Binocular open-view system to perform estimations of aberrations and scattering in the human eye

Opto-Mechanical Eye Models, a Review on Human Vision Applications and Perspectives for Use in Industry

The purpose of this review is to aggregate technical information on existent optomechanical eye models (OME) described in the literature, for image quality assessment in different applications. Several physical eye models have been reviewed from peer-reviewed papers and patent applications. A typical eye model includes an artificial cornea, an intraocular lens or other lens to simulate the crystalline lens, an aperture as the pupil, and a posterior retinal surface, which may be connected to a light sensor. The interior of the eye model may be filled with a fluid to better emulate physiological conditions. The main focus of this review is the materials and physical characteristics used and the dimensional aspects of the main components including lenses, apertures, chambers, imaging sensors and filling medium. Various devices are described with their applications and technical details, which are systematically tabulated highlighting their main characteristics and applications. The models presented are detailed and discussed individually, and the features of different models are compared when applicable, highlighting strengths and limitations. In the end there is a brief discussion about the potential use of artificial eye models for industrial applications.

Method to reduce undesired multiple fundus scattering effects in double-pass systems

Double-pass systems rely on backscattering of light by the human ocular fundus to assess the optical quality of the eye. In this work, we present a method to reduce double-pass image degradation caused by undesired multiple scattering effects in the eye fundus. The reduction is based on combined data processing of simultaneous measurements using two different configurations: one symmetric with equal entrance and exit pupils and another asymmetric with unequal entrance and exit pupils. Under certain conditions, such scattering effects may be effectively suppressed. Measurements of human eyes show that, although multiple fundus scattering imposes a shift on the estimations, double-pass systems can be used to predict the optical quality of the eye within a population.

Opto-mechanical design of a dispersive artificial eye

We present an opto-mechanical artificial eye that can be used for examining multi-wavelength ophthalmic instruments. Standard off-the-shelf lenses and a refractive-index-matching fluid were used in the creation of the artificial eye. In addition to dispersive properties, the artificial eye can be used to simulate refractive error. To analyze the artificial eye, a multi-wavelength Hartmann-Shack aberrometer was used to measure the longitudinal chromatic aberration and the possibility of inducing refractive error. Off-axis chromatic aberrations were also analyzed by imaging through the artificial eye at two discrete wavelengths. Possible extensions to the dispersive artificial eye are also discussed.

Importance of Accommodation and Eye Dominance for Measuring Objective Refractions

PURPOSE

To explore factors affecting the difference between objective refractive data measured under monocular closed-field viewing and binocular open-field viewing.

DESIGN

Prospective observational case series.

METHODS

setting: Institutional.

STUDY POPULATION

Twenty-nine healthy volunteers (58 eyes; mean age, 38.4 ± 10.0 years; range, 25-60 years).

OBSERVATION PROCEDURES

Objective monocular refractions (MR) measured with the Nidek Auto Ref/Keratometer ARK-730A; objective binocular refractions (BR) and objective accommodative amplitude (AA) measured with the Grand Seiko Auto Ref/Keratometer WAM-5500; ocular dominance measured using the hole-in-the-card test; presence and magnitude of far/near (30 cm) phoria evaluated by the cover test and alternating cover test using a prism bar.

MAIN OUTCOME MEASURE

The difference between objective refractive data measured under monocular closed-field viewing and binocular open-field viewing.

RESULTS

The spherical equivalent (SE) of the BR was significantly (P < .001) more hyperopic by 0.51 ± 0.33 diopter (D) than the MR. The difference (BR minus MR) tended to decline with increasing age and decreasing AA (r = -0.231, P = .08; r = 0.223, P = .092, respectively). The correlation between age and difference in SE was significant in dominant eyes (r = -0.372, P = .047) but not in nondominant eyes (r = -0.102, P = .60). In nondominant eyes, the amount of near phoria was correlated significantly (r = 0.403, P = .03) with the difference in SE. The correlation was strong (r = 0.598, P = .01) in 17 subjects with more than 3 D of AA.

CONCLUSIONS

Binocular assessment of refraction is important for precise refractive therapy.

Response for light scattered in the ocular fundus from double-pass and Hartmann-Shack estimations

Double-pass (DP) and Hartmann-Shack (HS) are complementary techniques based on reflections of light in the ocular fundus that may be used to estimate the optical properties of the human eye. Under conventional data processing, both of these assessment modes provide information on aberrations. In addition, DP data contain the effects of scattering. In the ocular fundus, this phenomenon may arise from the interaction of light with not only the retina, but also deeper layers up to which certain wavelengths may penetrate. In this work, we estimate the response of the ocular fundus to incident light by fitting the deviations between DP and HS estimations using an exponential model. In measurements with negligible intraocular scattering, such differences may be related to the lateral spreading of light that occurs in the ocular fundus due to the diffusive properties of the media at the working wavelength. The proposed model was applied in young healthy eyes to evaluate the performance of scattering in such a population. Besides giving a parameter with information on the ocular fundus, the model contributes to the understanding of the differences between DP and HS estimations.