EyeTools Optometry Skills

97: 10 things I think are interesting

97: 10 things I think are interesting

  1. Cup? What is the cup?

The cup is space filled with vitreous gel. Most people have the same amount of retinal nerves all trying to get out of the eye and make their way to the brain. Some eyes are larger than others. Larger eyes have a larger hole for the retinal nerve fibres to pass through. If the hole is large and the amount of retinal nerve fibres is the same for most people a large hole won’t be completely filled with retinal nerve fibres. In the middle there will be a space; this is the cup. People with myopia have a large eye and a large hole, and therefore an obvious cup as not all of the hole is filled with retinal nerves. People with hyperopia have a small eye and a small hole, and therefore a small cup or no cup as the retinal fibres fill the hole completely. In a hyperopic eye sometimes the hole is so small that there is a squash and squeeze for the retinal nerve fibres to get out and this results in a crowded optic nerve head.

  1. Cross cyl

When a person accepts extra minus cyl when using a ± 0.25DC Jackson cross-cyl what they are really accepting is +0.25DS/-0.50DC, if you are working in minus cyl, and -0.25DS/+0.50DC if you are working. Add +0.25DS for every -0.50DC increase (and vice versa). They are accepting sphere and what I would call quite a lot of cyl. Sometimes practitioners change the cyl power in the trial frame but forget to change the sphere power. It is important to check if changing the sphere power maintains or improves clarity. In theory, changing the cyl and sphere power should collapse the blur circle to a sharp point focussed on the retina. It’s worth checking but also worth remembering that the person response and theory sometimes don’t agree. When they don’t the person response should always prevail.

  1. Reading and eye ache

When a person complains of headaches and eye aches that come with reading only there are several possible causes. One of them is subacute closed-angle glaucoma. As the person’s head is slightly inclined forward in the reading process position the iris moves slightly forward under the effect of gravity in an angle that is already narrow this can reduce the outflow of aqueous and cause a transient increase in ocular pressure which can manifest as eye and/or headache. In these circumstances conduct a Van Herrick test in the normal way and see what the grade is. A grade of 2 or less indicates a narrow anterior chamber angle and could account for the patient’s symptoms and warrant a referral.

  1. Shafers and dilation

Increase the field of view by dilating the pupil. This will increase your chance of seeing pigmented cells (released from the RPE and/or retinal blood cells). Ask the person to look up and then straight ahead. This will cause the detached vitreous to be swirled around and you can look for pigmented cells as it settles. If this is not done then if the pigmented cells are in settled vitreous that is below the pupil (because of gravity) then even though the pupil is dilated then you will not see the pigmented cells. The bottom line is the symptoms and/or signs indicate the possibility of a retinal detachment and/or retinal tear then dilate and get the patient to look up and straight will you use the slit lamp to investigate the anterior vitreous looking for pigmented cells.

  1. Vitreous floaters close and far

Floaters are located in the vitreous and are described by patients as floaters, bubbles, bugs, cobwebs, or dark spots that move during eye movement. Whether the patient and/or practitioner can see them depends on the location of the floaters.

When light enters the eye, floaters cast a shadow on the retina. It is this shadow that the patient ‘sees’ rather than the floater itself. The further away from the retina the floater is located the bigger the shadow and the more noticeable the floater is to the patient. The closer the floater is to the retina the smaller the shadow and the less noticeable the floater is to the patient.

A useful analogy is the position of the Moon. When the Moon moves to be between the Sun and the Earth, because of the Moon’s distance (around 239 000 miles) from the Earth, it casts a large shadow on the surface of the Earth, which is noticed by many thousands of people. This is known as a lunar eclipse. If the Moon were at cloud level, that is further from the Sun and closer to the Earth, the shadow would be much smaller and less noticeable.

So, small floaters in the anterior vitreous (far from the retina) which can be impossible for the practitioner to detect will cast a relatively large shadow on the retina and be very noticeable to the patient. Conversely, large floaters in the posterior vitreous (close to the retina) which can be very easy for the practitioner to detect will cast a relatively small shadow (if at all) on the retina and not be noticed by the patient.

