Many people are used to going through the motion of the different tests done during their eye exam visit, but many don’t know what is actually being tested. We would like to use this article to highlight some of the common tests done during pretesting. Pretesting is usually done in a different room before the patient is ready to see the optometrist by an optometric assitant, ophthalmic technician or an optician. Here are few of the most common eye tests done during the pretesting stage of your eye exam:
NCT (Non-contact Tonometry)
Non-Contact Tonometry is used by eye care professionals to measure the intraocular pressure in an individual's eye. Intraocular pressure is the fluid pressure within the eye. Intraocular pressure is useful to measure because it can determine if the patient is more likely to develop glaucoma. Glaucoma is when there is damage to the optic nerve and be caused by an increased intraocular pressure. The optic nerve is responsible for transmitting images to the brain. A Non-Contact Tonometer uses a puff into the individual’s eye. It measures the intraocular pressure by the eye’s resistance to the puff.
An auto-refractor is a computer-controlled machine that is used to provided an objective measurement of a person's refractive error and a starting point for prescription for glasses or contact lenses. Refractive error is a problem with focusing light properly onto the retina due to the shape of an individual's eye. Common types of refractive error are near-sightedness, which is when you can see objects near you clearly but object far away are not clear, and farsightedness, is when you are able to see objects far away clearly but are not able to see objects up close clearly. An autorefractor works by shining light into the eye and measuring how it changes as it bounces off the ocular fundus, which includes the retina, optic disc, macula, and fovea. An image of an object is shown to the patient moving in and out of focus and a number of measurements are taken of the reflection to determine when the eye is properly focused. When these figures are put together a level of correction needed for the patient is formed.
Auto-keratometry measures the anterior curvature of the cornea, which is the front of the eye. This test can be taken at the same time as the auto-refractor in some cases. An image is reflected off of two points in the cornea, and the relationship between object size, size of the image reflected and distance between the object and keratometer are all utilized to get the result of a minimum and maximum curvature valued for the cornea. This measurement helps with contact lens fittings.
Pachymetry is the process of measuring the thickness of an individual’s cornea. This measurement is taken just before the NCT is preformed. This is useful in regards to refractive surgery candidacy and certain corneal diseases.
Retinal imaging is an image that is taken of the inside of an individual's eye. It uses high-resolution imaging is used for the picture. This is used to assess the health of an individual’s retina. Within the picture an individual's retina, optic disk, and blood vessels can be seen. Retinal imaging is highly recommended when an individual has diabetes, since it can cause damage to the blood vessels in the retina.
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