Refractive Surgery Basics

(Click on the pictures below to see larger images)

Refractice SurgeryBasic Eye Anatomy

  • Tear film - Because of the physics of light, the tear film is very important. As light moves from the air to water, it changes speed and most of it is therefore focused by the tear film. This is one reason why patients with dry eyes or watery eyes do not see well.
  • Cornea - The clear window that you see through in the front of the eye. In conjunction with the tear film, it accounts for 60-70% of all the light focusing in the eye. By changing the shape of the cornea,one can change how the light that enters the eye is focused.
  • Iris - this is the colored part of the inside of your eye. The pupil is the empty space within the iris
  • Focusing of lightLens - Like the lens in a camera, the lens in your eye can add focusing power depending on whatyou are looking at. Surprisingly, the lens contributes to only 30% of the focusing of the eye
  • Retina - The nerve in the back of the eye that senses the focused light - If the retina is not healthy, vision will be poor no matter how well the light is focused.
  • Optic Nerve - This is the nerve that transmits the information sensed by the retina to your brain. The brain then interprets this information and processes it into sight - the subjective perception of our reality.

 

Understanding why you need glasses or contact lenses

  • Refractive errorsNearsightedness (myopia) - Able to see near, but not distance without glasses
  • Farsightedness (hyperopia) - Difficulty with both near and distance vision, sometimes not becoming significant until ages 25-40. This is different than Presbyopia (see below) which often makes this seem worse
  • Astigmatism - rather than a perfectly round ball, the eye is shaped more like a football. Click on the link to see a simulation of what someone sees with high astigmatism
  • Presbyopia (loss of near vision) - This is an aging process that affects all people, usually around age 40. The lens of the eye hardens with age and is no longer able to focus at close objects.
  • Most people are myopic or hyperopic because the length of the eye is too long or short. Light does not focus on the retina.

(Click on the pictures to see larger images)

 

Correction of visionCorrecting errors in vision (Refractive errors)

  • Whether correcting vision with glasses, contacts or surgery, the light must be focused on the retina. For myopic eyes, the light must be diverged before entering the eye and for hyperopic eyes, light must be converged.
  • Due to the optics of lenses, the distance between the correcting lens and the eye can cause distortion of vision.
  • For example, myopic (diverging) lenses tend to make things seem smaller than they really are. This is one reason why many patients feel they see better with contacts than glasses - there is less distortion of image size because the contact lenses are directly on the surface of the eye. In addition, because the contact is directly on the eye, peripheral vision is better because peripheral light rays are also focused
  • Contact lensesLASIK is no different than Glasses or Contact lenses in that it changes the way the light is focused as it enters the eye. By changing the shape of the cornea, the light is either converged or diverged. Astigmatism is corrected by making the curvature of the cornea equal in all directions - making the surface of the eye round.
  • Because LASIK is performed on the surface of the eye, the quality of vision tends to be more like that with contact lenses than with glasses. Things such as image size appear more normal and peripheral vision tends to be better than with glasses when looking in the distance.
  • Lens surgery, such as cataract surgery (replacement of the natural lens with a lens implant) can also correct vision. Insertion of a lens implant such as the Implantable Contact Lens can be performed. Alternatively the lens can be removed and replaced with a ReSTOR lens implant that is capable of focusing vision for both near and far.

 

 

LASIK steps

  • Evaluation and counseling
  • Cut and Lift a Flap in the cornea -
    This is the most important step, as a good result depends on having a good flap.
    At Vision Associates, we use the Intralase laser to cut the flap, rather than a blade which most surgeons use. This safer and more precise technique adds assurance that riskiest part of the procedure will go well.
  • Excimer Laser Treatment is then applied to sculpt the cornea under the flap into a shape that will correct the vision.
  • Replace Flap and allow for healing

Click here to learn more about the LASIK Procedure








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