To refer or not to refer for EDT’s?

Dr Peter Good

Consultant Clinical Scientist

Why refer for EDT’s?

• Unexplained visual loss• Hereditary retinal dystrophy• Nystagmus• Visual Function in paediatrics• Opaque Media• Trauma• Drug Toxicity

Indications for EDT tests

Indication VEP ERG PERG EOG OCT

Visual Loss

Heredo-macular

Nystagmus

Opaque Media

Trauma

Drug Toxicity

Unexplained visual loss

Is visual loss genuine

FVER & PVER

Site of Lesion VER, ERG, PERG

Potential acuity PVEP with threshold spatial frequency

Hereditary Retinal Dystrophy

Hereditary v Acquired OCT, ERG, EOG

Rod/Cone, Cone/ Rod OCT, ERG, EOG

Macular Dystrophy OCT, ERG, PERG, ?EOG

Night Blindness OCT, ERG, EOG

X-Linked Heterozygote EOG/ERG

Please don’t ask for paediatric EDT’s when macular developed

Nystagmus

Albinism Apkarian VEP

Cone, Cone/Rod, Rod/Cone ERG, OCT

CSNB ERG

Congenital Idiopathic VEP/ ERG

Delayed Visual Maturation VEP

Foveoschisis ERG OCT

Optic Nerve Hypoplasia/ SOD

VEP, USG

Visual Loss in Childhood

Potential Acuity Pattern Offset/ onset VEP

Cortical Blindness VEP

Nystagmus VEP, ERG, USG

Metabolic Disorders ERG

Bulls Eye Maculopathy ERG, PERG, OCT, PERG

ONH VEP USG

DVM VEP, ERG

Night blindness OCT, ERG, EOG

Opaque Media

Lens/ Corneal/ Vitreous Opacity

fVEP, ERG, USG

Metal IOFB VEP, ERG, EOG, USG

Trauma

• Retinal or Optic Nerve Trauma?

With Opaque Media fVEP, ERG, USG

Without Opaque Media VEP (f&p), ERG, USG

Drug Toxicity

Pheniothiazines EOG/ERG

Chelators EOG, VEP, ERG, PERG

Vigabatrin ERG, Visual fields

Ethambutol VEP

Quinine EOG, ERG, VEP, Fields

Hydroxycholoroquine/ Chloroquine

Rarely but OCT only

Tamoxifen VER, ERG, EOG, OCT

Roaccutane ERG DA

When not to request EDT’s

Choroidal, Macular off Retinal Detachments

Cataract without RAPD

Before MRI/CT

Acute Optic Neuritis (VA < 6/36), unless Functional

EDT’s in young children where family history of heredo-macular dystrophy

If VA > 6/9 in occlusion therapy

How to request?

• By referral letter to – Dr Peter Good– Consultant Clinical Scientist

• Visual Function request card• Clinically urgent EDT’S to be discussed with Dr

Good• Do not routinely fax letters to us!

We don’t have a crystal ball!

• Please give all patient details• Summary of ophthalmic findings• Which is the affected eye• Inform patient why they are attending