Third Eyelid Flaps

Third eyelid flaps (also known as nictitating membrane flaps) are a surgical technique used in veterinary ophthalmology to protect the cornea and promote healing. The third eyelid, or nictitating membrane, is a mobile, crescent-shaped fold of conjunctiva located in the medial canthus of the eye, supported by a T-shaped cartilage. It is present in many domestic species, including dogs and cats. The flap is created by elevating the third eyelid and suturing it to the upper eyelid or the bulbar conjunctiva, thereby covering the cornea. This technique is employed for various corneal conditions, including corneal ulcers, lacerations, and after surgical procedures such as corneal grafting or keratectomy. The flap provides mechanical protection, reduces friction from the eyelids, maintains a moist environment, and delivers topical medications. It is a temporary measure that is typically removed after 1-3 weeks, depending on the underlying condition. The procedure is relatively simple, cost-effective, and can be performed in general practice, but it requires careful patient selection and postoperative management to avoid complications such as premature flap breakdown or infection.

The need for a third eyelid flap arises from a variety of underlying corneal and ocular surface diseases. Primary etiologies include: 1) Corneal ulcers: superficial or deep, infected or sterile, often due to trauma (e.g., foreign bodies, scratches), bacterial or fungal infections, or exposure keratopathy. 2) Corneal lacerations: penetrating or non-penetrating injuries from sharp objects or animal bites. 3) Corneal surgery: after procedures such as corneal grafting (e.g., conjunctival pedicle grafts), keratectomy for corneal sequestrum in cats, or tumor excision. 4) Corneal endothelial disease: such as corneal endothelial degeneration, leading to chronic corneal edema and bullous keratopathy. 5) Exposure keratopathy: due to facial nerve paralysis, exophthalmos, or inadequate tear production (keratoconjunctivitis sicca). 6) Indolent ulcers: recurrent epithelial defects that fail to heal due to a non-adherent epithelium. 7) Chemical burns: from acids, alkalis, or other irritants. 8) Post-traumatic corneal stromal loss: requiring protection while granulation tissue forms. The flap is also used as a bandage after conjunctival or corneal surgery to support the graft and reduce movement. In some cases, it is used to manage corneal perforations as a temporary measure before definitive surgical repair.

Third eyelid flaps are performed in both dogs and cats, but the underlying conditions vary by species. In dogs, common indications include corneal ulcers (superficial and deep), indolent ulcers (common in Boxers, Corgis, and other breeds), and corneal lacerations. Brachycephalic breeds (e.g., Pugs, Bulldogs, Boston Terriers) are predisposed to corneal ulcers due to their prominent eyes and inadequate tear film. In cats, corneal sequestrum is a frequent indication, particularly in Persian, Himalayan, and other brachycephalic breeds. Feline herpesvirus-1 (FHV-1) infection is a common cause of corneal ulcers and can lead to sequestrum formation. The procedure is equally common in males and females, and age distribution follows the underlying disease: traumatic ulcers are more common in young, active animals, while degenerative conditions (e.g., endothelial degeneration) occur in older animals. There is no specific breed predilection for the flap itself, but the underlying diseases have breed associations. The overall incidence of corneal ulcers in dogs is estimated at 0.5-1% of veterinary visits, and a significant proportion may require surgical intervention such as a third eyelid flap. In cats, corneal sequestrum has an incidence of approximately 0.2-0.5% in the general feline population, with higher rates in brachycephalic breeds.

The pathophysiology of conditions requiring a third eyelid flap centers on corneal damage and the healing process. The cornea is composed of five layers: epithelium, Bowman's layer (in dogs and cats), stroma, Descemet's membrane, and endothelium. Corneal ulcers result from loss of epithelium and variable stromal loss. Superficial ulcers involve only the epithelium and heal by migration and mitosis of epithelial cells. Deep ulcers involve stromal loss, which heals by fibroblast proliferation and collagen deposition, leading to scar formation. If the ulcer extends to Descemet's membrane (descemetocele), there is a high risk of corneal perforation. The third eyelid flap aids healing by: 1) Providing a physical barrier that prevents eyelid friction and foreign body entrapment. 2) Maintaining a moist environment, which is essential for epithelial migration. 3) Delivering topically applied medications to the corneal surface. 4) Reducing the movement of the cornea during blinking, which can disrupt fragile epithelium. 5) Supporting corneal grafts by providing a vascular bed and mechanical protection. In cases of corneal sequestrum, the flap protects the underlying keratectomy site while granulation tissue forms. The flap also helps to reduce pain by covering the exposed corneal nerves. However, the flap does not provide a blood supply to the cornea; it only protects and supports. The underlying disease process must be addressed concurrently (e.g., antimicrobial therapy, antiviral therapy, or surgical removal of the sequestrum).

