Optometric Instruments

The phoropter, the optometric instrument used to determine the patient's prescription, was originally patented in the early 1900s by Henry De Zeng. Surprisingly the basic elements of this instrument haven't changed much since. Even the newest digital computer-automated refracting unit still uses the same basic system of lenses mounted on rotating discs. Optometric equipment today borrows from past invention and is improved upon by modern technology.

Pre-Testing Equipment

• A Snellen eye chart is commonly used to measure the patient's visual acuity.

  The Snellen letter chart or projector system is used to determine the patient's visual acuity. During this process a cover paddle is used to occlude the eyes alternately while checking visual acuity and to determine if a patient has a muscle imbalance. The non-contact tonometer (NCT) is a tabletop instrument used to determine intra-ocular pressure. An auto-refractor is used to obtain an estimate of the patient's prescription as well as the radius of the cornea. A keratometer is used to determine the patient's corneal curvature, while a lensmeter is used to measure the prescription in the patient's current spectacles.

Refraction Equipment

• A retinoscope is a hand-held instrument used for determining the patient's prescription objectively. A thin beam of light is directed into the pupil. How the beam of light reacts against the reflection in the pupil tells the examiner whether to add plus or minus lenses to the prescription. A phoropter is a system of rotating spherical and cylindrical lenses that are used to refine a patient's prescription.

Anterior Segment

• A slit lamp is a tabletop instrument that uses light and magnification to examine the anterior ocular structures, including the lids, lashes, cornea, conjunctiva, lens and iris.

Posterior Segment

• The ophthalmoscope provides a non-stereoscopic view of the retina.

  Fundus lenses are hand-held lenses used in conjunction with a slit lamp or binocular indirect ophthalmoscope for viewing the retina. These lenses come in varying levels of magnification and field of view. The binocular indirect ophthalmoscope is worn either on top of the head or mounted to a pair of spectacles. These instruments together provide light and magnification to provide a three-dimensional view of the retina. A direct ophthalmoscope is another hand-held instrument that uses light and varying degrees of magnification to provide a view of the retina. This instrument does not provide three-dimensional views, however.

Ancillary Testing

• A tonopen is a hand-held instrument used to determine intra-ocular pressure. A gonioscopy lens is specifically designed to view the angle between the iris and the cornea. Available in hand-held or tabletop versions, a pachymeter is used to determine the thickness of the cornea. The visual field analyzer is a tabletop automated instrument used to determine the patient's peripheral visual field, while the corneal topographer is tabletop instrument that provides a detailed map of the corneal surface. The topographer is used to detail corneal irregularities as well as provide an estimate of the refractive status and corneal radius.