One widely used visual acuity test is Snellen Test using Snellens chart or Log Mar chart (Bailey Lovie chart) available in customized sizes so that it can be easily printed and used at home by placing at 3mts (10 feet) and sitting exactly in straight front of the chart.
- Close one eye with the help of hand or place a cardboard in front of it.
- Read out loud the letters that are seen with the uncovered eye.
- Typically, try to read smaller and smaller letters until you can no longer accurately make those letters out.
- Every line in the chart has its measurements and units of visual acuity mentioned in metric and decimal values.
- This process is then repeated with the other eye.
- If the user is not able to see the letters at the specified distance, then he/she requires Eye Checkup immediately.
- You can easily book appointment for Eye Checkup at Home by qualified optometrists.
CHECKUP BY OPTOMETRISTS
- After Vision screening with the same chart Optometrists use instruments for accurate power check up.
- With the help of pinhole, optometrist can realize the extent of vision that could be corrected.
- With the help of Autorefractometer, retinoscopy and Lensometer (if any) findings, refraction can be proceeded.
- Fogging & JCC to be performed as per requirement to give exact spherical, cylinder and axis.
- Final conclusion and confirmation of prescription has to be finalised after Duochrome test for every patients/customers.
DUOCHROME TEST PROCEDURE
Principle: Chromatic Aberration
- This test cannot be performed for customer whose vision is less than 20/30 or 6/9 even with full correction.
- This test has to be performed in dark room so that the pupil dilates and induces chromatic aberration.
- It is asked to the customer "Are the black letters more clearer in the red background or in the green background?"
- In Myopia if the patient says green is more clearer, it means that overcorrection was done. So, power is reduced in -0.25 step.
- In Hypermetropia, if the patient says red is more clear, it means that overcorrection was done. So, power is reduced in +0.25 step.
- In Myopia end result should be that the letters are more clearer in RED but also readable in GREEN.
- In Hypermetropia end result should be that both are equally clear.
- Afterwards, checkup needs to be done binocularly (with both eyes open).