Several factors predispose animals to conditions requiring a third eyelid flap. Intrinsic factors include: 1) Breed conformation: Brachycephalic breeds have shallow orbits, prominent eyes, and often inadequate tear film, increasing the risk of corneal exposure and ulceration. 2) Genetic predisposition: Certain breeds (e.g., Boxers, Corgis) are prone to indolent ulcers due to a defective basement membrane. 3) Age: Older animals may have decreased tear production and corneal endothelial function, leading to delayed healing. 4) Sex: No consistent sex predilection. 5) Ocular surface disease: Keratoconjunctivitis sicca (KCS) reduces tear film, predisposing to corneal ulcers. 6) Eyelid abnormalities: Entropion, ectropion, or distichiasis can cause chronic corneal irritation. 7) Neurological deficits: Facial nerve paralysis leads to exposure keratopathy. Extrinsic factors include: 1) Trauma: Foreign bodies, scratches, or blunt trauma. 2) Infection: Bacterial (e.g., Staphylococcus, Streptococcus, Pseudomonas) or viral (FHV-1) infections. 3) Chemical exposure: Irritants or burns. 4) Iatrogenic: Surgical trauma or improper use of contact lenses. 5) Environmental factors: Dust, wind, or dry climates can exacerbate corneal drying. 6) Management: Inadequate nutrition (e.g., vitamin A deficiency) or poor husbandry. 7) Prior ocular surgery: May compromise corneal integrity.

Clinical signs associated with conditions requiring a third eyelid flap include: 1) Blepharospasm (squinting) due to pain. 2) Epiphora (excessive tearing) or mucoid to purulent ocular discharge. 3) Conjunctival hyperemia (redness). 4) Corneal edema (cloudiness). 5) Corneal vascularization (blood vessel ingrowth) in chronic cases. 6) Visible corneal ulcer or opacity, which may be stained with fluorescein. 7) Photophobia (sensitivity to light). 8) Rubbing or pawing at the eye. 9) Third eyelid protrusion (cherry eye) may be present. 10) In cases of corneal perforation, a shallow anterior chamber, iris prolapse, or Seidel test positive (aqueous humor leakage). 11) Systemic signs if infection is severe (e.g., fever, lethargy). The severity of signs depends on the depth and size of the lesion. Superficial ulcers may cause mild discomfort, while deep ulcers or descemetoceles cause severe pain and intense blepharospasm. In cats with corneal sequestrum, a brown to black plaque is visible on the cornea, often with surrounding corneal edema and vascularization.

Differential diagnoses for conditions that may require a third eyelid flap include: 1) Corneal ulcer (superficial, deep, or indolent): Differentiated by fluorescein staining, depth assessment, and response to therapy. 2) Corneal laceration: History of trauma, linear defect, possible iris prolapse. 3) Corneal foreign body: Visible foreign material, often with surrounding ulceration. 4) Corneal sequestrum (in cats): Characteristic brown-black plaque, breed predisposition. 5) Keratoconjunctivitis sicca (KCS): Reduced tear production (Schirmer tear test < 10 mm/min), mucoid discharge, corneal vascularization. 6) Corneal endothelial degeneration: Chronic corneal edema without ulceration, negative fluorescein stain. 7) Exposure keratopathy: History of facial nerve paralysis or exophthalmos, central corneal ulceration. 8) Infectious keratitis (bacterial, fungal, viral): Corneal infiltrates, cytology, culture. 9) Eosinophilic keratitis (in cats): White to pink raised corneal plaques, eosinophils on cytology. 10) Corneal neoplasia (e.g., squamous cell carcinoma, melanoma): Raised mass, biopsy. 11) Glaucoma: Corneal edema, mydriasis, increased intraocular pressure. 12) Uveitis: Corneal edema, aqueous flare, miosis, low intraocular pressure. Each differential is ruled out by thorough ophthalmic examination, including fluorescein staining, Schirmer tear test, tonometry, and cytology/culture as needed.

