Purkinje Images: The Four Reflections Inside Your Eye and What They Tell Us

Did you know that a single light shining into your eye can create four different reflections? These reflections, called Purkinje images, reveal fascinating information about the eye’s anatomy, optical properties, and movements.

Eye clinic scene with doctor explaining Purkinje images to seated patient beside eye chart and anatomy poster.

What Are Purkinje Images?

Purkinje images, also called Purkinje-Sanson images, are reflections of light produced by the curved surfaces of the cornea and crystalline lens.

The human eye normally produces four primary Purkinje images, each originating from a different optical surface.

These reflections were studied by Czech physiologist Jan Evangelista Purkyně in the 1800s and later investigated by French ophthalmologist Louis Joseph Sanson.

Doctor shows seated patient a Purkinje images eye-care poster with slit-lamp diagrams and clinic text.

The Four Purkinje Images Explained

P1

Anterior cornea

Upright, brightest

P2

Posterior cornea

Upright, very faint

P3

Anterior crystalline lens

Upright, relatively large

P4

Posterior crystalline lens

Inverted, small

The fourth image is especially interesting because the posterior lens surface behaves like a concave mirror, producing an inverted reflection. The other three images are upright.

Why Are Purkinje Images Important in Optometry?

Although most patients never notice these reflections, they have several important clinical applications.

• Eye alignment: The first Purkinje image is the corneal light reflex used in the Hirschberg test to help evaluate strabismus.

• Eye tracking: Specialized systems compare Purkinje reflections to measure precise eye movements.

• Accommodation: Changes in lens reflections help researchers understand how the crystalline lens changes shape when focusing.

• Intraocular lens evaluation: Reflections can provide information about IOL positioning, curvature, and optical characteristics following cataract surgery.

A Simple Way to Observe Purkinje Images

An eye care professional can begin observing these reflections using a penlight in a dimly lit room.

• Ask the patient to look straight ahead.

• Shine a small light toward the eye.

• Observe the bright reflection on the anterior cornea (P1).

• With appropriate magnification, positioning, and illumination, additional, fainter reflections may become visible.

The first Purkinje image is easy to observe, while the others can be challenging to distinguish without specialized equipment.

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Clinical tests that use Purkinje images

Eye doctors use Purkinje images in several clinical tests, particularly to evaluate eye alignment, ocular movements, accommodation, and intraocular lens positioning.

The most common clinical application is the Hirschberg test, which uses the first Purkinje image (P1), the reflection from the anterior corneal surface.

Clinical test	Purkinje image	Clinical purpose
Hirschberg test	P1	Screens for strabismus and estimates eye misalignment
Krimsky test	P1	Quantifies ocular deviation using prisms
Brückner test	P1 indirectly	Compares red reflexes to screen for ocular abnormalities and misalignment
Corneal reflex assessment	P1	Assesses ocular alignment and fixation
Purkinje eye tracking	P1 and P4	Measures precise eye movements
Accommodation analysis	P3 and P4	Studies crystalline lens movement and curvature changes
IOL tilt and decentration analysis	Lens/IOL reflections	Evaluates implant position after cataract surgery

The Brückner test primarily assesses fundus red reflexes, rather than directly measuring a Purkinje image.

2. Hirschberg test: The most practical in-office application

Equipment: Penlight or transilluminator.

Procedure:

1. Position yourself approximately 40 to 50 cm from the patient.

2. Ask the patient to fixate on your penlight.

3. Shine the light centrally toward both eyes.

4. Compare the position of the corneal light reflex in each pupil.

5. Look for asymmetry suggesting strabismus.

Interpretation:

• Symmetric reflections: Generally consistent with ocular alignment.

• Temporal displacement of the reflex: Suggests esotropia.

• Nasal displacement of the reflex: Suggests exotropia.

• Vertical displacement: Suggests a vertical ocular deviation.

A common clinical approximation is that 1 mm of corneal reflex displacement corresponds to roughly 15 prism diopters, although this varies with individual ocular anatomy and measurement technique.

3. Krimsky test: Measuring the deviation with prisms

The Krimsky test builds on the Hirschberg test by adding prism lenses.

How to perform it:

1. Have the patient fixate on a penlight at approximately 40 cm.

2. Observe the first Purkinje image in each eye.

3. Place a prism in front of an eye and adjust the prism strength.

4. Increase or decrease prism power until the corneal reflections appear symmetric.

5. Record the prism power required to neutralize the deviation.

For example, if symmetry is achieved with 20 prism diopters, the estimated deviation is approximately 20Δ. Prism orientation depends on the direction of the deviation and the Krimsky technique used.

4. Purkinje imaging for IOL positioning

One of the more specialized applications is evaluating intraocular lens tilt and decentration after cataract surgery.

Clinicians or researchers can analyze the locations of the P1, P3, and P4 reflections to estimate lens position. This is particularly relevant for premium IOLs, where significant decentration or tilt can affect optical performance. Quantitative measurements generally require specialized instrumentation.

Clinical pearl for your Purkinje images blog

P1 is the most clinically useful Purkinje image during a routine comprehensive eye examination. It is the basis for the Hirschberg and Krimsky tests, particularly helpful when evaluating young children or patients unable to reliably perform cover testing.

P3 and P4 become more relevant when studying accommodation, crystalline lens optics, and IOL positioning.

I would add a section titled “Clinical Applications of Purkinje Images: From Strabismus Testing to Cataract Surgery” to your OPT-ISM blog, highlighting the Hirschberg and Krimsky tests as two procedures doctors can readily perform in the office.

The Takeaway

Purkinje images demonstrate how the eye functions as a sophisticated optical system. Four reflections from two structures, the cornea and crystalline lens, provide valuable information about eye alignment, lens behavior, and ocular movement.

At OPT-ISM Eye Care, understanding the science behind vision helps us provide comprehensive eye care and explain the remarkable ways our eyes work.

Test Your Knowledge: 5-Question Purkinje Images Quiz

1. How many primary Purkinje images are produced by a normal phakic eye?

A. Two

B. Three

C. Four

D. Six

2. Which surface produces the first Purkinje image (P1)?

A. Posterior cornea

B. Anterior cornea

C. Anterior lens

D. Posterior lens

3. Which Purkinje image is inverted?

A. P1

B. P2

C. P3

D. P4

4. Which Purkinje image is normally the brightest?

A. P1

B. P2

C. P3

D. P4

5. Which clinical test uses the first Purkinje image to help evaluate ocular alignment?

A. Amsler grid

B. Hirschberg test

C. Ishihara test

D. Schirmer test

Answer Key:

1. C. Four primary images originate from the anterior and posterior surfaces of the cornea and crystalline lens.

2. D. P1 is the bright reflection from the anterior corneal surface, commonly observed during corneal light reflex testing.

3. B. P4 is inverted because reflection from the posterior crystalline lens surface produces an inverted real image.

4. A. P1 is the brightest and easiest to identify because of the reflection at the air-cornea interface.

5. B. The Hirschberg test compares corneal light reflex positions between the eyes to screen for ocular misalignment.