What are Aberrations?
An aberration is a flaw or imperfection in the way that an optical system constructs images. Aberrations can occur in any optical system, such as mirrors or the lens inside of a camera. Aberrations also happen in the human optical system, the eye. If an aberration is present in the optical system, it can make images look distorted or blurry. Aberrations may occur due to having large pupils, a high glasses prescription, or artifacts on the lenses of the glasses. Aberrations in the eye can be classified into two types: high order and low order. Low order aberrations can be fixed by wearing glasses or contact lenses. High order aberrations are uncommon but they cannot be corrected by wearing glasses or contact lenses.
If the glasses you wear have aberrations, it may cause blurry vision, headaches, distortion of images, and color changes in the vision. Low order aberrations include refractive errors like nearsightedness (myopia), farsightedness (hyperopia), and astigmatism. High order aberrations include coma, spherical aberrations, and chromatic aberration.
Key Takeaways
- Aberrations are abnormalities of the eye’s optical system that cause visual issues like blurry vision, headache, and distorted vision.
- Lower order aberrations like astigmatism, myopia, and hyperopia can be fixed by wearing glasses or contact lenses.
- Higher order aberrations like chromatic aberration, coma, and spherical aberration cannot be corrected with glasses.
Understanding Aberrations
The human eye is an optical system. The elements of the optical system of the eye are the lens and the cornea. The lens is located inside the eye, and it moves forward and backward to focus images. The cornea is the clear layer that covers the front of the eye. The lens focuses on objects to make them clear, and the cornea bends light. Like any other optical system, the eye can also have errors that make its image blurry. These errors are known as aberrations.
Lower Order Aberrations
Low order aberrations are fixed by wearing glasses or contact lenses. Examples of low order aberrations are:
- Tilt: This aberration changes the way that a ray of light travels. The eye’s curvature is not smooth, which causes light rays to get deflected.
- Nearsightedness (myopia): occurs when the eye is too short and the image falls behind the retina. An example of a nearsighted prescription is -2.00.
- Farsightedness (hyperopia): occurs when the eye is too long and the image falls in front of the retina. An example of a farsighted prescription is +1.00.
- Astigmatism: occurs when the front of the eye, the cornea, is not perfectly round. The eye cannot focus light to a point.
Higher Order Aberrations
High order aberrations are rare. Only 10% of aberrations are high order aberrations. High order aberrations cannot be corrected with glasses. Examples of high order aberrations are:
- Chromatic aberration: This type of aberration causes abnormal halos or glow around lights. For example, looking at lights, one may see a rainbow halo or a blow glow. Chromatic aberration is the property of the lens, and certain types of lenses have more chromatic aberration. For example, polycarbonate material has more chromatic aberration, whereas plastic and glass lenses have the least amount of chromatic aberration.
- Coma: This aberration causes a comet-shaped blur. It occurs when one edge of the pupil receives light and focuses it from the opposite side.
- Trefoil: This aberration reduces the quality of color vision.
- Spherical aberration: This aberration makes it hard to focus light on a single point. It causes glare and blurry vision.
Aberrations Diagnosis
Low order aberrations (nearsightedness, farsightedness, and astigmatism) are diagnosed in an eye exam by checking the glasses prescription. High order aberrations are commonly diagnosed with wavefront analysis technology. High order aberrations are rarely measured, but the measurements may be done prior to eye surgery. For example, high order aberrations are measured prior to LASIK refractive surgery.
Treatment
Glasses, contact lenses, and refractive eye surgery correct lower-order aberrations. Higher order aberrations typically require surgery to correct. High order aberrations cannot be treated with glasses. Higher order aberrations can be reduced by choosing certain lens materials such as plastic or glass.