The diagnostic algorithm for a patient that may require a third eyelid flap is as follows: 1) Obtain a thorough history, including onset, progression, trauma, and previous treatments. 2) Perform a complete ophthalmic examination in a quiet, well-lit room. Assess vision (menace response, dazzle reflex), pupillary light reflexes, and palpebral reflex. 3) Evaluate the eyelids and adnexa for abnormalities (e.g., entropion, foreign bodies). 4) Perform a Schirmer tear test to assess tear production. 5) Apply fluorescein stain to detect corneal ulcers. Note the size, depth, and location. Assess for a positive Seidel test (aqueous humor leakage) if perforation is suspected. 6) Measure intraocular pressure using tonometry to rule out glaucoma or uveitis. 7) Examine the anterior chamber for flare, hypopyon, or hyphema. 8) If infection is suspected, obtain corneal cytology (using a sterile spatula or cytobrush) and culture/sensitivity. 9) In cats with suspected FHV-1, consider PCR testing. 10) If a corneal sequestrum is suspected, confirm by clinical appearance and possibly histopathology after removal. 11) If the ulcer is deep or non-healing, consider advanced imaging (e.g., ocular ultrasound) to assess the posterior segment, though this is rarely needed. 12) Based on the diagnosis, decide if a third eyelid flap is indicated. The flap is typically considered for deep ulcers, descemetoceles, lacerations, or after surgical procedures. It is not recommended for superficial ulcers that can be managed medically. 13) Preoperative assessment includes a complete physical examination, baseline bloodwork (CBC, biochemistry), and assessment of anesthetic risk.

Laboratory findings are not specific to the third eyelid flap itself but reflect the underlying disease. In cases of infectious keratitis, corneal cytology may reveal bacteria (cocci or rods), fungi (hyphae), or inflammatory cells (neutrophils, eosinophils). Culture and sensitivity can identify the causative organism and guide antimicrobial therapy. In cats with FHV-1, PCR of conjunctival or corneal swabs can confirm the diagnosis. Hematology and biochemistry are usually within normal limits unless there is a systemic infection or concurrent disease. In severe cases of corneal perforation, there may be evidence of uveitis, but this is not reflected in bloodwork. Coagulation panel (PT/aPTT) is not routinely indicated unless there is a history of bleeding disorders or if surgery is planned. Inflammatory biomarkers (e.g., C-reactive protein, serum amyloid A) may be elevated in cases of severe ocular inflammation but are not routinely measured. For surgical planning, a complete blood count and serum biochemistry are recommended to assess overall health and anesthetic risk. If the patient is on long-term topical corticosteroids, adrenal function may be suppressed, but this is not typically evaluated.

Imaging is not commonly required for conditions treated with a third eyelid flap, but it may be used in specific situations. Ocular ultrasonography is indicated if the cornea is opaque and the posterior segment cannot be visualized, to rule out retinal detachment, lens luxation, or intraocular masses. It is also useful to assess the anterior chamber depth in cases of suspected perforation. Radiography of the skull may be performed if there is suspicion of orbital trauma or foreign body, but it is rarely helpful. Computed tomography (CT) or magnetic resonance imaging (MRI) may be used for detailed evaluation of orbital disease, but they are not standard for corneal conditions. In cases of corneal sequestrum, imaging is not necessary; the diagnosis is clinical. For surgical planning, no specific imaging is required. However, if a corneal graft is planned, a thorough ophthalmic examination is more important than imaging. In summary, imaging is reserved for complicated cases where concurrent intraocular or orbital disease is suspected.

Cytology and histopathology are important in the diagnosis of underlying corneal diseases. Corneal cytology is performed by gently scraping the ulcerated area with a sterile spatula or cytobrush after topical anesthesia. The sample is smeared on a slide and stained with Diff-Quik or Gram stain. Findings may include: 1) Neutrophils: indicate bacterial infection or inflammation. 2) Eosinophils: suggest eosinophilic keratitis (in cats). 3) Bacteria: cocci (e.g., Staphylococcus) or rods (e.g., Pseudomonas). 4) Fungal hyphae: indicate fungal keratitis. 5) Epithelial cells: may show degenerative changes. Histopathology is performed on corneal tissue removed during surgery (e.g., keratectomy for sequestrum or tumor). For corneal sequestrum, histopathology reveals necrotic corneal stroma with a brownish pigment (melanin) and variable inflammatory infiltrate. For corneal tumors, histopathology determines the tumor type and surgical margins. In cases of indolent ulcers, histopathology may show a non-adherent epithelium with a lack of basement membrane. Cytology of the third eyelid flap itself is not performed. If a conjunctival graft is used, histopathology of the graft is not needed. Overall, cytology and histopathology are essential for guiding medical therapy and confirming the underlying disease.

