Diagnostic Ophthalmology

History and clinical signs

A 7-month-old male Yorkshire terrier cross was examined at the ophthalmology service at the Western College of Veterinary Medicine for evaluation of ocular abnormalities in the right eye. The menace responses, palpebral, occulocephalic, and direct and consensual pupillary light reflexes were present bilaterally. Schirmer tear test (Schirmer Tear Test Strips; Alcon Canada, Mississauga, Ontario) values were 22 and 20 mm/min in the right and left eyes, respectively. The intraocular pressures were estimated with a rebound tonometer (Tonovet; Tiolat, Helsinki, Finland) and were 21 and 14 mmHg in the right and left eyes, respectively. Fluorescein staining (Fluorets; Bausch & Lomb Canada, Markham, Ontario) was negative bilaterally. On direct examination a circular opacity was noted in the posterior aspect of the right lens. Following application of 0.5% tropicamide (Mydriacyl; Alcon Canada, Mississauga, Ontario), biomicroscopic examination (Osram 64222; Carl Zeiss Canada, Don Mills, Ontario) revealed the opacity to involve the posterior lens cortex and lens capsule of the right eye. There was vascularization present within the opacity. Indirect ophthalmoscopic (Heine Omega 200; Heine Instruments Canada, Kitchener, Ontario) examinations were completed bilaterally and a linear blood vessel was noted extending from the central aspect of the posterior lens capsule to the optic nerve in the right eye. No abnormalities were detected in the left eye. Photographs of the right eye at presentation are provided for your assessment (Figure 1).

Figure 1.

Retroilluminated (left) and directly illuminated (right) photographs of the right eye of a 7-month-old Yorkshire terrier cross.

What are your clinical diagnosis, differential diagnoses, therapeutic plan, and prognosis?

Discussion

The clinical diagnosis was persistent, hyperplastic, primary vitreous (PHPV) and incipient cataract of the right eye. PHPV is a congenital anomaly resulting from failure of regression of the primitive vitreous and hyaloid vascular system, as well as hyperplasia of the mesodermal elements of these components (1,2). PHPV may be unilateral or bilateral. The most common clinical manifestation of PHPV is leukocoria (white pupil) resulting from a white plaque of tissue containing blood vessels attached to the posterior lens capsule (2).

Dog breeds in which PHPV is inherited include the Doberman pinscher, Staffordshire bull terrier, Bouvier des Flandres, and miniature schnauzer (2–5). It occurs sporadically in other canine breeds and other species (1,6–10). The complete pathogenesis of PHPV is unknown. The primitive or primary vitreous is located between the developing lens and retina. It consists of blood vessels of the hyaloid system, mesenchymal cells, collagenous fibrillary material, and macrophages (11). The hyaloid artery (HA) penetrates the primary vitreous through the optic fissure and grows toward the posterior pole of the lens where it branches and develops into a vascular network around the primitive lens forming the tunica vasculosa lentis (TVL). After day 45, the hyaloid vascular system starts to regress, and regression is usually complete by 2 to 4 wk after birth. Incomplete regression of the hyaloid system can result in a patent hyaloid artery (PHA), persistent hyperplastic tunica vasculosa lentis (PHTVL), or PHPV (1,2,12,13). Manifestations of PHA range from a white connective tissue strand attached to the posterior lens capsule, to patent blood vessels extending from the posterior lens capsule toward the optic nerve (14). Manifestations of PHTVL include fine white strands or blood vessels attached to the posterior lens capsule with possible extension around the equator of the lens (1). PHPV involves not only failure of regression of the hyaloid artery system but includes hyperplasia of the mesenchymal tissue of the primary vitreous. In addition to a retrolental fibrovascular plaque, PHPV may also manifest with lenticular anomalies such as cataract, microphakia, lens coloboma, posterior lenticonus, and lens capsular disruption. Additionally, the vascular components may be disrupted causing intralenticular hemorrhage (2).

The differential diagnosis for PHPV includes other causes of leukocoria such as cataract, retinal detachment, inflammatory infiltrates in the vitreous, and intraocular neoplasia (1,2). Diagnosis of PHPV is based on direct examination and the clinical findings of a retrolental plaque of white fibrovascular tissue located against the posterior polar lens capsule. Ocular ultrasound is useful if opacification of the cornea, anterior chamber, or lens prevents direct visualization of the posterior lens (8). The ultrasonic appearance consists of a hyperechoic lens and retrolental mass, representing cataract and fibrovascular tissue, with or without a hyperechoic strand extending from the central retrolental tissue toward the optic disk, representing a persistent hyaloid artery (8).

Ocular complications arising from PHPV include vision loss due to cataract, hyphema, vitreous hemorrhage, uveitis, retinal detachment, and secondary glaucoma (7,8). There is one case report of intraocular sarcoma associated with lens capsule rupture related to PHPV in a dog (10). Although the pathogenesis of the malignancy was not conclusive, there were similarities with post-traumatic ocular sarcomas of cats, which are frequently a sequela of lens capsule rupture (14–16).

The treatment of PHPV depends on the severity of the condition and presence of concurrent ocular complications. Small plaques not causing vision deficits may be monitored for progression of cataract. Topical anti-inflammatory therapy is indicated if cataract is causing lens-induced uveitis. Vision loss associated with cataract may be treated with phacoemulsification; however, this is complicated by the variable retrolental anomalies. For example, surgery may be complicated by an incomplete or disrupted posterior lens capsule and may require transection of the hyaloid artery and anterior vitrectomy (1). Surgical outcomes may be less favorable than standard cataract surgery due to these added anatomical abnormalities (1,2). No treatment was initiated in this dog due to the lack of clinically appreciable vision deficits or ocular complications. However, it was recommended that the dog return for re-evaluation on a 6-month to yearly basis to monitor the possibility of cataract progression and complications such as uveitis and intraocular hemorrhage.

The prognosis for PHPV is variable and depends on the degree of severity. Affected dogs should be monitored throughout life for development of complications which may be sight and globe threatening. Screening ocular examinations are indicated in breeds with inherited forms of the condition but should be completed after 6 wk of age. In these breeds, affected dogs should not be bred.