OPHTHALMIC DIAGNOSTIC MEDICATIONS

WHICH CLASSES OF DRUGS? Cycloplegics Mydriatics Anesthetics

WHY USE DIAGNOSTICS?

Ocular media and fundus examination Enhancing retinal photography; optical

coherence tomography Refraction through cataracts when pupils are

small Cycloplegic refraction Techniques where anesthesia is required

CYCLOPLEGIA It is the paralysis of the ciliary muscle of the eye, resulting in loss of accommodation.

CYCLOPLEGICS Cycloplegics work by binding to effector sites in

the ciliary muscle thereby blocking action of acetylcholine.

Pupillary dilation is an (unwanted) side effect and its onset precedes cycloplegia.

The optometrist should ensure there are no angle anomalies before instillation of cycloplegic drop.

CYCLOPLEGICS Cycloplegics are most often used in

children in the presence of esotropia or esophoria or when latent hypermetropia is suspected.

Another use is to impose penalization of a dominant eye in amblyopia.

COMMON CYCLOPLEGIC DRUGS

Atropine Cyclopentolate Tropicamide

ATROPINE Atropine is a strong cycloplegic agent. Atropine Sulphate is used 0.5% and 1% 

as eye drops; and 1% eye ointment. Muscarinic antagonist. Peak effect of the drug is in 2-3 days. Duration is 7-10 days.

TROPICAMIDE Tropicamide (Midriacyl) is also a short-

duration cycloplegic available in 0.5% and 1% solutions.

For young adults 3 to 4 drops of the 1% solution, separated by a few minutes, will bring about full cycloplegia in about 30 minutes.

Recovery occurs within 6-8 hours.

CYCLOPENTOLATE Short duration cycloplegic agent available

in 0.5% and 1% solutions. Cycloplegia occurs within 30 to 45 minutes

and persists for as long as 24 hours. For children aged 6 to 16, one drop of 1%

solution For adults one drop of 0.5% solution.

SIDE EFFECTS Blurring of vision Patient cannot read Photophobia  Dry mouth Flushing of the face Fever

CONTRAINDICATIONS abnormally shallow anterior

chamber dislocation or subluxation of the

crystalline lens.

MYDRIATICS

Mydriatics dilate the pupil to facilitate a more thorough examination of the fundus, lens periphery and vitreous. They are mostly used on elderly patients, as older pupils are usually smaller and lens opacities and abnormal retinal conditions are not uncommon.

MODE OF ACTION

The pupil dilator muscle is innervated by the sympathetic nervous system and sympathomimetic drugs will cause a contraction of the dilator muscle causing mydriasis. Sympathomimetic drugs also have little effect on accommodation.

MYDRIATICS USES Mydriatics are used to examine properly the

ocular media and ocular fundi Retinoscopy through small pupil and cataract Recent onset of floating vitreous opacities,

especially if accompanied by the symptoms of flashing light.

Fundus photography.

ANTIMUSCARIANIC MYDRIATICS

TROPICAMIDE1. Tropicamide is the antimuscarinic mydriatic of choice

today.

2. Normally available in 0.5% and 1.0% strengths, the weaker solution is used most often for mydriasis; the 1% strength is used for cycloplegia.

3. Tropicamide is quick in onset and short in duration (Onset in 20-30 minutes and duration of cycloplegic effect is 6-8 hours)

All cycloplegics can be used as mydriatics but the effect is usually too long lasting. The following have been used in the past:

CYCLOPENTOLATE The mydriatic concentration of cyclopentolate

is 0.1% (compared with 0.5% and 1.0% for cycloplegia). However, this strength is no longer available and if cyclopentolate is used as a mydriatic then significant cycloplegia will accompany its use.

HOMATROPINE At one time, homatropine was the principal

mydriatic. The mydriatic effect commences in 10–20 min and is maximal in 30–40 min.

Recovery takes the same time as cyclopentolate if a miotic is not used, but it can be as prolonged as 3 day.

CONTRAINDICATIONS Patients using pilocarpine for the treatment of glaucoma Narrow-angle glaucoma Abnormally shallow anterior chamber (due to the risk of

angle-closure glaucoma) Dislocation of the crystalline, or an intraocular lens An intraocular lens of the anterior chamber or iris-

supported type.

SYMPATHOMIMETIC MYDRIATICS

Phenylephrine is the only sympathomimetic mydriatic in regular use. It is available in a variety of strengths but 2.5% and 10.0% are most often used.

PHENYLEPHRINE Mydriasis commences in about 10 min and is

maximal in 30 min; the mydriasis lasts for several hours.

There is little doubt that sympathomimetics produce less effect on accommodation than antimuscarinics, and some authors (Kanski 1969) suggest that phenylephrine produces mydriasis without any cycloplegic effect at all.

ANESTHETICS Local anaesthetics are chemical

agents that reversibly block the transmission of nerve impulses along sensory fibres.

MODE OF ACTION Sensory information passes along nerve fibres via

electrical impulses, or action potentials. When the nerve is at rest, the interior has a negative charge. An action potential is generated by the influx of sodium ions into the interior of the nerve, giving it a positive charge (depolarization). The nerve fibre is returned to its resting potential (negative state) by the efflux of potassium ions (repolarization). The action potential is then generated along the axon by successive depolarization and repolarization of adjacent regions.

INDICATIONS FOR USE Foreign body removal Tonometry Contact lens fitting Gonioscopy Certain diagnostic procedures like

Schirmer’s test.

ANESTHETICS Among the topical anaesthetics, the most widely

used agents are proparacaine hydrochloride 0.5% (Alcaine), benoxinate 0.5% and tetracaine 0.5%.

The instillation of 1 drop of these compounds renders the corneal epithelium insensate within 15 seconds.

Reapplication will enhance the anaesthetic effect