the eye blog
EYE CARE INFO & UPDATES
Naturally, when people have blurry vision they think they might need glasses. And yes, in many cases, glasses may be all they need to fix their blurred vision after having a thorough eye examination at an optometrist.
Sometimes, however, glasses cannot fix a person's blurred vision, at least not entirely. Most of the time this may be due to age-related eye changes such as cataracts, glaucoma and macular degeneration, but occasionally it can also happen to younger people.
Recently I had in my practice a young patient who came in for a second opinion about his eyes. He had seen an optometrist in a shopping centre a little while back and was prescribed glasses for the first time there. He was concerned that his vision was still blurry even with his glasses on.
After taking a detailed history I proceeded to test his eyes, and soon it became apparent to me what his eye issues were and why he was still having problems with his vision. He had a condition called keratoconus ('cone-shaped cornea') — a progressive eye condition that causes the front surface of the eye, the cornea, to become thin and distorted. Unlike normal astigmatism (unequal eye surface curvature across two meridians, like an egg shape), which is very common, in keratoconus the eye surface is vastly uneven and irregular. That means light entering the eye is scattered in many different directions, and not focused at a point or in one plane.
This eye surface irregularity means the lenses in the glasses he was prescribed with cannot fully correct his vision deficit and blur, as glasses can only bend (or refract) light in up to two meridians. Unfortunately he wasn't explained this by his previous optometrist. It's possible the other practice didn't have the instrument to properly diagnose his condition.
We use an instrument called a corneal topographer to accurately measure the shape of the eye surface when we suspect a case of keratoconus or other conditions that cause distortions in the cornea. With the data captured we can instantly produce a 3D topographical map of the cornea, as illustrated below, to show the contours of the eye surface and any irregularities present. This instrument is also used for advanced contact lens fitting, Ortho-K and dry eye analysis.
What can be seen in the images below (of the right and left eyes) are areas of surface distortion, with a steep area (in red) resembling a cone shape. This is a classic case of keratoconus. With this condition, the best way for him to see clearer (than what is possible with glasses) is to wear special rigid contact lenses, to effectively provide his eyes with a new, smooth optical surface. These specially made contact lenses are individually designed for each eye using the 3D topography maps, to ensure of ideal fitting lenses on the distorted eye surfaces.
EYECARE CONCEPTS — ADVANCED EYE CARE & CONTACT LENS PRACTITIONER — MELBOURNE
This follows from my last eye blog, Ortho-K: How Does It Work?
How long does Ortho-K take to correct vision?
The length of time it takes for Ortho-K overnight lenses to fully correct your vision will depend on your pre-treatment prescription and your individual eye shape. Other factors include quality and length of sleep each night (7-8 hours is ideal), consistency in wearing the lenses regularly, rigidity of the eye surface layers, the cornea, that can vary from person to person, lens design parameters, pupil size, presence of and amount of astigmatism to be corrected and the curvature of the eye surface.
In my practice, all our Ortho-K patients have enjoyed significant improvement in their vision even after just one night of lens wear. Typically a patient with a medium level of short-sightedness, say -3.00 dioptres of myopia, will have over half of this prescription (around -2.00D) corrected already at their first review, in the morning following their first overnight wear of the lenses. By the end of week 1, he or she will have about 85% (around -2.50D) of their prescription corrected, and this further improves in the 2nd week to achieve 6/6 or 20/20 vision.
Some patients experience faster vision correction progress, and some slower — this is normal as each individual's eyes are different. Some optometrists or websites may claim to be able to achieve 20/20 vision after one night of Ortho-K — while this may be possible in some cases with a simple prescription, I prefer my patients to have a realistic expectation of their treatment progress and outcome.
As part of our Ortho-K Package for first time wearers we can provide, where needed, a spare pair of glasses made with a mild correction to help you see clearly during your first few weeks of Ortho-K treatment. This pair of glasses is also helpful for those who wish to wear their Ortho-K lenses every 2nd or 3rd night, instead of every night. As the treatment effect begins to wear off the glasses help to support their vision until they resume Ortho-K lens wear. Ortho-K vision correction is flexible, not everyone will need to wear their lenses nightly, depending on their personal vision needs and the holding time of their Ortho-K treatment.
Individuals with astigmatism (uneven eye surface curvatures) tend to take a little longer to reach optimum vision. This is because the corneal reshaping involved in an eye with astigmatism is more complex. Astigmatism is corrected using customised dual-axis Ortho-K lenses. Some patients have astigmatism in one eye and not in the other, and these patients often will have faster vision correction in the eye without astigmatism, and with about 1 week difference between the two eyes in reaching the optimum vision outcome.
Higher levels of short-sightedness (high myopia of over -6.00D) will also take longer for good visual outcome to occur, as greater amounts of eye surface flattening is required. Typically around 3 weeks for full or close-to-full correction is my advice to patients with high myopia considering Ortho-K lenses. During this initial period when treatment effect is gradually building we supply temporary soft contact lenses in steps of decreasing power to support the individual's daytime vision. With higher prescriptions it is normal for an individual to experience some ghosting and halos around lights, particular in dim conditions and at night. This usually improves with time as the Ortho-K treatment effect increases across a wider area on the eye surface.
