Purpose: In vivo imaging of the retina is becoming an increasingly important research method. General anesthesia rapidly compromises the corneal surface, which increases scattering. In addition, wavefront aberrations limit the maximum imaging resolution. Three common methods of stabilizing the air-cornea interface and reducing scattering are the use of a contact lens, a microscopy slide coverslip, or mineral oil. These methods have not yet been analyzed regarding their impact on scattering and wavefront aberrations.
Methods: Nineteen eyes of 19 rats were analyzed with a custom-made Hartmann-Shack (HS) wavefront sensor. The amount of scattering was determined by analysis of the HS spot width, and the wavefront was reconstructed for the naked eye and each scattering-reducing method. Their effect on optical quality was determined by calculating the modulation transfer function (MTF).
Results: The three methods applied significantly reduced scattering but were differentially effective, with the coverslip performing the best and the mineral oil the worst. The root mean square (RMS) of the wavefront aberration, as well as the intereye variability of the RMS, was significantly smaller with the contact lens than with the coverslip. The MTF was best for the contact lens and worst for the coverslip, which was also illustrated by image simulations.
Conclusions: The coverslip, contact lens, and mineral oil, when applied to the cornea, all reduced scattering. The best-performing method, the coverslip, increased wavefront aberrations. Overall, the contact lens had the best influence on image quality, and it appears to be the method of choice for high-resolution retinal imaging in rats.