Furthermore, patients also often report that their floaters become more noticeable and sometimes more bothersome when they are in a bright environment and/or looking at a featureless scene such as a clear blue sky, a plain white wall or the screen of a device. The extra light enhances the appearance of the shadow while the featureless scene means there is little to mask the shadow.

  1. Old MAR versus new MAR. Why no break up with the new

Many people will lead their sunglasses or driving glasses in their car, but be warned, extreme heat will break down your coatings with time and cause peeling and distortion.  If you have to leave your glasses in your car, make sure you have them in a case and try to park your car under a covered deck or under some shade to reduce high-temperature exposure. If you are consistently exposing your glasses to extreme temperatures, just expect that you may need to replace your glasses more consistently as well. Professions like chefs or kitchen workers who expose their glasses to high temperatures and steam may have to replace their glasses more regularly as a result.

Old coatings didn’t expand at the same rate as the plastic lens material in heat. As the plastic lens expanded in heat the coating was stretched and when repeated several times lead to the breakdown of the coating surface. New coatings have expansion properties similar to the lens material. Coatings are matched to different types of lens material. As the lens itself expands the coating expands about the same amount. This is why new coatings maintain their integrity longer than the old generation one coatings. Still best not to leave your glasses where they will get hot, lying exposed when reading on the beach or on the dashboard of a car when it is sunny.

  1. Find the patient’s why

During history and symptoms, you need to find out the patient’s why. For example, if you discover that they are having problems with night-time glare and they don’t have an antireflection coating or the one they have is broken up. You can advise them to have an anti-reflection coating. I advise an antireflection coating because you have problems with night-time glare. If you advise something and the patient asks why you need to have found something in history and symptoms or during your examination that can answer the why question. Even if they don’t ask why, you need to explain why.

  1. RPE cells move

The retinal pigment is located in a layer of the retina called the retinal pigment epithelium (RPE). The pigment cells can become mobile as part of retinal ageing changes, sometimes caused by the toxic stress associated with many years of sunlight exposure. Yes RPE cells can crawl. The retinal pigment epithelium is a retinal layer that is one cell thick. As the pigment cells move they leave a gap in the RPE. Through this gap, the pale sclera becomes visible. The pale gaps are referred to as hypopigmentation and, when present with macular hyperpigmentation and intermediate and/or large drusen, lead to the diagnosis of age-related macular degeneration. The pigment can crawl around in your skin as well. My forearms are a good example of pigment movement caused by age and sunlight damage.

  1. Why are people with myopia predisposed to retinal detachment?

Everyone has the same amount of retinal material but we have different-sized eyes. A person with -5.00DS will have a larger eye than a person with +5.00 or an emmetrope. All will have similar amounts of retinal material so the retinal material in the -5.00 eye is stretched in order to cover the back of the eye. It’s like trying to carpet a room when the amount of your carpet isn’t enough to easily cover the room. You pull it and stretch it to make it fit and hammer in the nails or glue. The carpet just about fits now and covers the room but it is under some tension. Dropping something on it may cause a tear to develop and whole and eventually the carpet will come away from the floor and detach from the skirting board and fold back on itself. Just as with a rhegmatogenous retinal detachment.

  1. People with floaters can be helped with a nutritional supplement

The vitreous gel is bombarded with sunlight during waking daylight hours. This causes oxidative chemical reactions within the gel and the chemicals produced are harmful to the elements that make up the gel. This is why the gel also contains anti-oxidants which neutralise harmful chemicals. These antioxidants pass from the retina and retinal/choroidal blood into the vitreous through diffusion. With the passage of time, the anti-oxidants become depleted and the balance shifts in favour of the harmful chemicals. They change the structure of the vitreous elements. Fibrils which were perfectly separated to allow transparency now clump together. These cast shadows on the retina which are seen as floaters. Taking a nutritional supplement full of vitreous anti-oxidants (Vitrocap N) keeps the balance in favour of the anti-oxidants. Floaters can be prevented; current floaters disappear and age-related shrinkage and liquefication prevented or delayed. It’s shrinkage and liquefication that can lead to a retinal detachment and/or retinal tear.