8. Evaluation and therapeutic surgical methods for eye diseases diagnosis and therapy.

What are the three main coats of the eye?

1. Outer coat (cornea, sclera)

2. Middle coat (uveal tract: iris, ciliary body, choroid)

3. Inner coat (retina)

What are the two parts of the ciliary body?

Pars plicata and pars plana

What is the iridocorneal angle?

The junction of the cornea, iris, and ciliary body where the highest amount of aqueous humour flows

What is the vitreous chamber?

The space filled with a transparent, gelatinous substance that maintains the eye's shape

How does aqueous humour flow?

From the posterior chamber through the pupil into the anterior chamber. Its production and outflow are continuous.

What are the posterior segments of the eye?

Vitreous, retina, and choroid

What are the three components of the tear film?

1. Lipid (from meibomian glands)

2. Water (from lacrimal glands)

3. Mucin (from conjunctival goblet cells)

What is the function of cranial nerve II (optic)?

Sensory to the central nervous system (vision)

What is the function of cranial nerve III (oculomotor)?

Motor. Innervates the dorsal, medial, and ventral rectus muscles and provides parasympathetic innervation to the iris (constriction)

What is the function of cranial nerve IV (trochlear)?

Motor. Innervates the dorsal oblique muscles

What is the function of cranial nerve V (trigeminal)?

Sensory. Provides sensation from the eye (cornea, conjunctiva, lacrimal gland) and skin around the eye

What is the function of cranial nerve VI (abducens)?

Motor. Innervates the lateral rectus and retractor bulbi muscles

What is the function of cranial nerve VII (facial)?

Motor and sensory. Controls the ability to blink (n. facialis → n. auriculopalpebralis)

What are the stages of an ophthalmologic examination?

1. Signalment

2. Anamnesis

3. Examination

What information should be gathered during an ophthalmic anamnesis?

1. Whether the problem is bilateral or unilateral

2. If a whole litter is affected

3. Duration of the problem

4. Specific details about the problem

5. Any prior treatments

6. Assessment of visual impairment (orientation)

7. Presence of other illnesses

8. Any incoordination/weakness/personality changes

9. Current medications

10. Changes in food/water intake

What structures are examined during a complete ophthalmic examination?

Eyelids, cornea, conjunctiva, sclera, anterior chamber, iris, pupil, lens, fundus, periorbital structures, and orbit

What is adspection in an ophthalmic examination?

Visual inspection of eye symmetry, eye bulb movement, direction of movement, discharge, pain (blepharospasm, photophobia), and eyelash position (entropion, ectropion)

What are examples of specific ophthalmologic examinations?

1. Neurological tests

2. Schirmer’s tear test

3. Tonometry

4. Tear film quality

5. Microbiological and cytological exam

6. Fluoresceine stain

7. Jones test

8. Gonioscopy

9. Seidel test

10. Ophthalmoscopy

What are the neurological tests used in an ophthalmic examination?

1. Vision tests

   1. Cotton test

   2. Maze test

   3. Menace response

2. Neuroophthalmic tests

   1. Palpebral reflex

   2. Pupillary light reflex and dazzle reflex

   3. Corneal reflex

   4. Basal reflex

What does failure of all vision tests suggest?

Central blindness

Why is cotton used in the cotton test?

It drops without sound or smell, providing unbiased tracking

How is the cotton test carried out?

Can perform by testing each eye by covering the other with a hand, but this often distracts the dog too much and ruins the result. Better just drop cotton on each side of the head

What does the cotton test assess?

Sensory structures and visual pathways (CN II) and motor innervation to eye muscles (CN III, IV, VI)

How is the maze test carried out?

Place obstacles in the way and call the pet to navigate through them. Repeat in both light and dark environments

What does the maze test assess?

Visual pathways (CN II)

How is the menace reflex test carried out?

Move hand or object in front of eye in a manner to not disturb the air or fur. Blink response.

Absent in young animals → learnt response seen at 2 months and older

What does the menace reflex assess?

Sensory structures and visual pathways (CN II) and blink ability (CN VII). It is a learned response seen from approximately 2 months of age.

How is the palpebral reflex tested?

Touch medial and lateral canthus of the eye elicits a blink

What does the palpebral reflex assess?

Sensation from the eye and associated structures (CN V) and blink ability (CN VII). Testable from 2 months of age.

How is the pupillary light reflex assessed?

Constricts the pupil in response to light.

Direct (pupillary response to light in same (ipsilateral) eye) and consensual (pupillary response to light in contralateral eye).

What does the pupillary reflex assess?

Optic nerve (CN II) and oculomotor nerve (CN III) function. Lack of response can indicate damage to these nerves, the brainstem, or the influence of depressant drugs.

DOES NOT ASSESS VISION!

What is the dazzle reflex?

It is manifested as a bilateral, partial blink reflex in response to a bright light. The anatomical pathway responsible for this reflex is poorly understood. However, this test is a very useful substitute for the PLR in cases when the pupils can't be seen, such as in cases of severe corneal oedema or hyphema

How is the corneal reflex assessed?

Blink reflex when cornea is touched with a cotton-tipped applicator moistened with 0.9% saline

What does the corneal reflex assess?

