Purkinje images
Purkinje images are reflections of objects from the structure (anterior surface of the Cornea,
posterior surface of the Cornea, anterior surface of the lens and posterior surface of the lens) of
the eye.
Purkinje Images are also known as Purkinje reflexes and as Purkinje–Sanson images or Catoptric
images.
Purkinje–Sanson images are named after Czech anatomist Jan Evangelista Purkyně (1787–1869) and
after French physician Louis Joseph Sanson (1790–1841).
At least four Purkinje images are usually visible.
The first Purkinje image (P1) is the reflection from the anterior or outer surface of the cornea.
The second Purkinje image (P2) is the reflection from the posterior or inner surface of the cornea.
The third Purkinje image (P3) is the reflection from the outer (anterior) surface of the lens.
The fourth Purkinje image (P4) is the reflection from the inner (posterior) surface of the lens.
Unlike the others, P4 is an inverted image.
Purkinje image P1 is the brightest of the four, then P3 and P4 (P3 and P4 have about the same
brightness), then P2.
The third and fourth Purkinje images can be visible from within the eye itself.
Light reflected away from the surfaces of the lens can in turn reflect back into the eye from the rear
surface of the cornea.
The first and fourth Purkinje images are used by some eye trackers, devices to measure the position
of an eye.
The cornea reflection (P1 image) used in this measurement is generally known as glint.
Clinical use of Purkinje images:
The Purkinje images are one of these eye-tracking methods that can be used to detect both the
movement and the position of the patient's eye.
The optometrists commonly use both the P4 and the P1 of the Purkinje images in detecting the eye
position and movement.
In diagnosis of immature and mature cataract –
In immature cataract 4th Purkinje images is diffuse.
In mature cataract the 4th Purkinje images is absent.
P I has meny clinical application including Keratometry and Corneal Topography.
Also used to measure angle Kappa (angle of deviation) in Hirschberg Test.
P I and P IV can be used for tracking the direction of gaze by Dual – Purkinje image technique, which
uses the relative position of these reflections to calculate the direction.
In case of Aphakia, 3rd and 4th Purkinje images are absent.
In case of Pseudophakia, all four Purkinje images are present.
Which Purkinje image is erect ?
Of the four images, P4 is the only inverted image while the others are erect images due to how it
reflects from the inner surface of the lens.
What happens to the Purkinje image during accommodation?
Purkinje image III is nearly double the size of image I and during accommodation it moves from the
vitreous into the crystalline lens.
Purkinje IV is inverted three quarters the size of image I, lies in the crystalline lens and moves slightly
towards the retina.
What is Catoptric image?
Catoptric image is also known as Purkinje- samson image.
