Optician India

No matter where in the World I examine people’s eyes, dry eye is a problem. People complain of burning eyes, dry eyes, watery eyes, gritty eyes, sore eyes, tired eyes and variable vision. Those of you who have worked with people with dry eye will know how difficult it is to tell those who have watery eyes that they have dry eye! More on that later. People with dry eye are uncomfortable and their quality-of-life is reduced. Dry eye can make people miserable.

It’s simple to diagnose but difficult to treat. Treatment requires persistence and resilience by the person who has dry eye and by the clinician managing it. For diagnosis, I have focussed on those tests which are low cost, simple and quick to perform and that would typically be available in standard optometric practise and conducted by generalist. At the end of this article I will provide a reference for these interested in more advanced, more expensive investigations that a clinician specialising in dry eye diagnosis and management or working in refractive surgical practice might use.

By way of reminder, below is a simplified image of the constituents of the tear film.

I have focussed on what I call basic dry eye and not that caused by systemic disease. There are three types of basic dry eye. Evaporative dry eye caused by a poor quality lipid layer, aqueous dry eye caused by a reduction in the quantity of tears and a combination of evaporative and aqueous dry eye. In my experience, most dry eye is caused by a poor quality lipid layer.

Typically I become aware that a person might have dry eye when, during history and symptom taking, I ask if they are having any problems with their eyes and/or their vision. When a person tells me that their eyes feel dry, or gritty, or sore or they burn or their vision is better after a blink or any combination of these symptoms I’m alerted to the possibility of dry eye. This would then trigger further questions:

Is your vision affected and does it improve immediately after blinking? A yes answer to this strongly suggests a tear film problem.

Are the symptoms worse in one eye or about the same in each eye? Typically the same in each eye.

Is there anything that triggers these symptoms. For example, being outside on a windy day.

Do the symptoms occur in certain environments? For example, driving in the car with the aircon on, or being in a room with heating on.

Any systemic changes? For example, menopause-natural hormone changes in women.

Are you taking any medicines? For example, antihistamines, antidepressants, high blood pressure medications, diuretics or acne treatments.

Do you wear contact lens. Contact lenses and/or contact lens solutions can disrupt the tear film.

Have you had any eye surgery? Anything that involves interfering with the corneal nerves can cause dry eye or make a mild dry eye become moderate or severe.

Other questions are:

When did these symptoms start? When do they occur? Are they bothering you? Do you do anything that stops or reduces the symptoms? Have you had these symptoms before? What do you think is causing them?

This is not an exhaustive list. My follow-up questions depend on the responses to my headline questions.

It’s during the history and symptom taking that I tackle the paradox of watery eyes being caused by dry eye. I say their tears are too thin to stay in their eyes and their tears run out causing the eyes to make more tears which also run out, or words to that effect.

There are many formal questionnaires that can be used to obtain information about dry eye. Two I have highlighted here are:

The Ocular Surface Disease Index questionnaire, a 12-item self-administered instrument used to assess dry eye symptoms and their impact on vision-related function over the past week. It includes sections on ocular symptoms like sensitivity to light, grittiness, pain, vision-related functioning (such as reading or computer use) and environmental triggers (like wind or air conditioning). Scores, ranging from 0 to 100, are categorized to indicate normal, mild, moderate, or severe ocular surface disease, with higher scores showing greater disability. A score of 0–12 indicates a normal ocular surface, 13–22 mild dry eye, 23–32 moderate dry eye and 33–100 severe dry ey

The Standard Patient Evaluation of Eye Dryness (SPEED) questionnaire, evaluates frequency and severity of dry eye symptoms through eight questions. The questionnaire covers symptoms typical in dry eye; dryness, grittiness, scratchiness, irritation, burning, watering, soreness, and eye fatigue. Patients grade frequency of symptoms on a 4-point scale (Never, Sometimes, Often, Constant) and the severity on a 5-point scale (No problems, Tolerable, Uncomfortable, Bothersome, Intolerable). The numeric values for each answer are totalled, with overall scores ranging from 0 to 28. A score of 1-4 indicates mild dry eye symptoms, 5-7 moderate dry eye symptoms and 8+ severe dry eye symptoms.

It’s very important to remember that some people with dry eye do not have symptoms. In a study by Viso et al. (2012), 21.9% of their participants with Meibomian gland dysfunction (this can cause dry eye) had no symptoms. You might be thinking why is it important to diagnose dry eye in a person that doesn’t have any symptoms because a person without symptoms is very unlikely to agree to treatment. People who want refractive surgery such as laser vision correction or refractive lens exchange will need to be investigated (and treated) for dry eye even if they don’t have symptoms. Asymptomatic pre-surgery dry eye may affect the readings of tests necessary prior to surgery, such as corneal topography and axial length. Inaccurate measures can lead to post-surgery refractive surprise. No one likes a surprise after eye surgery! Also, people with a substandard pre-surgery tear film (even if asymptomatic) are more likely to have dry eye post-surgery. There is a very strong case to be made for treating asymptomatic dry eye prior to a person undergoing refractive surgery.

