Ординатура / Офтальмология / Английские материалы / Veterinary Ocular Pathology A Comparative Review_Dubielzig, Ketring, McLellan_2010

the condition is defined by the age of first appearance, and because of that, the definition may differ between authors (Fig. 3.23)

•Congenital cataract, in isolation, is very unlikely to be seen in a pathology laboratory because the eye is not likely to be painful, the health of the animal is not likely to be adversely affected, and there is an effective surgical therapy

•Congenital cataract is often associated with more complex syndromes involving other ocular abnormalities, including microphthalmos, PHPV/PHTVL, PPM and/or anterior segment dysgenesis

•Although inherited forms of congenital cataract are recognized in a wide range of species, congenital cataract often occurs sporadically, or as a result of maternal exposure to toxins, infection, or other in utero insult during lens development

•Congenital cataract, as any cataract, can affect the lens in a variety of morphological patterns

■Lesions involving the lens capsule and epithelium

–Disorganization of the lens epithelium

–Posterior migration of lens epithelial cells

–Duplication of lens capsule

■Lesions involving the relative formation of the nucleus and cortex

–Nuclear cataract is most likely to be encountered in isolation

■Cortical cataract.

Hereditary cataracts

•Morphologically, most breed-related cataracts are cortical cataracts that are not present at birth. Hereditary cataract is discussed further in Chapter 10.

Goniodysgenesis and other anterior segment dysgenesis syndromes (Figs 3.24, 3.25)

Goniodysgenesis is also known as pectinate ligament dysplasia, and mesodermal dysgenesis (Figs 3.24, 3.25). There are 1100 cases of dogs with a diagnosis of goniodysgenesis in the COPLOW collection.

•This morphologic variant is an important risk factor in development of ‘primary glaucoma’ of dogs; the glaucoma syndrome will be discussed in more detail in Chapter 13

•Morphologic features of goniodysgenesis

■Gross appearance as described by gonioscopy in vivo, or by direct inspection with a dissecting microscope during gross evaluation

–The normal pattern of the primary pectinate ligament is replaced focally or in broad sheets by a solid band of uveal tissue, that may be fenestrated to a variable degree

■Microscopic appearance of goniodysgenesis in the normotensive eye

45

–The hallmark feature is a solid sheet of iris-like tissue extending from the base of the iris to the termination of Descemet’s membrane

Classically this membrane should have both pigment cells and dense collagen, similar to the canine iris

The termination of Descemet’s membrane is distorted by branching, bulging, or both

In the normotensive eye, the ciliary cleft is open and the corneoscleral trabecular meshwork is readily identifiable.

Peter’s anomaly and persistent pupillary membranes (Figs 3.26, 3.27)

There are 10 cases of Peter’s anomaly in the COPLOW collection, six in dogs and four in cats.

46

•The defining feature of Peter’s anomaly is a congenital defect in the posterior cornea, resulting from failure of normal keratolenticular separation

■Segmental defect in Descemet’s membrane and endothelium (required abnormality)

■Clinically, there is a segmental corneal opacity

■Attachment of uveal tissue to the posterior surface of the cornea

–Pigmented tissue

–Vascular tissue

–Uveal strands stretching from the iris to the cornea focally or multifocally

■Usually not associated with congenital glaucoma

•The defining feature of persistent pupillary membranes is vascularized uveal strands or membranes stretched across the

pupil, extending from one side of the iris to the other, or to the anterior pole of the lens.

