Power-adjusted aberrometer

ES 2 397 047 T3

DESCRIPTION

Aberrometer with power adjustment

Field of the invention

The present invention relates to ophthalmic instruments and, more particularly, to aberrometers having automated power adjustment.

Background

Accurate characterization of wavefronts produced by an eye is desirable in the field of ophthalmology to facilitate correction of the imaging system of an eye through surgery and / or manufacture of corrective lenses.

Although various types of aberration measuring apparatus (hereinafter "aberrometers") are known, Hartmann-Shack type aberrometers are widely used in commercial ophthalmic applications. Figure 1 is a simplified schematic illustration of an example of a Hartmann Shack 100 aberrometer.

During use, a beam of light from a light source 110 in the aberrometer is directed towards the cornea C of an eye E and onto the retina R via the beam splitter 120. The light is reflected from the retina and is projected through the cornea, and forms an aberrant wavefront. The aberrant wavefront re-enters the aberrometer, striking a series of microlens 130. The light forms a series of d11-dln spots on sensor 140. The locations of the spots relative to the locations that the spots would have occupied in the absence of wavefront aberrations provides data that is used to characterize the wavefront and thus detect aberrations. FIG. 2 is a graphical illustration of exemplary intensity values ​​in a representative area of ​​sensor 140 (including a plurality of dij spots).

A transcendental reference in the field of ophthalmic wavefront detection is the document by Liang et al., “Objective measurement of wave aberrations of the human eye with the use of a Hartmann-Shack wave-front sensor”, Journal of the Optical Society of America, Vol. 11, No. 7, pp. 1-9 (July 1994). Improvements to the technique of Liang et al., Id, are taught in the document by Liang and Williams, "Aberrations and retinal image quality of the normal human eye", Journal of the Optical Society of America, Vol. 4, No. 11 , P. 2873-2883 (November 1997), and in Williams et al., US Patent No. 5,777,719.

United States Patent Application Publication No. 2003/0009156 A1, which is considered the closest prior art to the present invention, describes an aberrometer adapted to illuminate the retina of a subject at different levels of illumination, to generate a image based on light reflected from the retina and to determine whether or not certain test spots are usable based on criteria such as pixel intensities associated with a test spot.

The ability to accurately measure aberrations and use the measurement information in corrective applications depends on the ability to accurately determine the location of the centers of the spots associated with each microlens in a series. An inability to accurately detect the centers of all spots in the image frustrates the characterization of wave aberrations and subsequent procedures that rely on those characterizations.

Typically, the coordinates of the center Cx, Cy of an image spot are calculated by calculating the centroid (that is, the sum of weighted values ​​of the intensity of the incident light I (x, y) at points (x, y) over sensor 140). Many factors can play a role in thwarting an accurate determination of the centroid. One such factor is the attenuation of light as it passes through parts of the patient's eye. The cornea and lenses of the eye tend to become increasingly opaque with age. The light can also be severely dimmed by the presence of cataracts. Figure 3 illustrates an exemplary aberrometer detector output image for a normal eye, while Figure 4 illustrates an exemplary aberrometer detector output image for an eye of a cataract patient. As a result of the attenuation of the light passing through the cataract, the image spots in the affected region are very faint and may be barely detectable or completely undetectable. The result of such attenuation is that the center coordinates of the corresponding image spots cannot be determined with the desired precision, resulting in unsatisfactory measurements of aberration in the eyes of affected patients.

Summary

Aspects of the present invention relate to the automatic setting and selection of an appropriate light level in an aberrometer based on the quality of the data obtained at different light levels. Some embodiments and some advantages of those embodiments are summarized in this document. Other embodiments and benefits may not be

ES 2 397 047 T3 explicitly described.

One aspect of the invention relates to a method comprising automatically setting a power level of light emitted by a light source; illuminating a retina of a patient with the light emitted by the light source; receiving, at a sensor, light reflected from the patient's retina; provide a signal based on the received light; determining whether the signal meets one or more signal quality criteria; automatically setting a second level of light power emitted by the light source; and re-illuminating the patient's eye, receiving the reflected light, providing the signal, and determining if the signal meets the signal quality criteria. The advantages of this aspect include facilitating the collection of optical data at a suitable power level that is determined and set automatically rather than manually.

