Contact Lenses and Space Exploration

By Sam Winnegrad, MBA, NCLE-AC

Learning Objectives:

Upon completion of the course, participants will be able to:

1. Describe how space exploration and its science can be used to describe a way to understand contact lenses.
2. List the principles of contact lens fitting.
3. Explain how each of the contact lens fitting principles make for confident fitting and happy patients.

Faculty/Editorial Board:

Sam Winnegrad is a master optician who has instructed anatomy and physiology of the eye and other various ophthalmic courses for Roane State Community College in Harriman, Tennessee. He has also taught for Highline College's online optician program out of Des Moines, Washington. Sam is a technical speaker for the American Board of Opticianry and National Contact Lens Examiners. Sam holds a master's degree in business administration and a bachelor's in science, but above all, he treasures his license to practice opticianry.

Credit Statement:

This course is approved for one (1) hour of CE credit by the National Contact Lens Examiners - NCLE, Ophthalmic Level 2, Course number CTWJHI116-2

---

INTRODUCTION

This course has been approved for one (1) hour of Ophthalmic Level II continuing education credit by the NCLE. To earn NCLE credit, please review the questions and take the test at 2020mag.com/ce. Note: As of January 2020, no tests will be graded manually. Please call (800) 825-4696 for more information.

THE SUN

The sun is a yellow dwarf star at the center of our solar system. It provides all our light and controls our climate. Though the sun is one of the smaller star varieties, it is still much larger than the Earth. It is estimated that 960,000 Earths could be contained within the dimensions of the sun. In fact, the mass of the sun is equal to that of 99.8 percent of the entire solar system. All the planets that revolve around the sun pale in comparison to its enormity. The sun exerts a gravitational pull on the planets, which allows them to maintain a precise and uninterrupted orbit. The centration and stability of the sun is crucial to the sustenance of the Earth and the entire solar system.

Contact lenses, as well, need to maintain proper centration to offer stable vision and comfort. Soft toric lenses offer excellent vision, but they must remain properly oriented. There are various methods for stabilizing these lenses. Prism ballast is when a prismatic shape is used to stabilize the lens. It is not the weight of the prism that enables the lens to be stable. It is the way that the upper lid interacts with the thinner section of the lens. Truncation is when a section of the inferior portion of a lens is removed. This is many times used in conjunction with prism ballast. Peri-ballast is another technique for lens stabilization and centralization. This is where prism is added to the lens, but it is kept entirely out of the optical zone of the lens. Peri-ballast is helpful for patients who experience diplopia with prism ballast lenses. All contact lenses that correct for astigmatism have manufacture markings on them which tell us when they are oriented properly on the wearer. When evaluating a lens for proper fit and orientation, it is crucial to see where these marks equilibrate to on the wearer. This is where we utilize the principle of LARS (left add, right subtract). If a lens is drifting to the left, we add those degrees of shift to the patient’s refractive axis. If a lens moves to the right, we subtract that movement from the refractive axis. This is an incredibly useful and foundational principle of toric lens fitting.

MERCURY

Mercury is the closest planet to the sun. It is also the fastest planet, traveling around the sun at a speed of 112,000 miles per hour, completing an entire orbit around the sun every 88 Earth days. Mercury is the second most dense planet in the solar system after Earth and has an iron core. Interestingly, the temperature of Mercury can shift 1,100 degrees Fahrenheit in just one day. Even so, the poles of this planet can be quite cold and are even thought to hold ice formations. This temperamental nature of Mercury has much to do with its proximity to the sun. Just as planets are affected by their proximity to the sun, refractions are also affected when they are interpreted through contact lenses as they are placed directly on the cornea, as opposed to eyeglasses which sit 12 to 14 millimeters in front of the eye.

Vertex distance is defined as the distance between the back of the corrective lens and the front surface of the eye. After a patient is refracted in the exam chair, it is important that the vertex distance compensation is considered when the refraction is 4 diopters or greater. A refraction of less than 4 diopters has a negligible effect on one’s vision when going from an eyeglass position of wear vertex distance to a contact lens in situ. Refractive powers of 4 diopters or greater will have a noticeable effect on the wearer when transitioning from a refracted vertex distance to a contact lens prescription. All lenses that move farther away from the eye will effectively seem more plus powered to the wearer. For example, someone who is refracted behind the phoropter with a 12-millimeter vertex distance to a +9.00 correction should be fit with a +10.00 diopter contact lens. This is because the +9.00-diopter lens is behaving like a +10.00 lens during the examination because of the vertex distance. Minus powered lenses produce the same effect and will behave “more plus” when placed on the eye, as compared to the refraction. For example, a -9.00 diopter refraction converts to a -8.00 diopter contact lens.

