Kathryn L. Wotman, DVM, DACVIM Jeffrey E. Bowersox, DVM ... · Veterinary Ophthalmology -Corneal erosions Spontaneous Chronic Corneal Epithelial Defect (SCCED) Post-operative removal

Kathryn L. Wotman, DVM, DACVIM Jeffrey E. Bowersox, DVM, DACVO

Veterinary Specialty Center of Delaware

Contact Lenses-use in

Veterinary Ophthalmology

-Corneal erosions Spontaneous Chronic Corneal

Epithelial Defect (SCCED) Post-operative removal of

distichia or ectopic cilia Efficacy of drug delivery via

contact lens Evaluated as UV protection

in animals with chronic superficial keratitis

Contact Lenses

Bausch and Lomb Plano Lenses Soft hydrophilic contact lens Lens material-balafilcon A

(silicone polymer) Hydrogel lenses that allow

prolonged use (up to 30 days in people)

Intraocular Pressure Measurement

Tono-Pen XL Applanation tonometry Based on the principle that the

force required to flatten a certain area of a sphere is the same pressure inside this sphere (Imbert-Fick Law) A total of three measurements are

obtained and a mean is calculated Requires topical anesthesia In humans : affected by central

corneal thickness (CCT), corneal rigidity and refractive surgery (Chirara . Surv of Ophth 2008; 53) positive correlation between CCT and

IOP

Intraocular Pressure Measurement

TonoVet Rebound tonometry Round-tipped probe is

electromagnetically expelled to come into contact with and rebound from the corneal surface and this rebound motion (i.e. deceleration of the probe) is used to estimate the IOP

A total of six measurements are taken and averaged

No topical anesthetic required Topical anesthetics shown to have

no effect on rebound readings (Gorig et al. AJVR 2006; 67, Rusanen et al. Vet Ophtho 2010 vol 13, 1)

In humans : affected by central corneal thickness (CCT), corneal rigidity and refractive surgery (Chirara. Surv of Ophth 2008; 53) positive correlation between CCT

and IOP

Determine if intraocular pressure measurement (IOP) is affected by wearing a contact lens in the canine eye

Determine if applanation vs. rebound IOP reading is more affected by contact lens

Animals Mostly staff owned

dogs with no known ocular abnormalities

Routine ophthalmic examinations performed (KW & JB)

Method Dogs appropriately restrained

in sitting position IOP measurement taken after

application of topical proparacaine with TonoPenXL and TonoVet

Contact lenses placed in both eyes IOP measurement again taken

with TonoPen XL and TonoVet with lenses in place

8 dogs included, 16 eyes 7.6 mean age 2 Yorkies, 3 large mixed breeds, 2 small mixed

breeds, 1 Jack Russell Terrier 6 age-appropriate ophthalmic exams, 1 bilateral

incipient cataracts, 1 SCCEDs OD + pigmentary keratitis OS secondary to chemical burns

Average Across Left and Right eye

TonoPen w/out lens

TonoPen with lens

TonoVet w/out lens

TonoVet with lens

MEAN 10.19 9.63 10.13 11.31

STD DEVIATION

2.81 2.99 2.68 3.30

IOP measured in mmHg

Average Across Tonometer

Without contact lens With contact lens MEAN 10.16 10.47 STD DEVIATION 2.70 3.21

IOP measured in mmHg

RESULTS

Good agreement with IOP measurement between TonoPen and TonoVet without contact lens

There was no effect of having a contact lens in (or not) on the IOP measurement using either TonoPen or TonoVet p< 0.01

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Without lens With lens

IOP

(mm

Hg)

Lens condition

Tonopen

Tonovet

A contact lens can remain in place when checking IOPs with either the TonoPen or TonoVet….in dogs with IOP in the normal range

Good agreement with findings in humans The effect of hydrogel and silicone hydrogel contact

lenses on the measurement of intraocular pressure with rebound tonometry (Zert F, et al. Contact Lens & Anterior Eye 34 (2011) 260-265). Rebound tonometry (ICare) can be reliably

performed over silicone hydrogel contact lenses (not plano lenses) 36 people, OD tested with and without contact lenses

Good agreement with findings in humans Applanation tonometry in silicone hydrogel contact

lens wearers (Allen RJ, et al. Contact Lens & Anterior Eye. 30 (2007) 267-269)

IOP can be reliably measured by applanation tonometry (Goldmann) over silicone hydrogel contact lenses Compared IOPs of 20 normal eyes with and without

contact lenses (w/=15.55 +-1.70mmHg) and (w/out=16.05+-1.90mmHg) with a mean difference of -0.5+-0.89mmHg

Good correlation to previous canine studies Intraocular pressure measurement through two

types of plano therapeutic soft contact lenses in dogs. (Miller PE, Murphy CJ. Am J Vet Res. (1995) Nov; 56 (11): 1418-1420). The IOP was accurately estimated in dogs

(enucleated eyes) using the Mackay-Marg applanation tonometer with the soft contact lenses in place 8 normal enucleated eyes were used to test IOP via

Mackay-Marg tonometry and there was no significant difference in IOP readings with or without the contact lens in the IOP range < 30mmHg (not a clinically significant difference at IOPs > 30mmHg)

Accuracy of intraocular pressure measurements in dogs using two different tonometers and plano therapeutic soft contact lenses (Ahn J-T, et al. Vet Ophth (2011) online preview). TonoPen XL readings better correlated to actual IOP

readings (based on transducer determine IOPs) over a range of IOP with contact lens in place in enucleated eyes TonoVet tended to overestimate IOPs in enucleated eyes in

the 10-40mmHg range when contact lens was in place whereas TonoVet was more reliable than TonoPen XL without a contact lens

Authors suggest that rebound tonometer is more affected by central

corneal thickness (CCT) than applanation tonometer and contact lens artificially increases corneal thickness…TonoVet more affected?

Plano hydrogel contact lenses do not need to be removed in order to check IOP with either TonoPen XL or TonoVet in dogs Do not disturb the healing epithelium!!!!!

Special thanks to Dr. Mary Utter for the stats!! Other thoughts, experiences with contact

lenses? Do you leave them in or take out for IOPs?

What tonometer do you use with lenses in?