February Pulse Article (PART 8 OF 12, COMMON SMALL ANIMAL LENS DISORDERS)
February 18, 2019
In this month’s installment we briefly review some of the more frequently encountered disorders associated with the lens.
Persistent hyperplastic tunica vasculosa lentis(PHTVL) represents a failure of the vascular supply to the developing lens to regress, typically leading to cataract formation and visual impairment. Commonly affected breeds include the Doberman Pincher & Greyhound. Where indicated, the lens & associated vascular tissue may be surgically removed and patent vessels cauterized.
Nuclear sclerosisdescribes the progressive thickening of the lens due to ongoing lens-fiber deposition and resultant compression of the lenticular nucleus. Clinically, this process imparts a grey-blue appearance to the nucleus, typically becoming apparent after 7-8 years of age. Unlike cataracts, the presence of nuclear sclerosis not does impede the normal fundic view or reflex. Although a degree of refractive error may be associated with ageing changes, significant visual impairment is not generally noted clinically and neither medical nor surgical treatment is typically warranted.
Acataractdescribes any opacity of the normally transparent & avascular lens. Cataractogenesis occurs most commonly as a result of hereditary factors, however may also result from systemic disease (notably diabetes mellitus), lenticular trauma/inflammation, dietary deficiencies (notably associated with the use of milk-replacers), exposure to pharmacologic agents (notably ketoconazole), as a sequela to the retinal atrophies (RAs) & following exposure to therapeutic radiation. Changes may be unilateral or bilateral, symmetrical or asymmetrical and may develop over varying timeframes. Most breeds (& mixed breeds) may be affected by hereditary cataracts and multiple breed-related features including age of onset and rate of progression have been described. Lens-associated uveitis, if present, should be treated with topical anti-inflammatory agents in order to minimize the risk of subsequent glaucoma. Phacoclastic uveitis describes severe, acute intraocular inflammation as a result of the sudden exposure to lens-associated proteins following lens capsule lacteration or rupture. If significant visual impairment is present, cataract surgery & lens-replacment may be indicated (pending the results of pre-surgical diagnostic testing including electro-retinal function).
The canine or feline lens may becomeluxatedfrom their normal position within the patellar fossa posterior to the iris. This may be result of hereditary factors (predominantly abnormalities of the suspensory lens zonules and/or vitreous body), chronic intraocular inflammation, vitreous syneresis, glaucoma and/or trauma. Anterior lens luxation may be partial (termed “subluxation”) or complete such that the lens becomes displaced into the anterior chamber. Associated changes may include corneal edema, uveitis, varying degrees of cataract formation, the presence of degenerate vitreous material within the pupillary opening and/or anterior chamber and decreased or elevated IOP. Changes may be chronic or acute. Commonly affected breeds include multiple terrier breeds (Sealyham, Jack Russell Wire Haired Fox & miniature bull Terrier) & the Australian Cattle Dog. Subluxated lenses may be managed either medically or, more commonly, by surgical removal. The long term use of a miotic agent in the contralateral eye may be indicated in an effort to prevent similar pathology from developing. Complete anterior lens luxation is most appropriately addressed via surgical intracapsular lens extraction (ICLE) and limited automated vitrectomy.
Feline Post-Traumatic Ocular Sarcoma(FPTOS) represents a malignant intraocular neoplasm, which may develop following severe inflammation and/or traumatic injury to the ocular structures (particularly the lens). Neoplastic changes typically take several years to develop. FPTOS encompasses several morphological variants, all of which are associated with the significant potential for extraocular extension and/or distant metastasis. Clinically, changes are typically unilateral and may include corneal edema, keratitis, corneal ulceration, uveitis, iridal thickening and/or dyscoria, the presence of an intraocular mass, hyphema, retinal detachment, glaucoma and/or exophthalmos. The diagnosis of FPTOS is made based on clinical findings in conjunction with history. Soft tissue imaging modalities including B-mode ultrasonography, computed tomography (CT) and/or magnetic resonance imaging (MRI) may contribute to the clinical diagnosis, which is confirmed histologically either by biopsy or following enucleation/exenteration. As a result of the potential or the development of FPTOS, chemical ciliary body ablation (CBA), in order to manage glaucoma, is generally discouraged in cats.
Dr Esson is a board-certified veterinary ophthalmologist with more than twenty years of clinical experience and multiple areas of interest & expertise. His clinicVeterinary Ophthalmic Consulting is family owned & operated and he takes great pride & pleasure in working closely with his friends and colleagues in the greater Southern California veterinary community.