VENUS

Venus is the second planet from the sun and is one of the brightest objects in the night sky. Venus is sometimes referred to as Earth’s sister planet due to the fact that it is so similar in size and mass to that of Earth. Interestingly and counter-intuitively, Venus’ year is shorter than its day! It takes 243 Earth days for one complete Venus day, and it takes only 225 Earth days for Venus to orbit the Sun. Venus is also known for having an incredibly thick atmosphere—this, coupled with the fact that this planet is close in proximity to the Sun, ensures that Venus has an extremely dry climate. Similarly to how Venus’ dry climate makes it inhospitable for life, we know that patients suffering from dry eye syndrome can have a difficult time wearing contact lenses.

Keratitis sicca, commonly referred to as dry eye syndrome, can wreak havoc on the contact lens wearer. Patients who are suffering from this condition either have an issue related to the quality of the tears that are produced or the quantity of tears produced. The break-up-time test is used to determine the quality of the tear film. This test is performed with fluorescein dye and a slit lamp with diffuse illumination. The patient is asked to blink, and then it is determined how long it takes for the patient’s tear film to start “breaking up.” A break-up-time of less than 10 seconds is contraindicative to contact lens wear. Schirmer’s test is used to assess the quantity of tears produced. This test uses a strip of filter paper placed under the eyelids. After five minutes, the amount of moisture in the filter paper is measured for production. The average is 15 millimeters. As we age, we produce less tears, which makes wearing contact lenses more difficult. Many patients find the need to supplement their lenses with artificial tears to combat the dryness and re-establish a moist environment.

EARTH

The Earth is one of the inner terrestrial planets and the only one supporting life. It is also known as the “blue planet” as 70 percent of its surface is covered with water. It takes 24 hours for the Earth to rotate around its axis and just over 365 days to completely orbit around the Sun. More accurately, we can state that the Earth takes 365.25 days to completely orbit the Sun. Therefore, we add a day to our annual calendar every four years in February for a leap year. The rotation of the Earth and its orbit around the Sun permits us to define time in measurable meaningful units. Contact lenses are designed to be worn for particular time periods.

In simplest terms, a daily wear lens is designed to be worn for less than 24 hours. These lenses are intended to be cleaned and disinfected between wearing periods. On the opposite end of the spectrum is the extended wear lens, which is designed to be worn 24 hours a day for up to 30 consecutive days. These newer technology lenses permit greater oxygen transmissibility, allowing the cornea to receive vital nourishment. Daily disposable lenses are an increasingly popular option for wearers, as they are designed to be worn for just one day and then discarded. This is a very safe option, as it is less likely for patients to over wear their contacts. It is also one of the easiest to manage, as the need for multi-purpose cleaning and disinfecting solution and contact lens storage cases is eradicated. Only through educating patients on the dangers of wearing lenses for longer periods of time than what they are prescribed for will they understand the potential consequences. One of the most common ailments attributed to over wear of lenses is corneal ulcers, which can be both painful and sight threatening.

MARS

Mars is the fourth planet from the sun and the second smallest of all the planets. It is affectionately referred to as the “red planet” due to its red atmospheric glow. Interestingly, Mars has the highest mountains in our solar system, Olympus Mons, which are 69,000 feet high! The dusty atmosphere on Mars is incredibly thin, comprised of carbon dioxide, nitrogen and argon. Fascinatingly, there are also traces of oxygen; however, the oxygen on Mars is only 0.2 percent of the gases. In comparison, the Earth’s atmosphere is almost 21 percent oxygen.

Hypoxia is defined as a deficiency of oxygen. This is probably the most common adverse condition of the cornea related to contact lens wear. The cornea is necessarily avascular, which means that it has no blood vessels running through it to supply oxygen. This is important because the cornea is the primary refractive surface of the eye supplying on average +43.00 diopters of power. If the cornea had vessels within it, it would impede the light entering through it, and we would not be able to form crisp images. Instead of the cornea receiving oxygen through vessels, as with the other tissues of our body, it receives its nourishment through the pre-corneal tear film, through vessels that end in loops around the limbus and through the endothelium pumping aqueous into the cornea through deturgesence. Patients that over-wear their lenses are especially susceptible to hypoxia. If one’s eyes are lacking oxygen, new vessels may grow into the cornea. This is called neovascularization. Patients suffering from hypoxia may also have a temporary steepening of their cornea. This may appear conical, almost keratoconus-like. If a patient is exhibiting the signs of hypoxia, it is likely that they will need to reduce their wear time or be re-fit with a lens that permits greater oxygen permeability.

