Ординатура / Офтальмология / Английские материалы / Small Animal Ophthalmology Secrets_Riis_2002

Figure 7. Retinal hemorrhage in the nerve fiber layer of a cat.

Figure 8. A IO-year-old basset hound with intraretinal hemorrhages secondary to hypertension. These hemorrhages are located within the layers of the photoreceptors, outer nuclear, outer plexiform, inner nuclear, or inner plexiform.

Figure 9. A 7-year-old Norwegian elkhound with retinal hemorrhage and detachment secondary to renal disease. These hemorrhages are both preretinal and intraretinal.

36. ENDOPHTHALMITIS

Bruce H. Grahn. D.V.M.

1. What is endophthalmitis?

Endophthalmitis is an inflammation of the contents of the globe. Extension of the inflammation through the sclera and into the orbit is panophthalmitis. Endophthalmitis develops when there is disruption of the corneal, conjunctival, scleral, and blood-ocular barriers. Endophthalmitis affects both the anterior and posterior ocular segments. The etiology of endophthalmitis is diverse and may be septic and involve infectious agents that arrive from outside the eye. These agents may enter the eye through the ocular blood supply, through the central nervous system via the central spinal fluid and optic nerve, or by perforation of the cornea or conjunctiva and sclera. Nonseptic endophthalmitis may develop secondary to blunt trauma, cataracts, ruptured lens capsules, or other varied disruptions of the blood-ocular barriers.

2.What are the clinical manifestations of endophthalmitis?

Endophthalmitis is manifested by a variety of nonspecific signs of uveitis including miosis,

aqueous flare, hyphema, hypopyon, hypotony, synechiae, exudative retinal detachments, and hyalitis (Fig. I). Cataracts, ruptured lens capsules, and corneal or scleral perforations also may be present. When endophthalmitis arises from a systemic disease, there is often an accompanying general malaise, hyperthermia, altered respiration, vomiting, and diarrhea.

Endophthalmitis

Figure 1. Septic endophthalmitis that is developing secondary to corneal perforation. Note the neutrophilrich inflammatory infiltrates throughout the inside of the eye.

3.What are the two types of endophthalmitis?

Septic and nonseptic.

4.How is septic endophthalmitis diagnosed?

The classic clinical manifestations for this acute progressive uveitis include hypopyon, hy-

phema, hyalitis, and exudative retinal detachments. Once the vitreous becomes infected, the fundus usually cannot be visualized because of cellular and protein infiltrates. Detection of the

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VIII. Retina

37. ACQUIRED DISEASES OF THE FUNDUS

Michael G. Davidson, D.v.M.

1.What is a fundus?

The term fundus literally means the internal surface of an organ, farthest away from its open-

ing. The fundus of the eye is therefore the internal, posterior section of the eye that is seen with an ophthalmoscope. In small animals, the fundus is a composite of several different tissues including the optic nerve, sensory retina (and retinal blood vessels), choroid, tapetum (which is part of the choroid), and sclera.

2.What is the best way to examine the fundus?

The fundus is examined by a technique known as ophthalmoscopy, which can be performed

with either a direct method or an indirect method after the pupil is dilated with tropicamide. The direct method uses a direct ophthalmoscope headpiece and gives the examiner a highly magnified view but only of a very small portion of the fundus « 2% of the surface area). The indirect method uses a light source and an indirect ophthalmoscopy lens that is held in front of the eye, which gives the examiner a less magnified, but much larger field of view.

3. Which method of ophthalmoscopy is the best?

Although the direct method is technically easier, it is not possible to examine the fundus adequately with the direct method because of the small field of view, so the indirect method is preferred. However, the indirect method is technically more difficult to perform because the image viewed, called a "virtual image," is upside down and reversed. Thus, a lot of practice is required to become proficient at the indirect method.

4.When should I examine the fundus of my patients?

Ophthalmoscopy should be a part of a complete eye exam in patients with ocular disease of

any type, pupillary light reflex deficits, or vision loss. It should also be routinely performed in animals with undefined systemic illness or those with infectious, vascular, or neoplastic diseases, because many times these conditions affect the tissues of the fundus.

5.When I look at the fundus of a dog or a cat, how can I tell if it is normal or if a lesion is present?

Interpreting the appearance of the fundus can be challenging and requires a basic understanding of the layers of the fundus (see question 1) and the normal variations (Fig. 1). The most common variations of normal are those relating to the amount of pigment in the tissues of the fundus, the size and shape of the optic nerve, and the size and color of the tapetum. A good ophthalmology atlas helps in recognizing these normal variants, but mostly it requires experience and looking at a lot of normal animals.

6.What are the most common types of funduscopic lesions?

In the tapetal area of the fundus (which is usually the dorsal one-third to one-half), lesions

are characterized as being either hyporeflective if they are darker or grayer than the surrounding,

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Figure 3. Multifocal areas of exudate adjacent to a retinal blood vessel in the nontapetal fundus of a young domestic shorthair cat with retinitis

Figure 4. Two large hyperreflective lesions, with pigmented center, in the tapetal fundus of a dog. These lesions are caused by sensory retinal thinning or atrophy, and the pigmented lesion results from tapetal destruction and pigment proliferation.

