|Year : 2016 | Volume
| Issue : 2 | Page : 22-24
Does Topical Lignocaine Actually Produce any Mydriasis at All?
Nihar Ranjan Biswas1, Vinay Kumar Garodia2, Mahipal Singh Sachdev3, Harsh Kumar3, Supriyo Ghose4, Ashok Kumar Dubey5
1 Honorary Professor of Clinical Pharmacology, IGIMS, Patna, India
2 Dr. RP Center for Ophthalmic Sciences, All India Institute of Medical Sciences, Ansari Nagar, New Delhi, India
3 Centre for Sight, B-5/24, Safdarjung Enclave, New Delhi, India
4 Dr RP Center for Ophthalmic Sciences, All India Institute of Medical Sciences, Ansari Nagar, New Delhi, India
5 School of Medical Sciences and Research, Sharda University, Gr. Noida, U.P, India
|Date of Web Publication||15-Dec-2020|
Nihar Ranjan Biswas
Honorary Professor of Clinical Pharmacology Indira Gandhi Institute of Medical Sciences, Sheikhpura, Patna, Bihar
Source of Support: None, Conflict of Interest: None
Occasionally, some mydriasis is noticed apparently after the use of topical lignocaine. We wanted to definitely establish whether, under controlled conditions, topical lignocaine on its own realty dilates the pupil or not. Forty healthy eyes of 20 subjects were evaluated in a randomized controlled study. Pupil diameters were carefully measured using a rule pupillometer, before and after instilling a drop of 4% lignocaine or its vehicle as a control. In 20 eyes of 10 of these subjects, a second drop of lignocaine or vehicle was also used. The measurements taken at 10 minutes intervals upto 1 hour revealed no effect at all on the pupil size with either drops. Any ‘mydriasis’ noted clinically with lignocaine must be either because of contamination with a cycloplegic/mydriatic, or the potentiation effect of even a trace of the latter by lignocaine.
Keywords: Lignocaine, Mydriasis, Anaesthetic, Contamination.
|How to cite this article:|
Biswas NR, Garodia VK, Sachdev MS, Kumar H, Ghose S, Dubey AK. Does Topical Lignocaine Actually Produce any Mydriasis at All?. J Indira Gandhi Inst Med Sci 2016;2:22-4
|How to cite this URL:|
Biswas NR, Garodia VK, Sachdev MS, Kumar H, Ghose S, Dubey AK. Does Topical Lignocaine Actually Produce any Mydriasis at All?. J Indira Gandhi Inst Med Sci [serial online] 2016 [cited 2021 Dec 7];2:22-4. Available from: http://www.jigims.co.in/text.asp?2016/2/2/22/303378
| Introduction:|| |
Topical ocular anaesthetics play a vital role in the diagnosis and treatment of ophthalmic disease. Ophthalmologists have long used them for their ability to provide comfort to the patients undergoing testing and to permit minor surgical procedures. In our part of the world, lignocaine, (an amide), also known as lidocaine, is the most popular topical anaesthetic used, commonly available as Xylocaine®. Occasionally, some mydriasis is noticed apparently after the use of topical lignocaine. Many of us have seen this in our hospital practice, and many others may have also come across this situation though may be without reporting it. On searching the literature, we could not find any study about a possible mydriatic effect of lignocaine. We were curious to determine whether such a mydriasis, if any, may have something to do with the mechanism of action similar to that say of cocaine (which is known to act as a mydriatic by its indirect sympathomimetic effect,, besides its topical anaesthetic effect like lignocaine).
We actually planned a study to investigate lignocaine as a possible potentiator for the mydriatic action of tropicamide. Therefore, prior to this, we wanted to definitely establish whether, under controlled conditions, topical lignocaine itself really does dilate the pupil on its own or not.
| Materials and Methods:|| |
A double masked, placebo controlled, randomized clinical study was carried out after obtaining ethical clearance from the Institue’s Ethics Committee and written informed consent from the patients. A total of 40 healthy dark brown eyes of 20 subjects of both sexes were studied. Care was taken to include only those eyes that were on no form of topical medication and neither had any previous drops instilled in the eyes for at least 2 weeks prior to our test. The method of measuring the pupil size is detailed below. After taking the baseline measurements of both pupils, one of the eyes of each subject received a drop of lignocaine 4% while the other eye acted as a control and received a drop of placebo.
