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L. Diaz-Santana, N. D. Bull, K. R. Martin, C. Noack; Management of Wavefront Aberrations in the Rat Eye in vivo. Invest. Ophthalmol. Vis. Sci. 2010;51(13):2322.
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© ARVO (1962-2015); The Authors (2016-present)
In vivo imaging of the rat retina is compromised by an increase of scattering over time. Past studies have shown that the use of a coverslip (CS), a contact lens (CL) or a thin film of mineral oil (MO) can reduce this problem. We have modelled the effect of these different interfaces on wavefront aberrations using the Campbell and Hughes rat model eye together with the optics of the sensor used for wavefront measurements. Matched experimental pilot data of each condition was also collected.
A zemax model of the rat eye (Campbell and Hughes, 1981) was implemented. The aberrations as a function of eccentricity of the model eye up to 5 degrees were estimated under 4 different conditions: (1) The unmodified model eye , (2) the model eye with a CS, (3) with a CL and (4) with the MO. The total optical power of the model eye and optical interface (CS, CL or MO) varied between conditions. The optics of the wavefront sensor needed to compensate for it were also modelled in (2), (3) and (4). A custom made Shack-Hartmann (SH) sensor was also built. The ocular aberrations of 7 eyes from 4 Sprague Dawley rats were measured with a CS (thickness=0.130mm, Glass BK7) and MO (Johnson & Johnson). A second group of 5 eyes from 3 rats were measured wearing either a CL (Material PMMA, front surface r=3.253mm, Back surface r=3mm, apical distance=0.34 mm) or a CS. Viscotears (Novartis) were used to couple the CS or CL to the cornea.
In our modelling, when the optical coupling between the eye and sensor was taken into account, the mineral oil showed the best image quality over the whole +5 to -5 degrees field (Strehl >0.8), while the coverslip presented the worst performance with a rapid drop in image quality as a function of eccentricity (Strehl dropping from >0.8 to <0.3 over the field). Experimentally, for the in vivo data, the MO had a mean wavefront RMS of 0.36 +/- 0.12microns. The CS 0.8 +/- 0.62microns and the CL 0.43 +/- 0.21microns (in all cases defocus was removed)
The larger in vivo variability observed using a CS agrees with the simulated data from our model, as small misalignments of the eye with the wavefront sensor will result in a rapid change in optical quality. The opposite is true for the MO. These results imply that it is possible to design an optical interface to optimise image quality for high resolution retinal imaging by carefully taking into account the interaction between the optics of the rat eye and those of the imaging system.
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