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1.13 Decentered Corneal Light Reflex



To see a typical case presentation with decentered corneal light reflex, click here.

(1) A decentered corneal light reflex in one or both eyes of a patient who is fixating on a point light source held directly in front of him or her may indicate that the visual axis of one eye is not aligned with the fixation target; when this occurs a manifest strabismus is present.  Many tests for strabismus, for instance the Hirschberg and Krimsky tests, depend on the examiner's judgment of the position of the light reflection.  However, there are other nonstrabismic causes for a decentered light reflex that must be considered for correct interpretation of this finding. 

(2) On covering the fixating eye, the eye with the decentered reflex has made corrective movement to take up fixation.  Depending on the direction of this movement the patient has an esotropia, exotropia, right or left hypertropia or hypotropia.57, p.38

(3) The angle kappa is defined as the angle between the visual line (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).  A positive angle kappa (displacement toward the nose) of up at 5 degrees is physiologic.  A positive angle kappa may hide a small angle esotropia or cause pseudoexotropia, whereas a negative angle may simulate esotropia or hide exotropia.57, p.32

(4) Approximately 44% of patients with strabismic amblyopia have eccentric fixation, which may cause the light reflex in the amblyopic eye to become decentered.60  For instance, in nasal peripheral eccentric fixation the light reflex is displaced temporally.  In patients with parafoveolar or paramacular fixation, the displacement of the light reflex may be too minute to be detected by the examiner.  In such cases the diagnosis of eccentric fixation can only be made with the Visuscope or an ophthalmoscope with a fixation target that can be projected on the fundus.  The patient fixates this target while the sound eye is occluded.  The examiner notes the position of the fixation target on the patient's fundus.58, p.219

(5) A large positive angle kappa results from the temporal dragging of the macula in cases of retinopathy of prematurity (ectopic macula) when this eye is used for fixation.  Such patients have pseudoexotropia.  Visual acuity in such eyes is usually reduced but may remain normal or near normal despite the retinal distortion.  A vertical angle kappa occurs infrequently and may be caused by scar formation (for instance, toxocara canis infection) with the vertical dragging of the macula.

(6) Corectopia (decentered pupil) or coloboma of the iris may confuse the examiner regarding correct interpretation of the position of the light reflex.