The drug (lignocaine hydrochloride) was obtained as sealed Xylocaine® 4% colourless eye drops (ASTRA- IDL), transferred into fresh, clean, sterile vials in the pharmacy of our eye centre. Identical vials were filled with the placebo (vehicle for Xylocaine®, i.e., water for injection along with methylparaben 1 mg/ml) freshly prepared in our pharmacy. Both the drug and placebo filled vials were coded for this double masked study. The droppers used were selected to deliver a standardized uniform drop size. The vials and droppers were stringently cleaned and sterilized to avoid any possible chances of contamination with any otherdrug.
The coded drops were instilled in a standardized manner into the inferior cul-de-sac of each eye, which had been pouched by pinching the lower eyelid while the subject looked up. The subject was then asked to look down and the lower eyelid was allowed to come in contact with the globe, enclosing the administered solution in a kind of conjunctival pocket. The subject was then asked to close the eyes gently and not to blink or squeeze the eyelids for a minute as far as possible. This method of instillation was used to increase the contact time between solution and the cornea. Care was taken not to touch the dropper tip onto the subject’s eye.
The horizontal pupil diameter was noted as a baseline, and later at every 10 min intervals until 1 hour after instillation of drops. A Rule Pupillometer [Figure 1] with a least count of 0.5 mm was used to measure the pupil size using standardized low oblique illumination in similar dimly lit surroundings. The pupilometer was placed transversely at the mid level of the pupil as close to the eye as possible without touching it or the lashes, and the pupil size was compared to the semi-circles of different sizes [Figure 1]. Such a pupillometer has been used in previous studies and given reliable and reproducible results.
|Figure 1: The rule pupillometer (with a least count of 0.5 mm) used for measuring the pupil size.|
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In 10 of these 20 subjects, to heighten the mydriatic effect if any, each eye received a second drop of the same coded drug 5 min after the first drop. The pupil diameters were measured thereafter in the same manner as explained above.
| Results:|| |
The 20 subjects (M:F =12:8) ranged in age from 19 to 48 years. Their baseline pupillary diameters were from 3.0 mm to 4.5 mm with a mean of 3.5 mm. There was no significant difference between the pupillary diameters of both eyes in any of the subjects tested. After instillation of either lignocaine or placebo, there was no change in pupil size noted in any eye over the period of 1 hour. Even in the subjects who received two drops of either lignocaine or placebo, no change in pupil size could be detectable.
We found the rule pupillometer to be a very practical method for measuring the pupil size with 0.5 mm accuracy.
| Discussion:|| |
Rule pupillometer is an established device for measuring pupil size. It has an advantage over other methods for recording papillary diameter (like reticule of Goldmann perimeter, infra-red photography, entoptic measurement, etc.) in being simple, cheap portable and reproducible.
In our methodology, we have tried our best to remove any confounding factors. Normal eyes of healthy subjects were chosen with no known diseases like diabetes, neurological disorders, glaucoma, uveitis etc. or even senility, which can prevent or vitiate the pupillary dilation. These eyes had not received any other drop in the previous two weeks at least, to remove any possible other influences and also any possible chance of contamination of our dropper tip. The vials and the droppers used were fresh, clean, and sterilized to avoid any possibility of contamination. The study was double masked to eliminate any bias from the observer. As it turned out, decoding was not really required, as neither of the coded drops (lignocaine nor the placebo) changed the pupil size.
We find from our limited study that neither lignocaine alone nor its vehicle (methylparaben and water for injection) dilates the pupils. So it seems that lignocaine does not share the mechanism of action of cocaine as far as its effect on pupils is concerned.
Any ‘mydriasis’ noted occasionally with lignocaine in clinical practice is therefore not because of any direct mydriatic effect of lignocaine, but must be probably because of contamination somehow with a mydriatic. This contamination may occur from using the bottle or dropper used earlier for a mydriatic solution. This inadvertent admixture may even occur more likely with the tip of the dropper of lignocaine vial, which may get contaminated with a mydriatic while instilling the lignocaine drop, by unwittingly touching the patient’s eye, which has already received a mydriatic shortly before. This contaminated dropper tip of the lignocaine bottle perpetuates the mydriatic effect onto other eyes instilled subsequently with this “lignocaine”.
If topical lignocaine does potentiate the effect of an instilled mydriatic drug, then this even minute amount of mydriatic contaminating the drop of lignocaine instilled in further eyes may suffice to produce clinically evident mydriasis. The results of our further study in this area will be detailed in subsequent publications.
| References|| |
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