JUPITER

Jupiter is the fifth planet from the sun. It is also the largest of all the planets. The diameter of Jupiter is 11 times larger than that of the Earth. In fact, the mass of all the other planets combined would only amount to approximately 70 percent of Jupiter’s mass.

Scleral contact lenses are large contact lenses that vault over the cornea and rest on the sclera. The average cornea is approximately 11.8 millimeters wide in diameter. Conventional gas permeable lenses are smaller than this and rest on the cornea. Scleral lenses are especially useful in that they form a fluid reservoir between the posterior surface of the lens and the anterior of the cornea. Common conditions that are frequently fit with scleral lenses are keratoconus, irregular astigmatism and severe cases of dry eyes (also referred to as keratitis sicca). Keratoconus is a disease that is characterized by a progressive thinning of the cornea. The cornea will also become increasingly cone shaped as the disease progresses. Irregular astigmatism is when the principal meridians, the steepest and flattest, are not 90 degrees away from each other. Oddly enough, scleral lenses, though gigantic as compared to other lens types, are amazingly comfortable due to their large diameter and lack of lid interaction. Clinically, they provide excellent optics and a safe environment for the cornea. Modern technology has advanced scleral lens design to include brands that offer hybrid hard gas permeable lenses with a soft Hema peripheral skirt. Considering their comfort, utility and visual advantages, these lenses are projected to steadily increase in market share.

SATURN

Saturn is the sixth planet from the sun and is known as the jewel of the solar system for its beauty. Saturn has at least 62 moons that travel around the planet. The largest moon being Titan, which equals 96 percent of the mass that orbits around Saturn. Along with the multiplicity of moons surrounding Saturn are the gloriously famous rings. The rings around Saturn are made of ice, rock and dust particles, with some smaller than a grain of sand and others that are larger than a house. While Jupiter may be the largest of all the planets, Saturn is the second largest and arguably the most magnificent.

While particles around Saturn may be breathtaking, particles embedded into a contact lens matrix can be quite bothersome and problematic. Lens deposition is a constant threat to comfortable and healthy contact lens wear. The most common type of lens deposits is classified as organic. These are proteins, lipids and carbohydrates. There are also inorganic deposits such as calcium salts and phosphates. One common inorganic deposit is affectionately referred to as “jelly bumps.” These are round nodules made of calcium, lipids and cholesterol. Other deposits are environmental such as rust spots from tap water, or iridescence and grease from makeup. The best ways to thwart lens deposits are to practice good hygiene, follow recommended wear schedules and to properly clean, disinfect and store contact lenses. The care of contact lenses was made easier than ever with the advent of multipurpose solutions that clean, rinse and disinfect. Even though these solutions are convenience friendly, there are still a great number of patients who will choose to not follow their prescribed regimen. Frequent follow-up visits with contact lens patients are always the best course. Open-ended questions and the biomicroscope can reveal a wealth of knowledge.

URANUS

Uranus is known as the giant ice planet. It has a surface temperature of -327 degrees Fahrenheit. While the outer layers of the planet are made of hydrogen and helium, there is an icy inner mantle and a rock and iron core. It takes Uranus 84 Earth years to orbit around the sun. One of the most unusual characteristics of Uranus as compared to the other planets is its plane of orbit. All other planets have a nearly perpendicular axis with their orbital plane. Uranus remains tilted to where it effectively rotates on its side. This obscure axial rotation of Uranus can serve to remind us of the various forms of astigmatism that we encounter.

Astigmatism is defined as a deviation from a spherical curve which results in a distorted image. This is because light rays will not all meet at a single focus. Astigmatism manifests itself in the cornea, crystalline lens or both refractive mediums. There are two main categories of astigmatism, regular and irregular. Regular astigmatism is when the principal meridians are perpendicular (90 degrees apart). Irregular astigmatism is where the two principal meridians are not perpendicular (90 degrees apart). Irregular astigmatism is usually caused by trauma or a degenerative disease. Many times, patients with irregular astigmatism will benefit from scleral lenses, but are not usually correctable to 20/20 vision. There are three main types of regular astigmatism, namely with-the-rule, against-the-rule and oblique. With-the-rule astigmatism is when the vertical meridian is the steepest (falls within 30 degrees of the 90-degree axis). With-the-rule astigmatism is the most common type of astigmatism. Against-the-rule astigmatism is when the horizontal meridian is the steepest (within 30 degrees of the 180-degree axis). Oblique astigmatism occurs when the principal steepest meridian does not lie within 30 degrees of the vertical or horizontal axis. The contact lens technician is charged with mapping the curvature of the cornea and matching it with an appropriate lens, all the while making adjustments along the way to compensate for in situ behavior.

