Method 1: Corneal Refraction

Corneal refraction is an objective eye position examination method, which does not need subjective feedback from the examinee, and the examiner can directly obtain the results.

Inspection Method:
1. The examiner sits opposite to the examinee and asks the examinee to look forward.
2. Irradiate with a pen lamp 33cm in front of the subject and ask him to look at it.

If one eye of the corneal reflection point is located in the center of the pupil and the other eye is located on the nasal side of the pupil, it is exophoria.

If one eye of the corneal reflection point is in the center of the pupil and the other eye is in the temporal side of the pupil, it is esophoria.

Observe Light Spot Position:

1. The normal light spot is located at the center of the pupil of both eyes, deviated by 1mm, and the oblique angle is about 7 ° ~ 8 °.
2. The light spot is located at the pupil edge.

Tropia is 10 ° ~ 15 °

3. The light spot is located at the limbal

Tropia is 40 ° ~ 45 °

4. The spot of light lies between them

Tropia is 25 ° ~ 30 °

Attention Points:
Influence Of Kappa Angle           
The included angle formed by the line between the extraocular fixation point and the anterior pole of the cornea and the optical axis, that is, the included angle between the optical axis and the visual axis is kappa angle.

C-corneal geometric center     B-Posterior pole of eyeball      F-macular fovea      N-node     R-rotation Center           
AB-optical axis     OF-visual axis     OR-fixed axis     ∠OCA-kappa angle(K)     ∠ONA-viewing angle(α)

In practical work, the simplest measurement method is to let the examinee look at the 33cm point light source with one eye and observe the direction of the reflecting point of the pupil.

The reflecting spot is at the nasal side of the center of the cornea, which is a positive kappa angle, which seems to be exophoria.
The reflecting spot is in the temporal side of the central cornea, which is a negative kappa angle, which seems to be esophoria.

Kappa Angle Quantitative Measurement:

1.Perimetry

(2) Slit lamp

Generally, kappa angle is positive, generally 3 ° ~ 5 °. Excessive positive (negative) kappa angle often shows the appearance of exotropia or esotropia, that is, the so-called "Pseudostrabismus".

Due to the existence of kappa angle, the influence of kappa angle on the measurement results of corneal refraction test should be considered. The kappa angle of the fixation eye can be measured first. If the kappa angle is positive, the correction method is the measured value of exotropia minus kappa angle and the measured value of esotropia plus kappa angle.

Clinical Use:
1. When one or both eyes of the examinee fail to gaze well, they cannot stably and continuously gaze at the visual target directly in front
2. The eye movement function is very poor, or there are serious restrictive factors that make the eye unable to move
3. The examinee was young and had poor attention and could not cooperate