Retinal birefringence scanning (RBS) is a method for detection the central fixation of the eye. The method can be used in

pediatric ophthalmology Pediatric ophthalmology is a sub-speciality of ophthalmology concerned with eye diseases, visual development, and vision care in children. Training In the United States, pediatric ophthalmologists are physicians who have completed medical school ...

for

screening Screening may refer to: * Screening cultures, a type a medical test that is done to find an infection * Screening (economics), a strategy of combating adverse selection (includes sorting resumes to select employees) * Screening (environmental), a ...

purposes. By simultaneously measuring the central fixation of both eyes, small- and large-angle

strabismus Strabismus is a vision disorder in which the eyes do not properly align with each other when looking at an object. The eye that is focused on an object can alternate. The condition may be present occasionally or constantly. If present during a ...

can be detected. The method is not invasive and requires little cooperation by the patient, so it can be used for detecting strabismus in young children. The method provides a reliable detection of strabismus and has also been used for detecting certain kinds of

amblyopia Amblyopia, also called lazy eye, is a disorder of sight in which the brain fails to fully process input from one eye and over time favors the other eye. It results in decreased vision in an eye that typically appears normal in other aspects. Amb ...

. RBS uses the

human eye The human eye is a sensory organ, part of the sensory nervous system, that reacts to visible light and allows humans to use visual information for various purposes including seeing things, keeping balance, and maintaining circadian rhythm. ...

birefringent Birefringence is the optics, optical property of a material having a refractive index that depends on the Polarization (waves), polarization and propagation direction of light. These optically anisotropic materials are said to be birefringent (or ...

properties to identify the position of the

fovea Fovea () (Latin for "pit"; plural foveae ) is a term in anatomy. It refers to a pit or depression in a structure. Human anatomy *Fovea centralis of the retina * Fovea buccalis or Dimple * Fovea of the femoral head * Trochlear fovea of the fr ...

and the direction of

gaze In critical theory, sociology, and psychoanalysis, the gaze (French ''le regard''), in the philosophical and figurative sense, is an individual's (or a group's) awareness and perception of other individuals, other groups, or oneself. The concept ...

, and thereby to measure any binocular misalignment. __TOC__

Principle

Birefringent material has a

refractive index In optics, the refractive index (or refraction index) of an optical medium is a dimensionless number that gives the indication of the light bending ability of that medium. The refractive index determines how much the path of light is bent, or ...

that depends on the polarization state and propagation direction of

light Light or visible light is electromagnetic radiation that can be perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), corresponding to frequencies of 750–420 tera ...

. The main contribution to the birefringence of the eye stems from the Henle fibers. These fibers (named after

Friedrich Gustav Jakob Henle Friedrich Gustav Jakob Henle (; 9 July 1809 – 13 May 1885) was a German physician, pathologist, and anatomist. He is credited with the discovery of the loop of Henle in the kidney. His essay, "On Miasma and Contagia," was an early argument for ...

) are photoreceptor axons that are arranged in a radially symmetric pattern, extending outward from the

, which is the most sensitive part of the retina. When polarized light strikes the fovea, the layer of Henle fibers produces a characteristic pattern, and the strength and contrast of this pattern, as well as the orientation of its bright parts, depend on the polarization of the light that reaches the retina. An analysis of this pattern allows the position of the fovea and the direction of gaze to be determined. Binocular RBS has been used for diagnosing strabismus (including microstrabismus) in young children, and has also been proposed for diagnosing amblyopia by detecting strabismus and by detecting reduced fixation accuracy.

Limitations

However, also birefringent properties of the

cornea The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber. Along with the anterior chamber and lens, the cornea refracts light, accounting for approximately two-thirds of the eye's total optical power ...

and the retinal nerve fiber layer are sources of birefringence. Corneal birefringence varies widely from one individual to another, as well as from one location to another for the same individual, thus can confound measurements.

References

{{reflist Biometrics Eye procedures Ophthalmology Optometry Pediatrics Physical examination