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The EYE of the Tiger @_-
Transcript of The EYE of the Tiger @_-
Various types of laser surgery are used to treat refractive error:
LASIK and IntraLASIK, in which a knife is used to cut a flap in the cornea, and a laser is used to reshape the layers underneath to treat refractive error
Photorefractive keratectomy (PRK), in which the cornea is reshaped without first cutting a flap
Laser thermal keratoplasty, in which a ring of concentric burns is made in the cornea, which cause its surface to steepen, allowing better near vision
The eye can be in these types of conditions:
- Nearsightedness (Myopia)
- Farsightedness (Hyperopia)
A sense organ that allows us to use
to see everything around us!
Is the inability to sight objects clearly at a
The two types of visual receptor cells of the retina are:
TO CORRECT MYOPIA
Myopia vs. Hyperopia
- causes blurred vision. It makes the eye unable to focus an object into a fine, detailed image on
- This is due to an irregular or toric curvature of the cornea or lens.
- A 'toric' surface resembles a football. This optical shape gives rise to astigmatism in the eye.
- A toric lens has a different optical power and focal length. One of the lens surfaces is shaped like a "cap" from a torus, while the other one usually is spherical.
- Three main options exist for the treatment of astigmatism:
> toric lens glasses
> contact lenses (either hard contact lenses or toric contact lenses)
> refractive surgery
The LASIK Procedure
- The LASIK procedure involves a few steps; the creation of the corneal flap and the reshaping of the cornea with an excimer laser. Essentially, the excimer laser is used to reshape the cornea by removing tissue from its middle layer.
1. Eye drops are used to numb your eyes.
2. The patient will be asked to focus on a special light to fold away a corneal flap,
revealing the middle layer of the cornea.
3. The cornea is then reshaped by an excimer laser.
> for myopia: the cornea is flattened to reduce converging power of the eye. This is achieved by removing more tissue from the centre of the cornea than around.
> for hyperopia: the central cornea is steepened to enhance the converging power of the eye. This is achieved by removing more tissue from the periphery than the centre.
> for astigmatism: the cornea must be made more spherical (uniformly curved).
4. The corneal flap is then repositioned and held in place.
TO CORRECT HYPEROPIA
Is the inability to sight objects clearly at a
A contact lens is a thin, curved lens placed on top of the cornea that is used to correct refraction to the eye
- This type of blurred vision is caused by the light rays converging and focusing in front of the retina because the distance between the lens and retina is too wide. This also means that nearsighted eyes are longer than the normal eye
- Another cause would be a natural change in the shape of the eyeball. Less often, nearsightedness may be caused by a change in the cornea or the lens
- When we do work close up, (reading, using computers, watching TV) the eye muscles and lens become tensed, and the eyeball elongates to make the image form exactly on the retina. If this situation lasts for too long, the eye muscles cannot relax any more, and the mishappening becomes permanent
- can be worn in more harsh environments
- oxygen does not pass through to cornea
- is not as comfortable as soft lenses
- lens is able to get wet
- oxygen is able to pass through to the cornea
- is comfortable enough for daily use
Corrective contact lenses
are designed to help improve vision, most commonly by correcting refractive error.
Cosmetic contact lenses
are designed to change the appearance of the eye
Therapeutic contact lenses
protect an injured or diseased cornea from the constant rubbing of blinking eyelids thereby allowing it to heal faster
- The lens is a barrier to oxygen. The most prominent risks associated with long-term, chronic low oxygen to the cornea include ingrowth of blood vessel in the cornea and potential increase in myopia
- When combined with improper cleaning and disinfection of the lens, the risk of infection increases.
- People that suffer from dry eyes are particularly vulnerable to discomfort and episodes of brief blurry vision.
- cells that control the amount of light that our eyes receive (brightness). Rods are responsible for black-and-white and peripheral vision
- cells that control the colours that we see (we see approx. 10 million different colours)
RELATION TO OPTICS
it counteracts the increased curvature of your cornea or the increased length of your eye
we use concave lenses to direct light away from the center of the lens so they spread out before they hit the eye, and in doing so, we move the focal point of the light back so the light rays directly hit the retina
reshapes the curvature of your cornea
ophthalmologist makes a thin, circular cut that extends partly into your cornea. Then the layers will be removed from the center of your cornea to flatten its domed shape.
Optics involves the behaviour and properties of light, which include the instruments that use or detect it. Optometry is a profession concerned with the health of the human eyes. To help check the eyes, people have applied optics to further advance their technology. Take laser eye surgery for instance, one of the techniques used include LASIK, which is used to correct near and far-sightedness. The eyes also associate with reflection in a way, as you can see yourself if you look into another person's eyes.
Did you know? Optics began with
the making of lenses.
- The rays need to converge at the retina
- It can be corrected with:
> eyeglasses, which is the simplest and safest way to correct hyperopia
> contact lenses, which must be convex and work by becoming the first refractive surface for light rays entering the eye, causing a more precise refraction or focus
> or surgery, which can decrease or eliminate the dependency on wearing eyeglasses and contact lenses
- Use Corrective Lenses:
- Refractive Surgery:
- light rays converge
the retina, so the object is blurred
- this is because the distance between the lens and retina is too small hence these eyes are shorter than the normal eye
Or just go to space..
- it is spherical in shape
- the distance between the cornea and retina is not too long or short
- light rays converge directly on the retina making the image focused and vision clear
- made up of rods, and cones
- at the age of 13, the eye attains its full size
S - larger
A - upright
L - behind the lens
T - real
- with myopia, things that are closer to you seem clearer, while things that are farther away appear blurry
- with hyperopia, things that are farther away seem clearer, while things that are closer appear blurry
- myopia is caused by the eye being too long
- hyperopia is caused by the eye being too short
- myopia corrective lenses are concave
- hyperopia corrective lenses are convex
- with myopia the light lands in front of the retina
- with hyperopia the light lands behind the retina