Abstract
Purpose We investigated the effect of age and sex on corneal touch threshold (CTT) and duration of action following administration of 0.5% topical ophthalmic proparacaine and tetracaine hydrochlorides. Methods A prospective, randomized, subject-masked, crossover study design was used. Two hundred and forty human volunteers were enrolled in the study. Corneal touch threshold (CTT) was determined using a Cochet-Bonnet esthesiometer. CTT was measured every 15 seconds for the first 1-minute and at 5-minute intervals subsequently for a period of 40 minutes after the application of each anesthetic. CTT and duration of action of the ophthalmic solutions were tested for statistical significance using repeated measures ANOVA. Results The total duration of effect was 20 minutes for females and 25 minutes for males for both anesthetics. The total duration of the effect of both solutions decreased with increasing age; however, elderly participants had the longest duration (5 minutes) of the maximal effect (minimum CTT) of the two ophthalmic preparations. There was a significant influence of sex, F (2.39, 569.65) = 2.86, p=0.04; F (3.48, 828.19) = 4.41, p=0.003, and age, F (4.78, 566.18) = 8.97, p < 0.001; F (7.19, 852.56) = 20.55, p < 0.001 on CTT following application of proparacaine hydrochloride and tetracaine hydrochloride, respectively. Conclusion CTT and duration of anesthetic effect after instillation of 1 drop of 0.5% proparacaine hydrochloride and 0.5% tetracaine hydrochloride vary based on sex and age.
Highlights
Assessment of corneal touch threshold (CTT) using the esthesiometer has been studied in corneal pathologies, preoperative and postoperative corneal surgeries, to verify predictive sensibility deficits of unrecognized pathologies [1, 2]. e corneal sensibility and the duration of the anesthesia are fundamental in anterior segment surgeries, especially in complex interventions involving the cornea and the lens [1, 2]
Local anesthetics are primarily weak bases that are made up of three important components: an aromatic ring, an intermediate-length ester or amide linkage, and a tertiary amine [4]. ese components contribute to their lipid solubility, the extent of protein binding, and dissociation constant [5,6,7,8,9,10], which are correlated with their potency, duration of action, and onset, respectively [11, 12]
Oertel et al [21] reported a trend of higher serum concentration of a local anesthetic in older healthy subjects versus young participants. e authors attributed this finding to lean body mass, increase in body fat, and decrease in total body water in the elderly
Summary
Assessment of corneal touch threshold (CTT) using the esthesiometer has been studied in corneal pathologies, preoperative and postoperative corneal surgeries, to verify predictive sensibility deficits of unrecognized pathologies [1, 2]. e corneal sensibility and the duration of the anesthesia are fundamental in anterior segment surgeries, especially in complex interventions involving the cornea and the lens [1, 2].Anesthetics are medications that block sensation, and they work by blocking neural impulses [3]. E corneal sensibility and the duration of the anesthesia are fundamental in anterior segment surgeries, especially in complex interventions involving the cornea and the lens [1, 2]. Local anesthetics are primarily weak bases that are made up of three important components: an aromatic ring, an intermediate-length ester or amide linkage, and a tertiary amine [4]. Age-related changes such as an increase in body fat, decrease in lean body mass, Journal of Ophthalmology the affinity of serum protein to protein-bound drugs, and decrease in total body water affect drugs absorption, distribution, metabolism, and elimination [14,15,16,17,18,19,20]. E authors attributed this finding to lean body mass, increase in body fat, and decrease in total body water in the elderly Oertel et al [21] reported a trend of higher serum concentration of a local anesthetic (articaine) in older healthy subjects versus young participants. e authors attributed this finding to lean body mass, increase in body fat, and decrease in total body water in the elderly
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