DGH 3000B Operators Manual Rev Dec 1998

TABLE OF CONTENTS

I.

Introduction ... 1

II.

Features ... 7

III.

General Description ... 8

IV.

Power-Up And Programming Sequence ... 12

V.

A-Scan Measurements ... 14

VI.

Setting Up The DGH 3000B... 18

VII.

Explanation Of Display Messages ... 21

VIII.

Manual Gain Control... 24

IX.

Test Block Mode... 26

X.

Diagnostic Mode... 28

XI.

Setting Up The DGH 3000B For IOL Computations... 29

XII.

The Holladay Formula And The Personalized Surgeon Factor... 35

XIII.

IOL Calculation Instructions... 42

XIV.

Important Notes ... 48

XV.

Warranty ... 50

XVI.

Specifications ... 51

i

I.

INTRODUCTION

Ultrasound is sound of a frequency level too high to be heard by the human ear; however, sensitive equipment can send and receive these ultrasonic impulses as well as analyze information about anything these impulses strike along their route of travel. Every time a sound impulse strikes an interface, some sound is reflected (bounces off), and some sound is refracted (passes through). The amount of reflected and refracted sound varies with the density of the interface it strikes. Reflected sound acts much like a rubber ball being thrown at a wall. Sound hitting an interface perpendicularly will reflect back along the same path that it approached (Fig. A). Sound hitting an interface at an angle will reflect at an angle away from the source (Fig. B). The refracted sound will continue on at a lesser amplitude because of reflected energy lost at the interface. By means of sophisticated equipment, sound impulses can be sent and their reflections can be converted and displayed on a visual screen in the form of a linear display with spikes related to interfaces that the impulses intersected. By looking at the height (intensity) of the spike, one can predict the angle at which the sound is striking it (Fig. A & B).

Figure B

Figure A

Taking into consideration the above properties and applying them to ophthalmology, one can predict the alignment of an ultrasound beam through the eye. This alignment is crucial to the accuracy of measurements that will be used for IOL calculations. Fig. C illustrates an ultrasonic pattern typical when alignment along the visual axis is met. Please note the two high spikes representing the anterior lens and -1-

posterior lens interfaces, along with a strong spike representing the retinal interface. Conversely, Fig. D illustrates a pattern representing misalignment. Improper measurements could be obtained with this incorrect alignment. Most older A-Scans require the operator to decide when proper alignment has been met. This is normally done by the operator looking at a display to view the spikes relating to the anterior lens, posterior lens, and retinal interfaces. This is very difficult to master when the operator’s attention must be moved from the patient to the equipment. Reproducible results are particularly difficult between two or more operators.

Figure C

Figure D

The DGH 3000B A-Scan incorporates a very sophisticated pattern recognition program that automatically checks for proper alignment. It looks for the proper pattern of spikes as well as going a major step further by looking at the retinal spike for particular signal characteristics which are produced only by retinal interfaces. This recognition is accomplished quickly (1,000 times per sec.) and without removing your attention from the patient. Another important property of ultrasound is that it cannot travel through air. It must have a medium of substantial mass for transmission. Different materials or densities of materials will conduct sound at different speeds or velocities. Liquids or substances containing large amounts of water conduct ultrasound very well. -2-

It has been proven that the following relationship exists: the denser the material, the faster sound is conducted through it. Using this relationship, Ophthalmic A-Scans can obtain distances in the eye by performing a two step process. First, a pulse of sound is timed as it travels through the eye, reflects off the retina, and returns to the transducer. Second, a length is calculated from the travel time by analyzing the time in comparison to the speed of sound through the eye. It has been established that the speeds of sound for ophthalmic structures are as follows:

Most ophthalmic ultrasonic units use an average speed of sound of 1550 m/s for phakic eyes and 1532 m/s for aphakic eyes. The DGH 3000B is programmed to automatically use the proper speed for the eye you wish to read. Another important area of concern in obtaining accurate measurements for IOL power calculating is corneal indentation. Logic would dictate that if you indent the very thing you are measuring, a false or shortened value will be obtained. Logic also dictates that as soon as you touch something that is soft, you will immediately indent it. This is true of the eye and corneal indentation. In recent years, other A-Scan manufacturers claimed that they can prevent corneal indentation by making their probes with soft water filled tips. This may have lessened indentation, but it fell short of eliminating it. The inconvenience and mess associated with water filled probes far outweighed their advantage. Through a second pattern recognition program, The DGH 3000B will automatically disregard readings with corneal indentation present. So, through a simple and fast technique, accurate ultrasonic measurements can be obtained.

