Contact Lenses for Presbyopia (Contact Lenses)

Overview of Contact Lenses for Presbyopia

Presbyopia is a natural change that happens as we age, making it harder for our eyes to focus on things up close. It isn’t due to an error in how our eyes refract, or bend, light. It first starting getting addressed through different types of lenses over seventy years ago.

The first steps towards correcting this were made by Fienbloo in 1938 with the creation of bifocal contact lenses. These lenses have two different focus areas in a single lens: one for things far away and another for things close up. These designs continued to develop over the next few decades with significant contributions from people like Williamson and Freeman.

De Carle proposed a lens that could allow the eye to switch between focusing on near and far objects at the same time in 1957. Around the same time, Wesley and Jessen created a lens with a central area for seeing distant objects, and the surrounding area for seeing closer objects. Jessen then went on to design another lens that can focus on multiple distances which was named the aspheric bifocal contact lens in 1961.

“Why do we need presbyopia-correcting contact lenses?” you might ask. Well, bifocal glasses have their limitations. They require you to tilt your head to see near objects, do not provide a full visual field, and can distort images. Also, constantly switching between regular glasses and reading glasses can be annoying – not to mention that some people may feel self-conscious about age-related changes. Contact lenses can help solve these problems by allowing for clear vision at multiple distances.

Anatomy and Physiology of Contact Lenses for Presbyopia

Why some people lose their ability to focus on objects up close as they age, a condition known as presbyopia, is not fully understood. There are many theories, and most fall into two categories: those that involve changes in the lens of the eye and those that involve parts of the eye outside the lens.

The first group of theories suggests that presbyopia happens because of aging-related changes in the structure and flexibility of the lens, the part of the eye that focuses light onto the retina. Some ideas suggest changes like the lens hardening, the distance between the edge of the lens and the tiny muscles that change its shape getting smaller, and the lens becoming less flexible are the culprits.

Other theories focus on problems outside the lens, such as the small muscles that change the shape of the lens not functioning properly, the connective tissues that link the lens and the muscles losing their flexibility, or changes in the gel-like substance that fills most of the eye.

Let’s take a look at some of these theories:

Helmholtz: This theory suggests that when you look at something far away, the lens is relatively flat. When you try to focus on something close, the muscles around the lens contract and pull the lens into a more rounded shape to increase its focusing power. As you age, the lens may become harder, so it can’t change shape as well, leading to presbyopia.

Coleman: According to this theory, the tiny fibres connecting the lens and the muscles, called zonules, act a bit like the pillars of a bridge. They control the natural curvature of the lens. When these muscles contract to focus on something close up, they create a pressure change in the eye, which alters the lens shape.

Schachar: This theory differs from the others and suggests that when you try to focus on something close, the muscles surrounding the lens contract, which increases the pressure on these zonules and changes the lens shape. As we age, the lens keeps growing but the size of eye’s outer layer remains the same, so these connections may lose their flexibility, affecting the ability to focus.

Also, presbyopia is often associated with lens aging. For example, in early stages (Stage 1) there is a change in lens flexibility which corresponds to the beginning of presbyopia and in later stages (Stage 2) it affects night vision due to a decrease in contrast sensitivity and changes that degrade our vision quality.

Why do People Need Contact Lenses for Presbyopia

When deciding whether glasses are the right choice for a person, there are a few factors to consider. Firstly, we have to think about the individual’s vision needs and what their job involves; certain roles may require good vision, for example. Other important factors include the person’s ability to use both eyes together (binocularity) and their ability to perceive depth (stereopsis).

Then we have to consider the person’s age, as older people may need ‘presbyopic add’, which refers to the addition of lens power in glasses needed to see up close as we age. Additonally, we have to take into account whether the person strongly desires a life without glasses, and whether they are willing to bear the costs associated with using glasses which can be expensive in certain cases. Essentially, we need to determine if the person is motivated to lead a glass-free life.

When a Person Should Avoid Contact Lenses for Presbyopia

There are several reasons why a person might not be able to wear contact lenses. These include:

If someone has dry eyes due to inadequate tear film (fluid on the surface of the eye), contact lenses may cause discomfort.

People with problems affecting the surface of the eye, also known as ocular surface disorders, may find wearing contacts difficult.

If someone has conditions like Ptosis (droopy eyelids), Lid retraction (eyelid pulled back too far), or Lax lids (loose eyelids), they might have trouble wearing contacts.

Other eyelid conditions, like a high-riding lower eyelid or Lid lag (delay in moving the upper eyelid when looking down), can make contact lens use challenging too.

