some kind to the facial nerve that supplies it. In severe cases, where there is corneal exposure that cannot be lubricated adequately, but there is every hope the palsy will recover, a reversible procedure that can support the lid margin temporarily is required. As the recovery may take several months, the procedure needs to hold for that long.

The traditional temporary tarsorrhaphy, where the margins are freshened and then sutured together on bolsters, tends to stretch vertically, or even give way, sometimes within weeks. Moreover, tarsorrhaphies, whether temporary or permanent, are traditionally placed laterally. The lower lid sag and resultant widening of the vertical palpebral aperture in paralytic ectropion is

often more severe medially than laterally. Therefore a lateral procedure, whether temporary or permanent, will not correct this well. Furthermore, an equivalent medial procedure to the temporary lateral tarsorrhaphy would need to last longer than a few days or weeks. The pillar tarsorrhaphy fulfils these requirements [43]. Its closing of the lid margins medially protects the globe at the expense of cosmesis, but with the advantage that they can be reopened when required at a later date with good cosmetic outcome (Fig. 1.7).

The effect of this procedure depends on the principle that raw surfaces will stick together and heal in that position, and that the larger the raw surface area the better the healing. After infiltration with

vasoconstrictive local anaesthetic, the upper and lower lid margin grey lines are scored 2–3 mm deep with a thin pointed blade (e.g. D11 or a feather blade as used for paracentesis through a cornea) from the level of the medial limbus of the cornea to just lateral to the puncta. The incisions are then extended anteriorly and posteriorly to form an “H” (Fig. 1.8). The posterior margins are sutured together with a long acting absorbable suture such as 6/0 vicryl. The anterior margins are everted forwards and sutured together with 4/0 silk or vicryl over bolsters like pouting lips, ensuring the extended raw surfaces are in close contact (Fig. 1.9). The stitches remain in situ for at least 3 weeks or until they loosen and can be removed with the bolsters, without disturbing the newly healed pillar. This can be left as is, or reopened with a blade under vasoconstrictive local anaesthetic when it is no longer required.

In adults, a certain amount of horizontal age-related laxity is usually necessary to acquire an acute ectropion. In the presence of involutional changes, a trigger such as blepharospasm or conjunctival oedema may result in transient ectropion. Ocular pain or irritation from a corneal foreign body or ulcer may be sufficient to cause orbicularis spasm; sudden onset of conjunctival oedema, as in allergic reactions, may cause tarsal ectropion (Fig. 1.10). Clearly, the stimulating cause needs to be corrected and, in the case of allergy, the offending chemical needs to be removed from the

a

1.3.4 Lower Lid Ectropion Sutures

Acute ectropion can be congenital or acquired. If the conjunctiva becomes sufficiently oedematous, then the lid cannot return to its usual position. In congenital cases, this occurs soon after birth, is usually bilateral and associated with anterior lamellar shortage. Conservative management involves lubricating the conjunctiva, then pushing it back into place by manually inverting the everted lids and applying pressure pads. These are kept in place for 24–48 h; this is usually sufficient for the conjunctival oedema to resolve enough not to push the lid out into an ectropion. Rarely, inverting sutures are required for formal corrective surgery for laxity/skin shortage.

b

Fig. 1.10 Acute allergic ectropion. (a) Eversion with conjunctival oedema; (b) inverting sutures on bolsters