Optometric Testing - How Accurate Is it?




We tend to accept the recommendations of eye-care professionals such as optometrists and ophthalmologists (specialists in medical and surgical eye problems). They are the experts, right?
Within optometry (a healthcare profession concerned with the eyes) there are commercial factors that come into play. An optometrist earns his money by selling glasses, so the more expensive frames and glasses he can sell the better. The testing may often be just a minor procedural step. So how accurate are the tests?
The editors of the British Consumer Magazine Which? asked student optometrists to visit 39 eye-care locations in England and Scotland, including supermarkets, national and regional chains, and independent outlets.
The researchers asked for routine eye tests and those who wore glasses said they had lost them so that their glasses could not be used for reference purposes. The results of these tests were then judged by a panel of experts appointed by Which?
Which? judged 17 of the 39 examinations it studied to be poor or very poor because it said essential tests were not carried out.
Seven led to inaccurate prescriptions, which the consumer group said could cause headaches or blurred vision.
One Which? researcher, whose eyes needed help to enable them to work together, was put at risk of blurred vision, left with useless glasses that would make reading difficult and driving dangerous, and was given unsuitable prescriptions on six of her eight visits.

Who's best?

The big chains were not found to be any better or worse over the 39 visits, the investigation found. Only one visit received an “excellent” rating, an exemplary visit to a branch of Rayner Opticians.
Large chains such as Boots/Dollond & Aitchison had two visits rated “good”, two “OK” and one “poor”, and Specsavers received one visit rated “good”, with two “OK” and one “very poor”.
At the other end of the scale, small independent retailers had three visits rated “good” and one “poor”.
The experts criticised one branch of Boots for recommending the “updating” of some varifocals, and one branch of Tesco for telling the customer his prescription had changed, which could have led to a purchase. In five visits, Which? researchers reported feeling some pressure to buy glasses: three were at Boots/Dollond & Aitchison, one at Rayner, and one at an independent retailer.
Source: BBC NEWS | Health | Study exposes 'flawed' eye tests, 29 August 2007, http://news.bbc.co.uk/2/hi/health/6968501.stm
In some cases the owners of optometric shops tell their optometrists to sell as many progressive lenses as possible, since these are much more expensive than regular glasses. Or worse, as mentioned in the Which? reports above, they tell customers that their prescriptions have changed thereby implying that new glasses are needed.
There is ample reason to be alert since only one out of 39 visits to optometrists in England and Scotland resulted in an excellent rating.
It should have been 39 out of 39.
There are two tests that are commonly performed by an optometrist. The simple one is called a sight test and the more comprehensive one is called an eye exam (according to Doctors of Optometry Canada).
Source: http://doctorsofoptometry.ca/eye-exam-vs-sight-test/ 2/2 What is a sight test?
Optometrists recommend that most people should have their eyes tested every two years. Your eyes and the area around them will be examined, to look for signs of injury, disease or abnormality. During your appointment you may see more than one practitioner, who tests your sight to check the quality of your vision and your eye health, or a dispensing optician who fits you with glasses. If you already wear glasses or contact lenses, remember to take them with you.
In technical terms, a sight test describes a refraction to determine the lens power required by relying on a combination of computerized tests using automated equipment.
The comprehensiveness and accuracy of these automated sight tests is limited. Eye muscle coordination is unaccounted for, and eye fixation and alignment, pupil size, corneal or lens irregularities, patient movement and attention, and something called instrument myopia can influence the test results. This last problem is created by the eye’s tendency to over-focus when looking through a machine such as used in the test.
This can lead to an inaccurate measurement of refraction. Also the eyes have to adapt to the lens the patient is looking through.
Optometrist Divya Divzz says. “I myself am an optometrist and I agree with this. But optometrist computerised testing (Auto-refraction) is helpful, saves times and increases accuracy in manual retinoscopy. An experienced expert can correctly obtain the proper axis of astigmatism cylinder power. But in my experience the computer axis is more accepted by the patient. We should not blindly just give auto refractor correction, the patient must be given the proper correction.”
Optometrist Rajesh Radhakrishnan says, “It is a fact that the autorefractor (AR) overestimates myopia and underestimates hypermetropia. Nothing can take the place of a dilated cycloplegic (using eye drops) refraction done by the eye-care practitioner. Just take a look at the change of power estimated by the AR before and after dilating. These are actual figures from patient records. Of course, this is an extreme case in a young child of nine. AR should not be the basis of refraction in children. Period.”
Source: Exchange on Facebook
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An eye exam includes:

A case history of past and present vision and medical issues, as well as a detailed family history.
  1. An analysis of the patient’s visual needs at home, work, school, and play. In some instances, this may necessitate questions about the patient’s school/work environment and recreational activities in order to accurately determine the patient’s visual demands.