People with numbness in the cornea (the clear front surface of the eye), known as Corneal anesthesia, might not feel comfortable wearing contacts.

Conditions like Sjogren’s Syndrome and Steven-Johnson Syndrome, which can cause severe dry eyes and other problems, may prevent a person from wearing contacts.

Cost can be prohibitive. Contacts, particularly speciality ones, can be expensive.

If someone is allergic to any ingredients in the contact lens solution, they should not wear contacts.

A person with larger pupil size may have issues with fitting and vision quality.

If contact lenses ride too high in the eyes, they might not be comfortable.

Patients who lack motivation in properly caring for and handling contacts are not ideal candidates.

Sometimes, people simply can’t tolerate wearing hard, rigid gas permeable (RGP) lenses due to comfort issues.

Equipment used for Contact Lenses for Presbyopia

Contact Lenses for Age-related Vision Loss

Bifocal Lenses

These kinds of lenses have two parts with varying ‘strength,’ allowing you to see clearly both near and far. They can be made in different types, including Rigid Gas Permeable (RGP) lenses or lenses made from a soft, flexible material called hydrogel. Bifocal lenses can function in one of two ways – either you switch (or ‘alternate’) between different parts of the lens when you look at objects near or far, or both parts work at the same time (referred to as a ‘simultaneous’ or ‘segmented’ design).[2]

Simultaneous Vision Contact Lenses

These lenses let light in from objects that are far away, close up, and at a moderate distance, all at the same time. They provide vision for objects both close and far at the same time, and they don’t move around on your eye. Your brain decides which image is important (distance or near), and ignores the other one.[15] The parts of the lens that correct your vision for near and far are placed directly in front of the pupil (the part of your eye that lets light in). This type of lens can be broken down into three different variations:

– Concentric
– Aspheric
– Diffractive[16]

Benefits

These lenses can be made as rigid gas lenses or soft lenses. They let you see both near and far at the same time—the bigger your pupil is, the better these types of designs work for you. These lenses are affected by light but don’t depend on where you’re looking (or ‘gaze’). They tend to be more comfortable than segmented designs. They are also easier to fit, and work much like single-vision lenses.[17]

Drawbacks

These lenses are not great in dim light and can cause your vision to become blurry, impacting your ability to perceive fine details and variations in brightness (contrast sensitivity). They also depend on the size of your pupil, can make it harder to see at intermediate distances, and can make it difficult to test for an accurate glasses prescription (over-refraction).[18] These lenses can’t be made in a design for people with astigmatism (when your eye isn’t completely round but is more squashed or football-shaped), and can sometimes cause you to see double images (ghosting) or multiple, separated images (double vision) of a single object. These lenses can also make colors seem to separate (chromatic aberration).[19] These lenses can take a while to get used to (weeks to months in some cases), are hard to design, and need to be made very precisely. They are made out of materials with low Dk (a measure of how much oxygen they let through to your eye), have a small optical zone (the area that helps you see clearly) of 5 mm, and need to fit well on your eye to work properly.[20]

Concentric Simultaneous Lenses

These are a type of lens with a clear separation between the areas for seeing near and far. They can be made to make things near or far seem to be in the center of your vision. The different parts can be put on either side of the lens, but they’re usually on the front side. The different parts can be between 3-4mm, and how well the lens works is dependent on the size of your pupil.[21]

Aspheric Bifocal Simultaneous Vision Lenses

This is a type of gradual (or ‘progressive’) lens where the front and back curves of the lens are changed to allow for seeing near and distant objects at the same time. The zones can be put on either side of the lens. There can be a center-distance (C-D) & center-near (C-N) areas.[22]

The curve on the back side of the lens allows for viewing distant objects, while the curve on the front side of the lens allows for viewing near objects. The power of these lenses changes evenly across the lens. These are not true bifocal lenses but improve the depth of vision and the depth of the visual field connected with near vision. These lenses also provide a version of a monovision mechanism, where one eye is corrected for distance and the other for near vision.[23]

Diffractive Lenses

These kinds of lenses have rings like you see in a type of lens called Fresnel prisms. They are made up of multiple zones of increasing size, arranged in circles. These are the best fit for moderate nearsightedness. These lenses provide high-resolution and sharp images. The size of your pupil doesn’t usually affect how well these lenses work. These are high-quality lenses that are easy to fit.[24]

Drawbacks

These lenses don’t work well in dim light and can make driving at night difficult.

