Nictitating Membrane Gland Prolapse (PNMG) in Veterinary Ophthalmology
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Questions and Answers

What is the current understanding of the mode of inheritance of nictitating membrane gland prolapse?

The mode of inheritance appears to be complex and potentially multigenic.

What is the proposed etiological mechanism of nictitating membrane gland prolapse related to connective tissue?

A weakness or laxity in the connective tissue anchoring the NMG to the periorbital tissues.

Why is it important to replace rather than excise the prolapsed nictitating membrane gland?

Because the gland contributes to tear production, especially in breeds predisposed to keratoconjunctivitis sicca.

What is the significance of the nictitating membrane in terms of physical protection and immune function?

<p>The nictitating membrane provides physical protection of the cornea and is an important contributor to the secretory immune system.</p> Signup and view all the answers

What were the findings of Saito's study on the effects of third eyelid removal on lacrimation?

<p>A decrease in lacrimation of 26% within 3-7 months, but values recovered to near normal after 1 year.</p> Signup and view all the answers

What were the effects of third eyelid removal on the corneal epithelium, according to Saito's study?

<p>A decrease in tear breakup time, positive vital staining, and morphologic changes of the corneal epithelium, indicating a lack of barrier function.</p> Signup and view all the answers

What was the treatment used to successfully treat the conjunctivitis observed in the dog’s left eye within the first two weeks following nictitating gland surgery?

<p>A combination of framycetin and dexamethasone phosphate ointment (FradexamTM) three times daily for 2 weeks.</p> Signup and view all the answers

What was the reason for aspiration of the fluid-filled mass on the left nictitating membrane?

<p>To alleviate the fluid-filled mass.</p> Signup and view all the answers

What were the Schirmer tear test 1 readings in the right and left eyes, respectively?

<p>19 mm/min OD and 16 mm/min OS.</p> Signup and view all the answers

What type of suture material was used in cases 1 and 2?

<p>6–0 coated braided lactomer 9-1 (PolysorbTM)</p> Signup and view all the answers

What was the purpose of collecting fluid and submitting a piece of the wall of the mass in case 3?

<p>For bacteriological examination and histological examination respectively</p> Signup and view all the answers

What was observed upon eversion of the nictitating membrane?

<p>A soft nonpainful mass, 20 mm in diameter, extended from the base of the NM to its leading edge.</p> Signup and view all the answers

What was the result of the fluorescein staining test?

<p>Negative.</p> Signup and view all the answers

What was the dosage of amoxicillin and clavulanic acid administered postoperatively in cases 1 and 2?

<p>10 mg/kg of body weight amoxicillin and 2.5 mg/kg of body weight clavulanic acid</p> Signup and view all the answers

What was the finding in the superonasal quadrant of the left eye based on slitlamp biomicroscopy?

<p>Mild keratitis with slight corneal neovascularization and edema.</p> Signup and view all the answers

What was the additional topical treatment used in case 2, besides tobramycin drops?

<p>Indomethacin drops and artificial tear substitutes</p> Signup and view all the answers

Why was an Elizabethan collar used in each dog after surgery?

<p>To prevent the dog from interfering with the surgical site</p> Signup and view all the answers

What was the duration of postoperative medical treatment in cases 1 and 2?

<p>10 days</p> Signup and view all the answers

What was the composition of the external layer of the cyst wall?

<p>The external layer of the cyst wall was composed of stratified squamous epithelium, with rare PAS-positive goblet cells.</p> Signup and view all the answers

What was present under the mucosa in the collagenic connective tissue?

<p>Some lacrimal acinar structures were present under the mucosa in the collagenic connective tissue.</p> Signup and view all the answers

What was the composition of the internal side of the cyst wall?

<p>The internal side of the cyst wall was composed of a discrete lining of flattened cells.</p> Signup and view all the answers

What was the result of immunostaining for cytokeratin in the conjunctival and internal cyst linings as well as the lacrimal lobules?

