Table 1.

Reference table for refractive error, axial length, change in reference arm position, and the relative length to an adult scan.

Group age	Refractive error (D)	Axial length (mm)	Increase in reference arm Δ Gen 3 engine (Readout units)‡	Increase in reference arm Δ/2 Gen 3+ engine (Readout units)¥	Relative scan length to adult scan length (%)
30–35 wks	−1	15.1	97	−48	63
35–39 wks	0.3	16.1	86	−43	67
39–41 wks	0.4	16.8	79	−39	70
0-1 mos	0.9	17.4	72	−36	73
1-2 mos	0.3	18.6	59	−29	78
2–6 mos	0.5	18.9	56	−28	79
6–12 mos	0.6	19.2	52	−26	80
12–18 mos	0.7	20.1	43	−21	84
18 mos–2 yrs	0.9	21.3	30	−15	89

^‡With respect to Gen 3 Engine (Older Bioptigen system), a higher number is equal to a shorter reference arm length on each system used.

^¥The per turn change in reference path length is two times that of the Gen 3 reference arm. The direction is reversed so that larger numbers refer to larger distances.