Page 28 - VETcpd - Vol 6 - Issue 2

Peer ReviewedVETcpd - Ophthalmology

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Eyelid surgery in dogsEyelid disease is a relatively common occurrence in general practice. The location and structure of the eyelids means that they can be the victim of a vast array of disease entities, the clinical management of which includes surgery in many cases. An understanding of the function of the eyelids is important before considering surgery. This article reviews the surgical management of canine lid masses and conformational abnormalities, predominantly entropion.

Key words: Eyelid surgery, blepharoplasty, Hotz-Celsus, wedge resection

IntroductionThe eyelids in most of our domestic species consist of a superior (upper), inferior (lower) and nictitating membrane (third eyelid). Although reasonably simple in their anatomy, the eyelids perform a range of vital functions. These include protecting the eye from physical injury and maintaining ocular surface health, and therefore vision. The eyelids are subject to a vast range of possible disease entities. There are a variety of diseases specific to the eyelids but, owing to their location at a mucocutaneous junction, they can also be affected as part of a wider dermatologic or systemic disease process. Eyelid diseases can be divided into the traditional categories of congenital and developmental, traumatic, inflammatory and neoplastic but regardless of aetiology, clinical management is almost always surgical. This article will therefore focus on the surgical management of some common canine eyelid problems; eyelid masses and simple conformational defects. For information surrounding surgery of the third eyelid, readers are directed to an earlier article by Rose Linn-Pearl (VetCPD Journal, Vol 5, Issue 2, 2018).

Anatomy and functionIt is important to consider the anatomy and function of the eyelids before contemplating any surgery. The eyelids perform numerous roles including:• Protection of the eye from

physical injury• Entrapment of foreign material before

it contacts the globe• Limiting evaporative loss of tears• Production of glandular secretions.

In addition, the blink reflex aids distribu-tion of the preocular tear film and directs drainage of tears toward the nasolacrimal canaliculi to remove toxic waste. Blinking may be elicited in response to tactile or

noxious stimuli applied to the eyelids, conjunctival or corneal surfaces. This reflex is subcortical, mediated by the trigeminal nerve (afferent arm) and facial nerve (efferent arm).

From superficial to deep, the eyelids consist of three layers with a number of adnexal specialisations, which vary slightly between species (Figure 1A). Haired skin forms the outermost surface, which is thinner and more pliable than skin in other loca-tions. Cilia line the outermost edge of the upper eyelid margin and serve a protective role. Below this are the skeletal muscles responsible for blinking, which extend to a fibrous tarsal plate responsible for provid-ing structural rigidity and containing the Meibomian glands. The Meibomian glands open at the eyelid margin and their secre-tion (meibum) forms the superficial lipid layer of the pre-ocular tear film. When viewed collectively at the eyelid margin, the orifices form the surgical landmark known as the ‘gray line’ (Figure 1B). Lining the inner surface of the eyelids is the palpebral conjunctiva, which reflects at the conjunctival fornix to become the bulbar conjunctiva overlying the globe.

The eyelids can be divided clinically into four regions: the dorsal and ventral eyelid margins, the medial canthus and the lateral canthus, collectively forming what is known as the palpebral fissure. In most of our veterinary patients the dorsal eyelid is the largest and most mobile. The palpebral fissure is oval as a result of distinct liga-mentous attachments and opposing muscle groups (Figure 2), which ensure normal eyelid opening and closing i.e. blinking.

The medial canthal ligament forms a rela-tively tight attachment between the medial canthus and the underlying subcutaneous tissues and periosteum. The lateral canthus is more mobile, particularly in dogs, where the ligament is poorly developed and

Katherine E L Manchip BSc(Hons) BVSc PGDipVCP MRCVSECVO Resident in Veterinary Ophthalmology at South Devon ReferralsKat graduated from the University of Bristol in 2012, having also completed an intercalated degree in Veterinary Conservation Medicine. She worked in general small animal practice in London for four years before completing a small animal rotating internship at the Royal Veterinary College (RVC). She is currently in the second year of an ECVO Ophthalmology Residency at South Devon Referrals.