<p>The conjunctival and internal cyst linings as well as the lacrimal lobules were positive for cytokeratin labeling.</p> Signup and view all the answers

What was the result of immunostaining for vimentin and α-smooth muscle actin?

<p>Immunostaining of both superficial and deep layers was negative for vimentin and α-smooth muscle actin.</p> Signup and view all the answers

What conclusion can be drawn from the microscopic findings?

<p>The microscopic findings support a conjunctival external border of the sample and an internal epithelial lining of the cyst lumen, probably of lacrimal origin.</p> Signup and view all the answers

What is the main concern in differentiating between conjunctival cysts and lacrimal gland cysts?

<p>The lining may become attenuated and the myoepithelial cells may disappear, making differentiation difficult.</p> Signup and view all the answers

What characteristic of conjunctival cysts distinguishes them from lacrimal gland cysts?

<p>Stratified squamous epithelium with possible goblet cells and a mucinous content.</p> Signup and view all the answers

What is the primary difference between dacryocoele and lacrimal gland cysts?

<p>Dacryocoele lacks an epithelium lining, whereas lacrimal gland cysts have an epithelium lining.</p> Signup and view all the answers

What is the significance of the nictitating membrane gland in maintaining normal tear production?

<p>It is important in maintaining normal tear production, and may be the main source of tears in some dogs.</p> Signup and view all the answers

What is the potential consequence of excising the lacrimal gland, as observed in the study?

<p>Keratoconjunctivitis sicca may develop in a significant percentage of dogs.</p> Signup and view all the answers

What is the possible explanation for the decreased STT readings in the affected eyes of the first two cases?

<p>The imprisonment of tears.</p> Signup and view all the answers

Study Notes

Nictitating Membrane Gland Prolapse (PNMG)

  • PNMG is a condition with a complex and potentially multigenic mode of inheritance, but the exact pathogenesis remains unclear.
  • Several etiological mechanisms have been proposed, including weakness or laxity in the connective tissue anchoring the NMG to the periorbital tissues and lymphoid hyperplasia.

Surgical Treatment of PNMG

  • Definitive treatment of PNMG is surgical, and prolapsed glands should be replaced rather than excised to preserve the gland's contribution to tear production.
  • This is especially important in breeds prone to keratoconjunctivitis sicca.

Importance of the Nictitating Membrane

  • The nictitating membrane provides physical protection of the cornea and is an important contributor to the secretory immune system.
  • Removing the third eyelid can decrease lacrimation by 26% within 3-7 months, but values may recover to near normal after 1 year.

Case Study: Conjunctival Cyst Formation

  • A dog developed a fluid-filled mass on the left nictitating membrane after PNMG surgery, which was aspirated monthly for 3 months with adjunctive anti-inflammatory treatment.
  • Marsupialization was created by suturing the wall of the cyst to the adjacent NM conjunctiva, and the dog was discharged on the same day.

Histological Examination

  • Tissue sections showed a thick collagenic connective tissue lined externally and internally by epithelial linings, with a dense infiltration by neutrophils, lymphocytes, and plasma cells.
  • The internal side of the cyst wall was composed of a discrete lining of flattened cells, and the lining was positive for cytokeratin labeling.

Conjunctival Cysts vs. Lacrimal Cysts

  • Conjunctival cysts are characterized by stratified squamous epithelium with possible goblet cells and a mucinous content.
  • Lacrimal cysts can be differentiated by the presence of an epithelium lining and ductular retention.

Importance of the NMG in Tear Production

  • The NMG is important in maintaining normal tear production, and its removal can lead to keratoconjunctivitis sicca.
  • The principal lacrimal gland may be the main source of tears in some dogs, while the NMG is the primary source in others.

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Related Documents

Marsupialization of a Nictitating Membrane Cyst in Dogs (Veterinary Ophthalmology PDF)

Description

This quiz covers the complex inheritance and pathogenesis of Nictitating Membrane Gland Prolapse, a condition affecting animals, and its surgical treatment. Learn about the proposed etiological mechanisms and more.

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