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Spectacle wedge incision


Synonym(s): Partial spectaculectomy, Spectacle wedge resection

Introduction

  • Certain reptiles in the order Squamata including all snakes, worm lizards (amphisbaenians) and some lizards, eg tokay geckos, have fused eyelids with no palpebral fissure Ocular anatomy and physiology.
  • The fused eyelids form a transparent membrane over the globe, known as the spectacle. The spectacle is composed of skin and is relatively insensitive (cf the cornea).
  • Although the spectacle is highly vascular, under normal circumstances these vessels are not readily visible:
    • Vascularity can increase with inflammation and during ecdysis Ecdysis/dysecdysis.
    • Must be differentiated from disease.
  • The subspectacular space separates the spectacle and the cornea and is normally filled with the secretions of the Harderian gland, which provides lubrication and easy movement of the globe (although this is limited in reptiles). The thick, oily Harderian glandular secretions have a high reflective index and are also thought to have some optical importance.
  • The Harderian gland is posterior to the orbit and drains into the subspectacular space in most spectacled species by several small ducts with a main opening into the lacrimal duct. The Harderian secretion flows from the subspectacular space through the nasolacrimal duct to the nose followed by the mouth.
  • Bacterial or fungal dermatitis, often associated with suboptimal husbandry Chelonia husbandry Lizard husbandry Snake husbandry and opportunistic infection can primarily involve or extend to the spectacle, resulting in intraspectacular dermatitis.
  • Microbial infection can occur within the subspectacular space and may be unilateral or bilateral. This often manifests as a subspectacular abscess. Subspectacular infection can occur as a result of a penetrating spectacular trauma (including those caused by parasites such as Ophionyssus spp mites Acariasis), as an extension of conjunctivitis, through hematogenous spread, or via an ascending infection through the nasolacrimal ducts from the oral cavity.
  • Obstruction of the nasolacrimal system in spectacled species will result in accumulation of tears, ie Harderian secretions, in the subspectacular space resulting in pseudobuphthalmos. Chronic increase in pressure within the subspectacular space can lead to corneal damage or even to the globe itself.

Uses

Advantages

  • For diagnostic investigation:
    • Biopsy of the spectacle for histopathology and microbial culture and sensitivity
    • To access material within the subspectacular space for cytology and microbial culture and sensitivity.
  • As a therapeutic procedure:
    • To enable debridement and/or flushing of the subspectacular space and instillation of topical medication.
    • To resolve distension of the subspectacular space in pseudobuphthalmos by creation of a temporary fistula.
  • Under experimental conditions, resection of 25% of the spectacle in royal pythons (Python regius showed no increased risk of ocular or subspectacular infection and resulted in normal spectacle morphology after three months.

Disadvantages

  • Aggressive excision of the spectacle (considered to be >25-30%, ie a wedge incision over 90 degrees) can result in excessive loss of the tear film and desiccation of the cornea.
  • Recurrence of pseudobuphthalmos is common if treated solely by this technique.

Technical problems

  • The small size of ocular tissues in reptile will typically require access to an operating microscope or surgical loupes for magnification, as well as ophthalmic/fine surgical instruments.
  • Overly aggressive excision of the spectacle may occur iatrogenically or be required for therapeutic purposes, which risks excessive tear film loss and corneal desiccation.

Alternative techniques

  • None reported, although placement of a temporary suture across the free borders of the spectacle after resection has been described to minimize tear film loss and corneal desiccation if an excessive portion of the spectacle has been resected.
  • In pseudobuphthalmos, treatment of a blocked nasolacrimal duct or conjunctivoralostomy to create a new drainage canal should accompany a spectacle wedge resection ipsilaterally to reduce likelihood of recurrence.

Time required

Preparation

  • Should be relatively short, although ophthalmic surgery in venomous reptile species Venomous species would require additional precautionary measures and equipment and should always be under the guidance of an experienced venomous reptile handler and ideally, an experienced venomous reptile veterinarian.

Procedure

  • Around 30 min or less: exact timeframe would depend on veterinary expertise and level of patient sedation/anesthesia required.

Decision taking

Criteria for choosing test

Risk assessment

  • Clinical status of the animal and concurrent disease: demeanor, vital signs, bloodwork (complete blood count, serum biochemistry and electrolytes).
  • Ability to safely handle patient, particularly applicable to venomous species.

Requirements

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Preparation

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Technique

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Aftercare

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Outcomes

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Almeida D, Kennedy M & Wendt-Hornickle E (2022) Snake sedation and anesthesia. Vet Clin North Am Exotic Anim Pract, 25 (1), 97-112 PubMed.
  • Smith Fleming K M (2019) Ocular surface disease in reptiles. Vet Clin North Am Exotic Anim Pract 22 (1), 109-121 PubMed.
  • Perry S M & Nevarez J G (2018) Pain and its control in reptiles. Vet Clin North Am Exotic Anim Pract 21 (1), 1-16 PubMed.
  • Da Silva M A, Bertelsen M F, Heegaard S & Garner M M (2015) Spectacular manifestations of systemic diseases of the snake: a histopathological description of four cases. J Zoo Aquarium Res (2), 43-46 JZAR.
  • Maas A, Paul-Murphy J et al (2010) Spectacle wound healing in the Royal Python (Python regius). J Herpetol Med Surg 20 (1), 29-36 VetMedResource.

Other sources of information

  • Millchamp N J (2022) Ophthalmology of Serpentes: Snakes. In: Wild and Exotic Animal Ophthalmology: Volume 1: Invertebrates, Fishes, Amphibians, Reptiles and Birds. Eds: Montiani-Ferreira F, Moore B A & Ben Sholma G. Springer, Switzerland.
  • Divers S J (2019) Surgery: Principles and Techniques. In: BSAVA Manual of Reptiles. 3rd edn. Eds: Girling S J & Raiti P. BSAVA, UK.
  • Lawton M P C (2019) Eye. In: Mader's Reptile and Amphibian Medicine and Surgery - E-Book. 3rd edn. Eds: Divers S J & Stahl S. Saunders, USA.
  • Lawton M P C (2019) Ophthalmology. In: Mader's Reptile and Amphibian Medicine and Surgery - E-Book. 3rd edn. Eds: Divers S J & Stahl S. Saunders, USA.