Application Scope Of Covering Method:

1. The eyeball has motor function
2. Both eyes have the ability to gaze

1. Covering Method

1.1 Operation Method: the examiner and the examinee sit facing each other, ask the examinee to look straight ahead, cover the examinee's eyes alternately, and observe the eye position movement of the uncovered eyes
1.2 Inspection Distance: 33cm and 5m
1.3 Judgment Method:
Complete immobility of both eyes - Normal Ocular Position Or Phoria
Naked eye moves from outside to inside - Exotropia
Shift of uncovered eye from inside to outside - Esotropia
1.4 Note: Because the Phoria is only manifested in the change of eye position of the covered eye, the examiner can not see it. It is necessary to further check the phoria by covering method.

Hand Occluder(ZYB-II)  From Xingda Vision
The part covering the eyes is a convex translucent arc. When in use, the examiner can see the eye position of the covered eyes of the examinee.

2. Removing Covering Method 

2.1 Operation Method: cover one eye and observe the movement of the other eye. The other eye looks at the target in front of it. After covering it for more than 5 seconds, withdraw the hand occluder from the eye and observe the eye position movement of the covered eye.
2.2 Inspection Distance: 33cm and 5m
2.3 Judgment Method:           
Remove covered eyes without displacement - Normal Ocular Position Or Tropia 
Remove covered eyes moving from inside to outside - Esotropia          
Remove covered eyes moving from outside to inside - Exophoria           
Right eye moves downward or left eye moves upward - Right Hyperphoria        
Left eye moves downward or right eye moves upward - Left Hyperphoria      
2.4 Note: The covering time should not be too short.It needs 5 seconds.

Analysis Of Covering Method And Removing Covering Method

3. Alternating Covering Method 

3.1 Operation Method: cover the eyes of the examinee alternately, make the eyes look at the target alternately, and observe the movement direction of the eyes at the moment of removing the cover.           
3.2 Inspection Distance: 33cm and 5m           
3.3 Judgment Method:
Completely immobile eyes - No Strabismus           
Moving from the inside to the middle - Esophoria Or Esotropia           
Moving from the outside to the middle - Exophoria Or Exotropia 
4. Note: Some tropia begin to show phoria, and show obvious tropia after repeatedly covering both eyes.           
The above three eye position inspection methods can only objectively check the movement direction of the eye position. The specific degree of strabismus in the eye position cannot be quantitatively checked. It is necessary to cooperate with the prism to further quantitatively check the eye position.