Cyclorefraction and its significance

Hira Nath Dahal

What is cycloplegia?• It is the paralysis of the

ciliary muscle of the eye ,resulting in the loss of visual accommodation.

• Accommodation is the ability of the lens to change its refractive power to view the near objects clearly.

• It is brought about by the contraction of the ciliary muscles.

What are cycloplegics?

• Agents causing cycloplegia .

• Cycloplegics inhibit the action of the acetylcholine on the effectors sites innervated by the autonomic nerves.

• They block the muscarinic receptor sites.

• They are also called as anti- muscarinics, cholinergic antagonists.

Cholinergic innervations to eye

• Originate within the Edinger – Westphal nucles located within the mesencephalon.

• The preganglionic parasympathetic fibers emerge from the EWN ,exit the CNS , through the third cranial nerve and proceed to ciliary ganglion.

• Synapses takes place with post ganglionic fibres at the ganglion .The post ganglionic fibres enter the globe through the short ciliary nerve and terminate on the iris sphincter muscle and the ciliary body.

• Neurotransmitter in the effectors site is acetylcholine

Parasympathetic action in eye

• The pupil size is determined predominantly by the varying degree of the parasympathetic innervations to the sphincter muscles.

• The contraction of the sphincter muscle cause the constriction of the pupil.

• The innervation to ciliary body cause contraction of the ciliary muscle to induce accommodation.

• Sympathetic?• The degree of the parasympathetic innervations to the

sphincter in iris and the ciliary muscle is governed by the impact of the pupillary reflex, the light reflex and the near reflex.

Cholinergic receptors

• The cholinergic rceptors in human eye have been found in the iris sphincter and the ciliary body.

• It is of the muscarinic type.Other is nicotinic receptor mainly found in the skeletal muscles.

• Five sub types of muscarinic receptors(M1-M5)have been identified.

• The muscarinic agonist action at the receptor costricts the pupil, contracts the ciliary muscles and in general lower IOP.

• The inhibition of these receptors by the cholinergic antagonist induce the

pupillary dilatation paralysis of accommodation

Cycloplegic refraction?

• It is the procedure to objectively determine the refractive status of the eye when the accommodative action of the eye is totally paralysed.

• Commonly called as cyclorefraction or wet retinoscopy.

Brief history• Reviewed by Bannon in 1947

• He noted that Pliny(23-79AD) discussed the use of various herbs to dilate pupil for the treatment of corneal ulcers, cataracts and other ocular conditions.

• During 18th century atropine and other dilating drops were used for cosmetic purpose.

• It was only in 1811 that the cycloplegic action of atropine was noted.• It was known only when Dr William Wells ,a london oculist , found

that a patient whose pupil were dilated was also found to have failure of accommodation.

• He found the change in accommodation from 7.00 to 1.00 in less that 45 minutes and that the power of accommodation did not returned for 8 days after he instilled belladona to young physicians left eye.

History...

• Cycloplegic refraction was put in scientific basis by Donders .

• It was universally accepted after the publication of the Donders the “ Anomalies of accommodation and refraction of the eye” in 1864.

Cycloplegic agents

Cholinergic antagonists Currently five mydriatic- cycloplegic

cholinergic antagonist are available for topical use.

Atropine sulphate Homatropine hydrobromide Scopolamine hydrobromide Cyclopentolate hydrochloride Tropicamide

Atropine

• Naturally occuring alkaloid • First isolated from the belladona plant(atropa

belladona).• Non selective muscarinic antagonist.• Most potent mydriatic and cycloplegic agent

presently available.• Depending on concentration mydriatic may last

upto 10 days and cycloplegia for 7to 12 days.• Commercially available as the sulphate

derivative in 1% solution or 1% ointment.

Action parameters of atropine

• Cycloplegia begin within 12 to 18 minutes

• Reach to maxium in 106 minutes.

• Accommdation began to retain in 42 hours

• Full accommodation ability usually attained within 8 days.

• Mydriatic effect begain in 12 minutes, reach maxium in 26 minutes and reach initial stage in 10 days.

Clinical use cyclorefraction• Often used for cycloplegic refraction in young ,

actively accommodating children with suspected latent hyperopia or accommodative esotropia.

• It is not typically used for the routine cycloplegic refraction in school aged children or adults due to the prolonged paralysis of accommodation that cause patient handicapped in near vision.

• The use is warranted in the case of esotropia with suspected accommodative component.This may lead to the permanent deviation.

Other usesTreatment of myopia use of atropine may

prevent or slow down the progession of myopia by avoiding the tension due to accommodation.

Treatment of amblyopia. used for mild and

moderate amblyopia as and alternative to occlusion.It is called penalization.

Side effects

Ocular side effects

• Direct irritation from the drug itself.

• Allergic contact dermatitis.

• Risk of angle closure glaucoma .

• Elevation of IOP in patients with open angles.