I work in a standard practise without a specialty in dry eye so I use the free form questions I have described above, but I have colleagues who work in standard practise who prefer to use formal questionnaires when evaluating dry eye symptoms. They tell me that having a pre-treatment score is useful as they can compare within treatment and post-treatment scores to it. Collapsing the symptoms down to one number helps people understand how treatment has helped. In my experience clinicians working in dry eye specialty clinics will always use a formal dry eye questionnaire.

Investigation of lipid layer

I start with the least invasive tests first.

Blink rate

A normal blink rate for an adult is around 15 times per minute. You can count how many blinks the person makes in a minute. Ask them to look across the room and to blink normally. Make sure your timing of a minute is accurate; use a timer. Anything less than 15 blinks per minute could be an indicator of a cause of dry eye.

15-second blink test

For the 15-second blink test for dry eye, ask the person to look straight ahead and to try not to blink for at least 15 seconds.  If the person blinks before 15 seconds are up, or if discomfort sets in, it may indicate dry eyes. Again make sure your timing of 15 seconds is accurate; use a timer.

Tear break up time

Some clinicians dismiss tear break-up time saying it’s too variable, it depends on how the test is performed, how it’s timed and the environment in the room. Well, there are many tests in an eye examination that are variable and depend on how the test is performed but they are still useful tests. Tear break-up time provides useful information on the quality of the lipid layer and that helps in diagnosis and treatment of dry eye. A low tear break-up indicates a poor quality tear film and probably Meibomian gland dysfunction. My practise is to conduct non-invasive tear-break-up time first, as there is very little interference with the tear film, and then the fluorescein (invasive) tear break-up time.

For each of these the timing process is key. I use the timer in my phone. The timer in a digital watch can also be used. The key is to make sure the timer is zeroed and that you can activate and stop it without looking at it. It’s important to be looking at the tear film through the slit lamp when the timer is activated and still looking at the tear film when the timer is stopped. There’s a large area on the screen of my phone that I can touch, to start and stop the timer, with a finger without looking at screen.

Non-invasive tear break up time

Non-invasive tear break-up time is a test that measures tear film stability by projecting a pattern onto the eye and timing how long it takes for the pattern to become distorted or break after a blink. I project the mires of my keratometer, using low light. Just bright enough for me to be able to see the mires and not so bright that heat from the keratometer bulb might affect the tear film or cause the person photosensitivity. I project the mires in sharp focus onto the tear film and ask the person to blink three times. As they come out of the third blink and the upper lid is at its highest I tell them not to blink and at the same time start the timer. When the mires start to become distorted and/or there is a break in one or more of the circles I stop the timer, tell the person they can blink and note the elapsed time on my timer in seconds. I repeat this two more times on the same eye and average the three readings. I repeat three times for the other eye. I then have an average non-invasive tear break up time for each eye. < 5 seconds is indicative of a poor or unstable tear film. 5–10 seconds is suspicious of a developing instability in the tear film. > 10 seconds considered normal, indicating a stable tear film.

Keratometer mires used in the measurement of non-invasive tear break-up time.

Fluorescein (invasive) tear break-up time

I drop some sterile saline onto a fluorette and shake the surplus off on to a tissue. I ask the person to look up, pull down the lower lid and touch the flat side of the fluorette to the bulbar conjunctiva. If there is no active front of eye disease (such as conjunctivitis or blepharitis) I use the other side of the fluorette for the other eye. If there is active front of eye disease in the first eye I use a new fluorette on the second eye. I ask the person to place their chin on the chin rest of the slit lamp and head against the bar. Using low illumination from the temporal side of the person I illuminate the cornea using the cobalt blue (purple) light.

I make sure there is enough light and fluorescein in the eye to see the fluorescing tear film. I may need to add more fluorescein or make the light a little brighter. I ask the person to blink three times. As they come out of the third blink and the upper lid is at its highest I tell them not to blink and start the timer. When the first dark patch appears I stop the timer, tell the person then can blink and note the elapsed time on my timer in seconds. The dark patch indicates there is no tear film on that part of the cornea. I repeat this two more times on the same eye and average the three readings. I repeat three times for the other eye. I may have to add more fluorescein during this process depending on how quickly the tears with fluorescein drain from the eye, but usually I don’t need to. I then have an average non-invasive tear break up time for each eye.

