Observing peculiar entoptic phenomena relating to a large air bubble inside his eye provided a little comedy relief for Professor Nathan Efron during his otherwise taxing ophthalmic journey of retinopexy, cryopexy, vitrectomy and IOL surgery.
During each of my three vitrectomy procedures I have had a large air bubble inserted into my eye to act as a tamponade. I was given two key instructions: (a) do three days of posturing (which I told you about in my last blog), and (b) don’t go climbing mountains or flying anywhere in aeroplanes until the bubble has resolved. The reason for the latter instruction is that outside air pressure decreases with altitude, so the higher you ascend, the more the bubble inside your eye will expand.
Now I think it is unlikely that the air bubble would expand to such an extent that it could damage the internal ocular structures, and it would be impossible for my eye to explode because the eyeball has been demonstrated to be able to withstand an internal pressure of 60 atmospheres before rupturing. Notwithstanding these considerations, I decided to heed to this advice: no mountain climbing or flying for me over the next fortnight! This did mean, however, that I had to carefully schedule my vitrectomy surgeries around my busy travel schedule; I am often flying interstate or overseas for conferences.
When the air bubble is inserted towards the end of a vitrectomy procedure, it almost completely fills the vitreous chamber, then gradually resolves into a progressively smaller bubble over a period of about 11 days. I will never forget the casual remark made by Bill’s assisting surgeon immediately following my first vitrectomy. Referring to the bubble in my eye, he said “You’ll have a lot of fun with that”. How prophetic that comment was!
Observing the world with a bubble in my eye evoked long-forgotten memories of esoteric concepts that I was forced to grapple with when studying Physiological Optics 101 some 40 years ago, relating to visuospatial perception – concepts such egocentric, oculocentric and head-centric localisation. These theories, which in general relate to how you perceive the direction of objects, were turned on their head because all of a sudden I had a new intraocular point of reference – a large air bubble.
Frightened by the thought that I could do further damage to my retina, I concluded that discretion is the better part of valour
Over or Under?
The first dilemma I had to get my brain around was the question of whether I was looking over or under the bubble during the first few post-vitrectomy days when the bubble was very large. I remember Bill mentioning to me that for the first few days after the vitrectomy I would gradually start seeing more of the world over the top of the bubble. Well, that’s how it actually looked… except that I knew that the bubble inside my eye was rising upwards, and I should have been seeing under the bubble, not over it. But then I recalled perhaps the most fundamental principle of visual optics, which is that the world is imaged on your retina upside down, with the brain interpreting what you see as being the correct way up.
So, the reason I could see ‘over’ the bubble, is because light was passing under the bubble forming a partial image on my inferior retina, which was then perceived as viewing over the top of the bubble.
Over the first few days following my vitrectomy, I could see more and more of the world above the bubble, albeit shimmery like looking through water. The curve of the bubble became more pronounced as it reduced in size. Of course, this view was only possible when wearing glasses to correct my high myopia. By about four days following surgery, I realised that I could see the entire bubble if I looked down to the floor, because looking down centred the bubble within my eye.
While looking down one day I decided to check the time and was surprised to observe a significant magnification effect. When viewed through the bubble, my wrist watch seemed a little darker and still had a shimmering appearance. It also appeared to double in size. So, it was like looking through a tinted magnifier made of water! (Figure 1). I figured that this was a somewhat diminished version of the high magnification effect that Professor David Atchison explained to me in relation to my experience of viewing grime on the back of my spectacle lens a few hours after my vitrectomy.
It occurred to me that my macula was apparently attached and working, and there was no flying angel of death, although my overall vision still was not good enough to be certain about this.
I also noticed other peculiar entoptic phenomena when the bubble was still large. In certain lighting conditions, I observed strange faint, parallel, vertical striations in my superior visual field; I attributed this to light reflections off the inferior surface of the bubble reflecting onto my inferior retina. Again, in certain lighting conditions, I observed a strong image of my retinal vessels (which fortunately looked in good shape). I noticed that I could see the dark edge of the bubble even with my eyes closed when looking towards bright light.
Peculiar Bubble Formations
From day four through to day eight post-vitrectomy, the bubble was free to move around a lot and occasionally adopted different appearances, as depicted in Figure 2. Sometimes a small bubble would appear next to the main large bubble; this was the ‘mother and baby’ appearance. The bubble sometimes split evenly, conjuring up notions of mitotic division. Two small satellite bubbles resting against the large bubble reminded me of the black Mickey Mouse ears I once owned (about 55 years ago). Numerous tiny bubbles resting on the single large bubble was the mother with octuplets. Oh what fun!
Another interesting observation when the bubble was small was that if I looked down and kept very still, I could observe a very obvious two-phase wobble of the bubble in synchrony with my heart beat. The two phases of the bubble wobble presumably were caused by hopefully normal sequential ventricular contractions. Counting the number of bubble wobbles over a fixed time period was a much simpler way of measuring heart rate than feeling for a pulse in my wrist.
On day nine post-vitrectomy, I decided that the bubble was so small I could go about my normal activities, and perhaps even return to work. It was a Sunday, so I decided to go for a walk on the beach with Suzanne. As I commenced my walk, I noticed that, with each step, the tiny bubble ricocheted around inside my eye at great speed. At first I was bemused by this, but then quickly became concerned. I figured that, according to the same principle by which a large bubble acts as a tamponade, a small bubble violently ricocheting around inside my eye might be having the same physical effect as a small stone bouncing around inside my eye; that is, there may be some form of physical effect of this small bubble hitting against my retina.
No-one at the clinic warned me of this; I formed the impression that once the bubble was small enough, I could resume normal activities, unlike immediately following my vitrectomy when ‘intense physical activity’ was prohibited (nudge nudge, wink wink). Frightened by the thought that I could do further damage to my retina, I concluded that discretion is the better part of valour, discontinued my walk and sat on a bench while Suzanne continued on. I wonder whether those undergoing a vitrectomy should be warned about this, and advised to refrain from all forms of physical activity until the bubble has completely subsided.
The bubble eventually become so small that it appeared as a tiny black dot, moving around very slowly. Then, right on cue on day 11, just as I was advised, the bubble had vanished.
I had quite enjoyed my bubble play.
Professor Nathan Efron is a researcher at the Institute of Health and Biomedical Innovation and School of Optometry and Vision Science, Queensland University of Technology. He is currently president of the Australian College of Optometry and vice-president of the International Society for Contact Lens Research.