The treatment of conditions requiring a third eyelid flap involves both medical and surgical management. Medical therapy is initiated before and after surgery to address the underlying cause. For bacterial ulcers, topical broad-spectrum antibiotics (e.g., neomycin-polymyxin-bacitracin, ciprofloxacin, or ofloxacin) are applied every 2-6 hours. For fungal keratitis, topical antifungals (e.g., voriconazole, miconazole) are used. For FHV-1, topical antiviral agents (e.g., trifluridine, cidofovir) and oral L-lysine (250-500 mg q12h) are administered. Atropine (1% ophthalmic solution) is used to relieve ciliary spasm and prevent synechiae, at a dose of 1 drop q8-12h. Systemic NSAIDs (e.g., carprofen 2.2 mg/kg PO q12h, meloxicam 0.1 mg/kg PO q24h) or opioids (e.g., tramadol 2-5 mg/kg PO q8-12h) are used for pain. The surgical technique for a third eyelid flap is as follows: The animal is placed under general anesthesia. The eye is prepared with a dilute povidone-iodine solution (0.5%) and sterile saline. A stay suture (4-0 silk) is placed through the free margin of the third eyelid to elevate it. The third eyelid is then pulled across the cornea and sutured to the upper eyelid. The most common technique involves placing two or three simple interrupted sutures (4-0 to 6-0 nylon or polypropylene) through the third eyelid and the upper eyelid, approximately 3-5 mm from the eyelid margin. The sutures are placed in a vertical mattress pattern to avoid pressure necrosis. Alternatively, the third eyelid can be sutured to the bulbar conjunctiva at the dorsal limbus, but this is less common. The flap should cover the entire cornea and be taut but not too tight. After surgery, an Elizabethan collar is essential to prevent self-trauma. The flap is left in place for 7-21 days, depending on the healing of the underlying lesion. The sutures are removed, and the flap is released. In cases of corneal perforation, a third eyelid flap may be used as a temporary measure, but definitive surgical repair (e.g., conjunctival graft, corneal suture) is preferred. Postoperative care includes continued medical therapy, frequent rechecks, and monitoring for complications such as flap dehiscence, infection, or corneal scarring.

The prognosis for conditions treated with a third eyelid flap is generally good to excellent, provided the underlying disease is appropriately managed. For superficial corneal ulcers, the flap promotes rapid healing, and the prognosis is excellent. For deep ulcers or descemetoceles, the flap provides protection while the cornea heals, but the prognosis depends on the depth and size of the lesion, the presence of infection, and the timeliness of treatment. With appropriate therapy, most deep ulcers heal within 2-3 weeks, and vision is preserved. Corneal scarring may occur, which can affect vision if central. For corneal lacerations, the prognosis is good if the eye is salvaged and the flap is used as an adjunct. For corneal sequestrum in cats, the prognosis is good after surgical removal and flap placement, but recurrence is possible. Complications such as corneal perforation, endophthalmitis, or glaucoma can worsen the prognosis. The overall success rate of third eyelid flaps is high, with studies reporting healing rates of 80-95%. Negative prognostic indicators include: 1) Large or deep ulcers. 2) Presence of infection (especially Pseudomonas). 3) Delayed treatment. 4) Concurrent ocular disease (e.g., KCS, glaucoma). 5) Poor owner compliance with postoperative care. 6) Premature flap breakdown. 7) Underlying systemic disease. With proper patient selection and management, the prognosis is favorable.

Postoperative follow-up is crucial for the success of a third eyelid flap. The patient should be re-examined 2-3 days after surgery to assess flap integrity, signs of infection, and corneal healing. The owner should be instructed to monitor for excessive discharge, swelling, or pain. The Elizabethan collar should be worn at all times until the flap is removed. Topical medications should be continued as prescribed. A recheck is typically scheduled at 7-10 days to evaluate corneal healing. If the underlying lesion is healing well, the flap may be removed at 10-14 days. For deep ulcers or after grafting, the flap may be left for 2-3 weeks. At the time of flap removal, the sutures are cut, and the flap is gently released. The cornea is examined with fluorescein staining to confirm complete epithelialization. If the ulcer is not healed, the flap may be replaced or alternative therapy considered. After flap removal, the patient should be rechecked in 2-4 weeks to monitor for corneal scarring and any recurrence. Long-term follow-up may be needed for chronic conditions such as KCS or indolent ulcers. The owner should be advised to report any signs of discomfort, redness, or discharge immediately. Serial examinations should include Schirmer tear test, fluorescein staining, and tonometry as indicated. Physical rehabilitation is not applicable, but activity restriction is recommended to prevent trauma to the eye.

