between Mydriatics and Cycloplegics
Aims and background
Mydriatics and cycloplegics
are drugs that cause an increase in pupil size by paralysis of ciliary muscles
in opposing ways. This impacts visual acuity and accommodative convergence¹. Irrespective
of this, they allow thorough fundoscopic examinations, correction of latent
refractive errors and many other purposes².
The aim was to compare and
analyse the impact different dilating drops have on the human eye. Various measurements
were derived over a set time to allow appropriate comparisons.
The chosen mydriatic drug was
tropicamide and for cycloplegic, cyclopentolate. Both have been associated in
causing angle closure glaucoma, however the risks are low³.
Two subjects were required. One
had a drop of 1.0% cyclopentolate for 60 minutes and the other had 0.5% and
1.0% concentrated tropicamide (CT) in each eye respectively for 42 minutes.
Prior to instillation, a series of observations and baseline measurements were performed.
With a distance prescription on, the amplitude of accommodation and accommodative
lag/lead were measured and monitored every six minutes following instillation, alongside
pupil diameter. After completion, intraocular pressures and baseline
measurements were re-checked.
1.0% cyclopentolate proved to
be more effective with its quick onset, rapid decline in accommodation and accommodative
lag, along with overall longevity of effect. Similar characteristics were seen
in mydriatics, both mirroring a similar trend with the 0.5% CT having the lowest
impacts. The derived p-values showed insignificance, thus displaying a limited difference
between the drugs. Both agents suspend accommodation for
cycloplegic refractions and cause pupil dilation for
fundoscopic examinations, but mainly have different durations of impact.
Variations between subjects require
consideration as it influences results. Both participants had dark eyes which generally
require greater instillation of drops for adequate dilation?. Other factors such as age and genetics also influence
dilation size, but to a low percentage?.
Side effects of drugs is
another area that must be considered in the comparison. It has been discovered
that tropicamide causes minimal systemic and ocular reactions compared to
cyclopentolate. On the contrary, cyclopentolate has been associated with
reactions like a sting sensation, nausea and vomiting¹.