Paralysis of the ciliary muscle of the eye: what is cycloplegia

By Cristiano Antonino On Mar 27, 2023

In ophthalmology, the term cycloplegia is used to define a paralysis of the ciliary muscle of the eye

This involuntary muscle is located inside the eye and allows the shape of the crystalline lens, the natural lens that, together with the cornea, converges light rays onto the retina allowing vision, to change.

The action of the ciliary muscle allows a change in the eye’s ability to focus, enabling the vision of closer objects (accommodation).

Therefore, paralysis of this muscle will produce symptoms similar to those of presbyopia.

Those who find themselves in the condition of cycloplegia, and we will see below how it can occur, will experience a more or less acute difficulty in focusing on objects close to them.

The causes of cycloplegia are many, but certainly the most common is induced cycloplegia

Through this condition, in fact, many ophthalmologists can initiate a thorough test of the eye. To do this, specific drugs are used, usually in the form of eye drops, called Cycloplegic drugs.

These are aimed at blocking the contraction activity of the ciliary muscle and to a varying extent can also cause dilation of the pupil (mydriasis) allowing the health of the eye to be analysed and its posterior segment to be visualised.

The effects of this condition are many and the explanation is simple: the ciliary muscle is responsible for many functions of the eye, first and foremost focusing.

Furthermore, this muscle makes it possible to see objects at different distances.

This makes it difficult to perform everyday activities, such as reading, looking at a smartphone and even driving for varying lengths of time.

Cycloplegia in children

Cycloplegia in children is certainly more delicate than in adults.

Indeed, eye tests can be very complex to perform on very young children.

In order to proceed with a diagnosis of visual defects, such as hypermetropia or myopia, the ophthalmologist may require the use of eye drops that can relax the ciliary muscle causing cycloplegia.

Of course, the paediatric eye examination presents different difficulties, in fact even the simple instillation of drops of an eye drops inside the eyes can take longer with sometimes suboptimal cooperation in younger children.

However, testing in a cycloplegic condition is essential in young patients, as the action of the ciliary muscle, which is more tenacious at this age, can mask ‘latent’ refractive defects, leading to suboptimal correction of the hypermetropia or myopia present.

Moreover, the effects of these products on children can last up to more than 24 hours, usually characterised by difficulty in focusing on nearby objects.

Thanks to this specific test, which is non-invasive for adults but slightly more complex for children, various vision defects can be diagnosed from a very young age.

Among these pathologies are:

exotropia
anisometropia
hypermetropia
asthenopia
accommodative spasm

Particularly in children under the age of four, this test is essential, because some of these conditions, such as the so-called ‘lazy eye’ (amblyopia), can only be effectively treated by intervening at pre-school age.

Cycloplegia test

The cycloplegia test is a medical examination that varies in duration.

In adults it is often less important to obtain a complete cycloplegia than a complete dilation of the pupil (mydriasis), so the examination may be quicker.

But if a paediatric eye examination is being performed in some situations, it may be necessary to obtain complete cycloplegia even by administering the cycloplegic drug several times and then waiting several minutes until the drug is fully active.

This test is minimally invasive and allows the health status of the eye to be investigated in a short time, as well as its reaction.

The most common cycloplegic drugs are atropine, cyclopentolate and tropicamide

During the medical test, eye drops are applied to the eye and cycloplegia is induced.

This makes it easier for the ophthalmologist to detect any refractive errors in the eye.

Cycloplegia is also accompanied by mydriasis, allowing the retina and posterior structures of the eye to be examined.

Refraction

Specifically, the cycloplegia test is used to assess and analyse the eye’s ability and power of refraction.

To do this, it is necessary to use medication that blocks the ciliary muscle of the eye.

This makes it possible to analyse the refraction of the eye without it being affected by the tone of the ciliary muscle.

Refraction testing is also used to detect various refractive defects in adults.

These include the best-known vision difficulties such as:

myopia
hypermetropia
astigmatism

Especially in adults, this test is essential for those undergoing refractive surgery.

In fact, prior to surgery, it is necessary to verify the correct refractive power in the patient who is to undergo the operation.

Cycloplegia drugs

Cycloplegic drugs are those medicines that aim to bring about paralysis of the ciliary muscle.

These drugs are in fact made using active ingredients capable of stopping this muscle and blocking its activity for a limited period.

Among the active ingredients, the most widely used and best known are:

homatropin
atropine
tropicamide
cyclopentolate

Among the characteristics of these active ingredients is their anticholinergic action.

This word describes the ability of these products to block the effect of acetylcholine.

More simply, these drugs block muscarinic receptors.

Furthermore, these products are not only used for cycloplegic activity, but also to inhibit the iris sphincter muscle.

This induces a mydriatic effect, i.e. dilation of the pupil.

Therapeutic indications

The application of cycloplegic drugs, as anticipated, is primarily for diagnostic purposes.

In fact, these drugs are used for a great many tests, which are indispensable in order to carry out eye examinations to investigate the health status of different parts of the eye.

Tests for cycloplegia are not the only field of application of these drugs.

In fact, there are other therapeutic indications in which cycloplegic drugs are used.

These include:

treatment for inflammation of the eye, specifically uveitis. These drugs make it possible to relax the muscle and treat the inflamed area more easily, especially in the anterior segment. Specifically, atropine is used;
cycloplegic drugs are also used in some specific treatments for strabismus, in particular homatropine used as an adjunct in the rehabilitation of amblyopic eyes;
if one wishes to induce mydriasis and cycloplegia in a short time for specific medical purposes, cycloplegic drugs are the most useful.

Usually, cycloplegic drugs that induce cycloplegia are produced in the form of eye drops

This format is essential to achieve the desired effect locally and ocularly, thus avoiding systemic effects.

These drugs are usually used by doctors and professionals.

In fact, when one goes for a specific examination at the ophthalmologist, the eye drops are administered to the patient directly by the doctor or healthcare personnel.

During the eye examination, a few drops of this medicine are applied, usually acting within 20 minutes.

This gives the medicine time to act.

Medications for cycloplegia can be applied at one time or in several smaller doses and it may be necessary, especially in children, to wait longer than the canonical 20 minutes.

In some more special cases they may also be administered several days earlier.

In this case, the patient does not come into contact with the medicine and does not need a prescription as he/she does not purchase it himself/herself.

In cases where these drugs are prescribed together with specific therapies, however, not only prescriptions may be required but it is absolutely necessary to follow the doctor’s instructions.