Guidelines for Prescribing Glasses in Children

Prism Diopter/Degrees Converter

True Deviation with Myopic Spectacle Power

Spectacle Power →
Angle↓ 
-1 -2 -3 -4 -5 -6 -7 -8 -9 -10 -12 -15 -20 -30
5 5 5 5 4 4 4 4 4 4 4 4 4 3 3
10 10 10 9 9 9 9 9 8 8 8 8 7 7 6
15 15 14 14 14 13 13 13 12 12 12 12 11 10 9
20 20 19 19 18 18 17 17 17 16 16 15 15 13 11
25 24 24 23 23 22 22 21 21 20 20 19 18 17 14
30 29 29 28 27 27 26 26 25 24 24 23 22 20 17
35 34 33 33 32 31 30 30 30 29 28 27 25 23 20
40 39 38 37 36 36 35 34 33 33 32 31 29 26 23
45 44 43 42 41 40 39 38 37 37 36 35 33 30 26
50 49 48 47 45 44 43 43 42 41 40 38 36 33 29
60 59 57 56 55 53 52 51 50 49 48 46 44 40 34
70 68 67 65 64 62 61 60 58 57 56 54 51 46 40

True Deviation with Hyperopic Spectacle Power

Spectacle Power→
Angle↓
+1 +2 +3 +4 +5 +6 +7 +8 +9 +10 +12 +15 +20 +30
5 5 5 5 6 6 6 6 6 6 7 7 8 10 20
10 10 11 11 11 11 12 12 13 13 13 14 16 20 40
15 15 16 16 16 17 18 18 19 19 20 21 24 30 60
20 21 21 22 22 23 24 24 25 26 27 29 32 40 80
25 26 26 27 28 29 30 31 32 33 35 37 40 50 100
30 31 32 32 33 34 35 36 38 39 40 43 48 60 120
35 36 37 38 39 40 41 42 44 45 47 50 56 70 140
40 41 42 43 44 46 47 48 50 52 53 57 64 80 160
45 46 47 49 50 51 53 55 56 58 60 64 72 90 180
50 51 53 54 56 57 59 61 63 65 67 71 80 100 200
60 62 63 65 67 69 71 73 75 77 80 87 96 120 240
70 72 74 76 78 80 82 85 88 90 93 100 112 140 280

Actual Value in Prism Diopter with two horizontal prisms

PD 20 25 30 35 40 45 50
20 42 47 53 59 65 71 78
25 47 53 59 66 72 79 86
30 53 59 66 73 80 87 94
35 59 66 73 80 87 95 103
40 65 72 80 87 95 104 113
45 71 79 87 95 104 113 123
50 78 86 94 103 113 123 133

Value of Prisms stacked in the same direction held over one eye

Prism 1st→
and Second↓
10 12 14 16 18 20 25 30 35 40 45 50
1 11 13 15 17 19 21 27 32 37 43 48 54
2 12 14 16 18 20 23 28 33 39 45 50 56
3 13 15 17 19 22 24 29 35 40 46 52 58
4 14 16 18 21 23 25 30 36 42 48 54 61
5 15 17 20 22 24 26 32 38 44 50 56 63
6 16 19 21 23 25 27 33 39 45 52 59 66
7 17 20 22 24 26 29 35 41 47 54 61 68
8 19 21 23 25 28 30 36 42 49 46 63 71
9 20 22 24 27 29 31 37 44 51 58 66 74
10 21 23 25 28 30 33 39 46 53 60 68 77
12 23 25 28 30 33 35 42 49 57 65 74 84
14 25 28 30 33 35 38 45 53 61 70 80 91
16 28 30 33 36 38 41 49 57 66 76 87 100
18 30 33 35 38 41 44 52 61 71 82 95 110
20 33 35 38 41 44 47 56 66 76 89 104 122
25 39 42 45 49 52 56 66 78 93 110 133 165
30 46 49 53 57 61 66 78 94 114 141 183 264
35 53 57 61 66 71 76 93 114 144 195 315
40 60 65 70 76 82 89 110 141 195 339
45 68 74 80 87 95 104 133 183 315
50 77 84 91 100 110 122 165 256

Visual Acuity Conversion Table

20 ft 6 m Decimal Log MAR
20/630 6/190 0.032 +1.5
20/500 6/150 0.04 +1.4
20/400 6/120 0.05 +1.3
20/320 6/95 0.06 +1.2
20/250 6/75 0.08 +1.1
20/200 6/60 0.1 +1.0
20/160 6/48 0.125 +0.9
20/125 6/38 0.16 +0.8
20/100 6/30 0.2 +0.7
20/80 6/24 0.25 +0.6
20/63 6/19 0.32 +0.5
20/50 6/15 0.4 +0.4
20/40 6/12 0.5 +0.3
20/32 6/9.5 0.8 +0.2
20/25 6/7.5 0.8 +0.1
20/20 6/6 1.0 0
20/16 6/4.8 1.25 -0.1
20/12.5 6/3.8 1.6 -0.2
20/10 6/3 2.0 -0.3
Vertex Distance Conversion

Vertex Distance Conversion