In some embodiments, the method comprises selecting an operating power based on signal quality criteria. Advantages of these embodiments may include making an objective power level selection, without subjective influence from a human technician, helping to ensure that a proper image of each patient's eye is obtained.

In some embodiments, the method comprises repeating the steps of illuminating the patient's eye, receiving the reflected light, providing the signal, and determining whether the signal meets the signal quality criteria until the signal meets the one or more quality criteria. Of the signal. Advantages of these embodiments may include a relatively fast and objective power level selection process that stops when signal quality is adequate.

In accordance with the aforementioned aspect of the invention, the method further comprises identifying a plurality of signal peak levels in the signal; identify a background level of the signal; determining a number of signal peak levels that exceed the signal background level by at least one predetermined value; and determining if the number is not less than a predetermined number. The advantages of this aspect include relatively fast processing of the received signal, one that can allow the quality of the signal to be evaluated without requiring a complete analysis of the received signal. Additional advantages may include the aspect that peak signal relative to background is, in some applications, a particularly useful and relevant measure of signal quality.

In some embodiments, the method comprises determining a number of signal peak levels that is between a first predetermined value and a second predetermined value. The advantages of these embodiments may include relatively fast processing of the received signal, one that may allow evaluating signal quality without requiring a complete analysis of the received signal. Additional advantages may include allowing the selection of a preferred or optimal range of peak signal levels.

In some embodiments, the method comprises identifying a background level of the signal; determining, for each of the plurality of peak signal levels, a signal-to-noise ratio; determining a number of signal-to-noise ratios that are not less than a predetermined value. Advantages of these embodiments may include relatively fast processing of the received signal, one that may allow the quality of the signal to be assessed without requiring a complete analysis of the received signal. Additional advantages may include the aspect that the signal-to-noise ratio is, in some applications, a particularly useful and relevant measure of signal quality.

In some embodiments, the sensor comprises a series of sensor elements. The method further comprises receiving light reflected from the patient's retina through a series of microlens to the series of sensor elements and generating a signal indicative of the optical power received in each of the sensor elements of the series of sensor elements. Advantages of these embodiments may include the advantages of using techniques associated with arrays of microlens to evaluate the optical properties of the patient's eye.

In further embodiments, the method comprises determining a plurality of center positions in the signal, each center position corresponding to one of the microlenses in the series of microlenses; determining an uncertainty in the center position for each of the plurality of center positions; determining a number of center positions that have uncertainties that are not greater than a predetermined uncertainty value; and determining if the number is not less than a predetermined number. Advantages of these embodiments may include the aspect of relating the quality of the signal directly to the precision with which the center of each peak can be determined, which in some applications may be a key parameter in obtaining a useful measurement of the optical properties of the signal. eye of the patient.

In some embodiments, the method comprises setting a light source power control signal. Advantages of these embodiments may include making the power level selection objective, without the subjective influence of a human technician, helping to ensure that a proper image of each patient's eye is obtained. In still other embodiments, the method comprises setting the light source power control signal by pulse width modulation. Advantages of these embodiments may include the aspect that pulse width modulation is a simple and reliable way to establish the power of a source of

ES 2 397 047 T3 light with an electrical control signal.

In some embodiments, the method comprises setting the attenuation of a filter in a beam path of the light emitted by the light source. Advantages of these embodiments may include the aspect that filters with arbitrary gradation can be provided to achieve whatever granularity of control is desired for a particular application.

Another aspect of the invention relates to an apparatus comprising a light source adapted to illuminate the retina of a patient; a sensor adapted to receive reflected light from the patient's retina and to provide a signal based on the received light; and a processor coupled to the sensor. The processor is adapted to establish a first level of power of light emitted by the light source; receive the signal provided by the sensor; processing the signal to determine if the signal meets one or more signal quality criteria; establishing a second level of power of light emitted by the light source; and repeating signal reception and signal processing.

In accordance with this aspect of the invention, the processor is adapted to set the second power level in response to determining whether the signal meets one or more criteria of the signal. In some embodiments, the processor is adapted to re-receive the signal and process the signal until the signal meets the one or more signal quality criteria. In further embodiments, the processor is adapted to select an operating power based on signal quality criteria. Advantages of these embodiments may include making an objective power level selection, without subjective influence from a human technician, helping to ensure that a proper image of each patient's eye is obtained.

