Some of the most common conditions that can affect your vision explained in layman’s terms, together with a breakdown of lens types used to counteract their effects.
Conditions that can be corrected
Anisometropia is an imbalance in the prescription between one eye and the other.
Astigmatism is a condition whereby the cornea is more curved along one meridian and less along another, resulting in a cornea that is rugby ball-shaped. Consequently, the eye cannot resolve images into sharp focus, no matter what distance an object is viewed from or how much the viewer accommodates.
Cataracts are changes to the lens of the eye that cause it to become progressively opaque, resulting in blurred vision.
Most cataracts occur later in life. In some rare instances a child may be born with cataracts or develop them early in life. These are known as congenital or paediatric cataracts.
In a long-sighted or hyperopic patient the eye is normally too short for the focussing power of the eye. Light rays enter the eye from a distant object and are focussed on a point behind the retina, resulting in an out-of-focus or blurred image.
Inability to wear spectacles
While many contact lens wearers choose to wear lenses rather than spectacles for cosmetic reasons, and some wear them for visual needs, there is a group of patients who cannot wear spectacles because they are allergic to frame materials, or have some facial injury or problem that means that conventional spectacles are not suitable.
Intolerance to moulded contact lenses
The diameter of most eyes falls within a limited range. By carefully selecting the correct base curve and diameter, a manufacturer can customise a lens design for any eye. If you are unlucky enough to fall outside of this stock size, then you may struggle to achieve the comfortable wear that most people experience.
Astigmatism is normally caused by the cornea being more curved in one direction than another. Fortunately, the maximum and minimum curves are normally at right angles to one another, resulting in a surface rather like that of a rugby football. Irregular astigmatism is normally the result of injury or keratoconus and occurs when the cornea is pulled into a distorted shape, due to scarring or the progression of a cone in keratoconus.
In keratoconus, the cornea, which is the clear dome-shaped structure at the front of the eye, bulges forward making the surface of the cornea irregular in shape and distorting vision through the affected part.
Similar to keratoconus and PMD, keratoglobus is a bulging caused by a thinning of the cornea. This weakens the structure and allows the pressure within the eye to push the cornea outwards into a cone shape, which gives the condition its name.
In a short-sighted or myopic eye the eye grows too long, and rays of light entering it from a distant object are focussed at a point in front of the retina, which means that the image appears blurred.
Myopia is not just an inconvenience to be corrected by glasses or contact lenses. Higher rates of myopia can give rise to more serious pathologies, such as retinal detachment, and the trend is towards higher and higher degrees of myopia.
Pellucid marginal degeneration (PMD)
Pellucid marginal degeneration, or PMD, is often confused with keratoconus, and indeed it is a type of irregularity affecting the cornea which results in visual impairment. PMD is caused by a thinning of a narrow band of the cornea between 4 and 8 o’clock, approximately 2mm in from the edge of the cornea and the white of the eye.
Post laser surgery
For 95% of people that have refractive surgery, the outcome meets their expectations. If a little regression occurs after surgery, an adjustment or “enhancement” can be performed after a few months to fine-tune the result.
Presbyopia is an inability to focus on near objects. It differs from hyperopia in that it’s primarily age-related.