Kathryn L. Wotman, DVM, DACVIM Jeffrey E. Bowersox, DVM, DACVO Veterinary Specialty Center of Delaware
Contact Lensesuse 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 20.00 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 IOP (mmhg) 18.00 16.00 14.00 12.00 10.00 8.00 6.00 Tonopen Tonovet 4.00 p< 0.01 2.00 0.00 Without lens With lens Lens condition
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?