In accordance with this aspect of the invention, the processor is further adapted to identify a plurality of signal peak levels in the signal; identify a background level of the signal; determining a number of signal peak levels that exceed the signal background level by at least one predetermined value; and determining if the number is not less than a predetermined number. The advantages of this aspect include relatively fast processing of the received signal, one that can allow the quality of the signal to be evaluated without requiring full analysis of the received signal. Additional advantages may include the aspect that signal peak relative to background is, in some applications, a particularly useful and relevant measure of signal quality.

In some embodiments, the processor is further adapted to determine a number of signal peak levels that is between a first predetermined value and a second predetermined value.

In some embodiments, the apparatus further comprises a series of microlenses and the sensor comprises a series of sensor elements. The sensor is further adapted to receive the light reflected from the patient's retina through a series of microlens, and the signal based on the light received is indicative of the optical power received in each of the elements of the sensor of the series of sensor elements. Advantages of these embodiments may include the advantages of using techniques associated with arrays of microlens to evaluate the optical properties of the patient's eye.

In further embodiments, the processor is adapted to determine a plurality of center positions in the signal, each center position corresponding to one of the microlenses in the series of microlenses; determining an uncertainty in the center position for each of the plurality of center positions; determining a number of center positions that have uncertainties that are not greater than a predetermined uncertainty value; and determining if the number is not less than a predetermined number. Advantages of these embodiments may include the aspect of relating the quality of the signal directly to the precision with which the center of each peak can be determined, which in some applications may be a key parameter in obtaining a useful measurement of the optical properties of the signal. eye of the patient.

In some embodiments, the processor is adapted to set a light source power control signal. Advantages of these embodiments may include making the power level selection objective, without the subjective influence of a human technician, helping to ensure that a proper image of each patient's eye is obtained. In further embodiments, the processor is adapted to set the light source power control signal by pulse width modulation. Advantages of these embodiments may include the aspect that such pulse width modulation is a simple and reliable way to power a light source with an electrical control signal. In further embodiments, the processor is adapted to set the attenuation of a filter in a beam path of the light emitted by the light source. Advantages of these embodiments may include the aspect that filters with arbitrary gradation can be provided to achieve whatever granularity of control is desired for a particular application.

Still other embodiments include other combinations of the functionality and / or features of embodiments particularly described herein.

ES 2 397 047 T3

Brief description of the drawings

Illustrative non-limiting embodiments of the present invention will be described by way of example with reference to the accompanying drawings, in which the same reference number is used to designate the same or similar components in different figures, and in which:

Figure 1 is a simplified schematic illustration of a Hartmann Shack aberrometer projecting light onto an eye and producing a plurality of spots on a sensor;

Figure 2 is a schematic illustration of exemplary intensity values ​​in a representative area of ​​the sensor in the aberrometer shown in Figure 1;

Figure 3 is an example of sensor output obtained by illuminating a normal eye with an aberrometer;

Figure 4 is an example of a sensor output obtained by illuminating the eye of a cataract patient with an aberrometer;

Figure 5 is a simplified schematic illustration of a Hartmann Shack aberrometer as described herein;

Figure 6 is a flow chart of one embodiment of a method in accordance with the present invention; and Figure 7 is a flow chart of one embodiment of a method in accordance with the present invention.

Detailed description

Definitions

For convenience, before a further description of the invention, some terms used in the specification and in the claims are collected here.

Between: As used in the claims, "determining whether X is between A and B" includes embodiments in which extreme values ​​are included as well as embodiments in which extreme values ​​are excluded.

"Not less than" includes realizations where the test is if A> B as well as realizations where the test is if A> B.

"Not greater than" includes embodiments where the test is if A <B as well as embodiments where the test is if A <B.

