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The purpose of
the practical sessions was to observe the differences in effects between two
anti-muscarinic drugs: Cyclopentolate (1%) and Tropicamide (0.5% and 1%). The
aim was to compare the effects of two drugs and the effect of concentration of
Tropicamide on pupil dilation, amplitude of accommodation, and accommodative
lag or lead for the purpose of cycloplegia and mydriasis. 

Cyclopentolate
is the cycloplegic drug of choice for optometrists, while Tropicamide is
typically used for mydriasis.  Both drugs
are anti-muscarinics, which work by blocking the acetylcholine receptor,
causing paralysis of the ciliary muscle and the iris sphincter muscle (Egashira
et al., 1993). Cycloplegics aim to inhibit accommodation to allow for a more
reliable estimate of refractive error, while mydriatics increase pupil dilation
for an easier fundus assessment (Manny et al., 2001).  For cycloplegia and mydriasis, the ideal drug
should have minimal side-effects and contra-indicators, with a rapid onset of
achieving the desired cycloplegic or mydriadic effect (Sani, 2016).

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            A
subject had one drop of Tropicamide 0.5% instilled in their right eye, and one
drop of Tropicamide 1.0% instilled in their left eye.  Another subject had one drop of Cyclopentolate
1.0% instilled in their right eye.  Pupil
diameters, amplitude of accommodation, and accommodative lag were measured at
six minute intervals.  Pupil reactions
and spherical change were also tested at different points.  Retinoscopy and subjective refraction were
performed prior to drop instillation and following the full onset of the drugs.

            The
current study’s results (Appendix) support Egashira et al. (1993) findings that
although Tropicamide can be used for cycloplegic refractions, Cyclopentolate results
in lower residual accommodation, which Egashira et al. (1993) suggests is more
accurate for latent hypermetropes.  Although
the final overall residual accommodation was lower for Cyclopentolate, two-tailed
t-tests showed significant no differences (p>0.05)
in residual amplitude of accommodation between Tropicamide 0.5% and Cyclopentolate
(p=0.186), Tropicamide 1.0% and Cyclopentolate (p=0.124), or between the two
concentrations of Tropicamide (p=0.213). 
Further, there was no evidence (p>0.05) of increased pupil dilation
between Tropicamide 1.0% and Cyclopentolate (p=0.436).  However, there was a difference (p<0.05) between Tropicamide 0.5% and Cyclopentolate (p=0.006) and between concentrations of Tropicamide (p=0.048), which suggests that Tropicamide 1.0% is the drug of choice for mydriasis because of its shorter duration of Cycloplegia compared to Cyclopentolate (Egashira et al, 1993).  The current study suggests that there are no significant differences in cycloplegia (t=0.32, p>0.05) between a 0.5% and a 1.0% dose of Tropicamide
which supports a study by Pollack, Hunt and Polse (1981).  There were no significant differences
(p>0.05) between the drugs for accommodative lag, which can be explained by
Chua et al.’s (2006) study that suggested that cycloplegia causes blurred
vision at near.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Appendix

 

Subject 1

Subject 2

 

Hair Colour

Brown

Blonde

Iris Colour

Brown

Blue

Drug

RE: Tropicamide 0.5%

LE: Tropicamide 1.0%

Cyclopentolate 1.0%

Minim Batch no.

RE: 2540N

LE:H2347

H2355N

Minim Expiry Date

RE:12/18

LE:10/18

10/18

 

Table
1-
Subject characteristics and dosage information

 

 

 

 

 

Figure
1-
Effects of 1.0% tropicamide, 0.5% tropicamide and 1.0 % cyclopentolate on pupil
diameter

 

Figure
2
– Effects of 1.0% tropicamide, 0.5% tropicamide and 1.0 % cyclopentolate on
amplitude of accommodation

 

 

Figure
3
– Effects of 1.0% tropicamide, 0.5% tropicamide and 1.0 % cyclopentolate on
accommodative lag

 

 

 

 

Tropicamide
0.5%

Tropicamide
1.0%

Cyclopentolate
1.0%

Baseline retinoscopy

+1.25/-1.00×180

+1.25/-1.00×180

-3.25/-0.75×180

Final Retinoscopy

+0.50/-0.50×90

+0.25/-0.25×90

-3.50/-0.50×180

Baseline Subjective

+0.50/-0.25×150

+0.50/-0.25×50

-3.25/-0.75×160

Final Subjective

+0.25/-0.50×90

+0.25/-0.25×90

-3.50/-0.50×180

 

Table
2
– Retinoscopy and subjective refractive results before instillation of
tropicamide or cyclopentolate and upon completion of all of the measurements

 

 

 

References

Chua, W.H. et al. 2006. Atropine for the
treatment of childhood myopia. Ophthalmology, 113(12), pp.2285-2291.

 

Egashira, S.M. et al. 1993. Comparison of
cyclopentolate versus tropicamide cycloplegia in children. Optometry
& Vision Science, 70(12), pp.1019-1026.

 

Manny, R.E. et al. 2001. Tropicamide (1%): an
effective cycloplegic agent for myopic children. Investigative
ophthalmology & visual science, 42(8), pp.1728-1735.

 

Pi, L.H. et al. 2011. Comparison of cycloplegic
retinoscopy using cyclopentolate or tropicamide eye drops in an epidemiologic
study of pediatric refraction among 1907 school-aged children. Scientific
Research and Essays, 6(3), pp.635-640.

 

Pollack, S.L., Hunt, J.S. and Polse, K.A.,
1981. Dose-response effects of tropicamide HCI. Optometry & Vision
Science, 58(5), pp.361-366.

 

Sani, R.Y. et al. 2016. Cycloplegic effect of
atropine compared with cyclopentolate-tropicamide combination in children with
hypermetropia. Nigerian medical journal: journal of the Nigeria Medical
Association, 57(3), p.173.

 

Yazdani, N. et al. 2017. Comparison of
cyclopentolate versus tropicamide cycloplegia: A systematic review and
meta-analysis. Journal of Optometry

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