Ophthalmic Equipment and Techniques

Chapter 131 Ophthalmic Equipment and Techniques



David A. Wilkie



OPHTHALMIC EQUIPMENT


The instruments and other equipment necessary for ophthalmic examination and surgery can be generally categorized as basic and advanced.



Diagnostic Equipment



Basic



• Penlight

• Direct ophthalmoscope with Finnoff transilluminator

• Indirect lens (20 diopter)

• Monocular biomicroscope

• Tonometer (Schiøtz) or Tonopen Vet (Mentor O&O)

• Miscellaneous
• Schirmer tear test strips

• Fluorescein stain

• Nasolacrimal cannula (23 gauge)

• Dilating agent (e.g., tropicamide)

• Topical anesthetic (e.g., proparacaine)

• Graefe forceps for third eyelid manipulation

• Kimura spatula for cytology


Advanced



• Biomicroscope (slit lamp)
• Monocular or binocular

• Indirect ophthalmoscope

• PanOptic ophthalmoscope

• Indirect lenses (15, 20, and 30 diopter)

• Applanation tonometer

• Gonioscopy lens

• Streak retinoscope

• Ultrasound (7.5, 10.0, and 20.0-50.0 MHz)

• Fundus camera

• Electroretinography


Surgical Equipment



Basic



• Magnifying loupes (4-6×)

• Colibri corneal forceps (0.3-mm teeth with tying platform)

• Bishop Harmon forceps (0.3- or 0.8-mm teeth)

• Barraquer needle holder (curved, without lock device; 9 mm × 0.85 mm jaws)

• Westcott tenotomy scissors

• Stevens tenotomy curved scissors

• Barraquer eyelid speculum

• Beaver blade handle

• Bard-Parker blade handle

• Desmarres chalazion clamp

• Strabismus hooks (two)

• Jamieson calipers

• Jaeger eyelid plate

• Irrigating cannula (23 gauge)


Advanced



• Operating microscope

• Right and left corneal section scissors

• Lens loop

• Angled tying forceps

• Carter sphere introducer

• Castroviejo cyclodialysis spatula

• Various intraocular forceps

• Diode or Nd:YAG laser

• Corneal trephines

• Phacoemulsification/irrigation-aspiration device

• Vitrector


Other



• Suture material

• 7-0 to 10-0 Vicryl or Dexon—ophthalmic spatula needle

• 9-0 nylon

• 6-0 monofilament—ophthalmic cutting needle (nylon, Surgilene, prolene)

• Blades
• #64, #63, and #65 Beaver blades

• #11 and #15 Bard-Parker blades

• Diamond or sapphire knives

• Irrigating solutions
• Ophthalmic balanced salt solution (BSS)

• Lactated Ringer’s

• Weck-cel surgical spears

• Prosthesis implants (18-19 mm)


OPHTHALMOLOGY TECHNIQUES


The general veterinarian in private practice should be able to perform the following routine ophthalmic procedures:


• Culture of the eye

• Schirmer tear test

• Tear breakup time

• Examination of the nictitating membrane (third eyelid)

• Direct ophthalmoscopy

• Indirect ophthalmoscopy

• Monocular biomicroscopy

• Fluorescein stain of the cornea

• Nasolacrimal irrigation

• Tonometry (Schiøtz, Tonopen)

• Conjunctival/corneal cytology

To properly evaluate and treat the patient with ocular disease, the clinician must have an accurate understanding of ophthalmic anatomy (Fig. 131-1).


image

Figure 131-1 Normal ophthalmic anatomy.


In addition, based on the information obtained by these diagnostic tests, the clinician should be able to arrive at a diagnosis and formulate a plan for further diagnostic tests or treatment or, if indicated, referral.



Culture



Indications



• Chronic, nonresponsive corneal ulcer

• Acute, severe melting corneal ulcer

• Purulent ocular discharge

• Infectious blepharitis


Equipment



• A sterile, moist, synthetic culture swab is preferable, but a sterile cotton swab can be used.