"Peak signal level" means a signal level that represents a local maximum in a signal that describes a distribution of light levels in space, such as a signal from a series of sensor elements. For example, in embodiments, a signal from a series of sensor elements (or any subset of a series of sensor elements) can be represented as a collection of local signal points or peaks (such as the signal represented in the figure 3 described further below). A "signal peak level" is a signal value that represents the strength of such a local signal peak. In embodiments, a signal peak level may be the local maximum signal at a single element in a series of sensor elements. In other embodiments, the peak level of the signal may be a spatially averaged or summed signal, such that the peak level of the signal actually contains contributions from more than one element in the series. A signal peak level is representative of the signal strength at a local peak, however determined or defined.

"Power level" is the radiant intensity (or any other measure of the power or intensity of light) measured at the light source, at the instrument output, or at any point along the light path.

A "row" of microlenses or sensor elements means any line of microlenses in a series of microlenses or sensor elements, whether oriented as a row or a column.

A "sensor" is any optical detector or series of optical detectors (sensor elements) to produce an electrical signal (digital or analog) indicative of the properties of the incident light (eg, optical power and / or spatial distribution of power optics).

"Signal quality criteria" means any criteria by which it can be determined whether a signal is adequate or optimized; some examples of signal quality criteria are described with more specificity below.

Overview of some realizations

Aspects of the present invention relate to methods of automatically establishing a power level of light emitted by the light source of an aberrometer and selecting a suitable power level to measure aberration in a patient's eye based on the quality of the data collected by the aberrometer. When the quality of the signal from an aberrometer is compromised, for example by light losses that occur when passing

ES 2 397 047 T3 through a cataract or other opacified region of the patient's eye, increasing the intensity of the light from the aberrometer light source can improve signal quality. Requiring technicians to manually adjust light levels, however, presents potential safety and repeatability issues. Additionally, a light level selected for one patient may not be appropriate for a subsequent patient. Additionally, relying on the subjective judgment of a technician as to the appropriate light level for any patient can result in images with inadequate data.

In embodiments of the present invention, the method comprises automatically setting a power level of light emitted by the light source and illuminating the retina of a patient with light emitted by the light source. For example, the light level can be set automatically as a result of a processor executing an instruction, as described below. The light reflected from the retina is captured in a sensor, a signal is generated based on the light received in the sensor. This signal is processed to determine if it meets one or more signal quality criteria. A new power level is set automatically, and the retina lights up again. A signal is generated at the new power level, and this new signal is also processed to determine if it meets the criteria for the signal.

An aberrometer in accordance with one embodiment of the present invention is schematically illustrated in Figure 5. As previously described in connection with Figure 1, light source 110 emits light that is directed into the patient's eye by divider 120. Light reflected from the retina of patient R passes through divider 120 and strikes the array of microlenses 130, where it is focused on spots on sensor 140.

In embodiments of the present invention, aberrometer 100 also includes processor 510. Processor 510 may include one or more microprocessors, central processing units (CPUs), computing devices, microcontrollers, digital signal processors, application-specific integrated circuits. or similar devices, or any combination thereof. Typically, a processor 510 will receive instructions (eg, from a memory or similar device), and will execute those instructions, thereby performing one or more processes defined by those instructions. In embodiments of the present invention, the action of processor 510 executing an instruction automatically sets the power level of light source 110. Processor 510 also receives the signal from sensor 140 and processes that signal to determine if it meets predefined signal quality criteria.

In some embodiments, the steps of setting a power level, illuminating the patient's retina, receiving the reflected light, and processing the signal are repeated, at different power levels, until the signal quality criteria are met. For example, the processor may be programmed to start at a low power level and gradually increase the power level until it reaches a power level at which the signal quality criteria are met. This power level can then be used to measure aberration in the patient's lenses. In embodiments, the processor is programmed to establish a new power level in response to determining that the signal fails to meet the signal quality criteria.

The flow chart of Figure 6 illustrates an example of an embodiment of a method in accordance with the present invention. In step 610, the power level of the light source is set, for example, by the processor executing an instruction and providing a control signal to the light source. At step 620, light from the light source is allowed to illuminate the retina of the patient as illustrated in Figure 5. In step 630, light reflected from the patient's retina is received at a sensor such as sensor 140. As noted above, in the aberrometer illustrated in FIG. 5, light is allowed to pass through the array of microlenses 130 before being received at sensor 140, such that light received at sensor 140 forms a spot pattern on the sensor. In step 640, a signal is provided (eg, by sensor 140 to processor 510) based on the light received at the sensor.

