The Rotterdam Ophthalmic Institute, which is affiliated with the Rotterdam Eye Hospital has a dataset that contains longitudinal visual field data of 139 glaucoma patients. The main page is here and the dataset was used for studies like Robust and Censored Modeling and Prediction of Progression in Glaucomatous Visual Fields.
I downloaded the data and did the following, I took from every patient the first visual field and calculated the mean sensitivity threshold of all the patients for every point, then I did the same for the last visual field. I substracted the mean sensitivities of the first and the last test and plotted the differences, here is the result:
Most of the points that lose sensitivity are nasally placed, well I expected that but I didn´t expect point B. That point is gaining sensitivity in both eyes, is located nasally and surrounded by points that are losing sensitivity, that´s odd. Then point A, it is located where the blind spot is and is losing sensitivity. Another thing is that point A and B are simetrically located and I thought it could be a transcription error and A and B are switched. To know more about those points I plotted an histogram for the thresholds at those points. I show you here point B for the right eye:
In the first visual field over 50 patients out of 138 didn´t saw that point and in the last one just over 30 people, also at the higher thresholds there are quite some people doing better in the last one. Let´s see the one for point A:
Here the difference is smaller and much more people didn´t see point A in both tests, as expected since it is the blind spot but that confirms that the points are not switched.
The fact that the same point in both eyes has that characteristic is quite interesting. I am going to leave it here by now and might look for it in a future article, meanwhile if you have any idea of why this is happening please let me know here or via linkedin.
Here is the code for the data preparation and for the graphics. I checked it but if you find a mistake there please also let me know.