Following on from his retinopexy, cryopexy and double vitrectomy procedures, galloping myopia has essentially forced Professor Nathan Efron to enter the next challenging phase of his personal ophthalmic journey – IOL surgery.
My right eye had settled down following a double vitrectomy and epiretinal membrane peel, so Bill advised he would review me again in four months’ time. I knew it was inevitable that my crystalline lens would eventually develop a degree of opacification, which would necessitate intra-ocular lens (IOL) surgery, but in reading the literature I discovered this could take anything from a few months to three years. As it turned out, another factor came into play that rapidly accelerated this time frame…
About three weeks following my vitrectomy procedures, I noticed my right eye had appeared to become a bit more myopic. Distance objects seemed clearer when I pushed my spectacles closer to my face, and I could see things clearly up close through the top (distance) portion of my varifocals.
I went with Suzanne into her practice so that we could work out what was happening. Now, before the vitrectomy procedures, my right eye refraction was -6.50/-1.25 x 175. It was now -8.25/-1.00 x 165 – a myopic shift of -1.75D. Vision was a ‘slow 6/7.5’, and the ‘flying angel of death’ (the term I use to describe a pesky little blind spot near my right macula) was still present. Given that my left eye refraction had unsurprisingly remained steady at -5.50/-1.50 x 170, I now had about 2.75D of anisometropia. For the time being, this optical conundrum was easy to solve; because I was wearing a monovision contact lens correction, all I had to do was order a new box of contact lenses for my right ‘reading’ eye that gave me a +1.75D add.
what’s the use of a near corrected eye with only ‘slow N6’ near acuity?
Intraocular pressures were fine at R15 L12mmHg, but on the slit lamp Suzanne observed substantially more yellowing in the posterior of my right crystalline lens than in my left eye. Examination of sequential post-vitrectomy OCT images showed that the slight post-surgical macular oedema had largely, but not completely, resolved.
We also ordered a new pair of varifocals in a non-rimless frame to make future lens changes easy. When these spectacles arrived a week later, I was surprised not to observe any untoward aniseikonia (visual distortion) resulting from the sizeable (2.75D) anisometropia.
Over the next three months, I noticed a further deterioration in my distance vision. On the day of my appointment with Bill, I went to Suzanne’s practice to recheck my refraction. My right eye was now -10.00/-1.00 x 165 – representing a whopping 3.50D myopic shift in a little under four months! This meant I was now 4.50D anisometropic, which was becoming optically and perceptually unmanageable. Clearly, we were going to have to proceed with IOL surgery.
Planning for IOL Surgery
Knowing that IOL surgery was imminent, I had to make a decision as to my desired post-surgical refractive outcome. As a successful and happy monovision contact lens wearer, I had been thinking for quite some time that the best outcome would be R -1.75DS L Plano. However, I now had to bring my flying angel of death into the equation. If I opted for monovision, what’s the use of a near corrected eye with only ‘slow N6’ near acuity? Maybe it would be better to aim for emmetropia in both eyes and use reading glasses for near?
After ruminating over this for some time, I concluded that near vision is about far more than just reading. It’s just as much about ‘general’ near vision activities; eating meals, looking at the time on your watch, shuffling things around on your desk, taking a quick look at your iPhone, generally inspecting objects at near etc. So I decided to take a bit of a risk and go for ‘surgical monovision’ as per my original plan, hoping that near acuity in my right eye would at least end up being reasonable for computer work, as well as generally looking at things at near.
When I saw Bill later that day, he confirmed the myopic shift and accelerated lens yellowing in my right eye, and agreed that it was time to go ahead with IOL surgery. A key point of discussion was how to deal with my astigmatism. Prior to my two vitrectomy procedures Suzanne had determined, using a Medmont E300 Corneal Topographer, that I had 1.3D corneal astigmatism, axis 160. Interestingly, in a recent newsletter that Suzanne had received from Bill (which he periodically sends to all optometric colleagues), he declared “For patients with greater than 1.75D astigmatism, we use a toric IOL. The interesting thing is that for patients with lower levels of astigmatism, the results with limbal relaxing incisions (or arcuate keratotomy) are very good.”
Well, I have never been a fan of the idea of making corneal incisions to alter refraction; I guess the old days of radial keratotomy are still clear in my mind. So, after discussing this issue with Bill, he agreed to use a toric IOL, despite this being below his preferred threshold for using toric IOLs. When my flying angel of death came up in discussion, Bill asked hopefully “So that still hasn’t gone away yet?”
Bill then directed his support staff to do a work-up for IOL surgery, and things started moving fast: auto-refractor, OCT, IOL Master, Pentacam, hand-held keratometry and A-scan, all in quick succession. The Retinal Acuity Meter, which uses pinhole-type technology to help determine if unexplained vision loss is due to maculopathy or cataract, predicted that, despite my flying angel of death, I would end up with distance visual acuity in my right eye of 6/6-2. This was somewhat comforting.
Bill also said that during surgery he would give an intraocular injection of Avastin (Bevacizumab). Given that I have a trace amount of background diabetic retinopathy, this seemed to me like a sensible prophylactic measure.
I was then handed over to Elaine (not her real name), Bill’s optometric assistant that day, for a ‘pre-surgical chat’. Elaine knew who she was speaking to, and said “I don’t need to tell you this, but I’ll tell you anyway”, and then proceeded to explain cataract surgery in very basic lay terms, and the risks attached. I sat there patiently and somewhat bemused as she went through her usual spiel, assuming that she was essentially doing this for medico-legal reasons.
After completing the pre-surgical work-up, I was handed over to the reception staff to complete consent formalities, receive the pre-surgery information pack, and make an appointment for the surgery. We decided to go ahead with surgery the following week.
(Click here to view larger image of Figure 1)
Just as I was leaving Bill’s rooms, I asked Elaine what IOL Bill would be inserting. I was told it would be a +14.50D Alcon SN6AT5 Acrysof IQ Toric IOL.
When I arrived home that evening, I decided to read up on this IOL and found the Alcon website which had a handy on-line calculator for determining the appropriate IOL. I opened this and entered the values I had to hand, from Suzanne’s pre-vitrectomy corneal topography analysis, and assumed a correction of 0.50D for surgically induced astigmatism (based on a 180° limbal incision). Suzanne stood behind me checking my input data. The result was that I would end up with 1.55D of corneal astigmatism after surgery, which should be corrected with an SN6AT4 IOL. This would result in residual post-surgical astigmatism of 0.16D x 75 (Figure 1).
Alarm bells started ringing. I looked up at Suzanne. Suzanne looked at me. Why was Bill planning to insert a SN6AT5 IOL, which is designed to correct corneal astigmatism in the range 2.06D to 2.56D?
Maybe I was missing something here. I hadn’t being paying attention to the corneal topography/keratometry readings obtained by Bill’s support staff in the flurry of pre-surgical work-up earlier that day. Maybe corneal topography is altered by vitrectomy, and Bill’s more recent corneal topography findings were different from Suzanne’s pre-vitrectomy measurements.
So what should I do? I didn’t have all the facts. Did Bill and his team know something I didn’t know? After all, they do this type of surgery maybe five to ten times a week. They must know what’s going on. But notwithstanding this, should I pick up the telephone anyway just to double check?
I decided not to make the call. It’s a decision I shall regret for the rest of my life…
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.