• Systemic side effects• Diffuse cutaneous flush.• Depressed salivation causing dry mouth and

increase thrist.• Fever• Urinary retention• Trachycardia• Excitments, restlessness, and hallucination• Speech distrubances.• Ataxia• Convulsion.

• In the literature it is mentioned that death of six reported cases have occurred in children 3 years of age or younger.

Atropine contraindications

• Hypersensitivity to the belladona alkaloid.

• Have open angle or angle closer glaucoma

• Have tendency towards IOP elevation.

Homatropine

• One tenth as potent as atropine.

• Shorter duration of mydriasis and cycloplegia.

• It is not the drug of choice for the cycloplegic refraction because of its prolonged mydriatic and cycloplegic action.

scopolamine

• Non selective antagonist

• Maxium cycloplegic occurs in 40 minutes.

• Last for 90 minutes and by the third day accommodation come to normal.

• Not a drug of choice.

cyclopentolate

• Introduced in clinical practice in 1951• Commercially available as 0.5%,1%,and 2% solution. Clinical use• drug of choice for the routine in nearly all age group,

especially infants and young children.• Faster onset of action and shorter duration of effect.• Equally effective as atropine in the case of older

childrens.• Full recovery of mydriasis and cycloplegia occur within

24 hours.• Cycloplegia occurs in 30-45 minutes of instillation.• For children under the age of 6 one or two drops of 1% is

used and for children above 6 , 0.5% is used.

Side effects of cyclopentolate• Ocular side effects• Transient stinging on initial instilation.• Allergic reaction to cyclopentolate are rare and may be

unrecognized by practioner.• Symptoms of irritation and diffuse redness , facial rash that

develope within minutes to hour of instillation.• Lacrimation ,stringy white mucus discharge and blurred vision are

prominent.• Systemic effects• Drowsiness• Ataxia• Disorientation• Distrubance in speech• Restlessness• Visual hallucination.

tropicamide

• Short duration cycloplegic available in 0.5 and 1% solution.

• Cycloplegia in about 30 minutes.

• Recovery occurs within 2-6 hours.

• It is considered inadequate for children cycloplegia.

• Widely used as mydriatic agent.

Choice of cycloplegic agents

The choice of drug depends on its strength duration of action duration of effect side effects.

Which drug do you choose for cycloplegia?

When is cycloplegia ready for refraction?

• The completeness of the cycloplegia is determined by assessing the residual accommodation by push up test.

• The mydriasis and cycloplegia do not complete at the same time.

• Unlike homatropine and tropiamide in the case of cyclopentolate the cycloplegia is completed prior to mydriasis, so often when there is complete mydriasis the cycloplegia is considerd to be complete for the refraction.

• If pupillary dilatation is used to determine whether cycloplegia is at the level of refraction , the refraction may be unnecessarily delayed or additional drug may be used unnecessarily.

Indications for cyclorefraction

The main aim of cyclorefraction is to revel the latent hyperopia that creats problem.

Types of hyperopiaAbsolute hyperopia- that which cannot be corrected by accommodation.

Axial hyperopia- due to axial length

Faculcative hyperopia- that which can be entirely corrected by accommodation.

Latent hyperopia- the degree of total hyperopia that is corrected by the physiological tone of ciliay muscle.

Manifest hyperopia-total hyperopia not corrected by physiological tonus of ciliary muscle.

Total hyperopia- manifest and latent combination.

Old patients- the need of cyclorefraction decrease makdely with age

• The patient beyond 40 is not expected to have latent hyperopia.

Young adults- only if latent hyperopia is a problem.Suspected if asthenopia is complained for near work, but do not have uncorrected hyperopia and other refractive and binocular abnormalities.

• Children if a child often preschool is seen with

convergent strabismus, to find if it is associated with accommodative component.

child having the significant esophoria , should also be undergone cyclorefraction, to find uncorrected hyperopia.

Other indications

• The child uncoperative for the dry retinoscopy.• If the difference in the refractive error of the eyes

is unusually greater.• In the case of oblique astigmatism to determine

the exact orientation of power axis.• If the unusually high astigmatism detected

during dry retinoscopy.• If the retinoscopy finding is much greater than

excepted in the case of hyperopic patient.

Post mydriatic treatment(PMT)

• Assessment of the finding of cyclorefraction by subjective means after the effect of cycloplegia is eliminated.

• If atropine is used ciliary tonus should be subtracted.

• Not necessary in the case of cyclopentolate.

• If blurring is complained with full power obtained from cyclo then?

Cycloplegic and non cycloplegic refraction

• Bannon(1947) did research taking 500 patients.• Results- in the younger age group more percentage showed more

hyperopia in cyclorefraction. cases in which the cycloplegic and non cycloplegic were same

was lower in younger group and highest in older group. certain showed less hyperopia.• In recent research done by Grosvenor and others taking 60

second year optometry students in 1984.• Results the refractive finding under maxium cycloplegia was within +/-0.25

D of the non cycloplegic finding for 41 students. In 19 subjects the cycloplegic refraction was found to be 0.5 to1.25D

more than non cycloplegic refraction.