Technique


The general principles and techniques for obtaining a culture from the eye are the same as for other organs.


1. Using a sterile swab moistened in transport media, obtain the sample in an aseptic manner from the area of concern; for example:
a. If the lesion is a corneal ulcer, touch the swab to the ulcer (do not place in the conjunctival fornix).

2. Do not use a topical anesthetic for this procedure because it may interfere with the growth of organisms.

3. Label the sample and submit for aerobic and possibly fungal culture and sensitivity testing. It should be streaked onto nutrient agar as soon as possible.

4. Perform culture in combination with cytology or, if applicable, polymerase chain reaction (PCR) testing, when an infectious agent is suspected.


Schirmer Tear Test



Indications



• Assessment of normal aqueous tear production

• Chronic pigmentary keratitis

• Epiphora, including chronic mucoid epiphora


Equipment



• Commercially available Schirmer tear test (STT) strips


Technique



1. Place the notched end of the test strip in the lower conjunctival fornix. Do not touch this end.

2. Hold the eye closed and allow the strip to remain in place for exactly 1 minute. If convenient, both eyes may be tested at the same time.

3. Remove the strip and, using the standard measurement on the package, measure and record tear production. Normal dogs secrete 15 mm or more in 1 minute. While the normal value in the cat is reported to be similar to the dog, cats can have very low STT values without clinical signs. It is thought that stress may decrease the STT value in cats, and results must be interpreted along with clinical signs.

4. Do not use topical anesthetic for this test because the objective is to measure the response of the eye to an irritant. This requires the response of the ophthalmic branch of cranial nerve (CN) V as the afferent arm and the parasympathetic fibers in CN VII as the efferent arm.

5. In addition to the Schirmer tear test, evaluation of the tear breakup time to assess the mucin portion of the precorneal tear film and corneal staining with rose Bengal are also tools used in the assessment of the precorneal tear film and corneal surface health.


Tear Breakup Time (TBUT)



Indications



• Assessment of qualitative aqueous tear production

• Chronic pigmentary keratitis

• Epiphora, including chronic mucoid epiphora


Equipment



• Fluorescein stain

• Blue light and magnification (a slitlamp works best)

• Watch with a second hand


Technique



1. Place a drop of fluorescein stain on the cornea. Do not rinse it off.

2. Hold the eyelids closed and place the slitlamp to your eyes and the blue light on the eyelids.

3. Open the eyelids and, holding them open, begin timing while examining the green precorneal tear film. Continue to hold the eyelids open. The precorneal tear film should appear as a uniform, continuous film across the cornea. When the tears begin to separate into an oil and water pattern, stop timing.

4. Normal tears will remain stable for approximately 21 seconds. Failure to form a normal tear film or early breakup indicates a qualitative tear film abnormality. This is a result of a loss of goblet cells and tear film mucin.


Examination of the Nictitating Membrane



Indications



• Chronic conjunctivitis

• Suspicion of a foreign body

• Abnormalities of the gland or cartilage

• Mass lesion of the nictitating membrane (third eyelid)


Equipment



• Topical anesthetic

• Atraumatic forceps


Technique



1. Examine the palpebral surface of the third eyelid by gently retropulsing the globe and allowing the nictitating membrane to prolapse passively while the lower eyelid is retracted. This is useful for assessing the mobility of the third eyelid and for protecting the eye when obtaining a conjunctival scraping.

2. Examine the bulbar surface of the third eyelid. This requires topical anesthesia.
a. The topical anesthetic of choice is proparacaine (Alcaine), which provides 10 to 15 minutes of anesthesia. Apply 2 drops of anesthetic and wait 2 to 3 minutes for the full effect.

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Aug 27, 2016 | Posted by in SMALL ANIMAL | Comments Off on Ophthalmic Equipment and Techniques

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