Wednesday, July 13, 2011

Improving visual quality after previous LASIK

About 2 months ago I saw a patient who had LASIK done in another clinic a few months previously. His vision when measured on the reading chart was actually very good-it was 6/6 without glasses in both eyes. However, he was very disturbed by his vision at night. He was unable to recognize faces when the surroundings got a little dark, and vision in such situations was just generally blurred. Before his LASIK, his power was only about 500 degrees short-sighted.

When we did his corneal maps (topography), it was obvious why he had such problems. The previously treated zone was small, and it was also slightly decentered upwards. Our aberrometer shows clearly his predicament. When his pupil is 3mm in diameter (in bright light), you can see the image of the 'E' is sharp. When his pupil enlarges to 6mm, all you see is a shapeless smudge.

Last week I performed topography guided enhancement LASIK for his left eye. A comparison of the pre and post-operative corneal topographies shows that the central blue/green area is now larger. Subjectively, his night vision is much improved and best of all, his daytime vision also improved to 6/4.8 without glasses.

LASIK ablation that is pseudodecentered upwards

Pseudodecentered LASIK ablation after enhancement


Vision simulation of large amount of aberrations
This case highlights an important aspect of LASIK which is often overlooked, sometimes because of the limitations of technology at a particular clinic. And that is-the quality of vision, on top of the spectacle power issues. In this day and age, we aim not just for minimal spectacle power after LASIK, but also the best quality of vision in all situations. There are limitations, such as for those with very high powers, because there will be issues with corneal thickness. But customizing a 'perfect shape' cornea should be possible for all those with low to moderate degrees of shortsightedness and astigmatism, such as in this case.

Sunday, January 23, 2011

Asia ARVO 2011

For the benefit of non eye doctors, Asia ARVO is essentially one of many conferences cum trade exhibitions for eye professionals. By attending these events, we hope to keep up to date and abreast of new developments. For the organisers, a successful event garners brownie points and prestige.

This event was held over the last 4 days at Resorts World Sentosa. I went without expecting too much in the way of new developments. But I was peasantly surprised. For me, these were the highlights:

1. Rho kinase inhibitor (ROCK inhibitor) Y-27632 has been found to be able to cause corneal endothelial cells to proliferate both in vitro and in vivo. To put you in the picture, corneal endothelial cells keep the cornea transparent but the unfortunate thing is-once they are damaged, to date, they have behaved like nerve cells-showing no inclination to repair themselves. So the traditional treatment for conditions where they are too damaged has been corneal transplants. Now we may have a medicine so that many can avoid these surgeries!
2. Intravitreal Avastin has been found useful for all stages of CRVO. Avastin blocks a vascular growth factor, which causes many of the complications of central retinal vein occlusion (CRVO). Finally, we have a clearer picture of the role of avastin in this condition.
3. Richard Spaide has done some remarkable work with OCT and choroidal vessel imaging. Apparently there are cases of unexplained visual loss which have now been shown to be correlated to loss of the choriocapillaris. And guess what? Viagra has been shown to increase the thickness of the choriocapillaris! On a more serious note we now need to see if other vasodilators like glyceryl trinitrate can do the trick on a more prolonged basis without too much in the way of complications...
4. Lenticule extraction with the Visumax laser (FLEX procedure) is associated with a fairly prolonged loss of best vision in 25% of patients! I have a feeling this is not going to work out too well...

Monday, January 17, 2011

Wavefront-guided and topography-guided customized LASIK: What do they mean and what's the big deal?

In recent years, the word 'customized' has become ubiquitous in LASIK treatments. If you're not doing customised treatments, if you're only doing standard treatments, you're out. But aren't all treatments customised, since they're customised according to the refractive error you have? Let me explain.

There are 2 things that so called customised treatments aim to control for, that so called standard treatments do not. One is ocular 'aberrations'. Most of us know that vision is affected by short or long sightedness, or astigmatism. But our vision is also affected by other irregularities of the cornea and lens, called aberrations. The chief ones which cause problems are 'coma' and 'spherical aberration'. When present in large degrees, they can cause glare and halos especially when the pupil is large at night. So these 'customised' treatments aim to treat the particular aberrations of the individual eye.