NEPTUNE

Neptune is the eighth and final planet in our solar system and was not observed until 1846. It cannot be observed with the “naked eye” due to its extreme distance from the Earth. In fact, Neptune is 2.8 billion miles away from the Earth. It is primarily made of layers of hydrogen, helium and methane with an inner rock core. The methane gas is what makes Neptune appear blue upon observation. The atmosphere of Neptune is also comprised of icy clouds and has the highest recorded wind speeds of all the planets within the solar system. Jupiter, Saturn, Uranus and Neptune are classified as gaseous planets with outer atmospheres comprised primarily of gases, with Neptune being the most distant.

Rigid gas permeable lenses were first common in the market in the late 1970s. Prior to their advent, most of the contact lenses being fit were hard polymethylmethacrylate (PMMA) material. At this time, most patients were transitioned over to the newer gas permeable materials, as they are a much healthier option for the wearer. Patients who wear PMMA lenses for prolonged periods of time generally fall victim to induced corneal distortion. This is generally due to hypoxia, which is a lack of oxygen. Patients who were re-fit in more breathable gas permeable materials, such as fluorinated silicone acrylate, would need time for their corneas to return to their pre-PMMA shape. That is why these patients are generally fit with RGP lenses that more closely resemble their pre-PMMA fitting characteristics. Besides allowing more oxygen transmission than traditional hard lenses, gas permeable lenses offer many other benefits. These lenses offer superior optics, when fit properly, as compared to soft Hema lenses. In fact, spherical gas permeable lenses can even correct for astigmatism of up to 3 diopters. This is in stark contrast to soft lenses, which drape the cornea and must always have a toric design to correct for astigmatism. Furthermore, gas permeable lenses are excellent at resisting surface deposits as compared to newer silicone hydrogel soft lenses. These lenses are also quite durable. Gas permeable lenses have waned in popularity due to the convenience of soft contact lenses, which can be worn intermittently with minimal adaptation time. New daily disposable type lenses are even more convenient as they banish the need for cleaning regimens.

PLUTO

For the sake of my childhood, and because it “just seems right,” we will discuss Pluto even though it was declassified as a planet in 2006 by the International Astronomical Union and is now referred to as a dwarf planet. The reason for this change was largely due to Pluto’s location in space and its relatively small size. In fact, one of the main reasons for the declassification is that Pluto is so small that it is unable to clear objects in outer space that cross its path. Pluto is even smaller than the Earth’s moon!

Lens diameter is the overall width of a contact lens measured from one end to the other in millimeters. Gas permeable lenses range in diameter from 7.0 millimeters to 10.5 millimeters. These are some of the smallest contact lenses. Soft contact lenses are much larger, with an average lens diameter of 14.0 millimeters. Soft contact lenses will completely cover the cornea and lie just beyond the limbal margin, whereas gas permeable lenses fall within the boundaries of the cornea. The diameter of contact lenses is related to many of the fit characteristics of a lens. In fact, the smaller the diameter of a lens, the looser the lens will fit. The opposite of this is also true. As one increases the diameter of a lens, it will also fit tighter. Sagittal depth is defined as the distance between a flat surface and the back surface of the central portion of a lens. Lenses with smaller diameters have less sagittal depth. These lenses will fit looser than lenses with an increased vaulting, or sagittal depth. Also interesting, lenses with larger diameters are often more comfortable than small diameter lenses due to less lid interaction. This is why large scleral lenses with diameters that usually fall within the range of 16 to 20 millimeters are often extremely comfortable.

CONCLUSION

Our solar system is both complex and majestic. The intricacies of our universe reveal the spectacular nature of the world around us. There are many parallels between planetary science and the field of contact lenses—it is all too easy to use the solar system to stimulate and engender an educational vigor for eyecare. Whether using the particles that comprise the mighty rings of Saturn to remind you of contact lens deposition or the dry climate of Venus to contemplate the effects of keratitis sicca, there are many points for mnemonic studies. Just as space exploration continues to uncover new scientific marvels, we are seeing incredible advancements in the contact lens market. These advancements permit us to evolve the way we view contact lens care and provide healthier, more effective lenses for our patients. We can truly “reach for the stars.”