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The only important measurement obtained via an A-Scan for IOL calculations is the axial length. Dimensions of other structural entities of the eye can prove useful; however, only a few A-Scans on the market are able to produce these. The DGH 3000B displays values for the anterior chamber, lens thickness, and axial length automatically each time a reading is made. These readings can be entered into the patient’s permanent record via the optional printer or the optional computer link. Obtaining accurate measurements for the axial length of the eye is only part of the challenge of predicting a correct IOL power for a patient. Many factors play roles in the procedure.

Axial Length Axial length measurement is the most important factor affecting IOL power calculations. An error of 1.0 mm affects the post-operative refraction by approximately 2.5 diopters.

Corneal Power Corneal power is the second most important factor affecting IOL power calculations. A keratometer is an instrument that measures the central 3.3 mm of the anterior curvature of the cornea in its two meridians. The readings are called Kreadings. There are two potential sources of error in keratometry. First, failure to calibrate the instrument can cause all readings to be in error by as much as 0.2 mm or 1.0 D. A second source of error is hidden in the dioptric scale of any keratometer. No keratometer measures the refracting power of the cornea in diopters. Keratometers measure the radius of curvature of the anterior corneal surface and then convert this millimeter measurement into diopters. The dioptric scale used for this conversion is based on an assumption, a fictitious refractive index. The true refractive index of the -4-

cornea is 1.376, but to obtain an approximation of the true refracting power of the cornea from only the radius of the anterior surface, a fictitious refractive index has to be used. This index varies with the make of keratometer. Common values are: 1.3375 1.336 1.332

(Haag-Streit, Bausch and Lomb) (American Optical) (Gambs)

A radius of 7.8 mm will thus read 43.27, 43.08, or 42.56 D respectively, depending on which keratometer is used. These differences may not be of much importance in contact lens fitting or the determination of corneal astigmatism. However, these differences are significant when calculating IOL power, which is a new application for the established discipline of keratometry. Any IOL power calculation formula which features the dioptric power of the cornea is subject to this source of error. With the same data, one may calculate IOL powers varying almost a diopter depending on the make of the keratometer used. With both potential sources of error in mind, consider that an error of 1 diopter in the measurement of the corneal power produces an error of about 1 diopter in the postoperative refraction.

Postoperative Anterior Chamber Depth The anterior chamber depth is the least important factor affecting IOL power calculations. An error of 1.0 mm affects the postoperative refraction by approximately 1.0 diopter in a myopic eye, 1.5 diopter in an emmetropic eye, and up to 2.5 diopters in a hyperopic eye. Preoperative measurement of the anterior chamber depth is of little value, and the actual position of the IOL after surgery cannot be accurately predicted so an estimate has to be used.

Surgical Technique Changes in corneal curvature are often noted postoperatively. This fact as well as differences between actual placement and predicted placement of the IOL can produce an error. An intraocular lens placed in the posterior segment requires a -5-

stronger power, and inserting the implant with the convex side backwards necessitates an even stronger lens.

Implant Power The implant power is measured differently by different manufacturers. This can result in variations between IOL companies.

Formulas Used There are basically two classifications of IOL formulas - Theoretical and Regression. All THEORETICAL formulas work on optical formulas based on a two lens system, the cornea and pseudophakic lens focusing images on the retina. REGRESSION formulas are derived empirically from retrospective computer analysis of data on a great many patients who have undergone surgery. Although similar results are obtained between regression and theoretical formulas for eyes that are considered average in length (23.5 mm), results may vary for eyes on the shorter and longer side of average. An ideal IOL prediction formula would be one that is derived empirically from a retrospective analysis of data on patients operated on by the same surgeon, using the same IOL, and obtaining measurements from the same equipment. This would be a personalized regression formula.

Summary Predicting preoperatively the IOL power is a combination of science and art. Accurate axial length and keratometry measurements must be obtained. These measurements must then be applied to the prediction formula that works best for the surgeon. With the majority of accuracy based on correct axial length readings, the importance of a simple, fast and accurate ultrasonic A-Scan is increased.

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II.

FEATURES

The DGH 3000B A-Scan is manufactured with high quality components that are designed and built using the latest technological concepts. The result is an advanced and powerful A-Scan that offers practicality and reliability. The following features are just a sample of the characteristics and capabilities of this unique unit.

