Eye Tests for Alström Syndrome: What ERG and OCT Show

The eye tests used in diagnosing and monitoring Alström Syndrome can sound intimidating — electroretinogram, optical coherence tomography, fundus photography, visual fields. Each test answers a different question about what the eyes are doing. This article explains each one in plain language, what to expect during the appointment, and what the results mean.

What it does

The ERG records the electrical response of photoreceptors and other retinal cells when the eye is exposed to flashes of light. It's the most useful test for identifying cone-rod dystrophy and is essential in diagnosing Alström Syndrome.¹

How it's done

A small contact lens or skin electrode placed near the eye picks up the retina's electrical signals as light flashes are delivered. The test usually takes 30–60 minutes.

In babies and young children, ERG is performed under sedation or general anesthesia for accuracy and comfort. In older children and adults, it's done awake with topical anesthetic drops.

What the results show

In Alström, the ERG typically shows:

• Reduced or absent cone responses — even early in life
• Initially preserved rod responses — declining over time
• Cone-rod pattern — distinguishes Alström from rod-cone (retinitis pigmentosa) patterns seen in conditions like Usher Syndrome

The ERG is the most reliable test for distinguishing cone-rod dystrophies from other inherited retinal diseases.

What it does

OCT uses light to take detailed cross-section images of the retinal layers, similar to how ultrasound uses sound waves. It shows the thickness and structure of each retinal layer.

How it's done

The patient sits at a machine with their chin on a rest, looking at a fixation light. The OCT scan takes seconds. No drops or sedation needed in cooperative children and adults; sedation may be used for very young children.

What the results show

In Alström, OCT typically shows:

• Thinning of the outer retinal layers — where photoreceptors live
• Disruption of the photoreceptor layer architecture
• Progressive changes over years that can be tracked with serial scans
• Sometimes preserved foveal architecture in younger children, declining with age²

OCT is particularly useful for monitoring disease progression over time and for research applications.

What it does

The pediatric ophthalmologist looks directly at the back of the eye after dilating the pupils with eye drops. They examine the retina, optic nerve, blood vessels, and macula.

How it's done

Drops dilate the pupils over 20–30 minutes. The doctor uses a bright light and lenses to examine the retina. Fundus photography may be added to document the appearance for comparison over time.

What the results show

In Alström, the fundus may look:

• Surprisingly normal in young children — even when ERG is abnormal
• Showing pigmentary changes with age — areas of pigment migration, attenuated blood vessels, optic disc pallor
• Macular changes in some adults — including bull's-eye maculopathy patterns

The mismatch between a relatively normal-appearing fundus and a clearly abnormal ERG in a young child is itself a clue toward Alström.³

What it does

Tests the extent of central and peripheral vision by mapping where in the visual field the patient can detect light stimuli.

How it's done

The patient looks straight ahead at a fixation point and presses a button when they see a light flash anywhere in their field. Done in older children and adults who can cooperate; not feasible in babies and toddlers.

What the results show

In Alström, visual fields typically show:

• Initially relatively normal fields in early childhood (with reduced acuity in the center)
• Progressive constriction as rod function declines
• Eventual severe field loss in adolescence and adulthood

Visual fields are useful for tracking functional vision and for some accommodation decisions (e.g., legal blindness criteria).

What it does

Tests the clarity of central vision at a distance.

How it's done

Standard charts (Snellen, ETDRS) for children old enough to read or recognize symbols. Picture-based charts (Lea symbols) for younger children. Preferential looking tests in babies and toddlers.

What the results show

In Alström, visual acuity typically:

• Is reduced from infancy
• Continues to decline through childhood and the teen years
• Reaches around 6/60 (20/200) by age 10 in many children
• Approaches no useful acuity by the early-to-mid 20s

What it does

Records the brain's electrical response to visual stimuli — measures whether the visual signal reaches the visual cortex.

How it's done

Electrodes on the scalp record brain activity while the patient looks at flashing lights or patterns. Useful in babies and young children when other tests can't be done cooperatively.

What the results show

VEP measures the integrity of the visual pathway from the eye to the brain. In Alström, VEP responses correlate with the degree of retinal dysfunction.

What it does

Tests the patient's ability to distinguish colors.

How it's done

Standardized plates (Ishihara, Hardy-Rand-Rittler, Farnsworth-Munsell) shown to the patient. Done in older children and adults.

What the results show

Color vision is reduced in Alström because of cone dysfunction. Patterns of deficit help characterize the cone-rod dystrophy.

The 2020 international consensus guidelines recommend annual ophthalmology visits including ERG, OCT, fundus exam, visual fields (when feasible), and visual acuity. Some centers do ERG every 2 years rather than annually because the absolute changes year-to-year are small.⁴

• Alström Syndrome Diagnosis Hub
• How Is Alström Syndrome Diagnosed?
• Cone-Rod Dystrophy in Alström Syndrome
• Eye Care Routine for Alström Syndrome
• Will My Child Go Blind From Alström Syndrome?

April 30, 2026.