Working model- it consists of a wooden board to which a circular disc graduated in degrees is fixed. The disc is fixed with a metallic pointer and graduated metallic arc. The angular position of the metallic arc to the eye can be read with the help of a pointer on the graduated disc. In the middle of the disc is a point which is rotation passes through all the radii along a spherical object corresponding to the surface retina. Perimeter ( Lister type )Automatically records field to 90 degree in all meridians. Thecrier mechanism is smooth, silent and invisible. The patientperceives only the test object to move. Spring check, giving anaudible click to each 15º of rotation of the arc in either directionrenders close scrutiny of dial plate unnecessary, and ensuresaccurate registration. The device can be thrown out of action ifsilent movement is desired. The marker a needle is housed in aretractable tube, sprung to sheath the pint when actuallymarking. A set of interchangeable and permanent washable testobjects is included with the instrument.

Working model- it consists of a wooden board to which a circular disc graduated in degrees is fixed. The disc is fixed with a metallic pointer and graduated metallic arc. The angular position of the metallic arc to the eye can be read with the help of a pointer on the graduated disc. In the middle of the disc is a point which is rotation passes through all the radii along a spherical object corresponding to the surface retina. Perimeter ( Lister type )Automatically records field to 90 degree in all meridians. Thecrier mechanism is smooth, silent and invisible. The patientperceives only the test object to move. Spring check, giving anaudible click to each 15º of rotation of the arc in either directionrenders close scrutiny of dial plate unnecessary, and ensuresaccurate registration. The device can be thrown out of action ifsilent movement is desired. The marker a needle is housed in aretractable tube, sprung to sheath the pint when actuallymarking. A set of interchangeable and permanent washable testobjects is included with the instrument.