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Refractive services

Types Of Refractive Errors:

Low Order Aberrations :

An eye that has refractive error when viewing distant objects is said to have ametropia or be ametropic. This eye, when not using accommodation, cannot focus parallel rays of light (light from distant objects) on the retina.

The word "ametropia" can be used interchangeably with "refractive error" as they refer to the same thing. Types of ametropia include myopia, hyperopia and astigmatism. They are frequently categorized as spherical errors and cylindrical errors which are generally considered as Lower order aberrations . They make up about 85 percent of all aberrations in an eye.

Spherical errors occur when the optical power of the eye is either too large or too small to focus light on the retina. People with refraction error frequently have blurry vision.

  • Myopia: When the optics are too powerful for the length of the eyeball one has myopia or nearsightedness.
  • Hyperopia or Farsightedness: This can arise from a cornea with not enough curvature or an eyeball that is too short.
  • Astigmatism: People with a simple astigmatic refractive error see contours of a particular orientation as blurred, but see contours with orientations at right angles as clear. When one has a cylindrical error, one has astigmatism.
High Order Aberrations :

No eye is perfect, which means that all eyes have at least some degree of higher-order aberrations. HOA are more complex vision errors than lower-order aberrations. These types of aberrations can produce vision errors such as difficulty seeing at night, loss of contrast, glare, halos, blurring, starburst patterns or double vision Higher-order aberrations comprise many varieties of aberrations. Some of them have names such as coma, trefoil and spherical aberration, but many more of them are identified only by mathematical expressions (Zernike polynomials). An eye usually has several different higher-order aberrations interacting together. They make up about 15 percent of the total number of aberrations in an eye. People with larger pupil sizes generally may have more problems with vision symptoms caused by higher-order aberrations, particularly in low lighting conditions when the pupil opens even wider.

Treatment Options :

The treatment options will vary from person to person depending upon the uniqueness of the eye in terms of amount of refractive power, the central corneal thickness (pachymetry) and the corneal curvature (Topography). The recommended treatment type will be personalized according to your corneal thickness, refractive errors, pupil size and other factors and. The best treatment option will be advised after detailed evaluation keeping in mind the patient's preoperative power, patient's expectations and requirements and counseled accordingly.


By way of Glasses or Contact lenses: Usually the preferred method for children till the refractive stability is achieved, which usually takes 18 to 19 years.


By way of Excimer laser(LASIK/PRK) or Implantable Collamer Lenses (ICL) depending on the Patients Native Corneal thickness, Amount of refractive errors and other eye conditions, which will be dealt with in detail in respective topics.

Laser Vision Correction

Laser Vision Correction is a permanent treatment. However, patients who are 40 years and above, may require reading glasses. During your consultation we will give you can an idea of the procedure and the level of vision you can expect. We need to ensure the patient is left with a definitive safety margin of Residual Corneal thickness after the end of the refractive surgery. More the refractive error, the more the amount of issue that is to be ablated to reshape the cornea, hence lesser the Residual corneal thickness after the surgery

  • If the corneal thickness is quite adequate for the power to be treated the patient is advised to undergo LASIK.
  • If the Corneal thickness is just enough or borderline for the amount of power to be treated, then Photorefractive Keratectomy is advocated.
  • If the Corneal thickness is too less even for PRK, then we defer Laser vision correction. The Patients are counseled then for Implantable Collamer Lens(ICL) Surgery.