Now, when most people talk about 'wavefront-guided', they are talking about 'whole eye' wavefront. But whole eye wavefront is affected by a few different things. It is affected by pupil diameter, it is affected by the state of focus of the eye (accomodation), and it constantly changes as the eye ages, primarily due to changes in the shape of the lens. Furthermore, most measuring systems for whole eye wavefront only measure several hundred points at most through the pupil.

Topography-guided LASIK, or more precisely 'corneal wavefront guided' LASIK, is LASIK based only on measurements of the cornea.This is advantageous, because the cornea does not change as much in shape throughout life-definitely less so than the lens. It does not change in response to pupil shape, nor does it change in response  to accommodation. Topographers measure corneal shape right out to the periphery, and typically measure in excess of 20,000 points. In most cases, corneal aberrations account for a majority of whole eye aberrations. It would thus appear that topography or corneal wavefront guided LASIK is the way to go.

Customised treatments also take your corneal curvature into account when delivering the treatment. Why is this important? Well, imagine yourself standing in the sun at noon, at the equator. Your shadow would be tiny, directly under yourself. If you were standing in London in winter at noon, your shadow would be much longer, because the sun's rays are coming at an angle. In a similar way, the laser's rays strike the cornea at an angle at the periphery of the cornea. If a cornea is of relatively standard shape, that's not a problem, because the laser has been programmed to treat relatively 'standard' eyes. However, if your cornea is more curved than normal, ie steeper at the sides, then the laser would strike your corneal periphery at a larger angle than normal and work less effectively. You could end up with a smaller optical zone than expected. You could end up with lots of night glare and halos.

So, go for customized LASIK if you can. Better still, go for Topography Guided/Corneal Wavefront Guided LASIK for best visual quality.

Thursday, January 13, 2011

Itchy eyelids? Crusty eyelids? The reality of Demodex

What's Demodex? They are mites, which are microscopic little critters with eight legs. They belong in the same class  of animals as spiders. While most have heard of house dust mites, few have heard or come across demodex, except maybe dog owners. This is despite Demodex infesting many of us, only we are unaware of their presence most of the time.

Demodex are readily accessible to inspection by most ophthalmologists, only many ophthalmologists are also unaware of their presence. When they infest the lash follicles, they are readily visible on high power with the slit lamp microscope. The video shows how I look for them-by pulling lightly and twirling the eyelashes. Before I do this I clean away all debris and dandruff like material with an alcohol swab. Then, pulling lightly on the lashes causes their tails to poke out, and further twirling the lash will cause the mass of demodeces to come out and lie on the skin surface. They look like tiny shiny rod shaped objects. They can then be scooped up with the tip of a forceps and I touch them lightly on the sticky side of a cellophane tape. I then stick them on a microscope slide and have a look on a compound microscope. The picture shows one that I caught recently. However, now that I've seen quite a few of them, I can readily identify them on the slit lamp alone.

So what? It seems to me that most people with blepharitis, especially anterior blepharitis and lots of debris near the eyelashes also have lots of demodex. Coincidence? Some people say demodeces are commensals. Well, I would say it's too much of a coincidence. Several papers by Scheffer Tseng have now come out about the pathological role of demodex in ocular surface disease. I still wonder about posterior blepharitis and meibomian gland disease. I often see this without demodex infestation of the lashes. It could be that there is deeper infestation within the Meibomian gland itself, by D Brevis, but we won't know for sure unless we can somehow put a scope up the gland or maybe test the Meibum by PCR for the demodex.

video
If you see Demodex, what do you do? Some would do nothing. I think that is reasonable if you see one or two of them in the odd follicle, and the patient is not symptomatic. But if there are lots, and the patient is itching like crazy or the lids are inflamed, then steps should be taken. Tea tree oil has been touted as being a great mite killer-but that would only work for the ones on the lashes. If there are any in the Meibomian glands one might have to resort to something  systemic like ivermectin. I don't see how the tea tree oil would get into the Meibomian glands. So there you have it-in a nutshell. My thoughts on Demodex and blepharitis. I do welcome your comments.

Thursday, January 6, 2011

My very first post

Although it was just last week that my colleague, Jerry Tan, suggested starting a blog, I have been curious and mulling over this for some time. Well, finally I have actually gone ahead and done it.

For this blog, I aim to  make accessible information about eye problems, and to write about things that happen in my professional life. I would also like to share  my opinion about certain eye conditions and would most welcome any feedback and alternative views.