Congenital failure in the formation of the anterior segment, anterior segment dysplasia or dysgenesis (Fig. 3.28)

•The defining feature is broad anterior adhesion of iris, or iris remnants, to the posterior cornea in association with abnormalities in Descemet’s membrane and endothelium. The space that normally represents the anterior chamber may be narrow or non-existent

•Lens may make contact with cornea within a defect in Descemet’s membrane

■This represents a failure of kerato-lenticular separation at the time of formation of the lens vesicle from the surface ectoderm

•May be associated with congenital glaucoma and buphthalmos, or with microphthalmos

•This diagnosis should be made with care. The diagnosis of congenital disease needs to be carefully differentiated from early life trauma with acquired anterior segment collapse. The presence of other features which cannot be explained by acquired disease, particularly trauma will aid in making the diagnosis of congenital disease

■In the COPLOW collection these diagnoses are made infrequently, as follows:

–Canine early life trauma causing collapse of the anterior chamber: 23 cases

–Canine anterior segment dysgenesis: 26 cases

–Feline early life trauma causing collapse of the anterior chamber: 19 cases

–Feline anterior segment dysgenesis: 16 cases

–Equine anterior segment dysgenesis: 9 cases.

Iris coloboma (Fig. 3.29)

Congenital segmental defect in the formation of the iris, leading to an abnormal pupil shape or a focal absence of iris tissue.

Scleral coloboma (Fig. 3.30)

Congenital segmental scleral defect leading to outward bulging (ectasia) of the sclera. May be associated with strabismus due to abnormal extraocular muscle insertion.

Congenital corneal edema in association with multifocal defects in Descemet’s membrane and endothelium (Fig. 3.31)

Rare cases of young animals with corneal edema and increased corneal thickness, otherwise unexplained, should be evaluated carefully for segmental defects of Descemet’s membrane and endothelial cells embedded in the posterior stroma.

Comparative Comments

The spectrum of congenital abnormalities seen in different breeds in veterinary medicine is similar to that encountered in humans, however, there is no clearly discernable ethnic or racial predominance in humans.

On the other hand, the link between specific developmental disorders and the human genome is, in general, much better worked out.

For example, trisomy 13 (Patau’s syndrome) is seen in one out of 14 000 live births.

SPORADIC CONGENITAL ABNORMALITIES

OF UNDETERMINED ORIGIN

Microphthalmia syndromes

•Microphthalmos may arise early in development due to abnormal development of the optic vesicle, or later in development through failure to establish intraocular pressure which normally contributes to growth and expansion of the globe

•Microphthalmia in horses (Fig. 3.32):

■There are six cases of congenital microphthalmia in horses in the COPLOW collection

■This syndrome is seen sporadically in foals that are otherwise fully developed and without other, systemic abnormalities

■The Thoroughbred is over-represented, but the condition has been observed in many breeds

■There is no known or suspected cause, and this condition is not believed to be inherited

■Affected animals are generally affected bilaterally but often not symmetrically

■Ranges in severity from a small but otherwise normal eye, ‘nanophthalmos’, to extreme microphthalmos with multiple ocular anomalies

50

■Microscopic findings may include:

–Microphthalmos

–Often see epidermal/hair follicular differentiation at the corneal limbus (dermoid)

–Aphakia or profound microphakia

–Failure to develop any normal anterior chamber

No Descemet’s membrane

No normal corneal endothelium (ciliary and iridal epithelium is often present but disorganized or cystic)

–Heterotopic development of fully differentiated tissue not appropriate to the globe in the anterior segment

Stratified squamous epithelium (can be cystic)

Glandular tissue

Cartilage.

Microphthalmia in white-tailed deer (Fig. 3.33)

•This condition shares many features of the condition in horses

•Affected fawns are well developed, with no identifiable congenital abnormalities in other systems

•There is no known cause, and there is no reason to believe that this condition is heritable. Environmental teratotoxicosis is suspected

A B

C D

A

B

Figure 3.31  Canine congenital corneal edema. (A) Gross photograph of both globes from a dog with corneal edema and extreme thickening. (B) Photomicrograph showing interrupted Descemet’s membrane (arrows) and dysplastic endothelium in a dog with congenital corneal edema.

Figure 3.30  Scleral ectasia and coloboma. (A) DSH, 6 months old: a large temporal and a smaller peripapillary area are present at the arrows. An upper lid agenesis was also present.

(B)Australian Shepherd, 2 years old: the arrows indicate a large area of scleral ectasia in the inferior nasal fundus.

