The visual acuity of each diabetic model was measured using a simple staircase method to determine the highest level of spatial frequency visible to each mouse in an OKT test. The averaged results of the three models can be found in
Figure 2. Consistent differences were noted between the db/db and db/+ groups. At 3 months, the db/db group showed a slight decrease in visual acuity compared with the db/+ group (9.2%,
P > 0.05). At 6 and 9 months, the difference became very significant (44.0% at 6 months,
P < 0.0001; 41.4% at 9 months,
P < 0.0001). These consistent differences resulted in a trend of declining acuity in the diabetic mice, which was demonstrated by the two-way ANOVA. There was a statistically significant difference in visual acuity by both diabetes status (
F1,122 = 69.84,
P < 0.0001) and by duration of diabetes (
F3,122 = 24.77,
P < 0.0001), and the interaction between the diabetes status and duration of diabetes was also significant (
F3,122 = 11.46,
P < 0.0001). For the Ins2
Akita diabetes model, a decline in visual acuity could be seen as early as 1.5 months of age (9.7%,
P < 0.05). However, this difference was not seen at 3 months, as the average for the WT mice demonstrated a transient decrease. The difference in visual acuity was observed again at the 6-month (13.8%,
P < 0.001) and 9-month time points (29.9%,
P < 0.0001). As with the db/db mice, acuity declined over the course of the testing period in control animals. Despite this, there was a significant difference in all three factors: diabetes status (
F1,206 = 47.45,
P < 0.0001), duration of diabetes (
F3,206 = 16.84,
P < 0.0001), and the interaction between them (
F3,206 = 6.279,
P < 0.001). The STZ group had an initial decrease in visual acuity at 1.5 months after STZ treatment and demonstrated a consistent decrease in visual acuity compared with the controls beginning at 3 months (12.1%;
P < 0.01) after STZ treatment. The difference continued to be observed at 6 months (15%;
P < 0.01) and at 9 months (18.7%;
P < 0.01). These consistent differences are mirrored by the two-way ANOVA test, which showed that, like the db/db and Ins2
Akita models, the diabetes status (
F1,200 = 25.83,
P < 0.0001), duration of diabetes (
F4,200 = 14.66,
P < 0.0001), and the interaction between the diabetes status and duration of diabetes (
F4,200 = 3.334,
P < 0.05) were also significant.