VISUAL SCREENING EQUIPMENT
Snellen Eye Chart
The first step in the visual assessment process is to test the visual acuity of the patient. On the Left is an example of a snellen eye chart. On the right is a "Tumbling E" eye chart made for diagnosing children and illiterate people (and people from countries who do not use the English alphabet like China), You can download a printable copy of the Snellen Eye Chart here.
With the occlusive paddle one isolates the tested eye and evaluates its acuity using a 20 foot eye chart. The one occludes the contralateral eye and tests its acuity.
The Pinhole tester is then used to see if the eye improves its visual acuity. In a purely refractive error deficit the vision should improve substantially. If the vision does not improve there is probably some other non-refractive, organic problem like a retinopathy, a macular degeneration, or a cataract. The patient needs to then have a fundoscopic exam with a qualified physician.
This serves as a great screening tool for the non-professional eye technician.
Opaque Occlusive Paddle
OPTOMETRIC DIAGNOSTIC EQUIPMENT
An autorefractor is an excellent device for diagnosis refractive error in patients. They easy to use and fully automatic, making diagnosis easy for non-ophthalmologists. The Nikon Retinomax pictured to the right costs around $9600.
The Phoropter is the device typically used by optometrists in their offices to prescribe glasses. It is a little bulky if one transports the required stand. The cost is around $2,500.
The trial lens set can be used to prescribe glasses. The patient wears the trial lens frames while the examiner exchanges the lenses until an appropriate strength is reaches. The approximate cost is $450.
The Focometer is much less expensive than an auto-refractor, needs no electricity, and never needs calibration. It functions like a telephoto lens. The patient turns the lens until the desired lens strength is reached. The cost is around $500.
The trial and error method is the most economic. One simply places all the differing strengths of eyeglasses in an ascending manner on the table and the patient tries each one beginning at the weakest continuing through the strongest until he/she finds the best lens strength for his/her refractive error. Essentially no cost is involved except the cost of the glasses which is $1 - 2 per pair.