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

Traumatic lens subluxation or luxation

This is rarely seen in isolation, as the forces required to disrupt the zonular attachments of domestic animals are generally associated with other signs of severe ocular trauma.

Retinal effects (Figs 5.11, 5.12)

Because of the precise anatomic and functional organization of normal retinal tissue, it is at great risk of damage associated with contusive injury.

•The neuroretinal tissue is ‘stretched’ across the posterior segment, and it has a semi-liquid consistency that makes it vulnerable to disruption by the shearing forces of a pressure wave propagating within it

■This type of injury can be associated with ‘whiplash’ forces, which may result from shaking, as seen in the

shaken-baby syndrome in human infants, or from a blow to the head

•If the damage is mild, the retina may not degenerate, and a return to function is possible

•If the damage to the retina is locally severe, the retinal tissue undergoes rapid degeneration. The damage occurs acutely, is non-progressive over the long-term, and it is often segmental

•Within the first 24 h, retinal contusion is associated with apoptosis and physical disruption

■Separation of the photoreceptor processes from the outer nuclear layer is seen in acute trauma

■Hemorrhage in the retina or vitreous

•Within 5 days, the severely affected retinal tissue becomes liquefied and phagocytes (gitter cells) predominate

•The end-stage is regional, severe retinal atrophy

■Retinal detachment and retinal tears are frequently seen

■A useful clue that trauma was involved as the cause of severe retinal damage is the finding of well-preserved blood vessels, seemingly ‘free in space’, separated from the atrophic retinal tissue adjacent to them.

Scleral effects, scleral rupture (Figs 5.13, 5.14)

There are over 240 cases of scleral rupture in the COPLOW collection in dogs and cats. Scleral rupture results from a deforming blow to the globe. The blow may or may not directly penetrate the globe but deformation of the globe results in rupture of the sclera at points of weakness. These weak points include the equatorial region adjacent to rectus muscle attachments and, less commonly, the posterior pole.

•Most commonly, scleral rupture is the result of blunt trauma without a penetrating component (Fig. 5.13)

■In these cases you will find the following features:

–Segmental uveal fibrosis in the region of the scleral rupture or defect

87

–A scleral defect, which typically extends from the equator radially towards the posterior pole

–Episcleral and orbital fibrosis with displaced fragments of pigmented uveal tissue or disorganized neural tissue of retinal origin

–Episcleral damage involving peripheral nerve tissue, with neuroma formation

•An example of trauma to the globe with both direct penetration and scleral rupture would be a ballistic injury (Fig. 5.14)

■In these cases, you will find the following features:

–An entry wound

–Uveal fibrosis in association with the scleral defect

If segmental uveal fibrosis but no scleral defect is found, it can be rewarding to cut deeper into the block in search of a scleral defect

–A scleral rupture starting at the equator that extends radially toward the posterior pole, but does not involve the optic disc

–Possibly an exit wound

–Metallic fragments

Polarized light can be very useful to identify tiny, metallic fragments, which otherwise may masquerade as melanin

–Extensive episcleral and orbital hemorrhage or scarring, depending on chronicity

–Displaced pigmented uveal tissue and disorganized neural tissue of retinal origin.

Comparative Comments

The retinal effects and scleral effects of blunt trauma are very similar in the human eye to those described for domestic animals.

88

PENETRATING INJURIES

Corneal penetrating injury (Fig. 5.15)

In the COPLOW collection, it is generally not possible to differentiate penetration of the cornea due to intrinsic, primary corneal disease with perforation (as discussed in greater detail in Ch. 8) from that due to penetrating trauma. Although traumatic penetrating injury to the cornea is undoubtedly important, the unique features and consequences of traumatic corneal penetrating injuries will not be specifically addressed in this chapter, because it is often not possible for the pathologist to establish the sequence of events.

Scleral penetrating injury (Figs 5.16, 5.17)

In the scleral penetrating injury cases recorded in the COPLOW collection, we have seldom been provided with a history of a traumatic event. There are features that suggest a penetrating injury to the sclera, which include the following:

•Episcleral, orbital, and/or subconjunctival fibrosis or fistulating inflammation

■If the inflammation is more severe in the superior part of the orbit/globe, this suggests injury related to an attack or a falling object

■If the inflammation is more severe inferiorly, this suggests penetrating injury related to an oral foreign body or a stick from below

–There are seven cases in the COPLOW collection, as well as cases published in the veterinary literature, with a recent history of dentistry and in some cases, accidental slippage of a dental instrument

•A full-thickness scleral defect

■This finding is good evidence of a penetrating injury but, unfortunately, is seldom found in the standard plane of section

•Some evidence of direct damage within the globe, that includes at least one of the following (Fig. 5.17):

■Lens capsule rupture

■Fistulous inflammatory tracts that extend through the uvea or retina

■Bacterial sepsis

■Identification of a fragment of foreign material in the section

–By far the most common foreign body found in tissues in the COPLOW collection is a plant fragment (32 cases). However, hair, mineral (three cases), bone, feather, metal, and plastic have also been found. Porcupine quills are not uncommon as causes of penetrating or perforating ocular injury in certain geographic locations.