South Devon Referrals South Devon Veterinary Hospital The Old Cider Works, Abbotskerswell, Devon TQ12 5GH

Tel: 01626 367972

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VETcpd - Ophthalmology

mostly replaced by the retractor anguli oculi lateralis muscle. This relative laxity is why conformational defects often affect the lower lid and lateral canthal area. Figure 2 summarises the function, innerva-tion and blood supply of the muscles of the eyelids.

Eyelid examinationWhen examining the eyelids a systematic approach is most helpful.

• The first step, and perhaps the most important, is to assess the eyelids at a distance i.e. in the waiting room, to get an idea of their true resting posi-tion. Eyelid conformation is the result of a number of factors, including the anatomical relationship between the eyelid, orbit and globe; size of the orbit; eyelid length; stability of the lateral canthus; and facial musculature. Many dogs will develop blepharospasm (involuntary tight closure of the eyelids) distorting eyelid conformation when handled around the face, especially those with painful chronic ocular conditions, as they will anticipate discomfort.

• The presence and nature of any ocular discharge should be noted, as well as its location. For example, mucus adhered to cilia/hairs contacting the cornea is an indicator that those hairs are causing corneal irritation. Abnormalities of the cilia are summarised in Figure 3.

• Blinking should be assessed. Is there complete closure of the eyelids, or lagophthalmos (inability to close the eyelids properly)?

• A ‘hands on’ examination should be performed both with the naked eye and with a light source (+/- magnification) to assess the periocular skin. Particular attention should be paid to the relation-ship of the upper and lower eyelid margins to the globe. This should also be assessed with the head in various positions. Both eyelid margins should be everted and examined closely to assess the Meibomian glands, palpebral conjunctiva, and the nasolacrimal puncta. The nasolacrimal puncta should be checked for number (there should be four in total) and size.

• Assessing eyelid conformation – this will be covered in more detail later in the article but it is important that it is assessed both before and after, applica-tion of a topical anaesthetic.

• An ocular examination should then be performed, including fluorescein

Figure 1: A. The layers of the eyelid B. The eyelid margin

A

B

Septum orbitale

Orbicularis oculi muscle

Haired skin

Gland of Zeis

Cilium

Gland of Moll

Meibomian gland

Tarsal plate

Palpebral conjunctiva

Fornix

Müller's muscle

Levator palpebrae superioris muscle

Palpebral conjunctiva

Figure 2: Action, innervation and blood supply of the eyelids

Levator anguli ocularis medialismuscle*

Angularis oculi vein

Medial canthal tendon

Orbicularis oculi muscle* Malar artery Malaris muscle

(dorsal buccal branch of the facial nerve

Levator palpebrae superious muscle (occulomotor nerve) and Müller's muscle (sympathetic)

Frontalis muscle.*

Superficial temporal artery

Retractor anguli oculi lateralis muscle*

Dorsal and ventral palpebral artery

BB

B

C

A

A

*Innervated by the palpebral branch of the facial nerve

The 'gray line' formed by the meibomian orifices

The meibomian glands can be visualised through the Palpebral conjunctiva, perpendicular to the lid margin

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staining. Any corneal disease, such as ulceration, should prompt further exam-ination of the overlying region of eyelid in case a foreign body or ectopic cilium has been overlooked.

Surgical principles and preparationThe aim of eyelid surgery should be to preserve or restore the normal anatomical relationship between the eyelid margins and the tear film, thereby preserving eyelid function. The highly vascular nature of the eyelids promotes rapid healing but it also means that tissue should be handled gently and sparingly to avoid excessive inflammation.

Conjunctiva heals particularly swiftly so this layer can be left to heal by second-ary intention, rather than risking suture material traumatising the corneal surface. Preserving the integrity of the eyelid margin is crucial, and the ‘gray line’ of the Meibomian gland orifices is an important surgical landmark. The figure-of-eight suture pattern is required when surgery involves a full thickness incision of the eyelid margin and magnification is usually required.

