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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
0.00
2.00
4.00
6.00
8.00
10.00
12.00
14.00
16.00
18.00
20.00
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?