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Very fast wave-front measurements at the human eye with a custom CMOS-based Hartmann-Shack sensor

Thomas Nirmaier, Gopal Pudasaini, and Josef Bille

Open Access Open Access

Abstract

We describe what we believe to be the first wave-front measurements of the human eye at a sampling rate of 300 Hz with a custom Hartmann–Shack wave-front sensor that uses complementary metal-oxide semiconductor (CMOS) technology. This sensor has been developed to replace standard charge-coupled device (CCD) cameras and the slow software image processing that is normally used to reconstruct the wave front from the focal-plane image of a lenslet array. We describe the sensor’s principle of operation and introduce the performance with static wave fronts. The system has been used to measure human-eye wave-front aberrations with a bandwidth of 300 Hz, which is approximately an order of magnitude faster than with standard software-based solutions. Finally, we discuss the measured data and consider further improvements to the system.

©2003 Optical Society of America

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Figures (11)
Fig. 1.
Fig. 1. Hartmann–Shack wave-front sensor with microlens array and image sensor in the focal plane (a) and exemplary spot pattern (b).

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Fig. 2.
Fig. 2. Architecture of the ASIC (a) and an individual focal-spot detector in the detector array (b).

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Fig. 3.
Fig. 3. Schematic of the resistive-ring network of WTA circuits, in which each neuron receives an input photocurrent from a photodiode row or column and establishes a binary output current.

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Fig. 4.
Fig. 4. Microphotograph of one corner of the sensor chip (a) and chip mounted on optic carrier (b).

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Fig. 5.
Fig. 5. Spot tracking with slow-moving (100-µm/s) (a) and fast-moving (10 mm/s) (b) focal spots.

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Fig. 6.
Fig. 6. Zernike-term standard deviation for a large and a small laser spot power.

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Fig. 7.
Fig. 7. Optical setup for wave-front measurements of the human eye (E), with laser diode (LD), beam splitter (BS), telescope (L1, L2, and PH), lenslet array (LA), and sensor (ASIC).

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Fig. 8.
Fig. 8. Measurement at the optical setup for wave-front measurements of the human eye with test subject

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Fig. 9.
Fig. 9. Time series of wave-front contour plots from a human-eye measurement with Δt=30 ms. The contour lines have 20-nm spacing.

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Fig. 10.
Fig. 10. Time series of defocus and coma magnitude (a) and wave-front rms error (b) measured at 300 Hz over 3 s.

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Fig. 11.
Fig. 11. Power spectral density of human eye’s defocus (a) and static defocus measurement (b) at lowest possible light power (~20 pW per spot). Also shown is the power spectral density of astigmatism (c) and third-order spherical aberration (d). Above a frequency of approximately 70 Hz no aberrations could be observed.

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Tables (1)

Tables Icon

Table 1. Spot-position uncertainty with the simple WTA circuit [σ(max)] and the resistivering network σ(centroid) at different spot powers.

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Equations (10)

Equations on this page are rendered with MathJax. Learn more.

[ ∂ W ( x , y ) ∂ x i , j , ∂ W ( x , y ) ∂ y i , j ] = ( Δ x i , j f , Δ y i , j f ) ,
( x ̂ , y ̂ ) = arg max i , j ( g ij )
( x ̂ , y ̂ ) = ( ∑ i ∑ j x ij g ij ∑ i ∑ j g ij , ∑ i ∑ j y ij g ij ∑ i ∑ j g ij ) .
I x , i = ∑ ( i , j ) ∈ M x , i g ij , I y , j = ∑ ( i , j ) ∈ M x , j g ij ,
( x ̂ , y ̂ ) = ( I R , x I L , x + I R , x , I R , y I L , y + I R , y )
I 0 = I src [ 0 , … , 1 , … , 0 ] ,
( x ̂ , y ̂ ) = ( x W , y W ) .
N i → I src , n with n = i mod w .
I 0 = I src [ 0 , … , 0 , 1 , … , 1 , 0 … , 0 ] ,
( x ̂ , y ̂ ) = [ med ( x W , k ) , med ( y W , k ) ] .
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