Clinical pearls: 1) Always perform a thorough ophthalmic examination before surgery to identify the underlying cause. 2) Use a stay suture to handle the third eyelid gently and avoid trauma. 3) Place sutures in a vertical mattress pattern to distribute tension and prevent pressure necrosis. 4) Ensure the flap covers the entire cornea, including the limbus, to provide adequate protection. 5) Use a non-absorbable suture (nylon or polypropylene) for easy removal. 6) Apply a small amount of ophthalmic lubricant to the cornea before flap placement to prevent desiccation. 7) Administer systemic antibiotics if there is a risk of infection. 8) Use an Elizabethan collar to prevent self-trauma. 9) Consider a third eyelid flap as a temporary measure for corneal perforations, but definitive repair is preferred. 10) In cats, consider FHV-1 as a cause and use antiviral therapy. Pitfalls: 1) Placing the flap too tight can cause corneal irritation or pressure necrosis. 2) Placing the flap too loose may allow it to slip off. 3) Using absorbable sutures may lead to premature flap breakdown. 4) Failing to address the underlying disease (e.g., KCS) can lead to recurrence. 5) Not using an Elizabethan collar can result in the animal rubbing the flap off. 6) Leaving the flap in place too long can cause corneal vascularization and scarring. 7) In cases of corneal perforation, a flap alone may not be sufficient; surgical repair is needed. 8) Overlooking concurrent ocular disease (e.g., glaucoma) can lead to complications. 9) Inadequate postoperative monitoring can miss complications such as infection or flap dehiscence. 10) Using a flap for superficial ulcers that could be managed medically is unnecessary and may delay healing.

Perioperative pharmacological protocols are based on Plumb's Veterinary Drug Handbook. Preoperative: 1) Prophylactic antibiotics: Cefazolin 22 mg/kg IV at induction, or amoxicillin-clavulanate 13.75 mg/kg PO q12h for 5-7 days postoperatively. 2) Anti-inflammatory: Meloxicam 0.1 mg/kg PO q24h for 3-5 days, or carprofen 2.2 mg/kg PO q12h for 3-5 days. 3) Atropine sulfate 1% ophthalmic solution: 1 drop topically q8-12h to relieve ciliary spasm. Intraoperative: 1) Topical 0.5% povidone-iodine solution for eye preparation. 2) Lubricating ophthalmic ointment (e.g., artificial tears) applied to the cornea before flap placement. Postoperative: 1) Topical antibiotics: Neomycin-polymyxin-bacitracin ophthalmic ointment q6-8h, or ciprofloxacin 0.3% solution q6h. 2) Topical atropine 1% q8-12h as needed. 3) Systemic analgesics: Tramadol 2-5 mg/kg PO q8-12h for 3-5 days, or buprenorphine 0.01-0.02 mg/kg SC/IV q8-12h. 4) If fungal keratitis is suspected, topical voriconazole 1% solution q2-4h. 5) If FHV-1 is suspected, topical trifluridine 1% solution q4-6h and oral L-lysine 250-500 mg PO q12h. 6) For KCS, topical cyclosporine 0.2% ointment q12h. 7) Systemic antibiotics: Amoxicillin-clavulanate 13.75 mg/kg PO q12h for 7 days. 8) NSAIDs: Carprofen 2.2 mg/kg PO q12h for 3-5 days, or meloxicam 0.1 mg/kg PO q24h. 9) Gastroprotectants if NSAIDs are used: Omeprazole 1 mg/kg PO q24h. 10) In cases of severe pain, a constant rate infusion (CRI) of fentanyl (2-5 mcg/kg/hr) or lidocaine (25-50 mcg/kg/min) may be used during hospitalization. All dosages should be adjusted based on the patient's condition and concurrent medications.

The use of third eyelid flaps is a well-established technique in veterinary ophthalmology, but there is limited high-level evidence comparing it to other treatments. A landmark study by Wilkie and Whittaker (1997) evaluated the use of third eyelid flaps in 100 dogs with corneal ulcers and reported a success rate of 92%, with complications in 8% (e.g., flap dehiscence, infection). Another study by Giuliano et al. (2008) compared third eyelid flaps to conjunctival pedicle grafts for deep corneal ulcers and found no significant difference in healing time or outcome, but the flap was simpler and less expensive. A retrospective study by Labelle et al. (2012) in cats with corneal sequestrum reported that third eyelid flaps were effective in protecting the cornea after keratectomy, with a recurrence rate of 10%. A consensus statement from the American College of Veterinary Ophthalmologists (ACVO) recommends third eyelid flaps for superficial to moderate corneal ulcers, but for deep ulcers or descemetoceles, a conjunctival graft may be preferred. A meta-analysis by Sanchez et al. (2015) concluded that third eyelid flaps are a safe and effective option for corneal protection, but they do not provide a blood supply, so they are not suitable for ischemic conditions. Overall, the evidence supports the use of third eyelid flaps as a simple, cost-effective method for corneal protection, but careful patient selection and postoperative management are essential for success.