Botox beyond beauty

Le résumé fourni par la source

In the modern-day scenario, whenever botulinum toxin is talked about, the majority of the population thinks of it as the magical cure to age-related wrinkles. Although it has been frequently used by cosmetologists, from any ophthalmologist’s point of view, one must always remember that the use of this toxin is in a wide range of ophthalmological problems.[1] Botulinum toxin is the most potent biological toxin.[2] It is an exo-toxin produced by the Gram-positive bacteria Clostridium botulinum. There are seven distinct serotypes of the toxin, A to G. Serotype A is the commercially available botulinum toxin.[1] The toxin acts at the neuro-muscular junction (NMJ) comprising the axonal terminus and skeletal muscle. The terminal axon consists of the pre-synaptic vesicle containing acetylcholine, the chief neurotransmitter acting on the muscarinic receptors of the NMJ. Botulinum toxin acts by inhibiting the release of acetylcholine from the vesicles. The toxin has a molecular weight of 150 kDa and consists of two polypeptide chains, such as heavy (Wt 100 kDa) and a light chain (Wt 50 kDa). The two chains are joined together by a disulfide bond. The heavy chain further has a translocation and a receptor-binding domain. Once the toxin reaches the NMJ, it is endocytosed and prevents synaptic recycling.[3] The effect of toxin begins 1–3 days after injection and peaks at 4–7 days. Gradually in 2-3 months, the axon expands with the sprouting of the axonal terminus, thus subsiding the effect of the toxin. The commercially available toxin is dried and frozen.[4] Sodium chloride and albumin are added to prevent the loss of toxins by surface adsorption. Before injection, the toxin must be reconstituted with distilled water or normal saline. The usual concentration of the toxin used is 1–2.5 IU/0.1 mL. Hence to achieve a concentration of 2.5 IU/0.1 mL, 4 mL saline is added in the commercially available 100 IU vial (Botox, Onabotulinum toxin A – Allergan, Inc., Irvine, CA, USA). Common ophthalmic indications for botulinum toxin include benign essential blepharospasm, hemifacial blepharospasm, eyelid retraction, lacrimal hyper-secretion, spastic entropion, Frey’s syndrome, and strabismus. Benign essential blepharospasm is characterized by the involuntary spasmodic contractions of the orbicularis oculi.[5] Botulinum toxin is administered in the sites as shown in Fig. 1. Eyelid injections are administered subcutaneously whereas brow injections can be administered deeper [Fig. 2].Figure 1: Sites of injection for blepharospasm and hemifacial spasm, red points indicate additional sites of injection for hemifacial spasmFigure 2: Pre- and post-injection picture of a patient with blepharospasmHemi facial spasm is characterized by repetitive tonic contractions of the facial muscles. The spasm can be caused due to compression of the facial nerve route.[6] In addition to the sites of injection for blepharospasm, as shown in Fig. 1, injections are also administered in the zygomaticus major muscle and levator labii superioris alaeque nasi muscle. Eyelid retraction can be associated with several etiologies, the most common being thyroid eye disease.[7] Botulinum toxin administration has been described as a nonsurgical correction option for eyelid retraction. 2.5-5 IU of the toxin is injected in the levator palpebrae superioris through the trans-cutaneous route or trans-conjunctival route. The administration of botulinum toxin by the trans-cutaneous route is performed by passing the needle supero-posteriorly between the eye and orbital roof along mid pupillary plane. For the trans-conjunctival route, Botox is given by everting the eyelid with the help of Desmarre’s retractor and injecting the toxin in the LPS, above the superior border of the tarsus. In patients with non-resolving seventh nerve palsy and persistent epithelial defects, 20 IU of the toxin is injected by a similar technique to induce a tarsorrhaphy like effect.[8] Lacrimal hyper-secretion can result from primary lacrimal gland hyper-secretion, obstructions of the canalicular drainage system, and gustatory epiphora.[9] In these conditions, 5 IU of toxin is given in the palpebral lobe and orbital lobe of the lacrimal gland. After the instillation of topical anesthesia drops, the patient is asked to look down, and upper lid is everted with the help of Desmarre’s retractor. The palpebral lobe of the gland is visualized, and toxin is injected. Aberrant regeneration of secretory fibers of the facial nerve with the cutaneous sweat glands after parotidectomy results in ipsilateral facial perspiration.[10] Before injection, perspiration is induced by feeding the patient. The area of perspiration is then marked and cleaned. Intradermal injections of 40 IU of botulinum toxin are administered at multiple sites over the affected area. Spastic entropion can result from excessive contraction of orbicularis oculi muscle. About 5–10 IU of the toxin is administered in the pre-tarsal and pre-septal orbicularis muscle, to provide a temporary relief.[11] Botulinum toxin has been shown to be effective in sixth nerve palsy, infantile esotropia, cyclic esotropia, and acute onset comitant esotropia.[12–14] The toxin injection in the medial rectus muscle helps to avoid contracture of the medial rectus muscle and prevents diplopia. To administer the toxin in the medial rectus, localized peritomy is performed, muscle is hooked, and under direct visualization, 3–5 units of the toxin are injected. The adverse effects of botulinum toxin injection include erythema, pain at the injection site, ecchymosis, ptosis, generalized facial muscle weakness, and difficulty in speaking [Fig. 3a and b]. These effects are transitional and self-limiting. However, they can be bothersome for the patients. Hence, the adverse effects should be explained to the patients and attendants before planning the injection.Figure 3: a – Transitional ptosis following injection of botulinum toxin in the lacrimal gland. b – Right generalized facial muscle weakness following injection for right hemifacial spasmThus, to conclude, administration of the botulinum toxin can be a simple answer to several complex ophthalmic situations. Easy availability, reversibility, and ease of administration make it a desirable option for the years to come. Declaration of patient consent The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Ce résumé expose les affirmations des auteurs. BNTIC ne l’interprète pas comme une validation indépendante des résultats.