Sensation from the eye and associated structures (CN V) and blink ability (CN VII). Lack of response may indicate cranial nerve or corneal damage.

What is the difference between basal and reflex tears?

Basal tears lubricate and nourish the eye (all three tear film components), while reflex tears (only aqueous) are produced in response to irritants.

How are basal tears evaluated??

The Schirmer tear test performed after application of local anaesthetic to the eye

What does the direct pupillary light reflex test?

The pupillary response to light entering the ipsilateral (same) eye (CN II and III).

What does the Schirmer tear test measure?

Tear production in mm/min.

How is the Schirmer tear test carried out?

Paper strip is folded (while in plastic -DO NOT TOUCH-) & hooked over lower eyelid. Tears begin to “travel” up filter paper.

What is a normal Schirmer tear test value?

15 mm/min or more

What values on the Schirmer tear test suggest or indicate KCS?

Up to 10 mm/min suggests KCS, below 8 mm/min indicates KCS.

When should the Schirmer tear test be performed in relation to other ocular tests?

Before other ocular tests to get an accurate value before epiphora is induced. Note whether the test is performed with the eye open or closed, ensuring consistency between both eyes.

How is the tear break-up time measured?

Put fluorescein into the eye, close & then open. See how long fluorescein will remain green. As soon as the green colour breaks, the calculation is stopped

What does the tear break-up time (TBUT) test assess?

Tear film quality (quantitative test for KCS).

What is a normal TBUT value in dogs?

24 seconds +/- 8.1 seconds

What methods can be used for microbiological and cytological examination of the eye?

Spatulas, blunt scalpels, and brushes. Ideal for identifying types of ulcers.

What does tonometry measure?

Intraocular pressure (IOP)

What is the difference between a TonoPen and a TonoVet?

The TonoPen requires topical anaesthesia, while the TonoVet does not.

How many times should the Tonovet be touched on the cornea?

6 times

What is the normal IOP in dogs?

15-25 mmHg

What is the normal IOP in cats?

17-22 mmHg

What precautions should be taken when performing tonometry?

The owner should not assist, as incorrect eye holding or pressure on the jugular vein can give inaccurate results.

What does fluorescein stain detect?

Corneal damage

What are the types of preparation of fluorescein stain?

1. Eyedrops

2. Strip

What is the problem with fluorescein eyedrops?

Large containers have high Pseudomonas infection risk as they proliferate in the fluid.

Smaller, one-time-use containers are available and safe to use

How should fluorescein strips be applied?

By touching the conjunctiva, not the cornea.

What is the Jones test?

Use of fluorescein to assess the integrity of the nasolacrimal duct. It will flow from the eye to the nose

What is gonioscopy?

Examination of the iridocorneal angle, where aqueous humour drains.

What does the Seidel test detect?

Corneal perforation. Fluorescein will show leakage of aqueous humour.

What are the types of ophthalmoscopy?

1. Direct

2. Indirect

What is the difference between direct and indirect ophthalmoscopy?

B. Direct ophthalmoscopy provides a direct, non-inverted image.

C. Indirect ophthalmoscopy provides an indirect, inverted (horizontally and vertically flipped) image.

What conditions can be investigated with ophthalmoscopy?

1. Anisocoria

2. Reflections (absence can indicate cataracts)

3. Opacities (pigment, corneal oedema)

4. Aphakia (aphakic crescent indicating lens luxation).

What are the surgical treatments for the eye and eyelids?

1. Eye globe removal (enucleation – transpalpebral or trans/subconjunctival)

2. Conjunctival graft

3. Corneal-scleral transposition

4. Penetrating keratoplasty

5. Gonioimplantation

6. Lens removal (phacoemulsification, intracapsular/extracapsular extraction)

7. Eyelid laceration repair

8. Temporary tacking suture for entropion, Y-V or modified Kuhnt for ectropion

9. Excision of eyelid tumours

10. Permanent lateral tarsorrhaphy (entropion)

11. Temporary complete tarsorrhaphy (proptosis).

What are some general treatments for eye conditions?

1. Antibiotics (gentamicin, neomycin, cephalexin, chloramphenicol)

2. Corticosteroids (dexamethasone, prednisolone)

3. Antifungals (itraconazole)

4. NSAIDs (flunixin)

5. ACE inhibitors (demacolin, neostigmine)

6. Glaucoma medications (carbonic anhydrase inhibitors, beta blockers, diuretics, mannitol).

When are corticosteroids contraindicated in the eyes?

In case of broken epithelium, may lead to release of collagenase and proteinase → eye damage

What can you use to check retinal activity?

Electroretinography

When is USG used?

When there is opacity and the inside of the eye cannot be seen

What diseases can cause exophthalmus?

Teeth abscess, tumours behind the eye, trauma, haemorrhage

Are there any autoimmune diseases affecting the eye?

Masticatory myositis

How can the fundus be assessed?

Dilate pupil (tropicamide; short-term mydriasis) then use ophthalmoscope

What is the commercial name for a tonometer?

Tonovet

What is the name of the surgical treatment for lens luxation?

Phacoemulsification