Combination of Fourier-Domain and Placido-Disc Technologies in the OA-2000

Tomey's OA-2000 Optical Biometer (Figure 1) provides noncontact, noninvasive, automatic measurement of axial length (AL), anterior chamber depth (ACD), lens thickness, and central corneal thickness (CCT) based on Fourier-domain technology plus Placido-disc–based corneal topography, according company literature.1,2 It provides enhanced usability, connects remotely to an ultrasound biometric unit for hard-to-read eyes, offers one-shot IOL power calculation, and provides an internal database for storage.

The compact unit can be installed on a small optical bench, yet it incorporates a large 10.4-inch monitor that tilts to suit the surgeon's gaze. Touching the center of the pupil in the display begins the acquisition with automatic alignment and capture. If automatic acquisition is difficult, manual acquisition can be performed with a joystick.

Up to seven sets of measurement data, such as CCT and ACD in addition to AL and keratometry, can be obtained in one quick shot. With this data, the device can perform a series of calculations throughout the patient's care, starting with the preoperative examination and including IOL power calculation, postsurgery data storage, surgeon A-constant optimization, and statistical processing.

The OA-2000 also includes Placido-disc corneal topography to measure the radius of corneal curvature and describe corneal shape. The topographer measures not only the standard 3-mm diameter optical zone but also simultaneously at 2.5 and 2 mm. It also creates a topography map to help determine the presence of irregular astigmatism and allow comparison of pre- and postoperative corneal shape. The maps are also helpful to assess eyes after LASIK and other corneal refractive surgery procedures. In the case of toric IOL implantation, the maps can also identify the axis at which the IOL is to be oriented.

The device's Fourier-domain A-scan technology provides high-speed tissue penetration capable of measuring through almost all dense cataracts (Figure 2). A search function automatically detects measurable points even in cloudy crystalline lenses. In rare cases of very mature cataracts, AL and CCT measurements can be done with the AL-4000 handheld ultrasound biometer (Tomey), which communicates with the OA-2000 via Bluetooth technology, according to the company. After biometric parameters are collected by the AL-4000, IOL power calculations, data storage, and other operations are carried out by the OA-2000.

The OA-2000's IOL power calculation function includes nine formulas, including SRK-II, SRK/T, Haigis, Holladay, Hoffer Q, and two formulas for eyes with surgically corrected corneal refractive power. Up to 15 IOL types can be supported. n