Diagnostic Ophthalmology

HISTORY AND CLINICAL SIGNS

A 10-year-old domestic short hair cat was examined by the ophthalmology service at the Western College of Veterinary Medicine. This cat was presented for evaluation of a cloudy left eye. The neuro-ophthalmic examination revealed an absent menace response in the left eye (OS), in addition to a dilated pupil and an incomplete direct pupillary light reflex (PLR) OS, as well as an incomplete consensual PLR in the right eye (OD). Palpebral and oculocephalic reflexes were normal bilaterally (OU). Schirmer tear test (Schirmer Tear Test Strips; Alcon Canada, Mississauga, Ontario) values were 19 and 18 mm/min in OD and OS, respectively. Intraocular pressures were estimated with a rebound tonometer (Tonovet; Tiolat, Helsinki, Finland) and were 17 and 47 mmHg in OD and OS, respectively. Fluorescein staining (Fluorets; Bausch & Lomb Canada, Markham, Ontario) of the cornea was negative OU. On direct examination using a transilluminator (Welch Allyn Finoff Transilluminator; Welch Allyn, Mississauga, Canada) abnormalities OD included mild iris hyperemia and slight cloudiness of the cornea. Abnormalities OS included buphthalmos, mild diffuse corneal edema, iris hyperemia, a dorsal aphakic crescent, and immature cataract. Following application of 0.5% tropicamide (Mydriacyl; Alcon Canada, Mississauga, Ontario) to achieve mydriasis, examination using a handheld biomicroscope (Kowa SL-17 Portable Slit Lamp; Kowa, Tokyo, Japan) OD had mild aqueous flare, keratic precipitates ventrally, mild iris hyperemia, and haziness and inflammatory cells within the anterior vitreous. Biomicroscopic examination OS revealed moderate aqueous flare, keratic precipitates, iris hyperemia, immature cataract, absence of lens zonules along the dorsal and lateral lens equator associated with the aphakic crescent, white flocculant material along the dorsomedial lens equator, and haziness and inflammatory cells within the anterior vitreous. Indirect ophthalmoscopic (Heine Omega 500; Heine Instruments Canada, Kitchener, Ontario) examination revealed vitreous haze OU, mildly blurring the view of the retina; however, the retina OS appeared detached. A complete physical examination was otherwise unremarkable. A photograph of the right and left eyes at presentation is provided for your assessment (Figure 1).

FIGURE 1.

Photograph of the right (a) and left (b) eye of a 10-year-old domestic short hair cat.

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Discussion

The ophthalmic diagnosis was panuveitis OU, as well as immature cataract, lens subluxation, and secondary glaucoma OS. Panuveitis is a term used to describe uveitis which involves both the anterior and posterior uvea. Common clinical signs of anterior uveitis include conjunctival hyperemia, miosis, aqueous flare, and a reduction of the intraocular pressure. Other clinical signs may include hypopyon, hyphema or fibrin in the anterior chamber, inflammatory cell adhesion to the endothelium (keratic precipitates), and iris hyperemia. Chronicity can lead to development of lymphoid nodules in the iris, pre-iridal fibrovascular membrane (PIFM) formation (clinically referred to as rubeosis iridis), and sequelae such as synechiae, secondary glaucoma, and lens luxation (1). Clinical manifestations of inflammation in the posterior uvea include vitreous haze caused by inflammatory cell and protein accumulation in the vitreous (hyalitis, vitritis), fluid or cellular infiltrates in the subretinal space, and exudative retinal detachments or hemorrhages.

The most common cause of glaucoma in cats is chronic uveitis (2). Glaucoma results from reduced aqueous humor outflow through the pupil or iridocorneal angle because of PIFM formation, complete posterior synechia causing pupillary block and iris bombé, or closure of the iridocorneal angle due to peripheral anterior synechia (2,3). Cataracts are also a common sequela of chronic uveitis and occur because of toxic effects of inflammation on lens cellular metabolism. In addition, inflammation around the equator of the lens contributes to zonular degeneration, and zonular breakage is further promoted by the globe stretching that occurs with chronic glaucoma (3).

