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Buphthalmos

BASICS

DEFINITION/OVERVIEW

Buphthalmos is an enlarged globe that is positioned normally in the socket.

ETIOLOGY/PATHOPHYSIOLOGY

An increase in IOP causing enlargement and distention of the globe secondary to chronic glaucoma.

SIGNALMENT/HISTORY

 There is no standard signalment for this disease.

 Common findings in the history may include tearing and squinting noted by the owners, as well as an asymmetry of the globes and loss of vision on the affected side(s).

CLINICAL PRESENTATION

 While buphthalmos can be bilateral, most cases in chelonians are unilateral.

 The corneal diameter of the affected eye is increased due to globe stretching.

 There may be blepharospasm and epiphora.

 Unlike exophthalmia, the conjunctiva and position of the nictitans is usually normal.

 There may be red ciliary flush (red ring around the cornea) and congested episcleral vessels.

 There may be lens luxation and/or cataracts in the affected eye(s).

 Retropulsion of the globe is normal but the globe itself may feel firmer than normal.

RISK FACTORS

Husbandry

 Diet and environmental factors are likely to have an effect on the development of cataracts.

 Cataract development in brumating tortoises has been associated with damage from freezing temperatures.

Others

 Trauma, especially if there is corneal penetration, can induce uveitis and cataract formation.

 The presence of a cataract may increase the chance of lens luxation and/or lens induced uveitis, both of which can lead to glaucoma.

DIAGNOSIS

DIFFERENTIAL DIAGNOSIS

 It is important to first differentiate between exophthalmia and buphthalmos.

 Glaucoma in chelonians is usually secondary to outflow obstruction of the aqueous humor, which is most often caused by uveitis, lens luxation, or intraocular neoplasia.

DIAGNOSTICS

 Physical examination findings should raise suspicion of buphthalmos, which is confirmed by finding elevated IOP.

 Normal IOP in three tortoise species has been reported to be 15.74 ± 0.2 mm Hg (Testudo hermanni), 14.2 ± 1.2 mm Hg (Geochelone denticulata), and 15.3 ± 8.81 mm Hg (Geochelone carbonaria) and in six turtle species at 5.42 ± 0.96 mm Hg (Emys orbicularis), 6.7 ± 1.4 mm Hg (Terrapene sp.), 8.3 ± 1.5 mm Hg (Terrapene sp.), 5.42 ± 1.7 mm Hg (Trachemys scripta elegans), 10.02 ± 0.66 mm Hg (Trachemys scripta elegans), 6.5 ± 1.0 mm Hg (Lepidochelys kempii), 3.8 ± 1.1 mm Hg (Lepidochelys kempii), and 4–9 mm Hg (Caretta caretta).

 Since most cases are unilateral, a significant difference in IOP between the eyes may be most indicative of a problem.

 Ocular examination and ultrasound are helpful in further evaluating the root cause, although the scleral ossicles can limit visualization.

PATHOLOGICAL FINDINGS

Chronically elevated IOP will lead to pain and blindness.

TREATMENT

APPROPRIATE HEALTH CARE

N/A

NUTRITIONAL SUPPORT

 Additional nutritional support is not necessary in most cases if the IOP can be brought down.

 If needed, tube feeding can be used to provide nutritional support.

CLIENT EDUCATION/HUSBANDRY RECOMMENDATIONS

 While buphthalmos can occur in any animal, those with husbandry deficiencies may be at increased risk.

 In addition to medical and surgical therapy, maximizing the husbandry of the animal will improve the chance for a successful outcome.

MEDICATIONS

DRUG(S) OF CHOICE

 As most of these cases present in a chronic state, vision is often already lost, and medications are used to control pain and slow the disease process during diagnostic evaluation, but enucleation as a salvage procedure is usually indicated.

