The average marmoset pupil diameter during treatment was 2.52 mm (range 2.26–2.76 mm), which resulted in 1.78 times greater exposure to the negative than to the positive power zone. The ratio of negative-to-positive contact lens surface area that corresponded to the pupils measured during treatment ranged from 65% negative-to-35% positive for a pupil diameter of 2.26 mm, to 52% negative-to-48% positive for a pupil of 2.76 mm, all of which resulted in greater overall exposure to hyperopic defocus. Since it was not possible to measure the effective refractive state through the multizone contact lenses, 19 additional marmosets were refracted wearing plano lenses to assess the potential effects that contact lens fit and centration might have had on the final effective refractive state (). The refractive changes induced by plano lenses at 0, 20, and 40 degrees on the nasal retina, as well as at 20 on the temporal retina were not significant. There was, however, a significant overall effect toward increased hyperopia (mean change ± SE +1.22 ± 0.33 D) at 40 degrees on the temporal retina (nasal visual field).
Refractive Effect of Plano Lenses (Ave ± SE) on 19 Marmosets
Biometric and refractive data were obtained pretreatment at 42 to 50 days of age, at baseline (B; 70–76 days old) and at four consecutive time points during the 12 weeks of treatment (T1 at 98–105, T2 at 126–133, T3 at 140–147, and T4 at 153–161 days old). At the beginning of treatment there were no differences in vitreous chamber depth or refraction (mean spherical equivalent [MSE]) between experimental (exp) and contralateral (con) eyes (exp VC 5.83 ± 0.06 mm, control VC 5.84 ± 0.07 mm, P = 0.11; exp MSE mean ± SE +0.65 ± 0.51 D, control MSE mean ± SE +0.08 ± 0.76 D, P = 0.54). The overall effective axial myopic and hyperopic defocus on treated eyes was +5.65 D and −4.35 D, respectively.
shows refractive and vitreous chamber depth data from treated and contralateral eyes (solid and empty symbols, respectively). The animals that were myopic at the end of treatment are indicated in red and the ones that were hyperopic in black. At baseline, three animals were myopic in both eyes (exp MSE mean ± SE −1.24 ± 0.0.60 D, control MSE mean ± SE −2.88 ± 0.92 D, ) and three more had myopia in both eyes by the end of treatment, meaning that six of 10 animals were myopic in both eyes when treatment concluded (myopic treated eye MSE mean ± SE −3.39 ± 0.78 D, myopic fellow eye MSE mean ± SE −3.21 ± 0.78 D, ), and eight were myopic on their contralateral fellow eyes (average of eight myopic contralateral eyes MSE mean ± SE −2.53 ± 0.72 D, ).
Spherical equivalent refractive state (D) and VC depth (mm) over time on treated eyes (solid symbols and lines) and contralateral control eyes (empty symbols, dotted lines). Solid and empty black symbols: those treated and contralateral eyes, respectively, (more ...)
describes the interocular changes in refraction and vitreous chamber over time, where it can be seen that four weeks into treatment (at T1) five of 10 experimental eyes were relatively more hyperopic than their contralateral control eyes (exp-con mean MSE ± SE +1.79 ± 0.52 mm), and seven were relatively smaller (exp-con mean VC ± SE −0.09 ± 0.02 mm). At T2, six of those seven animals still had smaller eyes (exp-con mean VC ± SE −0.08 ± 0.01 mm, ), but now nine were relatively more hyperopic on their treated than contralateral eyes (exp-con mean MSE ± SE +1.76 ± 0.34 mm, ). Those nine animals remained relatively more hyperopic in their experimental than control eyes at T3 (exp-con mean MSE ± SE +1.32 ± 0.21 mm, ), but two more experimental eyes grew less than their contralateral eyes and now a total of eight animals had smaller experimental than control eyes (exp-con mean VC ± SE −0.06 ± 0.01 mm, ). During the last two weeks of treatment, those same eight animals exhibited reduced VC growth in their experimental eyes (exp-con mean VC ± SE −0.06 ± 0.01 mm, ), and seven were more hyperopic (exp-con mean MSE ± SE +1.21 ± 0.47 mm, ).