• Simple to use. No complicated setup procedures to follow - very user friendly. • Solid transducer tip, 3.0 mm in diameter, for ease of applanation and visualization. • Large thirty-two character alphanumeric display simultaneously displays anterior chamber depth, lens thickness, and axial length. • Front panel keypad permits programming. • Front panel LED bar graph for displaying echo amplitudes. • Storage of measurement data for review. • Operator feedback. An audible signal indicates when the probe is properly aligned and when a valid measurement is complete. • Pattern recognition program yields accurate, reproducible measurements in a fraction of a second. • Personalized configuration allows the operator to preset pertinent information that will automatically be used or inserted into the A-Scan function. This information is permanently stored even when the unit is turned off. • Built in printer documents the A-Scan measurements and IOL power calculations generated by the unit.

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III.

GENERAL DESCRIPTION

Front Panel

Paper Door Latch When the thermal printer paper needs replacing, this latch is used to gain access to the twenty-eight column thermal graphics printer. The printer provides the operator with a permanent record. LED Bar Graph The LED bar graph consists of three columns of multi-colored LED’s used to indicate the amplitude of the anterior lens echo, posterior lens echo, and retinal echo respectively. Green LED’s indicate the echo signal meets the measurement criteria. Orange LED’s indicate the echo signal does not meet the lower limit criteria and red LED’s indicate the echo has saturated, exceeding the upper limit criteria. Display The display consists of two lines of sixteen characters and is used to present information to the operator. Paper Release -8-

This lever releases the thermal paper from the printer platen. “NEXT” - Next Entry Used to advance to the next entry during the setup (configuration) of A-Scan or IOL parameters. “SETUP” - Setup (Configure) Used to initiate and terminate the setup (configuration) of A-Scan or IOL parameters. “0” through “9” - Digits Used to input appropriate numbers for IOL calculations and A-Scan setup. “.” - Decimal Point Used to provide fractional data for IOL calculations. “+/-” - Sign Change Used to change the sign of the number appearing on the display. Probe Interface Connector located on the front panel which mates to the probe connector. “MANL GAIN” - Manual Gain Control Used to manually adjust the gain. “AUTO GAIN” - Automatic Gain Control Used to switch from one eye to the other during an A-Scan exam. Also used to return the unit to automatic gain control after being used in the manual gain control mode. “PRINT” Initiates print out. “PAPER ADV” - Paper Advance Allows the printer paper to be advanced. “NEXT MEAS” - Next Measurement Used to advance to the next measurement during the A-Scan measurement or IOL calculation review process. “PREV MEAS” - Previous Measurement Used to reverse to the previous measurement during the A-Scan measurement or IOL calculation review process. -9-

“IOL” - IOL Calculations Used to enable the IOL calculations. “PREV” - Previous Entry Used to reverse to the previous entry during the setup (configuration) of AScan or IOL parameters. “SELECT” Used to scroll through program options presented on the display. “DELETE” - Delete Measurement Used to delete an undesired measurement. Power Switch Rocker switch located on the lower right hand corner of the front panel. “CLEAR” Used to clear all measurements from memory and prepare the unit for the next patient, or to clear unwanted entries presented on the display. “ENTER” Used to accept options presented on the display. Also used to override the automatic gain control function.

Calibration Standard

Polystyrene block used to simulate aphakic axial length.

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Back Panel

Fuse Holder Contains the AC line fuse. IOL Calculation Firmware Module Firmware module where the IOL calculation formulas are stored. Unit Model Number & Serial Number Location of the model number and serial number for the DGH 3000B. These numbers are used to identify the unit. IOL Calculation Firmware Module Serial Number Location of the serial number for the IOL calculation firmware module. IOL Calculation Firmware Module Revision Number Location of the revision number for the IOL calculation firmware module. Contrast Control Used to vary the contrast of the 32 character display located on the front panel.

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IV.

POWER-UP AND PROGRAMMING SEQUENCE

1.

Plug the AC cord into a three prong outlet.

2.

Verify that the probe is connected to the front panel.

* * * CAUTION * * * When power is applied to the unit, the DGH 3000B will automatically set the internal gain of the unit to comply with the probe sensitivity. Therefore, it is imperative that the probe tip be clean and dry before the unit is turned on. Also, the temperature of the probe should be stabilized to within ±10°F of the temperature at which the probe will actually be used. Never turn on the unit with the probe attached after the probe has just been exposed to an extremely cold or hot environment. Always allow time for the probe to stabilize at room temperature.

3.

Turn on the unit by using the power switch located on the front panel.

4.

The unit will perform an internal self-test function and display the results. The display will also indicate whether or not an IOL Firmware Module is installed.

5.