"scars" or responds to insult, because it can't undergo a regenerative repair like most other tissues). This degeneration may be caused by a number of different diseases with different mechanisms including inflammation, ischemia, malnutrition, or an inherited type of degeneration called progressive retinal atrophy. Focal lesions resulting from inflammation of the retina can be thought of as an inactive lesions.

Figure 5. Multifocal depigmented lesions in the nontapetal fundus of a dog with inactive chorioretinitis.

9. What diseases should be considered if a hyporeflective lesion is seen in the fundus of a dog or a cat?

Remember that if the lesion is not due to dysplasia, then thickening of the retina is due to inflammatory cells, neoplastic cells, or edema. Inflammation involving the retina is commonly caused by a systemic microbial infection and less commonly by trauma or an immune-mediated inflammation or hypersensitivity. Any systemic infection has the capability of affecting the fundus in this way. When the retina is the primary tissue affected, this is referred to as a retinitis or retinochoroiditis, and when the choroid is the predominate tissue affected, it is called a chorioretinitis. It is useful to think about the different microbial agents in broad categories that include:

Bacterial Fungal Protozoal Rickettsial Viral

These hyporeflective lesions can also be caused by edema alone (with cells). When this occurs, the vascular system of the fundus is pathologically affected and leaks fluid into the retina. This often results from:

•Systemic hypertension

•Disease causing hyperviscosity syndrome (e.g., multiple myeloma or ehrlichiosis)

•Profound anemia and hypoxia of the vessels

Lastly, the hyporeflective lesions can be caused by neoplastic cells. The most common type of neoplasia affecting the fundus in this manner is lymphosarcoma. However, any malignant neoplasia is capable of metastasizing to the tissue of the fundus, and this should also be considered.

10.How can dysplasia be distinguished from these other causes of hyporefiective lesions?

Dysplasia affects certain breeds of dogs. American cocker spaniels, English springer

spaniels, King Charles spaniels, Labrador retrievers, and beagles are some of the common breeds, but there are many others. Dysplasia is generally bilateral and does not change in appearance over time. Dysplastic thickening of the retina often produces focal or multifocallinear lesions, whereas inflammation tends to cause multifocal circular lesions. If there is a systemic disease present that might cause inflammation, neoplastic infiltrate, or vascular insult to the retina, the hyporeflective lesion probably is not dysplasia. (See Chapter 40.)

11.If dysplasia is ruled out as the cause of a hyporefiective lesion, what should be done next?

Because there really are very few distinguishing or pathognomonic features of the different diseases that cause these lesions, the diagnosis cannot be made by ophthalmoscopy alone. The ocular exam has simply provided a clue that a systemic disease process is occurring. Therefore, follow the normal diagnostic steps including a thorough physical examination and a differential diagnosis list and perform the appropriate diagnostic tests to confirm or rule out these differentials.

12.What causes hyperrefiective lesions (or depigmented lesions in the nontapetal fundus), and what is their significance?

These lesions are caused by atrophy or degeneration of the sensory retina. Characterize the lesions as focal (or multifocal) or more diffuse. Causes of diffuse hyperreflectivity include:

•Progressive retinal atrophy (PRA), an inherited retinal degeneration occurring mostly in pure-bred dogs

•Sudden acquired retinal degeneration (SARD), an idiopathic retinal degeneration affecting mostly older, female, pure-bred dogs. Note that the fundus initially will appear normal with acute SARD; only after several weeks to months will the hyperreflectivity appear.

•Diffuse retinitis or diffuse vascular insult that has resolved

•Rarely, nutritional deficiencies such as chronic taurine deficiency in cats or vitamin E de-

ficiency in dogs

Focal or multifocal hyperreflective lesions are most commonly caused by either an inflammation or a vascular insult that has now resolved, causing a scarring of the retina. As with hyporeflective lesions, there is no pathognomonic appearance to these lesions suggesting one specific type of disease. In fact, these types of multifocal, degenerative lesions are often incidental findings and do not require any diagnostic evaluation (because the insult by which they were caused has already resolved).

13.If a hemorrhage is seen in the fundus, what does this imply?

As with most fundus lesions, there is nothing specific about the presence of a hemorrhage,

and both ocular and systemic diseases can cause this (Fig. 6). Examples of ocular disease that cause funduscopic hemorrhage include:

• Inflammation (chorioretinitis) -look for the other lesions of this syndrome

•Trauma

•Retinal detachment

•Developmental disorders such as persistence of the hyaloid artery system

Systemic diseases that cause fundus hemorrhage are the same conditions causing bleeding anywhere else in the body:

•Hypertension

•Coagulopathies such as clotting disorders, disseminated intravascular coagulopathy, thrombocytopenia

•Profound anemia (from hypoxia of the retinal blood vessels)

Thus, once again, the funduscopic findings often characterize the ocular condition or indicate that a systemic bleeding tendency is present. Proceed with the appropriate diagnostic evaluation based on ocular and physical examination findings.