Ocular therapeutics

1. Department of Veterinary Surgery & Radiology, PGIVAS, Akola
Dr. M. G. Thorat

3. Topical administration
 Only for cornea, conjunctiva, anterior part of sclera, iris, & ciliary
body (mild iritis or iridocyclitis).
 Topically applied preparations mix readily with the tears and
tend to wash away rapidly.
 Because of the nasolacrimal duct, topically applied drugs may
reach the mouth & get absorbed, which is not a problem.
 Drugs which rapidly penetrate mucous membranes will rapidly
enter the blood stream through the conjunctiva (e.g.,
apomorphine placed in the conjunctival sac will result in
vomiting within minutes). This can be a serious problem if
highly toxic drugs are used indiscriminately. For example, topical
cholinesterase inhibitors should not be used for the treatment of
glaucoma in cats because they can cause toxicity & death.

4. Types of preparations
1. Solutions:
 Least irritating, but have shortest contact time.
 They must be given frequently.
2. Suspensions:
 Similar to solutions.
 Disadvantages- they must be shaken well before use; they should
not be used in lavage systems because of the potential for
clogging tubes.
3. Ointments:
 Tend to last longer than solutions or suspensions, but, for
external disease, this usually is not significant.
 Tend to slow healing more than do solutions or suspensions.
4. Powders:
 These can be quite irritating & should not be used in the eye.

5. Vehicles of preparations
1. Aqueous: Readily mixes & flows away with tears. Aqueous solutions
may increase the rate of tear evaporation from the eye by washing
away the outer oily layer of the tear film.
2. Methylcellulose: Provides lubrication & greater contact time than
aqueous vehicles.
3. Hydroxyethylcellulose: Similar to, but more effective than
methylcellulose.
4. Polyvinyl alcohol: Similar to methylcellulose.
5. Polyvinylpyrrolidone: When used with ethylene glycol polymers,
produces a viscous 'artificial mucus' - has the greatest contact time of
all the liquids.
6. Oily bases (lanolin, mineral oil, peanut oil, petrolatum): In
solutions or ointments. Ointments are preferred immediately after
surgery due to reduction in eyelid motility. They should not be used
before or during an intraocular procedure.

6. Methods of topical ocular therapy
 Administration of ointments, solutions or
suspensions:
Maximum contact time
 Drop: 5-10 minutes - therefore, solutions or suspensions
must be given frequently to achieve their full potential.
 Ointment: about 20 minutes.

7. 1. Subpalpebral lavage:
 Most effective method of providing intensive topical
treatment.
 Used most frequently in horses when topical therapy
by other means would be difficult: when continuous or
frequent medication is needed, when the eyelids have
been sutured together, or when the individual is
difficult or dangerous to treat.

8.  One of the simplest ways to
achieve this is to use the MILA
International Subpalpebral Eye
Lavage Kit. This unit comes with
its own eyelid needle (trochar),
tubing and multiple injection
port.

9. 2. Cannulation of nasolacrimal duct:
 Alternate method to subpalpebral lavage in horses is the
use of a catheter in the nasolacrimal duct.
 Horses can pull these out; however, their ease of insertion
may offset this problem.
 Simply pass appropriate sized polyethylene tubing through
external meatus of nasolacrimal duct up to about level of
nasolacrimal sac. Tape is placed on the tubing near the
external meatus and the tape sutured to the nose. Enough
tubing is used to reach the halter or neck where it is
attached; medications can then be applied from a distance.

10. 3. Subconjunctival injection
 Indications
 When sustained, high concentrations of medication are
needed such as with stubborn corneal disease (e.g., pannus),
anterior uveitis, or scleritis.
 Disadvantage
 Be sure of your perceived need, because once the injection is
made, there is no turning back.
 Many of the medications are quite irritating by this route.
 Risk of introduction of infection
 Temporary pain associated with the injection.

11.  Technique :
 General anesthesia or sedation & topical anesthetic
is necessary
 Appropriately restraint the animal
 Injection is given under the bulbar conjunctiva.
 Injection should be placed as close to the lesion
site as practical to increases effectiveness.
 Raise the upper eyelid.
 Needle 25 or 27 gauge (with syringe attached) should be directed
tangential to the globe so that not to penetrate the globe.
 Quick thrust is used to enter the conjunctiva & the injection is
made; because of the tendency of globe to rotate away.
 Inject up to ½ ml in small animals and 1 ml in large animals.
 The therapeutic benefit from this type of injection lasts from
several hours to several weeks depending on the agent used.

12. 4. Retrobulbar injection
 For posterior uveitis, retinitis, and optic neuritis
 Although the experienced person can do this fairly
innocuously in the dog and the cat, it is safer and just
as effective to use systemic medication instead.
 Main use in veterinary ophthalmology is for optic
neuritis where high concentration of corticosteroid is
needed.

13. 5. Systemic administration
 Preferred method of treating diseases of the ocular posterior segment.
 Most medications are used at the regular recommended dose and rate.
 However, in certain instances, such as with optic neuritis, much higher
than usual doses of corticosteroids are used. Need to keep in mind that
there is a blood-ocular barrier similar to that in the brain.
 Blood-ocular barrier: The blood-ocular barrier normally keeps most
drugs out of the eye. However, inflammation breaks down this barrier
allowing drugs and large molecules to penetrate into the eye. As the
inflammation subsides, this barrier usually returns.
 The blood-ocular barrier is comprised of the following sites:
 Blood-aqueous barrier: The ciliary epithelium and capillaries of the iris.
 Blood-retinal barrier: Non-fenestrated capillaries of the retinal
circulation and tight-junctions between retinal epithelial cells
preventing passage of large molecules from choriocapillaris into the
retina.

14. 6. Intraocular injection
 This generally is used only during intraocular surgery
or as a last resort in endophthalmitis.
 It is recommended to contact a specialist before
considering this form of medication as the indications
are quite specific and there is great danger of losing
the eye if done incorrectly.