In step 650, the signal is processed (as further described below) to determine if the signal meets some predefined signal quality criteria. In the embodiment illustrated in FIG. 6, if the signal meets the signal quality criteria, the method is complete, and the aberration measurement can continue at the current power level of the light source. If the signal does not meet the signal quality criteria, a new power level is set (step 660) and the steps of illuminating the patient's eye (620), receiving reflected light from the patient's eye (630), providing a signal based on the received light (640), and determining whether the signal quality criteria are met (650) are repeated. In embodiments these steps 660 and 620-650 can be repeated until a power level is discovered at which the signal quality criteria are met. The power level that meets the signal quality criteria can then be used to perform the aberration measurement.

In still other embodiments, the processor is programmed to gradually advance through a predetermined sequence of power levels, receiving and storing (for example, in volatile memory or on a hard disk) a signal at each power level in the sequence. . In such embodiments, the processor can process the stored signal data after gradually advancing through the sequence of power levels, and select a power level that meets the signal quality criteria. This power level can then be used to measure aberration in the patient's lens.

ES 2 397 047 T3

An example of such an embodiment is illustrated in the flow chart of Figure 7. In step 710, the power level of the light source is set as in the embodiment illustrated in Figure 6. The patient's retina is illuminated at step 720. At step 730, light reflected from the patient's retina is received at the sensor. In step 740, a signal is obtained based on the light received at the sensor. This signal is stored by the processor, for example in volatile memory or on a storage medium such as a hard disk.

In the embodiment illustrated in Figure 7, the processor is instructed to gradually advance through a predetermined selection of power level settings (e.g., increasing a set amount from a minimum setting to a maximum setting) and store the data. signal for each of these power level settings. Therefore, in step 750, the processor determines whether signal data has been collected for each power level setting. If not, a new power level is established (step 760), and the steps of illuminating the patient's eye (720), receiving reflected light from the patient's eye (730), and obtaining and storing a signal in based on the received light (740) are repeated.

Once a signal has been collected for all desired power levels, the stored signals are each processed (as further described below) to determine whether each signal meets predefined signal quality criteria (step 770) . In step 780, an operating power is selected from the power levels whose signals meet the signal quality criteria. For example, the lowest power level that produces a suitable signal can be chosen. The selected power level can then be used to perform the aberration measurement.

Determination of whether the signal quality criteria are met

There are a number of suitable signal quality criteria that can be applied to determine whether the signal is suitable for aberration measurement. Any suitable method of analyzing signal quality criteria can be employed with the systems and methods of the present invention.

Generally, the signal comprises a number of light level peaks corresponding to microlens 130, as illustrated in Figures 2, 3 and 4. As described above, where the light is attenuated by cataract or other opacity in the patient's eye, the light level peaks may be too small for proper determination of the central position of the peaks. On the other hand, when the light level is too high, the sensor elements 140 can become saturated, which also introduces uncertainty in determining the center position. Due to the variation in opacity in different light paths through the patient's eye, the signal will generally include a number of peaks at relatively low light levels and a number of peaks at relatively high light levels.

Therefore, in some embodiments, the signal quality criteria can be defined as a number of peaks that have high levels that are in an acceptable range, that is, above a minimum light level threshold and below a maximum light level threshold. The minimum light level threshold can be, for example, the lowest peak light level that produces an acceptable determination of the center position of the peak. The maximum light level threshold can be, for example, a light level associated with a sensor element 140 saturated, or a light level slightly below that at which the sensor elements 140 become saturated.

In such embodiments, the processor analyzes the signal to identify a peak signal corresponding to each microlens in the series of microlens 130 (or, alternatively, a peak signal corresponding to each microlens in a subset of the microlents in the series, such as as a single row or column of microlenses in the series, or a set of microlenses corresponding to a region of particular interest in the patient's eye), and counts the number of peak signal levels that exceed a minimum light level threshold, are below a maximum light level threshold, or are in an acceptable range of signal levels. If that number exceeds a predetermined number, the signal is determined to meet the signal quality criteria. Alternatively, the processor counts the number of peak signal levels that are outside the acceptable range of signal levels, and determines that the signal quality criteria are met if that number is less than a predetermined number.

