Interesting fact: What are the uses of the red house and hot air balloon you see during an eye test?

"Look at the red house in the middle of the picture and don't move your eyes!"

"What are those red houses and hot air balloons you see when you have your eyes tested?"

What's the point of looking at these?

Fixed sight mark during optometry

The red house and hot air balloon are called fixation icons, which serve to fix the line of sight during eyesight testing.

Different computer ophthalmometers use different fixed vision icons, the red house and hot air balloon are the most common.

01Red House

02Hot Air Balloon

The red house you see when you are having your eyes tested is actually based on the Vik Church, which is located in Heidlissund, Iceland. It is a popular photo location for many tourists and professional photographers.

The instrument with the two icons of red house and hot air balloon is called "fully automatic computer ophthalmometer".

When you stare at a clear house, the optometrist will aim at your pupils and emit infrared rays into your eyes. Based on the image formed by the infrared rays in your eyes, the optometrist will determine whether you are nearsighted or farsighted, and the degree of your eyesight.

The degree measured by a computer ophthalmometer is only an approximate degree. This degree cannot be used directly to fit glasses. It needs further comprehensive eye testing by an optometrist and the final confirmed handwritten value to be the real degree.

Working principle of computer optometry

The light emitted by the computer ophthalmometer is refracted by the cornea, lens, aqueous humor, etc. of the eye to reach the retina, and then reflected back to the optical signal receiver of the computer ophthalmometer along the same path to calculate the refractive error of the human eye.

During this process, the degree measured by the computer ophthalmometer is easily affected by the accommodation function of the eye lens, and staring at the pictures of the red house and hot air balloons can help us relax the eye muscles and try to eliminate the interference of the accommodation function.

When the image is blurry, you can relax your eye muscles and prepare your eyes for eye examination in a relaxed and natural state. When the image is clear, you can fix your eyes' line of sight and let them look straight ahead.

Things to note when checking your eyesight

①True and accurate expression

During the whole optometry process, you should express your true feelings, especially during the lens insertion and trial wearing phase. The optometrist will constantly test you and ask you which one is clearer. If you can't judge, you will be asked to compare again. If you feel dizzy or see things distorted, you should give feedback in time.

② Take the initiative to make requests

When trying them on, you can ask to wear them for a while longer, usually 10-15 minutes.

Note: The optometry results of the computer ophthalmometer are for reference only. The specific glasses should be matched with comprehensive optometry to reach a final conclusion. After inserting the lenses and trying them on, it is necessary to ensure that you can see clearly and comfortably.