Previous required knowledge

In this section, you will find standard recommendations to measure and report your defocus curves for Congresses and Peer Review journals, however, ensure that you are already familiarized with the App reviewing consecutively the following 3 sections:

If you are already familiarized with the App you can copy the settings of the image (changing the Protocol name by your testing lens) and review the information below for understanding the most important steps.

Standard Procedure for Multifocal Lens Analyzer

We have developed a system for the automated measurement of visual acuity and contrast sensitivity defocus curves, now it is time to define a standard procedure to uniformly measure and report defocus curves around the world


1.1.- Have you switched the Auto-brightness and the Auto-Lock off?

The App has been developed to automatically set the brightness defined in the protocol each time the test starts. Anyway, it is recommended to maintain the "Auto-brightness" of your iPad switched off. This option could be found in different parts of the Settings section depending on your IOS version.

  • Last IOS versions:
    • Settings -> Accesibility -> Display & Text Size -> Auto-brightness -> Off
  • Old IOS versions:
    • Settings -> Display & brightness -> Auto-brightness -> Off

If you stay some time without interaction with your iPad the screen can also be automatically switched off. You can prevent this behavior by switching-off the auto-lock.

  • Settings -> Display & brightness -> Auto-lock -> Never

You can read more information about these steps in the following article:

1.2.- Are your iPad or iPhone properly connected to WIFI?

Multifocal Lens Analyzer requires of WIFI connection for two purposes:

  • Always for PRO users in order to validate the access to their PRO accounts.
  • For users who use an iPhone or another iPad as remote controllers, both devices should be connected to the same WIFI network to run properly.

1.3.- Have you switched on your iPad at least 15 minutes before to start the measurement?

All displays require some time to stabilize the brightness, even though the variation of brightness is considerably small our recommendation is to switch on the device 15 minutes before to measure the defocus curve, specially for contrast sensitivity.

1.4.- Is it necessary to maintain your screen clean and without reflections?

An iPad is a touch screen, therefore exists a risk the screen is not completely clean and this can affect especially the measurement of contrast sensitivity. Please, maintain your screen clean especially if you are going to test contrast sensitivity. On the other hand, some reflections can appear from light sources in the cabinet reflecting over the screen, take care this does not happen before starting to measure. Sit down in the place of your patient and check that no reflections appear over the screen.


2.1.- How I have to measure the subjective refraction?

Optimal subjective refraction targeting to infinity is quite important to ensure that the maximum peak of vision is located at the 0 D location (infinity) in the defocus curve.

Clinicians conducting refraction at a different distance for which the defocus curve is going to be measured could have a systematic shift in the defocus curve. To ensure perfect refraction targeted to infinity our recommendation is:

  • Take refraction at 4 meters. For instance, obtaining (+1.00)(-0.50)@90º at 4 meters.
  • Calculate the refraction at infinity adding -0.25 D, obtaining (+0.75)(-0.50)90º at infinity.

Include the value of the sphere in the "Additional information" section of the testing procedure before starting the defocus curve. The App will automatically calculate the combination of the required lens in order to use a single spherical lens. For instance, testing at 4 m from -1.00 to -4.00 D of defocus means that the first lens to use in the trial frame in combination with the cylinder of (-0.50)90º will be (+0.75)+(+0.25)+(1.00) = +2.00 D. The App automatically will calculate the required sphere after each defocus evaluation.

The theoretical explanation of this could be found in the article: Why do we measure the defocus curves at 2 m or 4 m and not at 6 m?

If you do not have an ETDRS chart for refracting at 4 m you can use the VisionC App on the same iPad for this purpose. 


2.2.- Is it required to explain the procedure to the patient?

Although Multifocal Lens Analyzer incorporates an automated Fast testing procedure which reduces the time around 50% in comparison to the conventional measurement of defocus curve, it is still a procedure requiring a longer testing time. For this reason, it is important to explain the procedure to the patient before starting and remarking messages about testing time and limit of vision: 

"I am going to show you a random letter (if you use Sloan). You only have to tell me if you can recognize it and thus what the letter is (if you use Sloan letters). After each answer, you will see that the letter becomes smaller or larger (clear or dark if you measure CSDC), at a certain point it will be so small (clear for CSDC) that it will be impossible to see it. At that point just say 'I don't see it' and we'll move on to the next one, don't worry it's normal that you don't see it because we're going to go to the limit of your vision which may even be above normal. The procedure will take around 7 or 8 minutes"


2.3.- What are the considered standard settings?

In the Database section, you will find the required instructions to create and assign a protocol to an exam. We recommend the following settings for the protocol:

  • Presentation distance: 4 m
  • Optotype: Sloan
  • Defocus Range: From +1.00 to -4.00 D
  • Extra step: No
  • Gammas: R: 2.19 G: 2.20 B: 2.22
  • Brightness (85 cd/m2): 41%

Create a protocol for each lens and use the previous configuration always it is possible. If you are going to measure the same patient at different environmental conditions (i.e. photopic and mesopic) you can use sufixes to name your protocol. For example, for MIOL1 you can create two protocols MIOL1_photo and MIOL1_meso with same device settings but different external settings.


3.1.- Monocular or binocular conditions?

The decision will depend on your purpose, if your purpose is to assess the performance of the MIOL you have to conduct the measurement in monocular vision. On the other hand, if your purpose is to understand the possible relationship between patient reported outcomes (questionnaires) and visual performance you have to conduct the measurement in binocular vision.

3.2.- With or without best distance correction?

Following the same reasonning that the previous point, if your purpose is to assess the performance of the MIOL you have to conduct the measurement with best distance spectacle refraction. On the other hand, if your purpose is to understand the possible relationship between patient reported outcomes (questionnaires) and visual performance you have to conduct the measurement in with the habitual correction of the patient, either with or without correction.

3.3.- Photopic or Mesopic environmental light conditions?

It is important to understand that the aplication always measure photopic retinal vision, but you can modify environmental light conditions from photopic to mesopic conditions to evaluate the influence of pupil diameter in visual performance.

3.4.- Visual Acuity or Contrast Sensitivity Defocus Curves?

You have two possibilities of measurement, we do not recommend to measure both. Our recommendation is to measure Visual Acuity Defocus Curve (VADC) always you are going to use the obtained results in a non-expertise forum or congress with attendees not familiarized with Contrast Sensitivity Defocus Curve (CSDC).

If you are looking for enhancing the detection of differences between lenses or to detect small changes in the optical quality we recommend CSDC. This metric has demonstrated to be more sensitive than visual acuity.

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