Alternating or Translating Bifocal Contact Lenses

These lenses can be made rigid gas-permeable or soft and have a part for reading located away from the center. To see clearly, you should look above for distance and below for near. These lenses usually shift in location so your vision switches between near and far.[25]

Considerations for Fitting Alternating Bifocals

These lenses need a pre-set power for near vision. The size, shape, and height of the near part above the bottom edge of the lens are taken into account. The thickness of the bottom edge of the lens, the balanced addition of a prism (which helps the lens stay in place), the thickness of the vertical middle of the lens, and its stability are also considered.[14]

Benefits

These lenses are great for people who need stronger close-up vision, those who need good depth perception at both distance and near, those who have less tolerance for blurry vision, and those who have not had successful trials with simultaneous lenses.[1]

Drawbacks

The patient may need to adjust their head position, attitude, and movement. The lens should move without changing its focusing power. The movement of the image may be an issue. The lens must move enough to cover most of the pupil with the near part. The lens must shift and recenter quickly. Non-ideal shifting might result in decreased visual acuity (sharpness of vision). This requires a balance between covering the pupil and shifting from looking down to near in down-gaze.[26]

Requirements

– It must cover the pupil.
– The lens must shift from looking down to near in down-gaze.
– The lens must fit properly to the front part of the eyeball.
– The lens must recenter quickly after blinking.
– The lens must be oriented correctly.
– The lens must be centered slightly lower in down-gaze.[27]

Things that might prevent you from using this lens

– Droopy eyelids
– Loose eyelids
– The lower eyelid sits high on the eye
– Large pupil
– Low blink rate
– The lens sits too high on the eye
– Patients who are not motivated
– Lower power needed
– Intolerance to rigid gas permeable lenses
– Activities involving close-up vision are performed with the eyes in their resting position[28]

Guidelines for Fitting Rigid Gas Permeable Bifocal Lenses

– The lens should fit on the flattest part of your cornea.
– The back optical zone diameter (BOZD) must be larger.
– The total diameter must be selected carefully.
– The lens should shift enough over the eye to ensure that the correct area of the lens can cover three-quarters of the pupil area for both distance and near vision.[29]

Monovision

Monovision involves correcting one eye for distance vision and the other for near vision. It works on the understanding that our vision system can reduce the focus of the less important image, and the desired object is seen clearly. In this type of lens configuration, some disruption in binocular vision (both eyes working together) occurs.[30]

Test for Dominant Eye

The main requirement for this test is the person’s arms and hands, and an object k

Preparing for Contact Lenses for Presbyopia

To evaluate your eye health and vision, your doctor will look at several things. These include how clearly you can see at different distances, how your eyes adjust to different amounts of light and distance, your ability to see different contrasts, how well you can see 3D images, your ability to focus on a single image with both eyes, and if you have dysphotopsia – which is an issue that causes you to see flashes of light, halos, or dark spots in your vision.

One standard way to check how well you’re seeing is to measure your high and low contrast visual acuity, which is the sharpness or clarity of your vision, in log Mar units. One study showed that people had better high contrast visual acuity compared to earlier studies with certain types of contact lenses. However, the ability to see clearly up close under high contrast conditions was similar to what’s been found in other research. Depending on the size of your pupils, your doctor might recommend different types of bifocal lenses.

Your eye doctor will also perform a thorough examination of the front and back parts of your eye to make sure there are no problems that might interfere with wearing contact lenses.

When it comes to fitting contact lenses, the strategy depends on how far your presbyopia, or age-related difficulty focusing on up-close objects, has advanced. There are three categories: early, mid, and late cases of presbyopia. Early cases might need simultaneous vision contact lenses which will need full correction in both eyes. The same goes for mid-cases of presbyopia, with the addition of translating contact lenses as an option too. Late cases of presbyopia would require translating contact lenses and monovision contact lenses, where only up-close or distance vision is corrected in one eye. Lastly, simultaneous vision contact lenses with a monovision modification could also be used.

How is Contact Lenses for Presbyopia performed

If you need contact lenses and have presbyopia, which is a condition that makes it hard for you to clearly see things up close, your lenses should be disposable types. It’s important to try these lenses for a while to make sure they work well for you. This trial period should last a realistic amount of time for you to get used to the lenses and provide feedback.

The strength of the lenses used during your trial should be very close to the power you need for your vision. Follow the fitting suggestions made by the lens manufacturer while you’re trying them out. Lenses that are colored or tinted can be easier to handle. You’ll also want to make sure the lenses meet your needs for seeing things up close, at a middle distance, and far away.

