1. Field of the Invention
This invention relates to an ophthalmic measuring method and apparatus, and more particularly to an ophthalmic measuring method and apparatus in which an optical system is used to project a laser beam at a selected spot in the camera oculi of a patient's eye, particularly in the anterior chamber thereof, and the laser light scattered therefrom is detected.
2. Description of the Prior Art
Measurement of floating cells in the anterior chamber is very important in the diagnosis of ophthalmic inflammation and uveitis. Conventionally a slit lamp microscope is often used for this, with grading being via the naked eye, while on the other hand a photographic measuring method has been developed to provide quantitative measurements. However, no method has yet been perfected that is readily applicable to clinical examinations.
With the conventional method of naked-eye measurement in which judgment can vary depending on the person making the measurement, the data thus gained lacks reliability. One solution has been a method of ophthalmic measurement in which laser light is projected into the eye and the light scattering from the eye is detected and analyzed quantitatively (see, for example, U.S. Pat. No. 4,711,542).
When measuring scattered laser light, light reflecting and scattering from the cornea, the iris, the crystalline lens, including artificial crystalline lenses employed following a white cataract operation, shows up as noise in the scattered laser light and in the measurement site in the anterior chamber, which degrades measurement accuracy, prevents measured values from being reproduced and can cancel out the signal components.
To overcome these drawbacks, U.S. Pat. No. 4,832,043 discloses an ophthalmic disease detection apparatus in which a laser beam is deflected so far as to exceed the slit width formed on a mask in front of a photoelectric converter. In this apparatus, an electric signal derived from the photoelectric converter when the laser beam is deflected outside the slit width is subtracted from an electric signal obtained when the laser beam is deflected within the slit width, thereby removing noise components based on the dark current in the photoelectric converter or unnecessary scattered light or reflected light. Such a method to remove the noise is insufficient because the light scattered or reflected from the cornea or crystalline lens, which behaves itself as noise, has strong directivity so that it can directly impinge on the mask, thereby reducing a S/N ratio.