Surgical preparation of the eyelids should be gentle. Eyelid hair should be carefully removed using small, specific clippers. The thin skin is easily traumatised, which may lead to increased swelling, irritation and self-trauma post-surgery. A bland ointment can be applied to the ocular surface to collect debris and hair during preparation and should be removed before flushing the region with a 1:50 dilution of povidone iodine aqueous solution. A minimum of three minutes contact time is required and aims to prevent damage to the corneal and conjunctival epithelium. Finally, the region should be flushed with 0.9% sterile saline.

Eyelid massesEyelid tumours are a relatively common finding in dogs. A survey conducted by Krehbiel and Langham (1975) classified 202 canine eyelid neoplasms by tumour type and biologic behaviour. Sebaceous gland tumours, papillomas and melanomas were reported to comprise 82.1% of the neoplasms examined with sebaceous gland tumours being the most common (44%). Benign tumours (75.3%) were more frequently encountered than malignant forms (26.7%) and were generally smaller. Metastasis was not observed. The average age of dogs at presentation was eight years and tumours were slightly more

commonly found on the upper eyelid than the lower.

Tumours of the Meibomian glands appear clinically as black, grey, brown or pink masses extending from the gland orifice. They frequently have an irregular or ‘cobblestone’ surface, and occasionally may extend through the palpebral conjunctiva. They are easily ulcerated if traumatised. Obstruction of the orifice can result in glandular rupture and leakage of lipid secretions into the adjacent tissue. This can cause a marked inflammatory response (peritumoural lipogranulomatous inflam-mation) giving the tumour a falsely large appearance (Labelle & Labelle 2013).

Surgical excision is the mainstay of therapy for localised eyelid tumours, sometimes in combination with cryotherapy, and is typi-cally curative. It is important to examine the underside of the eyelid thoroughly as what is visible at the eyelid margin is often just the tip of the iceberg (Figure 4). The appropriate surgical technique is dictated by the size and location of the mass. The aim is to achieve complete resection whilst maintaining anatomic accuracy and this is particularly important for the upper eyelid which moves over a greater area of the cornea. Wherever possible tissue should be submitted for histopathological evaluation. For smaller tumours (up to one third or less of eyelid length) a full

thickness wedge resection with a two-layer closure including a figure-of-eight suture pattern at the eyelid margin can be performed (Figure 5i). A four sided or ‘house-shaped’ resection achieves wider surgical margins for the equivalent length of eyelid margin removed (Figure 5ii). For larger masses requiring removal of greater than one-third of the eyelid margin, exci-sion will need to be combined with a lid lengthening procedure such as a sliding lateral canthoplasty (Figure 6) (Moore & Constantinescu 1997). Referral to a specialist should be considered in these cases, especially in breeds with a tight lid conformation (e.g. Chihuahuas, Yorkshire Terriers and Pugs).

Other eyelid masses that might be encountered, and possibly mistaken for a neoplasm, include a chalazion (an inspis-sated Meibomian gland) and hordeolum (a localised infection or ‘stye’). Chelazia are frequently incidental findings, but if causing corneal irritation or local inflammation, can be lanced and curetted under sedation or general anaesthesia. A hordeolum, which is painful, may require lancing but this should not be carried out until the abscess is pointing. This can be encouraged by using warm compresses. Lancing too early runs the risk of infection spreading to adjacent tissues so topical and systemic antibiotics should be administered concurrently.

Figure 3: Cilia and hair abnormalities of the eyelidA. Cross section of a normal upper eyelid. The normal cilia are positioned externally

to the Meibomian gland orificeB. Distichiasis – The cilium arises from within the Meibomian gland and exits the orifice.

This can then contact the cornea. Note the adherent mucus, a typical sign of corneal irritationC. Ectopic cilium – Arises from within the Meibomian gland and emerges through the palpebral

conjunctiva to contact the cornea, often perpendicularlyD. Trichiasis – Normal cilia or periorbital hair contacts the cornea as a results

of abnormal facial conformation e.g. facial folds or entropion

A

B

C

D