Purkinje Tree and Covid-19 Vaccine. During the current COVID-19 pandemic and massively increased vaccinations, there have been few ocular side effects reported with the  vaccine. 1) However conjunctivitis has occurred with Covid-19 infection and very rarely endophthalmitis has been reported.  I wish to mention an otherwise unreported association with visualization of a Purkinje Tree and Pfizer Covid-19 second vaccine. I am a 73 year old otherwise healthy retired male. I had an entoptic experience after I received my second vaccine.  With the first vaccine I had no visual side effects.  The afternoon of my second dose I took an hour long  nap, which was unusual for me.  When I woke up and opened my eyes I noticed a bilateral arborizing, interlacing dark pattern that lasted less than a second. This was opaque but without a ghost image and otherwise the wall, sheet,  and ceiling were seen clearly behind that network.   I experimented with opening and shutting either and both eyes looking at a white sheet beneath me, and found that especially with my dominant left eye I saw a pattern resembling my left eye retinal vascular tree.  The branches originated as single vessels  superiorly and inferiorly that branched down to smaller vessels  all on the right side of a disc type structure without duplication into an identifiable arteriolar and  venous system. Even with a light source moving over my left shoulder,  the image never lasted longer than a fraction of a second and fatigued quickly with repetition.  I laid back down and repeated the experiment of opening and shutting either eye while looking at a white ceiling. Then the image changed to a horizontally oriented pattern with two single black vessel type structures coming off a disc type structure.  The dark lines further branched and narrowed as they extended to the right and left off the disc type structure.  Again this lasted less than a second. It faded away rather than floated away. The image always appeared in the same area of my field of vision. It was peri-central when I looked at the wall and inferior to fixation when I looked at the ceiling.   The image would immediately move with eye movement, unlike a vitreous floater. Opening and shutting my left eye could refresh the image very briefly but that fatigued with repetition and could not be reproduced after 3-4 trials or without several hours between attempts. I did  translations of Purkinje?s description of the Tree (described here later.)  and had short term  partial success with his methods, except for pushing on  my eye, and using galvanic current,  which I did not attempt.  I declined a full exam but did  remember a lecture about Purkinje images.  He had the residents hold pen lights to the side of their eyes and move the light back and forth while he  described the Purkinje Tree. Afterwards he quizzed the residents about whether they could see it or not, with the ?humorous? disclaimer that it was a means of IQ testing if they could see it.  Half could.  It was of interest to me that  before I retired,  occasionally patients would mentions seeing the tree after an ophthalmoscopic exam.  I hoped to delight those patients by  telling them it was a form of IQ quiz and they had done well.  Two weeks later I was disappointed that I could no longer see the tree, but again declined an exam.  I am optically conversant, but physically adverse in seeking self care.   Purkinje first described the ?Tree?2) in his doctorate thesis in 1819. It was included in descriptions of other entoptic phenomena, performed mostly on himself. This was before the ophthalmoscope was discovered and before quality histological, serial sections were available.  He described holding a candle or using galvanic illumination in front of his eyes individually and moving it around.  He could see  black lines in a network that came off a central pit structure.  There were two lines inferiorly and superiorly with adjacent shadows and ultimately had size reducing branches.  He recognized these branching lines as retinal blood vessels, but could not discern any blood flow.  In 1825 he published a further volume 3) that dealt with experiments he subsequently had performed.  He found that by holding a sheet of paper with a hole in it that he moved around,  he could get a better view of the blood vessel pattern.  He could discern the macula and described anastomosing blood vessels superior to inferior.  A significant improvement in his discerning the blood vessel pattern was obtained with a safe amount of pressure on the superior lateral aspect of the eye.  With this he could recognized blood corpuscles and flow patterns and then labeled the lines as veins. He did not describe arteriole patterns.  So this leaves us with the question why this sudden awareness of the Purkinje Tree appeared in the time frame of a second Covid-19 vaccine.  This will require further reports to determine coincidence versus cause-effect.  This is a high stress time with Covid-19 deaths so prevalent. I had immediate relief after my second shot with a reduction of tension and increase in awareness of my general physical status as in the feeling of being hot or cold, sleepy or just fatigued, improved calmness, and the pertinent Purkinje Tree.  At sign in for the second series of Pfizer injections the RN on duty asked about side effects from the first shot.  She asked us to send a report in of any potential side effect then of the second shot and notified us that people were having more problems with the second shot than the first. Arm soreness, swelling, fever, chills, headache,  malaise, fatigue.  She gave us a print out list of known side effects, mostly systemic and all mild, but nothing ophthalmic.  With these things  in mind I was especially vigilant of any thing new in my general health or condition.  Most of the patients getting the shots were students and the congregating area was in a wing of a hospital.  This brought back the pleasant memory of my time in training and  my chief?s description of Purkinje?s Tree and perhaps enhanced the  brief ability to see the entoptic image.  In between times playing with this image my vision was normal and  my general health remained good, without symptoms of vascular compromise.