Uveitis may have exogenous or endogenous causes. Exogenous causes include blunt or penetrating ocular trauma, and corneal ulceration (1). Endogenous causes include systemic infectious disease [feline immunodeficiency virus (FIV), feline leukemia virus (FeLV), feline infectious peritonitis (FIP), toxoplasmosis, bartonellosis, cryptococcosis, histoplasmosis, blastomycosis, and coccidioidomycosis], primary ocular neoplasia (uveal melanoma, ciliary body adenoma, or sarcoma), metastatic neoplasia (carcinoma) or systemic neoplasia (lymphosarcoma), and immune-mediated or idiopathic conditions (4–7).

Etiological studies of uveitis are usually retrospective in nature and are limited by the variability of diagnostic testing performed. The average age of cats diagnosed with uveitis is ~8 y, and idiopathic uveitis is most common, reported in 37.5 to 45.7% of cases (4–7). The most common infectious cause of uveitis in cats is FIP, reported in ~15% of cases, with the median age of cats diagnosed with FIP being much younger, ~1.5 y of age (5,6,8).

After ruling out exogenous causes, the diagnostic workup for a cat with uveitis should not only include a complete ocular examination but also a thorough physical examination. Additional diagnostic testing may include a complete blood (cell) count (CBC), serum chemistry, urinalysis, thoracic radiographs, abdominal ultrasound, and select serological titers for infectious agents (1,4–8). Referral to an ophthalmologist for aqueous humour cytology may be helpful in diagnosing neoplasia such as intraocular lymphosarcoma but has been shown to have little diagnostic utility in cats with non-neoplastic uveitis (9–10). The extent of the work-up applied to each case will vary depending on many factors including clinical and physical examination findings, geographic location, and client finances. Idiopathic uveitis is a diagnosis of exclusion, when no underlying cause can be confirmed based on the systemic work-up conducted.

The general physical examination was normal in this cat and a CBC and serum chemistry analysis, as well as serology for feline immunodeficiency virus (FIV), and feline leukaemia virus (FeLV) were completed by the primary care veterinarian prior to referral. No significant abnormalities were noted in the bloodwork, the FIV/FeLV test was negative, and no further testing was completed. Idiopathic uveitis was suspected based on these findings.

As there was significant and painful intraocular disease and the left eye was irreversibly blind based on the neuroophthalmic examination with retinal detachment and glaucoma we recommended enucleation and histopathology, which was completed at the referring clinic. Enucleation can act as a therapeutic as well as diagnostic modality in cases like this. Histopathology of the enucleated globe revealed accumulations of inflammatory cells along the endothelium (keratic precipitates), moderate to large numbers of small lymphocytes and plasma cells within the iris and ciliary body, lymphoid follicles within the iris stroma and PIFM. Changes consistent with cataract were noted in the lens. There was mild lymphocytic/plasmocytic inflammation within the retina as well as loss of the inner nuclear and ganglion cell layer consistent with glaucomatous retinal degeneration. The diagnosis was chronic, moderate lymphocytic/plasmocytic uveitis and retinitis, cataract, and secondary glaucoma. No etiologic agents were noted on histopathology and neoplasia was excluded. Thus, the findings supported the diagnosis of idiopathic uveitis.

Treatment for uveitis in the right eye included topical prednisolone acetate 1% (Sandoz Prednisolone; Sandoz Canada, Boucherville, Quebec) and diclofenac sodium 0.1% (Voltaren ophtha; Novartis, Mississauga, Ontario), both 4 times daily. The cat has been followed with re-evaluation every 3 to 6 mo since enucleation and the frequency of these medications has remained at 3 or 4 times daily. The uveitis in this eye has improved significantly; however, a trace to mild amount of inflammation is consistently present despite treatment.

Idiopathic uveitis is the most common form of uveitis in cats and is a diagnosis of exclusion. It usually presents in middle aged to older cats, is usually bilateral, chronic, and does not commonly go into remission. Maintenance treatment is required long-term and is aimed at slowing the progression of sequelae such as cataract, lens instability, retinal detachment, and secondary glaucoma. The degree of control of intraocular inflammation achieved with anti-inflammatory therapy varies by individual cat. We continue to monitor this cat and although the eye is comfortable and is currently visual, the long-term prognosis is guarded.