The DGH 3000B will automatically set the internal gain of the unit to comply with the probe sensitivity. This is how the unit maintains consistent performance throughout the life of a transducer.

6.

When the initialization sequence is completed, the display will read: SELECT EYE OD

7.

Use the “SELECT” key to display the proper eye: “OD” or “OS” (the default is “OD”). Press “ENTER” to confirm your selection. The display will read: SELECT LENS TYPE CATARACTOUS

8.

Use the “SELECT” key to display the desired lens type: “Cataractous”, - 12 -

“Normal”, “Aphakic”, or “Pseudophakic” (the default is “Cataractous”). Press “ENTER” to confirm your selection. When the desired lens type is chosen, the appropriate program parameters for alignment criteria and velocity of sound are automatically installed so no further changes need to be made. NOTE: If the pseudophakic lens type is selected, the display will prompt the operator to select an artificial lens type: “PMMA”, “Silicone”, or “Other”. The display will read: 1 OD(S) AUTO GAIN NO MEASUREMENT 9.

This display indicates that the unit is now in measurement mode, i.e., the unit is ready to take measurements. Refer to Section V for a detailed description of the proper method for obtaining measurements.

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V.

A-SCAN MEASUREMENTS

1.

Perform the Power-up and Programming Sequence as described in Section IV.

2.

Position the unit for easy visibility during patient examination.

3.

Seat or lay the patient in a comfortable position so that the head can be positioned in almost a horizontal plane. Use a firm, comfortable head rest to prevent unwanted head movement.

4.

Anesthetize the cornea and ask the patient to fixate with their fellow eye on a spot on the ceiling or wall.

5.

Hold the probe in such a way that you can stabilize your hand on the cheek or forehead of the patient. This will help prevent indentation of the cornea or excessive movement.

6.

The probe can now be applanated to the cornea. This should be observed from a vantage point that allows the operator to look across the topography of the eye. This aids in seeing the exact moment when the probe touches the cornea so indentation of the cornea will not occur. Applanation should be made as close to the visual axis as possible. An aid in this can be to point the back side of the probe at the fixation target while touching the front portion to the center of the cornea. NOTE: When applanating the probe, one should be particularly careful that contact is made with the center of the probe tip.

7.

At the moment of applanation, the unit will start to beep repeatedly at a rate of approximately two beeps per second. This means that proper coupling has been achieved and sound pulses are being transmitted through the eye. The display at this time will indicate “TAKING MEASUREMENT”. If the beeping stops, this indicates that the probe is no longer applanated to the eye and a slight pressure of the probe should be applied.

8.

If the probe is in proper alignment when applanation occurs, a measurement will be obtained almost instantaneously as indicated audibly by three short, successive beeps. The measurements will be shown on the display as follows:

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LENS TYPE

DISPLAY MESSAGE 1 OD(S) AXL = XX.XX AC = Y.YY LNS = Z.ZZ

CATARACTOUS or NORMAL APHAKIC

1 OD(S) AXL = XX.XX

PSEUDOPHAKIC

1 OD(S) AXL = XX.XX AC = Y.YY

where “1” indicates the measurements have been stored in memory location 1. 9.

If the probe is not in proper alignment when applanation occurs, some minor adjustments may be needed. With the probe applanated, make some minor sweeping motions by moving the back portion of the probe in an X-Y plane. As the operator approaches the proper alignment along the visual axis, the repetition rate of the beeping sound will increase until a nearly constant tone is reached when proper alignment is obtained. During the alignment process, the LED bar graph will indicate the amplitude of the lens and retinal echoes being received. The criteria for proper alignment is that all echoes must be in the green section of the bar graph. Echoes in the orange section indicate that the amplitude is too low, while echoes in the red section indicate that the amplitude is too high.

10. As the unit reaches the maximum beep repetition rate, movement of the probe should be made in smaller and slower steps, so as not to pass through the area of proper alignment too quickly. As soon as proper alignment is achieved, the measurement will be obtained as indicated audibly by three short, successive beeps, provided there is no corneal indentation present. The display will indicate the measurement as shown in step 8. 11. If the beep rate reaches a constant tone during the alignment procedure, cornea indentation may be occurring. The DGH 3000B uses special circuitry that prohibits any measurements from being obtained if the cornea is being indented. If a constant tone is obtained, slowly withdraw the probe away from the cornea until the constant tone changes to pulsed beeping. Again, the pulsed beeping should be maximized as described in steps 9 & 10 until a measurement is obtained. 12. If a measurement is not obtained after a preset time period* of probe applanation, the unit will time out as indicated audibly by three short, successive beeps. The display will show a message indicating why a measurement was not obtained. Refer to Section VII for a list of the seven possible messages that will appear when no measurement is obtained and an explanation of each. At this point the operator should take the corrective action indicated by the display and reattempt taking a measurement. - 15 -

