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Effect of prolonged photoperiod on ocular tissues of domestic turkeys
Author(s) -
Leis Marina L.,
Dodd MaryMagdalene U.,
Starrak Gregory,
Vermette Catherine J.,
Gomis Susantha,
Bauer Bianca S.,
Sandmeyer Lynne S.,
SchweanLardner Karen,
Classen Henry L.,
Grahn Bruce H.
Publication year - 2017
Publication title -
veterinary ophthalmology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.594
H-Index - 50
eISSN - 1463-5224
pISSN - 1463-5216
DOI - 10.1111/vop.12395
Subject(s) - keratometer , cornea , emmetropia , ophthalmology , erg , anatomy , dioptre , intraocular pressure , biology , medicine , refractive error , eye disease , visual acuity , retinal
Objective The objective of this study is to investigate the structural and functional ocular changes that develop in turkeys exposed to a photoperiod of 23 h of light (23L) compared with a photoperiod of 14 h of light (14L). Procedures Ten‐day‐old Nicholas heavy strain poults were exposed to either a 14L or 23L photoperiod. Between 16 and 18 weeks of age, equal numbers of turkeys per treatment group underwent ophthalmic examination (biomicroscopy, indirect ophthalmoscopy) ( n = 14), refractometry ( n = 20), keratometry ( n = 20), tonometry ( n = 20), and full‐field electroretinography ( ERG ) ( n = 14). Postmortem analyses included orbital magnetic resonance imaging ( MRI ) ( n = 10) and light microscopy ( n = 24) at 18 weeks of age. Results Autorefraction revealed a median of −0.13 for sphere in both groups ( P = 0.69), which is approximately emmetropia. The radius of curvature of the cornea was significantly higher ( P = 0.0001) and the refractive power of the cornea was significantly lower ( P = 0.0001) in the 23L group. The astigmatic power was significantly greater in the 23L group ( P = 0.0001). Mean intraocular pressure did not differ between groups ( P = 0.085). Turkeys from the 23L group had significantly larger globes in nasotemporal ( P = 0.0007), dorsoventral ( P = 0.015), and anterioposterior ( P = 0.021) directions, and anterior chambers were more shallow ( P = 0.0002). ERG s revealed the 23L group to have lower a‐ and b‐wave amplitudes and significantly lower cone flicker amplitudes ( P = 0.0008). Light microscopic examination revealed 23L turkeys to have significantly decreased numbers of nuclei in the outer nuclear layer ( P = 0.0001) and inner nuclear layer ( P = 0.0186), and decreased choroidal thickness ( P = 0.0008). The prevalence of cataract in the 23L group was significantly higher ( P = 0.001). Conclusions Exposing turkeys to a prolonged photoperiod induces significant ocular disease.