If you wish to understand what to expect in an eye examination, this article in just for you?
Eye examination involves several tests to assess the eyeglass prescription and the eye’s health. An eye examination includes several steps and is usually performed systematically by either an optometrist or ophthalmologist in an eye clinic. The following components are generally included in a regular and detailed eye examination. However, the decision to skip, include or add certain components in an eye examination is best left to the eye care practitioner.
The eye care practitioner takes a detailed history during every visit. In this part of the examination, a series of questions will be asked, which includes past and present eye problems, history of any medication usage, family history as well as any health conditions like diabetes or hypertension (high blood pressure) that could have a bearing on the eye health. For example, fundus examination, which examines the health of the innermost layer of the eye, namely the retinal layer, becomes necessary as it could affect the blood vessels.
It is essential that when questions are asked, the person undergoing eye examination answers all of them truthfully and not hide anything from the examiner since history forms the basis of other components of an eye examination.
This component follows the history wherein the eyesight or visual acuity of the patient is measured with the help of vision charts (fig -). Several vision charts are available depending upon the age and language preference of the patient. Vision charts are also available for those who cannot read or write and pre-schoolers.
Eyesight is always checked one eye at a time with the other eye occluded for distance and near. In case a person wears prescription glasses, then vision is checked with the current prescription too. Patients who wear prescription glasses or contact lenses should bring them along during eye examination. In case of damaged or lost prescription, the same needs to be conveyed during the eye examination.
The eye care practitioner determines the eyeglass prescription of the eye during refraction. Even if the vision is normal during vision check, the refractive status is determined using an auto-refractor (fig…) or a small instrument called the retinoscope (fig…).
These tests give the eye care practitioner a starting point, which he/she uses to get a more accurate prescription based on patients responses and his own assessment. If a refractive error is determined, lenses of varying powers in plus or minus are presented before each eye and confirmed with the patient for clarity of letters in the vision chart.
The lenses could be spherical, cylindrical or a combination of both. The best combination of lenses, which give the best vision to the patient for distance and near, is determined and noted down as prescription. This part of the examination could take several minutes based on the responses from the patient.
Even if the patient is not answering truthfully (fortunately, such occasions are rare), the skilled eye care practitioner can get the right prescription.
Cycloplegic eye drops
In some cases, especially in children and young adults, eyeglass prescription is confirmed with eye drops to dilate the pupil and paralyze the active focusing muscles of the eye and give a more accurate idea of the eyeglass prescription to the eye care practitioner.
Checking for eye muscle coordination and strength
The eye care practitioner tests the muscles responsible for eye movements and their strength by asking the patient to track a moving object presented before the eyes, usually a pen torch or a bright object.
Complex softwares or binocular vision assessment devices may be used to assess the strength of essential eye muscles, which is compared with age normal values. Any case of muscle weakness or any eye deviation (squint) noted will be treated using vision therapy. A detailed exercise chart is made for vision therapy based on the type of weakness. Not all squints can be treated by vision therapy, and few need surgery.
A simple torchlight examination is a quick way to externally examine the eyes for any gross abnormalities and check for the functioning of the pupil. A torchlight examination is helpful in those patients who cannot be seated before a slit lamp bio-microscope for a detailed eye examination.
Slit Lamp examination
The eyes are viewed under a microscope and light source; this instrument is called a Slit-lamp wherein all the parts of the eyes from the eyelids and lashes are examined to the lens of the eye. With additional attachments, even the back part of the eye is examined. The eye is viewed in detail for any abnormalities in structure or function. Sometimes a dye is instilled in the eye to check for any tear film abnormality or cell damage.
Eye pressure evaluation
The intraocular pressure can be evaluated to check for a condition called Glaucoma. Increased eye pressures could damage the nerves of the eyes resulting in visual field loss and sometimes even associated with eye pain and redness.
A tonometer is an instrument used to determine eye pressure. There are several types of tonometers available. Some are blowing a puff of air on the eye, while others are momentarily depressing the cornea to determine the eye pressure. Depending on the method performed, the examiner may use local anaesthetics to temporarily numb the eye and cause the least discomfort to the patient.
In case elevated eye pressures are noted, further tests could be recommended, or the examiner makes a referral to a glaucoma specialist.
Remember, Glaucoma is a silent thief of vision. We often have elevated eye pressures, which cause damage to the eyes, and we don’t realize it until it’s too late.
Colour Vision evaluation
A person’s colour vision can be tested using a series of cards with multicoloured dots arranged in a pattern or number. Failure to recognize these patterns or figures could be due to colour blindness.
Fundus examination or ophthalmoscopy
This constitutes the last component of eye examination wherein the back of the eye is examined to view the innermost layer of the eye called the retina to check for its health. In addition to the retinal layer, the blood vessels, optic disc, and the middle layer called the choroid can also be examined. Examining the back of the eye is called fundoscopy or ophthalmoscopy. This can be performed with and without the use of dilatation drops. The use of dilating eye drops permits a more detailed view of the back of the eye, especially when some abnormality is suspected or in cases of any existing medical conditions or family history of eye diseases. On few occasions, a scleral depressor is used to assess the extreme periphery of the retina.
Fundus examination is mandatory in the following cases
- History of medical conditions like diabetes, hypertension (high blood pressure) etc
- Family history of eye diseases like Glaucoma, Macular degeneration, retinal diseases etc
- Sudden or recent loss of vision
- High myopia
- History of light flashing in front of eyes or seeing black spots
Once the eye care practitioner performs the required tests, he/she will communicate the observations made to the patient. An eyeglass prescription will be written for those requiring it. In some instances, further tests/referrals could be made based on the outcome of the preliminary examination. A second schedule for eye examination could be made for those requiring contact lenses, low vision care, detailed refraction, binocular vision examination, or fundus examination. It requires dilation eye drops resulting in temporary blurry vision and increased sensitivity to light.