(C)Australian Shepherd, 2 months old: an area of scleral ectasia is present at the arrow. (D) American Eskimo dog, 6 years old: in the subabinotic, atapetal right fundus, a large staphyloma is present between the arrows. The condition was bilateral.

■In Wisconsin, the condition is seen more commonly in areas where the land is used for intensive agriculture, with application of chemicals and intense irrigation. This may indicate a possible environmental cause

•Affected animals are always affected bilaterally but not always symmetrically

•Morphologic abnormalities include:

■Microphthalmos

■Opaque and pigmented cornea

■Aphakia, except focal differentiation of dysplastic lens cells

■Failure to develop any normal anterior chamber

–The deep corneal stroma resembles sclera in appearance

–No Descemet’s membrane

–No normal corneal endothelium

–Normal but disorganized iridal or ciliary epithelium may be present

■Heterotopic development of fully differentiated tissue not appropriate to the globe within the anterior segment

–Stratified squamous epithelium

–Glandular tissue

–Of 30 specimens examined from Wisconsin, no cartilage tissue was found. However, cartilage has been reported in eyes of fawns from other states

■Severely disorganized neuroretinal tissue often extends across the posterior aspect of the abnormal tissues of the anterior

segment. Within this disorganized neural tissue, there is often dysplastic lenticular differentiation.

Sporadic microphthalmic syndromes (Fig. 3.34)

Microphthalmos, with variable associated ocular anomalies, such as anterior segment dysgenesis, cataract, persistent pupillary membranes, PHPV/PHTVL, coloboma or retinal dysplasia, may be seen as a sporadic finding in any species.

Feline neovascular vitreoretinopathy (Fig. 3.35)

There are 10 cases of feline neovascular vitreoretinopathy in the COPLOW collection.

•This condition is generally not recognized until glaucoma develops at 6 months to 3 years of age, however the peripheral retina remains avascular which suggests that the condition is, indeed, congenital

•The hallmark lesions:

■Complete retinal detachment

■Unilateral in all affected animals to date

■Neovascular membranes within the vitreous body

■An avascular peripheral retina

■Pre-iridal fibrovascular membrane and peripheral anterior synechiae

•This syndrome shares many morphologic features with retinopathy of prematurity (ROP) in humans, which is also discussed in Chapter 11

■The ROP is a major concern in premature infants

subject to positive pressure ventilation with supplemental oxygen in the management of respiratory distress. In ROP the normal post-natal development of retinal blood vessels is interrupted because vasoconstriction occurs when hyper-oxygenated blood circulates in the retinal vasculature

–This leads to local hypoxemia and subsequent neovascular tufts which extend into the vitreous rather than developing along the inner retina

–Traction from the resulting neovascular membranes may lead to retinal detachment and blindness

–ROP is easily induced in newborn kittens by exposure to increased oxygen tension and then withdrawal

–In the spontaneous feline disease, there has been no known history of perinatal difficulties.

Kahrs, R.F., Scott, F.W., de Lahunta, A., 1970. Congenital cerebella hypoplasia and ocular defects in calves following bovine viral diarrhea-mucosal disease infection in pregnant cattle. J. Am. Vet. Med. Assoc. 156, 1443–1450.

Scott, F.W., Kahrs, R.F., De Lahunte, A., et al., 1973. Virus induced congenital anomalies of the bovine fetus. I. Cerebellar degeneration (hypoplasia), ocular lesions and fetal mummification following experimental infection with bovine viral diarrhea-mucosal disease virus. Cornell. Vet. 63, 536–560.

Brown, T.T., Bistner, S.I., de Lahunta, A., et al., 1975. Pathogenetic studies of infection of the bovine fetus with bovine viral diarrhea virus. II. Ocular lesions. Vet. Pathol. 12, 394–404.

Percy, D.H., Scott, F.W., Albert, D.M., 1975. Retinal dysplasia due to feline panleukopenia virus infection. J. Am. Vet. Med. Assoc. 167, 935–937.

Albert, D.M., Lahav, M., Colby, E.D., et al., 1977. Retinal neoplasia and dysplasia. I.