                                                  Blink                        Full tear film              Full tear film             Full tear film              Tear break-up

                                                  Timing starts as person comes out of a blink                                                             Timing finishes

Ten seconds or more is considered to be a normal fluorescein tear break-up time. Anything less than this indicates a poor quality tear film. A poor quality tear film can lead to a sensation of gritty, uncomfortable, sore and watery eyes, affect vision and affect measurements that are necessary prior to refractive surgery.

Lissamine green staining tests

The use of lissamine green falls between a general practise dry eye work-up and a specialty dry eye clinic work-up. Some clinicians working in general practise will use it. All clinicians working in specialty dry eye practise will use it. The lissamine green test uses a green dye to stain damaged or dead cells on the cornea and conjunctiva. A small amount of the lissamine green dye is applied to the eye. It has been recommended to wet a lissamine strip with saline, shake off any excess, apply to the eye after five seconds and then again after one minute using the same strip. It reveals areas of inflammation or cellular defects that appear green when viewed with white light through the slit lamp. It is a non-fluorescent, high-visibility greenish-blue dye that stains corneal and conjunctival cells that are devitalised or have damaged membranes, making them visible as green areas.

Lissamine green corneal staining

Lid wiper epitheliopathy (LWE) is an inflammatory condition of the upper eyelid's lid wiper region, caused by excessive friction leading to staining and cell damage. Symptoms include foreign body sensation, burning and discomfort, often occurring in patients with dry eye. Lid wiper epitheliopathy affects the marginal conjunctiva of the upper eyelid, a part of the eyelid called the ‘lid wiper. It's a mechanical inflammatory condition where the epithelial cells of the lid wiper are damaged. This damage occurs due to increased friction as the eyelid wipes the ocular surface during blinking. It is caused by inadequate lubrication between the lid and the conjunctiva due to dry eye and/or abnormal blinking patterns.

Meibomian gland dysfunction

Meibomian gland dysfunction occurs when the Meibomian glands become blocked, resulting in reduced or poor quality oil (Meibum) secretion. Symptoms include dry eyes, burning sensation, blurry vision,and irritation. It can be caused by a variety of factors, including inflammation, bacterial infection, aging, and hormonal changes. There are some very sophisticated instruments and techniques that can be used to evaluate the Meibomian glands that are in the realm of the speciality dry eye clinic so I haven’t described them here.

My practise, is to check the opening of the glands on the lower and upper lids and look for clear liquid. Healthy Meibum is clear.

Clear (healthy) Meibum

Cloudy, thick (unhealthy) Meibum.

If the Meibum isn’t clear then this is a sign of Meibomian gland dysfunction and this will be a cause of dry eye symptoms.

Investigation of aqueous quantity

Again I start with the least invasive measurement.

Tear meniscus height

The tear meniscus height test is a non-invasive ocular surface assessment used to measure the height of the liquid meniscus that forms at the lower eyelid margin to estimate tear film volume.

A horizontal narrow slit beam is shone onto the eye to view the cross-section of the tear meniscus. The height of the beam can be adjusted to estimate the meniscus height. It is best assessed approximately two seconds after a blink, as this allows the tears to stabilise without triggering reflex tearing.

                           Horizontal slit beam on the tear meniscus                    Measurement of the tear meniscus height

The tear meniscus height is a reliable indicator of the total volume of tears on the ocular surface. A value of less than 0.25 mm is suggestive of aqueous deficiency. The shape and regularity of the tear meniscus can provide qualitative information about the quality and stability of the tear film.

Schirmer test

The Schirmer test has been criticised for being so invasive that it’s results are invalid. I don’t know whether this has been tested formally. Placing the strip of filter paper in the eye could cause irritation and this could cause an increase in aqueous production causing an overly high estimation of tear volume. Nevertheless, it remains popular especially in speciality dry eye clinics and in some general clinics.

A strip of specialised filter paper is placed under the lower eyelid of each eye for five minutes to measure how much liquid is absorbed. Some practitioners ask the person to close their eyes and others to blink normally. Normal blinking make cause more of a sensation and more reflex tearing. After 5 minutes the strip is moved and the moistened part of the strip is measured in millimetres. The test measures basal (resting) and reflex tears, although a version using aesthetic can measure basal tears alone. A length under 10 mm is often considered low, with less than 5 mm indicating severe aqueous deficiency.

The Schirmer test

Reference:

Viso, Eloy, et al. Prevalence of asymptomatic and symptomatic meibomian gland dysfunction in the general population of Spain. Investigative Ophthalmology & Visual Science 53.6 (2012): 2601-2606.