Changes of Ocular Dimensions as a Marker of Disease Progression in a Murine Model of Pigmentary Glaucoma

Abstract

Purpose: The elevation of intraocular pressure (IOP), a major risk factor in glaucoma, is an important parameter tracked in experimental models of this disease. However, IOP measurement in laboratory rodents is challenging and may not correlate with some key pathological events that occur in the development of glaucoma. The aims of this study were to quantify changes in ocular morphology in DBA/2J mice that develop spontaneous, age-dependent, pigmentary glaucoma and to check the possible correlation of these parameters with IOP.

Method: Eye morphology was evaluated with MRI in DBA/2J, DBA/2J-Gpnmb⁺/SjJ, and C57BL/6J female mice ages 3, 6, 9, 12, and 15 months. The animals were anesthetized with isoflurane. A planar receive-only surface coil (inner diameter = 10 mm) was placed over each animal's left eye and the image was acquired with a 7T small animal-dedicated magnetic resonance tomograph and T2-weighted TurboRARE sequence. Ocular dimensions were manually quantitated using OsiriX software. IOP was measured with rebound tonometry.

Results: In the control animals, no age-related changes in the ocular morphology were noted. Since 6 months of age, the anterior chamber deepening and elongation of the eyeballs of DBA/2J mice was detectable. We found a significant, positive correlation between IOP and axial length, anterior chamber area, or anterior chamber width in C57BL/6J mice but not in DBA/2J mice. However, after excluding the measurements performed in the oldest DBA/2J mice (i.e. analyzing only the animals ages 3 to 12 months), we demonstrated a significant positive correlation between IOP and anterior chamber width.

Conclusion: High-resolution magnetic resonance imaging of the eye area in mice enables reproducible and consistent measures of key dimensions of the eyeball. We observed age-dependent alterations in the eye morphology of DBA/2J mice that mostly affected the anterior chamber. We also demonstrated a correlation between some of the ocular dimensions and the IOP of C57Bl/6J mice and DBA/2J mice with moderately advanced glaucomatous pathology.

Keywords: DBA/2J; MRI; glaucoma; intraocular pressure; ocular biomechanics; ocular dimensions.

Figure 1

Quantification of ocular morphology. (A) Areas of anterior chamber (AC), lens (L), vitreous chamber (VC), and retina (R). (B) Dimensions: axial length (AL), equatorial diameter (ED), anterior chamber depth (ACD), anterior chamber width (ACW), lens thickness (LT), vitreous chamber depth (VCD), retinal thickness (RT), optic nerve head diameter (ONH), and optic nerve diameter (ON).

Figure 2

Age-dependent changes in eye morphology in C57BL/6J (first row, A–E), DBA/2J-Gpnmb⁺/SjJ (second row, F–J), and DBA/2J (third row, K–O) mice. DBA/2J mice display anterior chamber deepening (arrow) and optic disc cupping (arrowhead).

Figure 3

Quantitative analysis of eye morphology in C57BL/6J, DBA/2J-Gpnmb+/SjJ, and DBA/2J mice. (A) axial length, (B) globe area, (C) anterior chamber depth, (D) anterior chamber area, (E) iridocorneal angle, (F) vitreous chamber depth, (G) vitreous chamber area, and (H) retinal thickness. Means ± SD. *P < 0.05, **P < 0.01, ***P < 0.001, ****P < 0.0001 DBA/2J vs. C57BL/6J; ^#P < 0.05, ^##P < 0.01 DBA/2J-Gpnmb⁺/SjJ vs. C57BL/6J. Two-way ANOVA followed by Dunnet’s multiple comparisons test.

Figure 4

Visualization and quantification of the retina after systemic administration of manganese. Left panel shows representative T1-weighted images of the eyes before (A, C) and 24 h after (B, D) intraperitoneal injection of manganese chloride in C57BL/6J (A, B) and DBA/2J mice (C, D). The arrowhead indicates optic disc cupping in DBA/2J mice. (E) Results of quantification of retina thickness in these mice before and after MnCl₂ administration. **P < 0.01; Kruskal-Wallis non-parametric ANOVA followed by Dunn’s multiple comparisons test.

Figure 5

Intraocular pressure (IOP) measured for DBA/2J (3 months, n = 12; 6 months, n = 40; 9 months, n = 34; 12 months, n = 38; 15 months, n = 42), for C57BL/6J (3 months, n = 17; 6 months, n = 27; 9 months, n = 14; 12 months, n = 14; 15 months, n = 19). Two-way ANOVA and post hoc Sidak’s test: ***P < 0.001, ****P < 0.0001. Means and SD (for the sake of clarity, error bars are drawn only above, for DBA/2J, or below, for C57Bl/6, the point representing mean values).

Figure 6

Relationship between intraocular pressure and selected ocular dimensions in C57BL/6J ages 3 to 15 months (first column - A, D, G), DBA/2J mice ages 3 to 15 months (second column – B, E, H) or DBA/2J mice ages 3 to 12 months (third column C, F, I). Graphs illustrate axial length (AL, A–C), anterior chamber area (ACA, D–F), and anterior chamber width (ACW, G–I). Dots represent single values, lines represent linear correlations. Respective R² (if applicable) and P values are placed inside the panels.