Interocular differences (treated eye-control eye) at pretreatment (pre-treat), baseline (arrow), and during treatment (T1–T4) in refractive error (D) and VC depth (mm) in multizone lens-reared animals. Each line represents one animal, and each (more ...)
The refractive state at baseline did not correlate with the refractive state after treatment (R2 = 0.23, P = 0.16) or the growth rates experienced during treatment (R2 = 0.18, P = 0.22).
A quadrant plot was used to display visually the changes in interocular refraction and vitreous chamber depth over time in multizone lens-reared animals (), and similar quadrant plots allowed the comparison with negative and positive-single vision lens-reared animals ().
Quadrant plot describing the relation between interocular differences (exp-control) in vitreous chamber depth (x axis), and refraction (y axis) in the multizone-lens reared group. The refractive and growth changes of each animal are represented with a (more ...)
Quadrant plots describing the relation between interocular differences (exp-control) in vitreous chamber depth (x axis), and refraction (y axis) in the positive single-vision reared group (blue arrows), and in the negative single-vision reared group ( (more ...)
shows how at the end of treatment (represented by an arrowhead), six of 10 multizone lens-treated animals had smaller and relatively more hyperopic experimental than control eyes. These compensatory changes qualitatively resembled the effects of those raised with single vision positive defocus (, exp-con mean MSE ± SE multizone +0.38 ± 0.46 D, positive +1.62 ± 0.44 D, P = 0.10; exp-con mean VC ± SE multizone −0.02 ± 0.03 mm, positive −0.06 ± 0.03 mm, P = 0.35), and were unlike those of single vision negative lens-reared animals, whose treated eyes were bigger and more myopic than the contralateral controls (, exp-con mean MSE ± SE multizone +0.38 ± 0.46 D, negative −2.13 ± 1.10D, P = 0.048; exp-con mean VC ± SE multizone −0.02 ± 0.03 mm, negative +0.12 ± 0.06 mm, P = 0.06).
The overall relation between interocular differences in vitreous chamber depth and refraction over time also can be noticed by the diagonal trend of the data in (R2 = −0.66, P < 0.001). The correlation remained significantly unchanged at each measurement during treatment and compared to baseline (ANOVA repeated measures, P > 0.05). Changes in CC, ACD, LT, RT, or CT did not change significantly during treatment (), and did not correlate with refractive state or vitreous chamber changes (all P > 0.05).
Interocular Differences in Biometry and Mean Spherical Equivalent Refraction over Time (Treated Eye-Control Eye, Mean ± SE): Pretreatment, Baseline, T1, T2, T3, and T4
The temporal characteristics of the effect that multizone lenses had compared to untreated, single vision negative and positive lenses showed no significant differences in growth rates between treatment groups before treatment started (P = 0.36, ). However, six weeks into treatment the interocular growth rates of multizone lens-reared animals were significantly lower than those of single vision negative lenses (growth rate mean ± SE multizone −1.0 ± 0.1 μm/day, negative single vision +2.1 ± 0.9 μm/day, P = 0.024, ), but similar to untreated (growth rate mean ± SE −0.2 ± 0.4 μm/day, P = 0.33, ) and single vision positive lenses (growth rate mean ± SE −2.2 ± 0.7 μm /day, P = 0.37, ). Later, between six and eight weeks of treatment, only the rates between single vision positive and negative lens-treated marmosets remained significantly different, with negative single vision lens-reared animals exhibiting higher interocular growth rates than positive, essentially zero at that time (growth rate-negative, lens-treated mean ± SE +2.7 ± 1.1 μm/day, positive lens-treated −9.8439 e−3 ± 0.5 μm/day, P = 0.043, ). After eight weeks of treatment all treatment groups showed similar interocular growth rates (P > 0.05, ).
Growth rates in multizone lens-reared marmosets (black), untreated (white), and single vision lens-reared marmosets (positive, blue and negative, red). Before treatment (pretreatment) and at early, mid, and late time intervals during treatment. The data (more ...)