AKXD28 develop ISA but not IPD. Representative iris phenotypes in aging AKXD28 (a-c and g, h) and D2 (d-f and i) mice are shown. Age and disease severity increase from left to right. (a, d) Two month old AKXD28 and D2 mice have a normal, complex iris morphology with clearly evident iris details including crypts, small central pupil, prominent peripupillary sphincter muscle, and pupillary ruff. (b, e) At 12 months AKXD28 (b) have iris stromal atrophy characterized by loss of iris detail, thinning of the iris stroma with exposure of the sphincter muscle (arrowhead in b), and mild transillumination defects (arrow). Dispersed pigment is not prominent in the anterior chamber. The eyes of similarly aged D2 mice (e) are more severely affected with both stromal atrophy and iris pigment dispersion. The stromal atrophy is characterized by abnormally shaped pupils, exposure of the sphincter, and loss of iris detail while the pigment dispersion is evidenced by the prominent accumulation of pigment on the front of the iris and lens (arrowheads in e). (c, f) 26 month old AKXD28 and D2 mice have marked stromal atrophy with enlarged irregular pupils, iris holes, and increased transillumination. In D2, severe loss of both iris stromal and iris pigment epithelium pigmentation due to the ISA and IPD phenotypes results in large transparent iris regions. In contrast, the AKXD28 iris remains generally pigmented due to the lack of IPD and retention of much of the pigment epithelium. Histologic analysis confirms the presence of ISA and lack of IPD in AKXD28 mice. (g) In a young AKXD28 mouse the iris has a robust stroma (S) and pigment epithelium (P) that are separated by the dilator muscle (masked by pigment in this section but located at the level of the arrows). (h) Although severity varies locally, the stroma of old AKXD28 mice is severely atrophied and almost non-existent in many places (arrow). The iris pigment epithelium (arrowhead) of old mice has a flattened morphology but remains remarkably intact considering the overall condition of the iris. (i) In old D2 mice, both the iris stroma and iris pigment epithelium are severely atrophic.