In other embodiments, the processor may count a number of individual sensor elements 140 that have signal values ​​that exceed a minimum light level threshold, that are below a maximum light level threshold, or that are at a acceptable range of signal levels. If that number exceeds a predetermined number, the signal is determined to meet the signal quality criteria. Alternatively, the processor counts the number of individual sensor elements 140 that have signal levels that are outside the acceptable range of signal levels, and determines that the signal quality criteria are met if that number is less than a predetermined number.

In other embodiments, the signal quality criteria may be defined as a number of signal peak levels that exceed a signal background level by a certain predetermined value. In such embodiments, the processor analyzes the signal from the sensor to determine a background level of the signal. The background level of the signal can be, for example, the level of the signal at a point that is halfway between two peaks

ES 2 397 047 T3 consecutive dmn as illustrated in figure 2. Alternatively, the background signal can be an average signal level in a region of points that is between consecutive peaks, or an average signal level in a plurality of said points or regions.

Having determined a signal background level, in embodiments the processor counts the number of signal peak levels that exceed the signal background level by a predetermined value. If that number is not less than a predetermined number, the signal is determined to meet the signal quality criteria. Alternatively, the processor counts the number of signal peak levels that do not exceed the background level at the predetermined threshold, and determines that the signal quality criteria are met if that number is less than a predetermined number.

In other embodiments, once the background level has been determined, the processor can determine a signal-to-noise ratio - the peak level of the signal divided by the background level - for each peak level of the signal. . Alternatively, the signal-to-noise ratio can be determined for each of a subset of the signal's peak levels (such as a subset of signal's peak levels corresponding to a column or row of the microlens array or corresponding to a reference of particular interest in the patient's eye). The processor counts the number of peak signal levels that have signal-to-noise ratios that exceed a predetermined signal-to-noise threshold. If that number is not less than a predetermined number, the signal is determined to meet the signal quality criteria. Alternatively, the processor counts the number of signal peak levels that have signal-to-noise ratios that do not exceed a predetermined signal-to-noise threshold, and determines that the signal quality criteria are met if that number is less than a predetermined number.

In still other embodiments, the signal quality criteria may be based on an analysis of a histogram of signal levels, corresponding to each of the individual sensor elements. From Figure 3, which is an image of the aberrometer detector output for the eye of a normal patient, it should be apparent that a plot of such a histogram for that image should present two prominent histogram peaks. A first peak in the histogram containing relatively low signal values ​​corresponds to sensor elements that record background levels or levels near the background of the signal. A second peak in the histogram containing points of a higher signal value corresponds to the points in the image of the aberrometer detector output. In contrast, in a histogram based on the image in Figure 4 (the aberrometer detector output for the eye of a cataract patient), the peak of the histogram containing higher signal elements will be smaller, since there are fewer high signal points in that image. As the power level of the light source 110 increases, more dots will appear in the central region of the image of the cataract patient's eye, and consequently the peak of the histogram containing higher signal elements will grow larger. Therefore, in embodiments, the signal level criteria may be a predetermined minimum number of signal levels at the output of the detector element that are at the second peak of the histogram. The processor determines that the signal quality criteria are met if the number of signal levels that are in the second peak of the histogram exceeds the predetermined minimum value.

In other embodiments, the signal quality criteria may be based on a spatial Fourier transform of the signal from sensor 140. The Fourier transform of the signal may be a two-dimensional Fourier transform of the entire signal or a portion of the signal. sign. Alternatively, it can be a one-dimensional Fourier transform of the entire signal or a portion of the signal, such as the signal corresponding to a single row of sensor elements. For a suitable signal like the one in Figure 3, the Fourier transform of the signal will be dominated by the spatial frequency corresponding to the separation between the points (and integer multiples of that frequency). For a signal like the one in Figure 4, which is compromised by opacification in the patient's eye, decreasing signal levels in the center of the image decreases the signal-to-noise ratio in the Fourier transform. . In an embodiment where the signal quality criteria are based on the Fourier transform, the processor can determine that the signal quality is adequate by determining whether a signal-to-noise ratio of the Fourier transform exceeds a certain predefined threshold. The signal-to-noise ratio can be determined over the entire spectrum, over some subset or span of the spectrum, or over a single frequency or set of frequencies. In embodiments, the Fourier transform is filtered before the signal-to-noise ratio is determined. For example, the Fourier transform can be filtered to remove the extremely low DC component and / or frequency component.