* The time duration allowed for a measurement cycle is preset at the factory for five (5) seconds. This time can be changed to meet the operator’s needs. Refer to Section VI for the procedure used to change this time duration. 13. After obtaining an acceptable measurement for memory location 1, the unit will sense when the probe has been removed from the cornea and advance to memory location 2. At this point, the probe applanation and alignment procedures described in steps 5 through 11 should be repeated until a measurement is taken and stored in memory location 2. 14. The measurement and storage of up to eight (8) different readings for each eye is possible with the DGH 3000B, depending on how many measurements the operator feels is necessary to evaluate for consistency and repeatability. 15. All measurements can be reviewed by pressing the “NEXT MEAS” or “PREV MEAS” keys. 16. If during the data review a reading is observed which is suspect because it does not agree with the other measurements, the measurement data in that particular memory location may be replaced with a new measurement as follows: a)

Scroll through the measurement data using the “NEXT MEAS” or “PREV MEAS” keys until the data which you desire to replace with a new measurement appears on the display.

b)

Press the “DELETE” key to delete the measurement from the display.

c)

Repeat the measurement sequence of steps 5 through 11 above until a new measurement is obtained.

17. After obtaining the desired measurements for the first eye (OD or OS), the operator may obtain measurements on the same patient’s other eye, if desired, by pressing the “AUTO GAIN” key, selecting the eye and lens type for the second eye, and repeating the measurement sequence of steps 5 through 11. NOTE: The measurement data for the first eye will remain stored in memory while measurements are being obtained on the second eye. 18. After the desired measurements on one or both eyes are obtained, the operator may obtain a permanent record by pressing the “PRINT” key. The unit will print out the following: a)

A header, which includes: i) Space to write the date, operator name, and patient name. ii) The eye measured (OD or OS). iii) The aqueous, vitreous, and lens velocities used in the ocular measurements. - 16 -

iv) The lens type. b)

The actual ocular measurements including axial length, anterior chamber depth, and lens thickness where applicable. Up to eight (8) measurements for each eye may be printed out.

c)

If enabled during the A-Scan setup mode (see Section VI), the print out will also include: i) ii)

A graphic representation of the corneal, lens, and retinal echoes which occurred during the actual measurement. The average of the 1 to 8 measurements taken on each eye.

19. All measurements will remain in memory until the “CLEAR” key is pressed. Pressing the “CLEAR” key will clear all measurements from memory, retest the probe, and the display will indicate “SELECT EYE OD”.

* * * CAUTION * * * When the unit is CLEARED, the DGH 3000B will automatically set the internal gain of the unit to comply with the probe sensitivity. Therefore, it is imperative that the probe tip be clean and dry before the unit is cleared. Also, the temperature of the probe should be stabilized to within ±10°F of the temperature at which the probe will actually be used. Never clear the unit with the probe attached after the probe has just been exposed to an extremely cold or hot environment. Always allow time for the probe to stabilize at room temperature.

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VI.

SETTING UP THE DGH 3000B

Setup (Configuration) Overview The DGH 3000B has been designed to allow the operator to set up certain default parameters to tailor the instrument to one’s needs. These parameters are permanently stored in non-volatile memory and are automatically recalled from that memory each time the unit is powered up. The parameters which can be set up, or configured, in the DGH 3000B are: 1.

The velocity of sound in aqueous/vitreous, cataractous lens, natural lens, PMMA lens, silicone lens, and a lens material which the operator identifies.

2.

The thickness of PMMA lens, silicone lens, and a lens material which the operator identifies.

3.

The measurement time duration.

4.

The content of the print out.

Configuration Description 1.

With the DGH 3000B in measurement mode, press the “SETUP” key and the display will read: SELECT SETUP ASCAN

2.

Press the “ENTER” key to begin the A-Scan setup mode. The display will show the first parameter and its factory default value: AQUE/VITRE VEL 1532 M/SEC Note: If the display indicates a velocity of sound other than 1532 m/sec, then the default value was previously changed by an operator.

3.

Press “ENTER” if you wish to accept the velocity of sound that is currently being displayed. To change the velocity of sound, use the numeric keypad to select a new number, and then press the “ENTER” key to confirm the new number. The - 18 -