Keratoconus

"Keratoconus is a vision disorder that occurs when the normally round cornea becomes thin and irregularly cone shaped. This abnormal shape prevents the light entering the eye from being focused correctly on the retina and causes distortion/blurring of vision.

In its earliest stages, keratoconus causes slight blurring and distortion of vision and increased sensitivity to glare and light. These symptoms usually appear in the late teens or late twenties. Keratoconus may progress for 10-20 years and then slow in its progression. Each eye may be affected differently. As keratoconus progresses, the cornea bulges more and vision may become more distorted. In a small number of cases, the cornea will swell and cause a sudden and significant decrease in vision. The swelling occurs when the strain of the cornea's protruding cone-like shape causes a tiny crack to develop. The swelling may last for weeks or months as the crack heals and is gradually replaced by scar tissue. If this sudden swelling does occur, your doctor can prescribe eyedrops for temporary relief, but there are no medicines that can prevent the disorder from progressing.

Eyeglasses or soft contact lenses may be used to correct the mild near sightedness and astigmatism that is caused by the early stages for keratoconus. As the disorder progresses and cornea continues to thin and change shape, rigid gas permeable contact lenses can be prescribed to correct vision adequately. In most cases, this is adequate. The contact lenses must be carefully fitted, and frequent check-ups and lens changes may be needed to achieve and maintain good vision.

In a few cases, a corneal transplant is necessary. However, even after a corneal transplant, eyeglasses or contact lenses are often still needed to correct vision."

Lens Coatings:

TINTED LENSES:

• Your prescription Lenses can be tinted to sunglass depth, which offers a stylish option along with UV eye protection.

• Other colours that are not listed or different depths of tint can always be ordered by phoning customer service on 0161 7900800

POLARISED LENSES:

• Cuts out horizontal glare e.g.: water surface glare when fishing and very useful when driving in wet condition
• Filters out 100% UV light
• Has a brown or grey tint

TRANSITION LENSES:

• React to sunlight by getting darker (available in brown or grey)
• Scratch resistant coating as standard
• UV filter as standard
• But, from my personal experience I have found a few of the following characteristics of these transition / photochromic lenses. I think you should know about these first before you proceed:
1. They do not go as dark as sunglasses.
2. They do not react very well in the car as the windscreen in the car filters the bulk of the UV and thereby prevents the reactolite lenses working effectively.
3. There is a residual pale tint on the lenses, even when you are indoors.

THIN AND LIGHT LENSES:

• Improves the appearance of your glasses
• Thinner and lighter than normal lenses

• 1.6 high index lenses are our standard thin lenses
• For the thinnest lenses available you can order 1.67 and 1.74 high index lenses by phoning customer service on 0161 7900800

ANTIREFLECTIVE COATING:

• Reduces reflection on lenses
• Reduces light scatter from car headlamps, very useful for night driving and reduces glare from the computer screen, therefore, very useful for computer users.

UV400 PROTECTIVE COATING:

• Blocks potentially harmful Ultraviolet rays from directly penetrating the lens through to the eye.

Can relieve eye strain

SCRATCH RESISTANT COATING:

• Protects the lens surface from potential scratches that may occur by everyday wear and tear. For example, putting glasses in your pocket, which has keys and other objects in them, or by putting glasses face down on the table.
• It is recommended that you look after your glasses and you should not put your glasses face down or place your glasses in a place where they can be scratched.
• Unscratched lenses give clearer and more comfortable vision.

Which Lens And Why?

Lenses are categorised by many variables. The most important of these variables is the “Refractive Index”. The other variables such as the V-Value are for scientific/laboratory reasons.

The higher the refractive index number is, the thinner the lens will be. Refractive means bending of light and index is the standardised numerical value to explain the extent of this bending of light. Therefore, if you have a high refractive index number, this would mean the light is bended more than lower refractive index. Thereby less of the lens mass is needed for that high prescription which would normally require more of a lens mass to bend the light rays to correct the eyesight.

Lens Types:

Plastic 1.53 (standard lens): The industry standard plastic lens is a 1.53 refractive index. This lens is ideal for most types of prescriptions. Anything from + or – 0 to 3.00 would look fine, i.e.: lens would not look thick. But, anything above 3.00 would then mean your lenses would look thick with this standard plastic lens.

Plastic 1.6: This lens is thinner than the standard lens above. Up to 25% thinner and lighter than standard lenses. Suitable for up to +6.00 and - 5.00. Anything out of this range would still make the lenses look thick, even with this 1.6 refractive index lens.

Plastic 1.67: Up to 35% thinner than standard plastic lenses. Ideal for lenses up to +7.00 and –7.00. Prescriptions above this range will still look thick.

Plastic 1.74: The thinnest plastic lens available on the market today. Up to 45% thinner than standard plastic lenses. Suitable for mid to high prescriptions.

Glass 1.7: Very thin lens. Suitable for high minus powers. High lens density and therefore, to keep the weight down this lens is best suited to not a large frame.

Glass 1.8: Extremely thin lens. Suitable for very high minus powers. High lens density and therefore, to keep the weight down this lens is best suited to not a large frame.

Glass 1.9: Thinnest lens in the world. Only used in extremely high minus powers. High lens density and therefore, to keep the weight down this lens is best suited to not a large frame.

How To Choose From The Lens Options:

Here I will explain in simple terminology the various lenses that you could opt to have. This will help you choose and decide which lens is best for you!

Optical lenses are available in Glass and plastic materials.

Plastic lenses are by far the most common lens type. I rarely prescribe glass lenses in my practice. However, if someone is an existing glass lens type wearer and prefers glass to plastic then it is recommended to stick with glass lens.

Below, I have outlined some of the characteristics that I have encountered with glass and plastic lenses:

GLASS: ADV:

• Harder lens surface protects the lens from minor scratches. (However, hard coating on a plastic lens counteracts this)

• Glass lenses are the better option for very high prescriptions.

DISADV:

• Brittle compared to plastic.

• Heavy compared to plastic.

Optically there is no real difference between modern day plastic lenses and glass.

A lot of manufacturers don’t manufacture glass lenses at all as they are not as popular as plastic. A bit like VHS and DVD!

Therefore, in my opinion for most people plastic lenses are better than glass