Abstract
This chapter introduces the reader to tests commonly performed in a binocular vision examination to determine a child's binocular status. The testings introduced in this chapter are all chairside techniques that do not involve a significant amount of extra equipment or time. The binocular examination consists of determining the ocular position and then accommodation, vergence, and ocular motor statuses. The ocular position consists of determining where the eyes point in space and if they are correctly aligned. Evaluation of ocular alignment and the ability to move the eyes with coordination can be determined with various techniques, including Hirschberg, Krimsky, cover test, as well as Modified Thorington, motor testing, and vergence ranges. This chapter will familiarize the clinician with the basics of binocular vision testing and improve the reader's comfort with the various elements of the binocular vision examination.
TopHirschberg Test
Indication
The Hirschberg test allows for an estimated objective assessment of ocular alignment. It is very useful in infants, toddlers, and children with developmental delays. It determines the presence of strabismus, as well as the direction, laterality, frequency, and magnitude of the deviation.
Background
The Hirschberg test estimates the amount of strabismus present based on the first Purkinje image. That is, the decentration of the corneal light reflex produced by a light source (e.g., a transilluminator) in the deviating eye compared to the corneal light reflex of the fixating eye. An equal or symmetrical corneal light reflex indicates alignment. An asymmetric Hirschberg reflex is confirmed by occluding each eye separately to determine the fixating eye and assessing angle kappa. Angle kappa (angle lambda) is the angle between the visual line and the pupillary axis. A positive angle kappa (displacement toward the nose indicated by a “+” sign) of up to 5 degrees can be physiologic. This slightly decentered reflex nasally is often noted as +0.5 mm. A negative angle kappa is when the reflex is displaced temporally and is recorded with a “-” sign. A positive angle kappa may mask a small angle esotropia or cause pseudoexotropia, whereas a negative angle kappa may simulate esotropia or mask exotropia. A 1 mm displacement is approximately 22 prism diopters (∆) in misalignment (Caloroso, EE and Rouse MW, 1993). The position of the corneal light reflex indicates the type of deviation (Table 1).
Table 1. Position of corneal light reflex and type of deviation
| Position of Corneal Light Reflex | Type of Deviation |
| Nasal | Exo |
| Temporal | Eso |
| Above | Hypo |
| Below | Hyper |
Key Terms in this Chapter
Binocular Vision: The ability to maintain visual focus on an object in one’s visual field with both eyes, creating a single visual percept.
Vergence: The simultaneous disconjugate movement of both eyes to maintain bifoveal fixation and fusion on a target. Convergence (eyes moving inward together). Divergence (eyes moving outward together).
Accommodation: The process in which the eye changes optical power to maintain focus on an object at varying distances. This is measured in diopters and decreases predictably with age.
Modified Thorington: A subjective method of determining the presence, direction, and magnitude of a horizontal and vertical phoria utilizing a Maddox Rod, transilluminator and Modified Thorington Card.
Angle Kappa: The angle between the visual line or line of sight (which connects the point of fixation with the nodal points and the fovea) and the pupillary axis (which is a line through the center of the pupil perpendicular to the cornea).
Strabismus (Heterotropia): A manifest deviation of ocular alignment that is present during binocular viewing conditions, observed during unilateral cover test. Tropias include exotropia (eye sits out), esotropia (eye sits in), hypotropia (eye sits down), hypertropia (eye sits up).
Heterophoria: A latent deviation that occurs when binocular viewing is disrupted, observed during an alternating cover test. Phorias include exophoria (eyes drift outward), esophoria (eyes drift inwards), hypophoria (eyes drift downward), hyperphoria (eyes drift upward).
Cover Test: Technique performed to evaluate the presence and magnitude of a heterophoria or a heterotopia (also commonly known as strabismus). A unilateral cover test determines the presence of a strabismus, and an alternating cover test determines the presence of a heterophoria.
Fused Cross Cylinder: A subjective in phoropter method to evaluate the accuracy of the accommodative response.