Year : 1984 | Volume
: 32 | Issue : 4 | Page : 213--216
Mydriasis-use of phenylephrine (a dose-response concept)
S Chawdhary, SK Angra, R Zutshi, MS Sachdev
Dr. Rajendra Prasad Centre for Ophthalmic Sciences, AIIMS., New Delhi, India
B44. Kailash Apartments, Lala Lajpat Rai Road, New Delhi-110 048
|How to cite this article:|
Chawdhary S, Angra S K, Zutshi R, Sachdev M S. Mydriasis-use of phenylephrine (a dose-response concept).Indian J Ophthalmol 1984;32:213-216
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Chawdhary S, Angra S K, Zutshi R, Sachdev M S. Mydriasis-use of phenylephrine (a dose-response concept). Indian J Ophthalmol [serial online] 1984 [cited 2023 Jun 2 ];32:213-216
Available from: https://journals.lww.com/ijo/pages/default.aspx/text.asp?1984/32/4/213/27391
Phenylephrine hydrochloride is a myd�riatic used widely for various indications. It is marketed in concentrations of 10% and 5% drops. Systemic cardiovascular effects like elevated blood pressure and arrythmias are reported by the use of 10% Phenylephrine in susceptible individuals,,,,,. The effectivity of lower concentrations (5% and 2.5%) for myd�riasis have been reported,, in races with blue irides. Blue irides respond favourably to 2.5% concentration while dark irides require 10% concentration. We endeavoured to study the effects of various dilutions of Phenylephrine hydrochloride in terms of effective mydriasis and cardiovascular mileu, inIndian popula�tion having brown irides.
MATERIALS AND METHODS
40. Indian patients, all with dark brown irides, in the age group 20-40 years, were sub�jects of this masked study. The criteria for inclusion in the study were normal general health, no systemic hypertension or diabetes mellitus. The cases with any active ocular dis�ease, shallow anterior chambers and patients on any systemic or topical drugs were excluded. The cases were divided into 4 groups of 10 patients each. Fresh aqueous solution of Phenylephrine hydrochloride was prepared in concentrations of 10%, 5%, 2.5 and 1.25%. The drugs were coded and used randomly. The pulse rate, systolic and dias�tolic blood pressure in sitting posture and pupil size on Goldmann perimeter telescope were noted at different time intervals. One drop of the drug was put every 1 minute three times in the lower conjunctival cul-de-sac. The parameters were recorded periodically as shown in [Table 1][Table 2][Table 3]. The code was broken at the end of the study. The results were analysed statistically.
The mean values of readings of heart rate. systolic blood pressure and diastolic blood pressure, and puillary sizes at 2, 4, 6, 8, 10, 15, 20, 30, 50 and 70 minute intervals are shown in [Table 1][Table 2][Table 3] respectively. It was observed through F values that differences in variation of heart rate, systolic and diastolic blood pressure after the use of drops at dif�ferent intervals were highly significant bet�ween different concentrations (10%, 5%, 2.5 and 1.25%). Less concentrated drops yielded lesser variation in heart rate and blood pre�ssure. However there was no statistically significant difference between concen�trations of 10%, 5% and 2.5% in achieving full mydriasis at 70th minute, while with the 1.25% concentration there was a statistically signifi�cant lesser effect (5.8�0.27 mm) in causing mydriasis at that particular time. The myd�riasis satisfactory for fundus examination (7.0 mm or more) could not be achieved by 1.25% drops whereas 2.5% drops achieved this [Table 3]. The pupillary size at 70 minutes with different concentrations of Phenyleprine is shown in [Figure 1].
The dilatation of pupil (mydriasis) has different indications e.g. fundus examinations, old age refractions, for visual gain in cataract etc. and degree of dilatation of pupil for each indication varies. All indications do not need full mydriasis.
In our study, we endeavoured to correlate the degree of mydriasis with safe and effective concentration of the drug Pheylephrine hydrochloride.
Phenylephrine is an effective and relatively safe drug for mydriasis. Side effects after topi�cal instillation of 10% drops includes tachycar�dia, elevated blood pressure and cardiac arry�thmias,,,,,. Hence, it may be unsafe in suscept�ible cases of cardiac disease, hypertension and aneurysms. We have observed that myd�riasis is achieved with almost equal rapidity with 10%, 5% and 2.5% concentrations of the drug. Mydriasis was delayed when 1.25% con�centration of the drug was used. Our obser�vations are in agreement with those of Meyer et als and Hadad et a1 who found that the dif�ference in mydriasis achieved with 10%, 5% or 2.5% concentration of Phenylephrine was not more than 0.5, mm. Rather, in our study we found no statistically significant difference between mydriatic effect of these concen�tations. The 2.5% concentration is equally effective and more safe than 5% concentra�tion. The concentration of 1.25% and 2.5% Phenylephrine as evaluated by us does not alter the cardiovascular mileu while the 5% and 10% concentration do effect this.
The mydriasis achieved by 1.25% drug is significantly less than that by 2.5%. By reduc�ing the concentration to 2.5% we have reduced the dose administered to 1/4 (1 drop of 10% Phenylephrine arpox. 6.6 mg) and with the use of 1.25% the dose administered is reduced to 1 /8 of the conventional dose. The mydriatic effect is not reduced with the use of 2.5% drops while it is slightly reduced with 1.25% concen�tration of Phenylephrine.
Higher concentrations instilled topically produce blanching and constriction of con�junctival blood vessels. This, when used for longer periods in cases where periodic instillations are required, can lead to local ischaemic changes and pigmentations. Lower concentration of 2.5% while producing effec�tive mydriasis may not produce such severe side effects.
It is evident from our study that lower con�centrations of Phenylephrine are equally effective in brown irides. This is contrary to the belief that the brown irides respond only to 10% Phenylephrine for mydriasis, as repor�ted by Barbee et al.
To achieve clinical and pharmacological goals of therapy (optimal effects, decimal hazard and minimum dose), it is recommen�ded that for routine dilatation of pupil 2.5% and for long term use 1.25% of Phenylephrine should be used i.e. 1:4 dilution of 10% Phenylephrine drops for mydriasis and 1:8 dilution of 10% Phenylephrine for long term use e.g. in cases where fuller mydriasis is not indicated.
Pupillary dilatations and cardiovascular side effects were studied after topical use of
10%, 5%. 2.5`x, and 1.25% concentrations of Phenylephrine hydrochloride in 40 Indian patients with brown irides. There was no statistically significant difference between the pupillary dilatations achieved with 10%,, 5% and 2.5% concentrations of Phenylephrine. The concentration of 1.25% of Phenylephrine could produce pupillary diatation of 5.8�0.27 mm. The potentially dangerous side effects are greatly avoided by diluting the drug to achieve the desired amount of pupillary dilatation.
We are thankful to Mr. Vijay Kumar Chhabra for help in statistical analyses.
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