Rule of 8s for determining the need for referral in childhood vision screening*

Age (years)	Rule of 8s	"Critical line" for normal visual acuity^¶
2	2 + 6 = 8	20/60
3	3 + 5 = 8	20/50
4	4 + 4 = 8	20/40
5	5 + 3 = 8	20/30
6	6 + 2 = 8	20/20

The patient's age plus the tens digit of the denominator of his or her visual acuity should be ≤8.
"If it equals eight, vision is great! Nine or more, vision is poor."

* Poor visual acuity is one reason for referral to an eye specialist. Other important indications for referral include abnormal red reflex, abnormal ocular alignment, eye preference, pupillary asymmetry, and abnormal instrument-based vision screening. Refer to UpToDate's content on vision screening in children for further details.
¶ The "critical line" is the line a child is expected to see normally and pass. Visual acuity at or better than this value is considered normal and referral is not necessary. If visual acuity is worse that this level, referral is generally warranted.

Source: Bhatt AR, Baylor College of Medicine, Texas Children's Hospital, 2016, personal communication.

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Rule of 8s for determining the need for referral in childhood vision screening*