  2. Measurement of the visual acuity of each eye, individually and together, both with and without corrective lenses.
  3. Binocular vision assessment (ability to see using both eyes together), as it relates to eye coordination, depth perception, and eye movements, or in some cases, eye-hand coordination.
  4. Colour vision evaluation as required.
  5. Assessment of the health of the eye itself both inside and outside using a bio-microscope, ophthalmoscope and a dilated eye examination when indicated. This could uncover anything from a minor deficiency of the tears, to a major retinal problem, or even a serious condition elsewhere in the body.
  6. A neurological assessment of the visual system including a review of the pupil reactions, ocular muscle reflexes and functions and an assessment of the peripheral vision.
  7. Screening for glaucoma, including testing pressure inside the eye, looking inside the eye at the retina and optic nerve, as well as performing peripheral vision tests.
  8. Diagnosis of the refractive status or prescription (focusing power of the eye) based on a combination of objective (measurements) and subjective (patient responses to questions) techniques.
All of the test results are used in the final analysis to determine the appropriate prescription lenses to treat refractive and visual problems, to develop a programme of eye training exercises, or to recommend medical or surgical treatment.
Recommendations for future eye-care can be made based on the history of the patient’s eye health and the results of the examination.
The final analysis of the eye exam will depend on the Doctor of Optometry’s professional knowledge, experience and judgment.
It is recommended that the patient have an eye exam every year.

What is an objective test?

Objective Refraction: An objective refraction is a refraction obtained without receiving any feedback from the patient. An objective refraction is obtained by using different instruments. The doctor will use a retinoscope or auto-refractor to measure the patient’s refraction without asking for subjective responses from him/her.

Retinoscopy:

One of the most common instruments used for objective refraction is the retinoscope. Using a retinoscope, the doctor will project a streak of light into the patient’s pupil. A series of lenses will be flashed in front of the eye (to prevent the eye from adjusting to the lens). By looking through the retinoscope, the doctor can study the light reflex of the pupil. Based on the movement and orientation of this retinal reflection, the refractive state of the eye is measured.

Auto-refraction:

Another instrument used for objective refraction is an auto-refractor. This is a computerised instrument that shines infrared light into the eye. This light travels through the front part of the eye to the back part of the eye, then back again. The information is bounced back to the instrument, giving an objective measurement of the refractive error. Auto- refractors are quick and easy to use, and require no feedback from the patient. (Auto-refractors are not accurate enough for prescriptions to be based on the print-out).

What is a subjective test?

Subjective Refraction: Subjective refraction requires responses from the patient. The doctor may use a phoropter to measure the patient’s subjective refractive error to determine the glasses’ prescription.
Typically, the patient will sit behind the phoropter and look at an eye chart. The doctor will change lenses and other settings while asking for feedback on which settings give the best vision.
Sometimes eye doctors prefer to obtain a cycloplegic refraction, especially when trying to obtain an accurate refraction in young children who may skew refraction measurements by adjusting their eyes. Cycloplegic eye drops are applied to the eye to temporarily paralyse the ciliary muscles of the eye.
Corboy, John M, MD and David J Norath, COT. The Retinoscopy Book: An Introductory Manual for Eye Care Professionals. Pp 7-12. Slack, Inc, 2003.
The human eye is capable of adapting to the environment as, after all, this is one of its purposes. Some ophthalmologists believe that you cannot obtain an accurate measurement without cycloplegia eye drops opening the eye wide and paralysing the muscles around the lens. This, of course, eliminates an attempt to adjust to the testing equipment. This is particularly a problem with young children, who have tremendous adaptability which, sometimes, leads to wildly different measurements from one doctor to another.
Applying eye drops to the eyes of small children usually produces an angry reaction and it does not improve the accuracy of the test. The main objective is to relax the eyes. However, this can be done equally well just applying hot and cold towels. In continental Europe it is only ophthalmologists who are authorised to use cycloplegia drops. Optometrists, with the exceptions of Holland, the UK and Ireland, are not allowed to perform cycloplegia refractions.

You are not a machine

Eyesight is influenced by many things such as how well you sleep, for example. We have all experienced how our eyes feel after an overnight flight. Ambient light has an influence of how well we see. The eye charts you typically see in hospitals with fluorescent light behind them, are not the best test in the world. The time of the day also influences the results of your test. If you go in the evening you will have a test of tired eyes.
It is also important to realise that your eyes adapt to any lenses put in front of them, otherwise you cannot see through the lens. So the photopter most optometrists use does not allow your eyes to relax but keeps adapting them to stronger and stronger lens power. The old- fashioned way with the retinoscope and the box of loose lenses employing the trial and error approach is better because it does not stress the eyes but takes a longer time. If this method is not used, you will be given a prescription that is the worst possible for your eyes and you will feel this when you put on the new glasses a few days later. They will be too strong. But if you allow yourself to become used to the stronger glasses your eyes will have to get worse in order to adapt to them.
The best test is done with eyes that are relaxed in the normal conditions you live in, not dark rooms with projected eye charts on the wall. The main problem is that optometrists and ophthalmologists are often pressed for time and a busy ophthalmologist may see a new patient every 15 minutes. Not a long time to get to know you.

Leo Angart

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