The EyeQue Personal Vision Tracker is able to measure refractive error in the following ranges:
Spherical measurement of +8.00D to –10.00D.
Cylindrical measurement of 0.00 to –4.00D.
Axis measurement from 1 to 180 in 1-degree increments.
If you typically have correction measurements outside of these ranges, you may not be able to measure your refractive error accurately. You will likely experience a warning while testing indicating that the range limit has been reached. Contact support@clearhorizonsoptometry.com for assistance.

There are a 2 main reasons that you might be experiencing this message on your device:
You may be unable to connect to the EyeQue Cloud: If you have limited, interrupted or no internet access you may not be able to connect to the EyeQue Cloud server. Without a connection to the server, your device cannot be verified and it will prompt you with this error. To re-establish a connection on an iOS device you will need to force close the app and the reload the app on your device. This should fix the issue and you'll be able to continue with the test. On an Android device you can tap on the "Try Again" button or force close the app like an iOS device. If you are still receiving the error, please contact support at support@eyeque.com to see if the issue is server side. If you are using an Android based smartphone, do not use the back button as it may leave any errors on the stack causing you to continue to see this error.
You phone is not compatible with our device:
Depending on the device that you are using, we may have not tested the device for compatibility or the device is not usable with the Personal Vision Tracker system. There is one main requirement that will determine if your device has a possibility of being compatible and that is the pixel per inch of the screen. If the current device has a PPI below 250 then it will not give an accurate enough reading with the EyeQue miniscope and will not be compatible. If your device does have the minimum PPI required, then it will not work.

The EyeQue miniscope is designed to work specifically with a smartphone. The latest list of supported smartphones and operating systems can always be found on our product page. EyeQue continues to test and calibrate the software to support the ever-growing list of smartphones on the market. As of March of 2018, we have updated our software to accept a plethora of smartphones that have a pixel per inch screen density of 250 or higher. This affects mostly Android users as there are many makes and models that have various screens on their devices. There are still gaps within our testing data so not all smartphones with such a high PPI will work. We continue to test and calibrate new devices so we can cover the ranges that have gaps of data.

The EyeQue PVT is registered with the US FDA as a Class 1 medical device with a 510K exemption. The components of the PVT are the miniscope and the EyeQue PVT app. The PVT also is RoHS and CE certified.

Refractive error, also known as refraction error, is a problem with focusing of light on the retina due to the shape of the eye. It generally occurs when the eye cannot focus images on the retina; the focus occurs before or after the retina. Refractive errors are corrected with eyeglasses, contact lenses, or surgery. Eyeglasses are the easiest and safest method of correction.

After each completed vision test in Test mode, your results will be uploaded and evaluated through EyeQue's powerful analytics contained in the EyeQue Cloud™. The EyeQue Cloud will determine a confidence level based on procedural consistency. A higher confidence level reflects a higher quality of test results, resulting in EyeGlass Numbers. Based on our study, the quality and accuracy of the EyeGlass Numbers is comparable to traditional auto-refractors used in the eye care industry. You must generate three consistent test results in order to view your EyeGlass Numbers. The measurements are accurate within +/- 0.5D.

If there is inconsistency in your test results, EyeGlass Numbers will not be displayed and you will be directed to contact EyeQue Support for more information. Please continue testing until you have successfully achieved three consistent tests.

Note: Practice Tests will not be calculated into your EyeGlass Numbers. Also, if you state that you have not removed your contacts or corrective lenses, those tests will be ignored when calculating your EyeGlass Numbers as well.