Suppurative endophthalmitis (Fig. 5.18)

•Suppurative endophthalmitis is the most common consequence identified in eyes removed after a penetrating injury

■Among dogs, the brachycephalic breeds (also prone to keratitis) are most likely to have suppurative endophthalmitis

–The Shih Tzu is the most commonly represented canine breed, accounting for 121 of the 954 cases in the COPLOW collection with this diagnosis

■Larger hunting breeds, perhaps due to their propensity for running through brush, are also prone to endophthalmitis related to perforating/penetrating injuries

•Common morphologic features of suppurative endophthalmitis associated with penetrating injury include (Fig. 5.18):

■A similarity in the degree of suppurative exudates throughout all of the compartments of the globe

■Lens capsule rupture

■Liquefactive necrosis of the retina

■Focal or multifocal, very localized neovascular extensions from the choroid into the subretinal space

–At COPLOW, these neovascular extensions are often referred to as ‘volcanoes’ because of their eruptive appearance

■A very early change, seen in acute cases, is the appearance of suppurative infiltrate within the choriocapillaris, before other exudates are apparent.

91

Septic implantation syndrome (‘cat scratch’ injuries) (Figs 5.19, 5.20) (see also Ch. 10)

•This is a canine and feline syndrome of endophthalmitis, often resulting from cat scratch injury, that can be defined by a specific set of morphologic criteria:

■There are 75 canine and 20 feline eyes in the COPLOW collection with endophthalmitis and features of ‘septic implantation syndrome’

■All ages are affected but there is a bias towards younger animals

•A definitive history of known cat scratch injury is seldom provided. However, when the inciting cause is known, it is often related to an incident involving a cat scratch

•A feature of this syndrome is a period of latency, during which the globe is relatively quiet, between the inciting injury and the onset of endophthalmitis that leads to enucleation

■A latency period of several months is typical, but latencies as long as 2 years have been observed among the cases in the COPLOW collection

•This syndrome is characterized by the following morphological features:

■Suppurative and histiocytic inflammation which intimately surrounds the lens

■Broad posterior synechiae, with spindle cells and collagen that are consistent with temporal chronicity

■Lens capsule rupture with suppurative inflammation extending into the lens substance

94

■About 60% of cases have identifiable bacterial colonies within the lens substance but away from the inflammatory cell infiltrate

–In affected canine eyes, bacteria are usually Gram-positive cocci

–In feline cases there is more likely to be a mixed population of bacteria.

Comparative Comments

The sequelae of perforating injuries in the human eye are similar to those discussed in the COPLOW collection.

CHEMICAL INJURY (Fig. 5.21)

In contrast to the situation in human ocular pathology services, submissions to COPLOW from cases affected by known chemical injury are extremely rare.

Acid burn

Acid exposure to tissue causes an instantaneous coagulation of the most superficial tissues, with precipitation of proteins, but the effect does not extend deeply.

A B

C

•Acute: coagulation necrosis of superficial epithelial and stromal tissues

•Chronic: granulation tissue response.

Alkali burn

Alkali exposure causes extensive damage due to its ability to penetrate deeply into ocular tissue.

•Acute: There is swelling and loss of the corneal epithelium and coagulation of conjunctival blood vessels. Tissue swelling and vascular damage extend deep into the tissue, with intraocular extension of these effects

•Chronic: tissue atrophy, collagenolytic lysis, and granulation tissue. Keratomalacia is associated with the release of collagenases from corneal epithelial and stromal cells, and from neutrophils.

Figure 5.16  Traumatic penetrating injury.

(A) Gross photograph of a canine globe with endophthalmitis due to a penetrating injury. (B) Subgross photomicrograph of a canine globe penetrated by a migrating porcupine quill. The arrow indicates the point of scleral penetration. (C) Photomicrograph showing the scleral penetration point from a slipped dental instrument.

Snake bite (Fig. 5.22)

There are three cases in the COPLOW collection of venomous snake bites directly to the globe.

•The damage is dominated by tissue lysis, presumed to be related to lytic factors in the venom

•Retinal and optic nerve tissue are notably destroyed, and seemingly liquified.

PROPTOSIS AND OPTIC NERVE

TRAUMA (Figs 5.23, 5.24)

There are 82 cases in the collection with a history of proptosis (anterior prolapse of the globe, which becomes entrapped by the eyelid margins behind the globe equator).

95

•Of these 82, 80 are dogs and only two are cats. Brachycephalic breeds, young dogs, and small terrier breeds are over-represented

•The time between proptosis and subsequent enucleation ranges from hours to months

•The morphologic features in enucleated canine globes with a history of proptosis include:

■Global optic nerve necrosis

–Most globes removed following proptosis have immediate total necrosis of the optic nerve tissue

–If removed within 4 days of proptosis, degeneration of the neuropil and apoptotic nuclear profiles will be observed within the optic nerve

–If removed 5–10 days after proptosis, optic nerve tissue malacia, dominated by macrophage cells (gitter cells) will be observed

–If removed 2 weeks or more after proptosis,

profound atrophy and fibrosis of the optic nerve will be observed

■Retinal effects

–The effects of retinal contusion (as described previously) may be observed

Detachment and/or retinal tear

Segmental malacia followed by atrophy

–A loss of retinal ganglion cells secondary to the optic nerve trauma may be observed and, when seen, the loss of ganglion cells occurs within days of the traumatic episode

■Corneal effects

–In proptosed eyes, acute and profound corneal necrosis occurs, because of desiccation, loss of innervation and/or loss of blood supply to the anterior segment. There can be a full-thickness devitalization of the corneal stroma. This is purportedly more likely to occur if avulsion of more than two extraocular muscles is recognized

–Loss of corneal sensation or reduced ability to blink may also contribute to chronic keratitis, following surgical replacement of a proptosed globe

■In rare cases, total infarction of the globe may occur after proptosis resulting in global necrosis of ocular tissues

■Orbital effects

–Muscle damage, orbital hemorrhage, and other effects of soft tissue trauma can lead to inflammation or scar tissue in the episclera and orbital tissue.