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Theory of Operation
AT550 Introduction
The AT550 is an advanced electronic tonometer which
acquires IOP (Intraocular Pressure) data from the eye and
also contains an innovative automated alignment system
which quickly aligns itself to the patient during the
measurement process.
Special Features of the AT550
The AT550 has special features which are not available on
other tonometers. The AT550 features are: it can be
serviced in the field, it has a port for installing software
upgrades, and it utilizes an auto alignment system.
Additional features contained in this instrument are an
automated L/R Detector, and a Travel Lock Assembly. A
description of the special features of the AT550 are as
follows:
Field Service
The calibration data of the AT550 is installed into a
single independent assembly (referred to as the
tonometer head assembly or “toolbox”) and can be
replaced at a remote location, not requiring the
complete instrument to be returned to the factory.
The optical head assembly is fully calibrated before it
is sent from the factory.
Software Installation
The operating system was designed to accept
upgrade options without making it necessary to
return the instrument to the factory. The access port
for this option is placed behind the printer door and
accepts a PC Card that is pre-programmed with the
applicable upgrades.
Auto Alignment System
Our patented "hands-free" auto-alignment technology
in this instrument removes the necessity to adjust any
joystick or chin rest. The patient simply leans
against the appropriate side of the forehead rest,
views a green fixation target, and then is ready for the
operator to initiate the measurement process. The
AT550 then aligns itself in front of the eye and
automatically acquires the appropriate data.
Left / Right Detector
Each instrument contains a Left / Right detector that
automatically detects which eye the instrument is
measuring. If the instrument can not select the
appropriate eye, a menu is displayed requesting that
the operator select the appropriate side.
Travel Lock Assembly
A travel lock assembly is provided within the
instrument to secure the positioning system during
transportation. This assembly ensures that during
transportation, the operational integrity of the
instrument is maintained.
Positioning System Operation
The new AT550 optimizes the alignment of the patient to
the optical system without the use of a joystick or the
necessity of a chinrest. The patient only has to set their
head against the left or right side of the headrest. The
measurement process then automatically aligns and
acquires the eye data quickly and accurately, as
requested by the operator. During the entire
measurement process, the alignment system verifies the
correct position of the patient to ensure that correct
positioning is maintained for accurate measurement
data. Refer to Figure OP-1 for a drawing of the
Positioning System Block Diagram.
Details of the Alignment System
The auto-alignment system of the auto-tonometer uses
two positioning LEDs (wavelength = 875 nm) and two
receiving cameras (plus other minor components) to
align the system to the patient.
When a measurement is requested by an input from the
operator (button push) the Motor Control Board applies
power to the right Position LED. The LED emits light
toward the eye. Some of the emitted light reaches the
eye and is reflected off the cornea and is sent to the 1st
Surface Mirror on the opposite side. This light is then
reflected off of the mirror and continues on through the
IR Filter, Position Lens, Spacer Lens and finally to the
Position LED Camera.
The Position LED Camera receives the light source data
and converts it to electronic data. This converted data is
sent to the Video Circuit Board, Control Board, I/O Board,
and Motor Board where it is processed using a
proprietary processing technique (a process for which
patents have been issued) to provide precise alignment
of the system to the eye.
After the right side Position LED Camera receives its data
the left side Position LED and camera alternately turns on
and acquires its data. The right and left side Position
LED's are alternately activated to allow for three
dimensional positioning. After data is acquired, from the
Video Circuit Board, the positioning system adjusts the
optical head assembly for best focus. This alignment
process continuously updates throughout the
measurement process.
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