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Introduction to the Phoropter
The phoropter is a complex lens holder designed to allow the examiner to change lenses efficiently and easily．It consists of four gros of controls．Controls that are labeled in Figure 3-6 are italicized in the text．
Ⅰ．Lens controls
The heart of the phoropter is its two sets of lens controls, one for spherical and one for minus-piano-cylindrical lenses．
A．Spherical lens control
The control for the spherical lenses is a large wheel at each side of the phoropter called the weak sphere dial．There is a strong sphere control which allows ±3.0 or 4.0 diopter changes in sphere．Inside the housing of the machine there are two sets of lenses mounted on large wheels．One wheel carries a set of lenses in 0.25 diopter steps．The other carries lenses in 3.0 or 4.0 diopter steps．The two wheels work together to provide total lens powers in the range of +20 D to -20 D in 0.25 D steps．
The net spherical power is shown on the sphere power scale．
B．Minus-piano-cylinder control
Minus-piano-cylindrical lenses are mounted in a wheel that rotates to bring different powers of lenses before the patient’s eye．The lenses in the cylinder wheel can also be rotated to vary the axis．
The cylinder is controlled by two knobs，the cylinder power knob, and the cylinder axis knob．The cylinder power is shown on the cylinder power scale．The cylinder axis indicators display the axis of the minus cylinder by the position of an arrow on a standard ophthalmic protractor, the cylinder axis reference scale．
Ⅱ．Auxiliary Lens Knob/Aperture Control
The auxiliary lens knob/aperture control determines what the patient looks through when behind the phoropter．The most frequent positions are Open，in which the aperture contains the lenses, and BLank or Occluded, in which the eye is completely occluded．
Most phoropters also contain a Retinoscopy Lens aperture，a +1.50 or +2.00 diopter spherical lens placed in the aperture in addition to the lenses indicated by the power scales．Additional apertures that are available on some phoropters include±0.50 diopter Jackson Cross Cylinders (JCCs)，pinholes (PH), red lens (RL)，Maddox rod(RMH/VMH)，Polaroid(P)，+.12D，and horizontal(10ΔI)or vertical(6△U)prisms．
Ⅲ．Ancillary Units
The phoropter has two or three ancillary lenses, that can rotate in front of the eye hole when desired．
A．Jackson Cross Cylinders Unit (JCCs)
The JCCs are marked with red dots or lines to indicate their minus-cylinder axis and with white marks to indicate their plus-cylinder axis．The handles are positioned 45° away from the cylinder axes．
B．Rotary Prism Unit
The rotary (or Risley) prisms have an indicator for the direction of the prism base and a scale to indicate their net prism power．With the zero in the horizontal meridian, the indicator is placed above the zero for base prism and below zero for base down prism．With the zero in the vertical meridian, the indicator is placed toward the nose for base in prism and away from the nose for base out prism．
C．Maddox rod
In some phoropters the Maddox rod is included as an ancillary lens rather then in the eye hole aperture．
Ⅳ．Adjustments
The phoropter contains controls for adjusting the phoropter to fit the patient．
A．PD knob
B．Leveling knob with spirit level
C．Vertex distance control
D．Pantoscopic tilt control |
