The assessment of the lacrimal system is similar to that for more simple lacrimal disorders (Chapter 15) but, in addition, a more extensive assessment of the eye, eyelids, medial canthus and lacrimal system is essential to establish a plan of management. In addition, the nasal structure and cavity should also be carefully examined.

Lacrimal canalicular obstructions may rarely be idiopathic, but are generally the result of infection (primary Herpes simplex and zoster, or Actinomyces canaliculitis), trauma (direct, iatrogenic or irradiation), cicatrising mucous membrane diseases (pemphigoid, chronic ocular medication, or topical drug reactions such as StevensJohnson syndrome), or involvement with tumours (papillomas or secondary to skin tumours). With these causes in mind, associated abnormalities should be sought during the ocular examination; for example, in the presence of a progressive disease such as ocular pemphigoid, it may be undesirable to place a canalicular bypass tube for fear of exacerbating inner canthal scarring or worsening an underlying dry eye syndrome.

The shape and position of the medial canthus should be assessed and, if abnormal, the lateral or vertical displacement should be measured relative to the midline and compared with the other side (if normal); the normal adult intercanthal distance is about 30mm, or 15mm from the midline to each canthus. The shape of the canthus may be relevant both for cosmesis and, where required, for the likelihood of being able to successfully place a lacrimal canalicular bypass tube.

Clinical assessment of the lacrimal system is directed towards establishing at what level obstruction lies (Chapter 10).With canalicular obstructions the length of patent canaliculus, both upper and lower, should be measured; the critical length in planning surgery is 8mm. Where there is at least this amount of one remaining canaliculus, it is generally feasible to perform a canaliculo-dacryocystorhinostomy (canaliculo-DCR). If there is less than 8mm, a Lester Jones canalicular bypass tube may be required unless the obstruction lies in the proximal canaliculus; in the latter instance the distal remnants of the canaliculi may be normal and may be opened into the tear lake by retrograde probing from within the lacrimal sac and canaliculostomy, or by direct cut-down along the eyelid margin and intubation of the openings. Although such procedures may be performed without dacryocystorhinostomy, it is more logical to perform DCR at the time of primary canalicular surgery. DCR not only increases canalicular conductance by having bypassed the physiological resistance of the nasolacrimal duct, but adequate primary rhinostomy allows the relatively straightforward closed placement of a canalicular bypass tube should the primary canalicular surgery fail to control symptoms.

Where there is blockage of each individual canaliculus, the length of patent canaliculus can be estimated clinically and dacryocystography is not possible. With common canalicular obstruction, where syringing leads to reflux of dye-free fluid from the opposite punctum (Chapter 10), a dacryocystogram is helpful in establishing the extent of common canalicular disease. Lateral obstruction, with complete obliteration of the common canaliculus, requires canaliculo-DCR whereas medial obstruction, due to adherence and fibrosis of the mucosal valve over the common canalicular opening, may be dealt with by excision of the membrane at the time of DCR and intubation.

There is no need for CT of the facial skeleton when considering lacrimal surgery after previous mid-facial trauma, provided that the presence of a nasal space alongside the site of future rhinostomy is established by clinical inspection or nasal endoscopy. Where there has been major facial trauma, however, CT of this region may be useful in case other procedures - such as septoplasty, sinus surgery or intercanthal wiring - are to be combined with the lacrimal reconstruction.

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