 If acute glaucoma is suspected, it is important to start treatment immediately with topical β‐adrenergic blockers (such as timolol) and CAIs (such as dorzolamide) BID to TID and mannitol (1–2 g/kg IV slowly over 20–30 minutes) to reduce IOP and preserve vision.

 If uveitis is suspected, systemic and topical antibiotics (such as ceftazadime 20 mg/kg IM or SC q48–72h) and steroids (prednisolone 0.25–0.5 mg/kg daily or dexamethasone SP 0.04–0.08 mg/kg daily) should also be instituted.

PRECAUTIONS/INTERACTIONS

N/A

FOLLOW‐UP

PATIENT MONITORING

Serial IOP measurements are useful to determine response to therapy.

EXPECTED COURSE AND PROGNOSIS

 Prognosis is related to the underlying cause of the glaucoma, which is not always readily identifiable.

 Enucleation of the diseased globe will resolve the issue in most cases.

MISCELLANEOUS

COMMENTS

N/A

ZOONOTIC POTENTIAL

Depends on the cause of the buphthalmos, but low to most often no zoonotic potential.

SYNONYMS

N/A

ABBREVIATIONS

 CAI = carbonic anhydrase inhibitor

 IOP = intraocular pressure

 IV = intravenous

 SC = subcutaneous

Suggested Reading

1 Chittick B, Harms C. Intraocular pressure of juvenile loggerhead sea turtles (Caretta caretta) held in different positions. Vet Rec 2001; 149(19):587–589.

2 Delgado C, Mans C, McLellan GJ, et al. Evaluation of rebound tonometry in red‐eared slider turtles (Trachemys scripta elegans). Vet Ophthalmol 2014; 17(4):261–267.

3 Espinheira Gomes F, Brandão J, Sumner J, et al. Survey of ophthalmic anterior segment findings and intraocular pressure in 95 North American box turtles (Terrapene spp.). Vet Ophthalmol 2016; 19(2):93–101.

4 Gornik KR, Pirie CG, Marrion RM, et al. Ophthalmic variables in rehabilitated juvenile Kemp’s ridley sea turtles (Lepidochelys kempii). J Am Vet Med Assoc 2016; 248(6):673–680.

5 Hochleithner C, Holland M. Ultrasonography. In: Mader, DR, Divers SJ, eds. Current Therapy in Reptile Medicine and Surgery. Saint Louis, MO: Elsevier Saunders; 2014:107–127.

6 Lawton, MPC. Reptilian Ophthalmology. In: Mader DR, ed. Reptile Medicine and Surgery. 2nd ed. St. Louis, MO: Elsevier Saunders; 2006:323–342.

7 Rajaei S, Ansari mood M, Sadjadi R, Azizi F. Measurement of intraocular pressure using Tonovet® in european pond turtle (Emys orbicularis). J Zoo Wildl Med 2015; 46(2):421–422.

8 Selleri P, Di Girolamo N, Andreani V, et al. Evaluation of intraocular pressure in conscious Hermann’s tortoises (Testudo hermanni) by means of rebound tonometry. Am J Vet Res 2012; 73(11):1807–1812.

9 Selmi AL, Mendes GM, MacManus C. Tonometry in adult yellow‐footed tortoises (Geochelone denticulata). Vet Ophthalmol 2003; 6(4):305–307.

10 Selmi AL, Mendes GM, MacManus C, Arrais P. Intraocular pressure determination in clinically normal red‐footed tortoise (Geochelone carbonaria). J Zoo Wildl Med 2002; 33(1):58–61.

11 Selmi AL, Mendes GM, MacManus C. Tonometry in adult yellow‐footed tortoises (Geochelone denticulata). Vet Ophthalmol 2003;6(4):305–307.

12 Somma AT, Lima L, Lange RR, et al. The eye of the red‐eared slider turtle: morphologic observations and reference values for selected ophthalmic diagnostic tests. Vet Ophthalmol 2015; 18(Suppl 1):61–70.

Author Christopher S. Hanley, DVM, DACZM