With very high prescriptions (eg. -8.00D short-sighted) it may not be possible to fully correct vision to 20/20 due to lens and biological limitations, in which case the individual may be left with a residual amount of short-sightedness (eg. -1.00D after a correction of -7.00D with Ortho-K for a -8.00D individual). This is termed 'partial correction'. Many patients with very high prescriptions are happy with a partial correction as it already significantly reduces their dependency on glasses, and if they do need to see clearer they can wear a light prescription pair of glasses during the daytime, rather than their usual thick and heavy glasses.
In summary, these are the typical timeframes for Ortho-K lenses to effectively correct vision in most individuals:
Low level myopia (less than -2.00D) — 3-4 days.
Medium level myopia (-2.00 to -4.00D) — 1 week.
Moderate level myopia (-4.00 to -6.00D) — 1-2 weeks.
High level myopia (more than -6.00D) — 2-3 weeks.
EYECARE CONCEPTS — ORTHO K PRACTITIONER — MELBOURNE
Ortho-K, short for orthokeratology, is a relatively new concept to many Australians. Most people may not have heard of it before, or know what it does, or how it works. If you're reading this page you probably want to learn more about Ortho-K and how it might help you or your child see clearer. In the next few eye blogs I will go into detail to explain everything you need to know about Ortho-K overnight contact lenses, which I believe is the future of vision correction.
What is Ortho-K?
Ortho-K is a special type of vision correction technology that uses a breathable rigid contact lens to change the shape of your eyes as you sleep. Also called Sleep Lenses or Night Contacts, you put on the lenses just before you go to bed, and when you wake up in the morning you remove your lenses and enjoy clear vision for the rest of your day, without wearing glasses or daytime contact lenses.
How does it work?
Ortho-K sounds amazing because it really is. Our Ortho-K patients find it incredible to get their clear vision back without needing to wear glasses or contacts during the day. No more dry eyes or discomfort at work, and for kids no need for the parents to worry about them losing their glasses or contacts at school. The science behind this technology is a little complex, but here's a brief explanation of how it works.
For correction of short-sightedness (blurred vision in the far distance, also known as myopia), an Ortho-K lens flattens a central 5-6mm zone of your eye's front surface, the cornea. This surface flattening is similar to what happens with laser surgery (LASIK), only that Ortho-K is a temporary and reversible process and laser surgery is permanent. Flattening the cornea by a precisely calculated amount bends light to refocus it onto the surface of your retina, restoring your vision.
An Ortho-K lens a specially designed rigid contact lens made to precisely fit the shape of your eye's surface. Every lens is tailor-made for each eye's shape and prescription. At Eyecare Concepts we use the sophisticated Medmont E300 corneal topographer (pictured below) with 102,000 individual points to scan your eyes' unique surface contours to generate 3D topographical maps of its shape. We then use this topography data and advanced computer simulation software to design your lenses to fit your eyes perfectly. The information we can capture is so precise that we can design the fitting of your lenses with an accuracy level measured in microns (0.001 mm).
The image below shows how an Ortho-K lens works on the eye to correct vision. The lens, together with the eye's natural tear layer and eyelid in its closed state during sleep, places gentle hydraulic forces on the eye's surface, to gradually mould its shape by the precise pre-determined amounts required to give clear vision. You never feel any addition pressure on your eyes while wearing the lenses during sleep as the forces are very gentle. The centre of the lens does not actually directly touch the centre of the eye's surface but rather it vaults over the centre, and supported by a very thin film of tears, by approximately 20 microns (0.02 mm) — less than half the thickness of a strand of human hair. This is the kind of precision involved.
The shape of an Ortho-K lens is different from other kinds of contact lenses. It is also technically known as a 'reverse geometry lens'. There are multiple curves on the back of the lens surface that create different pressure zones and for helping the lens to centre correctly on your eye as you sleep. The fluro-green areas on the right-side image show the areas where the shape of the lens changes from the central 'treatment zone' to the peripheral 'alignment zone'. This lens is fitting perfectly on the eye with a well-centred and even treatment zone, important for good, clear vision. The green glow is from fluorescein dye placed on the eye during the lens evaluation process. Normally the lens is completely clear.
The left-side image is a 3D topography map of an eye following Ortho-K vision correction — showing flattening of the central zone of the eye surface (circular area in green), surrounded by a peripheral band (in red) of surface elevation changes which also helps to control short-sightedness progression in children and teenagers (myopia control) using Ortho-K lenses.
Below is an example of one of our patients successfully fitted with Ortho-K lenses. The upper-left image is her natural eye surface shape before Ortho-K lens treatment. She had a prescription of -3.00 short-sighted plus a mild amount of astigmatism. The lower-left image shows the post-treatment shape of her cornea after Ortho-K lens wear. The red ring represents the positioning of her lens during sleep, showing excellent lens centration. On the right image the centre blue zone is the vision correction zone and is the ideal treatment effect that we are looking for. Her -3.00 prescription and astigmatism was fully corrected with Ortho-K, giving her 20/20 vision in just 1 week.
EYECARE CONCEPTS — MELBOURNE ORTHO K PRACTITIONER
Philip Cheng - B.Optom (Melb) Ocular Therapeutics (GCOT). Optometrist at Eyecare Concepts Kew East, Melbourne. An experienced eye care & contact lens practitioner with expertise in myopia control & orthokeratology.