Below is a chart indicating suggested lens strengths for patients with presbyopia. It’s based on the patient’s age and whether the lens is for the dominant or non-dominant eye. The ‘Dominant Eye’ is the one that provides a slightly greater degree of input to the visual part of your brain and is more often used when you’re performing actions that need precise focus. And the ‘Non-Dominant Eye’ is the other eye. Remember, these are just suggestions, and your eye doctor will help you make the best decision for your individual needs.

• If you are 46 years old or younger and have +1.25 power add, you need a lens with power 1 for the dominant eye and 1.25 for the non-dominant eye.
• If you are 47-48 years old and have +1.50 power add, you need a lens with power 1 for the dominant eye and 1.25 for the non-dominant eye.
• If you are 49-50 years old and have +1.75 power add, you need a lens with power 1.25 for the dominant eye and 1.50 for the non-dominant eye.
• If you are 51-52 years old and have +2.00 power add, you need a lens with power 1.5 for the dominant eye and 1.75 for the non-dominant eye.
• If you are 53-54 years old and have +2.25 power add, you need a lens with power 1.75 for the dominant eye and 2.00 for the non-dominant eye.
• If you are 55 years old or older and have +2.50 power add, you need a lens with power 1.75 for the dominant eye and 2.25 for the non-dominant eye.

Possible Complications of Contact Lenses for Presbyopia

• Punctate epithelial erosions: These are small spots of damage on the surface of the eye.
• Epithelial abrasions: These are scratches on the surface layer of the eye.
• Epithelial defects: These are areas where the surface layer of the eye is missing or damaged.
• Foreign body defects: These are injuries or damage caused by an object in the eye.
• Dellen: These are small thinned out areas on the surface of the eye.
• Mucin bells: These refer to abnormalities in the formation of the mucus membrane of the eye.
• Microcysts: Small, microscopic sacs filled with liquid that can appear in the eye’s surface.
• Vacuoles: Small, round spaces that appear within cells in the eye.
• Dimple veiling: A form of shadow that appears on the cornea, the clear front surface of the eye.
• Corneal edema: Swelling of the cornea.
• Acute and chronic hypoxia: Lack of adequate oxygen reaching the eye, can be short-term (acute) or long-term (chronic).
• Corneal anesthesia: The inability to feel pain in the cornea.
• Contact lens-induced keratitis: Inflammation of the cornea caused by wearing contact lenses. The inflammation could be due to different kinds of harmful microorganisms like bacteria (Staphylococcal, Pseudomonas), and parasites (Acanthamoeba).
• Sterile infiltrates: Clusters of cells that gather on the surface of the cornea without any present infection.
• Corneal neovascularization: Abnormal growth of blood vessels in the cornea.
• Limbal stem cell deficiency: Condition in which the stem cells in the eye that help to maintain and repair the cornea are insufficient.
• Corneal scarring: Permanent marks on the cornea typically due to injury or infection.
• Corneal warpage: Changes in the shape of the cornea.
• Corneal endothelial damage: Damage to the inner layer of cells in the cornea.
• Blindness: Complete loss of vision.

What Else Should I Know About Contact Lenses for Presbyopia?

Presbyopia contact lenses work differently from regular lenses. They create two focal points at the same time, meaning they don’t have to shift between close and distant focus. These lenses are designed to be symmetrical, so they don’t have to rotate to work properly.

The process of fitting these lenses can be broke down into a few steps:
1. Refraction – measuring how your eye refracts (or bends) light
2. Initial trial of lenses – picking the right lenses based on the refraction measurement and the fit
3. Setting time – waiting about 15 to 20 minutes after putting in the lenses
4. Overrefraction – additional refractive measurements, if needed
5. Near assessment – a test of your close-range vision
6. Send away after a trial – letting you take the lenses home after a trial period

In addition, it’s important to make sure your vision with both eyes is balanced. If you’re given the go-ahead, you may also trial extended-wear lenses that you can leave in for longer periods. The fitting process should also consider both close and distant vision, and give you enough time to adapt to the lenses for best visual performance. The doctor will also check if you are comfortable with single-lens or bifocal lenses. Having one eye set for near and the other for distance, a setup known as monovision, is another option that can be considered.

Lastly, setting realistic expectations before starting the trial fitting is crucial. The success heavily relies on understanding your needs, exploring various lens fitting options, receiving and understanding your feedback, and the enthusiasm of your eye doctor or optometrist.