In other embodiments, the signal quality criteria may be based on an analysis of the center positions of the peaks (points) in the image of the aberrometer detector output as determined by centroid analysis or any other technique used with aberrometers. by Hartmann-Shack. In such embodiments, the processor determines the center positions of at least a subset of the peaks (points), for example by centroid analysis, a curve fitting algorithm, or other suitable techniques. An algorithm used to determine the center position of a peak can return, in some embodiments, an uncertainty in the center position (including an uncertainty in the x dimension, in the y dimension, or both) that is a measure of precision with which determines the central position. In such embodiments, the processor can count the number of peaks having positions that are determined with an uncertainty less than a predefined maximum acceptable uncertainty. If that number exceeds a predetermined number,

ES 2 397 047 T3 determines that the signal meets the signal quality criteria. Alternatively, the processor counts the number of peaks that have positions that are determined with an uncertainty greater than a predefined maximum acceptable uncertainty, and determines that the signal quality criteria are met if that number is less than a predetermined number.

In still other embodiments, when analyzing compromised data such as that in Figure 4, the algorithm used to determine center positions may simply fail to converge on any center position at all for points in the low signal region of the image. The algorithm may return a meaningless value or an error indicating that the algorithm failed to find a center position. In such embodiments, the processor can determine whether the signal detection criteria are met by counting a number of center positions successfully returned by the algorithms to find center positions. In such embodiments, the selection criteria are met when the number of successfully determined center positions exceeds a predefined threshold.

Establishing the power level.

As noted above, processor 510 sets a light source power level from aberrometer 110, for example at steps 610 and steps 660 of Figure 6 or steps 710 and 760 of Figure 7. Any A suitable technique for automatically setting the power level of the aberrometer light source can be employed with the systems and methods of the present invention. In particular, embodiments of the invention include any combination of a technique for automatically setting the power level (including, but not limited to, those described below) with a technique for collecting and processing a signal representing light reflected from the patient's eye to determine if the signal meets signal quality criteria (including, but not limited to, those described above).

In embodiments, the power level of the light source is set by setting a power control signal that controls the light source. Generally, the power control signal can be a current or voltage that can be set by a signal controlled by processor 510. Any technique can be used to control a light source by current or voltage. For example, if the light source is a diode laser, its output power can be controlled by setting its operating current. If the light source is a lamp, its power can be controlled by setting a discharge voltage. In embodiments where the light source is a laser driven by a pump source, setting the power level of the light source can be accomplished by setting the power level of the pump. In still other embodiments, the light source may be a super-luminescent LED (SLED), the power of which is controlled by an applied control voltage or control current.

In embodiments, the light source is a pulsed laser and setting the power level of the light is accomplished by pulse width modulation. In such embodiments, the processor controls a pulse width of a control signal that is used to drive the light source. In pulse width modulation, the light source's output power is effectively increased by increasing the duty cycle - the percentage of a pulse duration for which the light source is on - of a light source. pressed. In embodiments using pulse width modulation, the peak output power can be constant while the average output power varies with the width of the pulse.

In embodiments, the power level of the light source can be set by including an electronically controllable variable filter in the beam path. Such a variable filter may include a filter having a variable optical density (variable continuously or in stages). Alternatively, the filter may comprise a polarization rotator followed by a polarizer. In other embodiments, a device such as a noise suppressor or other amplitude modulator with an output level that can be set electronically can be used anywhere in the beam path to set the power level of the light source. Additionally, to protect against setting the power level high enough to endanger the patient, the processor may be programmed not to exceed a maximum power level setting. In some embodiments, the light source itself is designed with a low enough maximum power output that a patient is not at risk of injury even at that maximum power output.

Having thus described the concepts of the invention and a number of exemplary embodiments, it will be apparent to those skilled in the art that the invention can be implemented in various ways, and that modifications and improvements will readily occur to those skilled in the art. Therefore, the embodiments are not intended to be limiting and are presented by way of example only. The invention is limited only as required by the following claims.