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Myopia
What is myopia and how does it change the shape of the eyes
Myopia, commonly known as nearsightedness, is a prevalent eye condition where close objects appear clear, but distant ones appear blurry. It occurs due to the eye's length being too long or the cornea excessively curved, causing light to focus in front of the retina. In the case of an eye growing too long, the shape of the eye becomes more prolate. In other words, the eye becomes longer in the anterior-posterior axis (front to back) compared to the transverse axis (side to side), giving the eye a more elongated or egg-like shape. This is opposed to an oblate shape, which would be more like a flattened sphere.
How do we address hyperopic de-focus
Peripheral hyperopic defocus can be corrected using innovative optical designs like Defocus Incorporated Multiple Segments (DIMS) lenses, soft multifocal contact lenses, and orthokeratology lenses. The DIMS lens design creates a 'myopic defocus' in the periphery of the visual field, reducing the stimulus for myopic progression. Soft multifocal contact lenses distribute light differently to reduce peripheral hyperopic defocus. Orthokeratology lenses reshape the cornea overnight to modify how light is focused during the day. All these strategies aim to slow down the progression of myopia by ensuring that light from both central and peripheral vision focuses correctly on the retina
Why do we want to slow down myopia progression
Controlling myopia progression is crucial due to the health risks associated with high myopia. High myopia increases the risk of several serious ocular conditions, such as retinal detachment, macular degeneration, glaucoma, and cataracts, all of which can lead to vision loss. Moreover, the elongation of the eyeball in high myopia can lead to staphyloma, a protrusion of the outer coat of the eye, causing further complications
Customised vs Standardised Management
The necessity for customized myopia control strategies, combining optical and pharmaceutical methods, stems from the fact that myopia progression varies greatly among individuals due to genetic, environmental, and lifestyle factors. A one-size-fits-all approach may not adequately address these individual differences, potentially leading to suboptimal results. By tailoring myopia control strategies — for example, selecting specific lens designs or combining them with pharmaceutical interventions like atropine — we can better cater to individual needs and lifestyle factors.
Eye Shape and peripheral de-focus
Peripheral hyperopic defocus in a myopic eye occurs when optical correction, such as glasses or contact lenses, is used to focus foveal vision — the sharp, central vision we use to read and recognize faces. However, while these corrections help with direct line-of-sight, they may inadvertently cause objects in the peripheral vision to focus behind the retina instead directly on it due to the prolate eye shape. This misfocus in the peripheral field, known as peripheral hyperopic defocus, is believed to stimulate axial elongation of the eye, thereby exacerbating myopia. As such, it has become a focal point in myopia control research and interventions.
Pharmacological treatment for slowing down myopia progression
Atropine is an effective tool for managing myopia progression. It is usually used in low concentration (0.01% to 0.05%) thus has a minimal effect on pupil dilation and accommodation. While its exact mechanism of action in myopia control is not fully understood, it is hypothesized that atropine blocks receptors in the retina or sclera, reducing stimuli that cause excessive eye growth. Studies have shown that even in low concentrations, atropine can significantly slow down the progression of myopia in children, making it a valuable component in myopia management strategies.
Stable prescription vs Stable eye size
Stable refraction and steady axial length are two different measures in monitoring myopia progression. Stable refraction refers to the halt or minimal change in the prescription needed to correct the refractive error, while steady axial length refers to the cessation or slowing of the elongation of the eyeball. While both are essential, axial length control is becoming increasingly important in evaluating the success of myopia control. This is because the elongation of the eyeball, represented by the axial length, is directly linked to the risk of developing myopia-related ocular complications, such as retinal detachment and myopic macular degeneration. Therefore, controlling axial length rather than just refraction better ensures long-term ocular health.
What are the known risk factors for rapid myopia progression
Genetic predisposition plays a significant role, with children of myopic parents being at a higher risk. Environmental factors, such as prolonged near work (like reading or screen time), and limited time spent outdoors can also contribute to faster progression. Early onset of myopia typically leads to higher degrees of myopia later in life. Certain ethnic groups, such as those of East Asian descent, have been observed to experience faster myopia progression.
How do we test myopic patient?
Our clinic utilises the Lenstar Biometer (by Haag Streit) to perform axial length measurements, an essential component in tracking myopia progression. While cycloplegic refraction can be slightly uncomfortable due to temporary glare, we recommend this procedure, especially if it hasn't been conducted previously, as it provides a more accurate measurement of refractive status without the influence of focusing muscles. Some evidence suggests that abnormal binocular vision can lead to myopia progression. As such, we incorporate binocular vision assessments into our comprehensive approach to managing myopia.
Want to read more on myopia control?
Numerous uncertainties persist in the realm of myopia control. These include determining the optimal Atropine concentration to employ, understanding potential side effects, addressing concerns about rebound after discontinuation, evaluating the effectiveness of orthokeratology in cases of low myopia, and exploring the potential to combine various treatments. These emerging insights will be incorporated in our forthcoming blog post updates.