Contact Lenses for Presbyopia

Anatomy and Physiology

The exact mechanism of accommodation loss in presbyopia remains controversial, and insights into the mechanism still need to be elucidated.[6] The presbyopia theories have been grouped into lenticular and extra-lenticular mechanisms. As per the lenticular theory, presbyopia results from senile changes in the crystalline lens, capsule of the lens, and zonules.[7]

It has been proposed that these changes result from nuclear sclerosis, reduced distance between the equator of the lens and the ciliary musculature, and reduced elasticity of the lens capsule. The other proposed theories are extra lenticular causes such as ciliary muscle dysfunction, loss of zonular elasticity, and decreased resistance of vitreous.[8]

The various proposed theories include

Helmholtz

The classical theory was put forward by Helmholtz nearly a century ago. This theory proposes that when the lens is at rest, it is relatively flat while viewing objects at a farther distance. While accommodating, the ciliary muscles contract and move the zonules both anterior and inwards.[9] The reduction in zonular tension, in turn, causes increased curvature of the elastic lens resulting in increased focusing power. As per Helmholtz, hardening of the lens with age results in reduced elasticity and change of lens shape during accommodation.[10]

Coleman

Coleman proposed the catenary theory. As per the catenary theory, zonules function like pillars of a bridge and regulate the natural curvature of the crystalline lens.[11] The curvature is changed by the opposite pressure changes in the two chambers (anterior and posterior). During accommodation, when the ciliary musculature contract, the curvature becomes steeper, and a pressure change is formed between the anterior and posterior chamber resulting in increased crystalline lens curvature in the central portion and flattening in the periphery.[12]

Schachar

As per Schachar, there is a different theory of accommodation which state that, at the insertion of the zonular fibers, there is a ciliary musculature contraction, which increases the tension of the zonular fibers and the lens capsule, resulting in a shape change of the lens during accommodation.[12] As the lens grows throughout life, equatorially and the scleral dimension remains stable after the first 20 years; this results in a gradual reduction in the elasticity of the zonules. Hence the proposed cause is the increased inability of the ciliary fibers to provide enough zonular tension to change the lens.[12]

Dysfunctional Lens Syndrome

The different stages of lens aging are classified as

Stage 1 -  There is a reduction in rigidity of the lens, corresponding to the stage of presbyopia.

Stage 2 - There is contrast sensitivity reduction and higher order aberrations reduction that affect night vision. This is seen in stages corresponding to the developmental; cataract, which further influences daily living.[13]

Indications

• Visual needs of the patient
• Occupational requirement
• Binocularity
• Stereopsis
• Presbyopic add requirement
• Motivation for a glass-free environment
• The cost involved with glasses
• Motivated patients for glass-free life[14]

Contraindications

• Tear film inadequacy or dry eyes
• Ocular surface disorders
• Ptosis
• Lid retraction
• Lax lids
• High riding of the lower lid
• Corneal anesthesia
• Lid lag
• Sjogren syndrome
• Stevens-Johnson syndrome
• Higher cost
• Allergic to contact lens solution contents
• Larger pupil size
• High riding lenses
• Poorly motivated patients
• Nontolerance to RGP lenses[3]

Equipment

Contact Lenses Available for Presbyopia

Bifocals

These lenses have two portions with different power. These are available in various forms as RGP lenses and hydrogel forms. The fitting of bifocal lenses is either based on the principle of alternating/ translating or simultaneous/ segmented design.[2]

Simultaneous Vision Contact Lenses

The light enters simultaneously from far, intermediate, and near. These lenses simultaneously provide both distant and near vision and are not dependent on contact lens movement. Distance or near one image is selected by eth brain, and the other image is ignored.[15] The distance and near zones of correction are placed ahead of the pupil. These can be further divided as follows:

• Concentric
• Aspheric
• Diffractive[16]

Advantages

These lenses are available as rigid gas lenses and soft contact lens designs. The pupil has simultaneous near and distance vision correction—the larger the pupil, the better the alternating designs. The lenses are light-dependent, but they do not depend on gaze. These are more comfortable than segmented designs. These lenses are easier to fit, and the fitting characteristics are similar to single-vision lenses.[17]

Disadvantages

These lenses are unsuitable for low illumination and give decreased visual acuity and contrast sensitivity. The lenses depend on pupillary size, compromise the intermediate vision and give difficulty in accurate over-refraction.[18] These are not available in the toric form, and ghosting or double vision is a problem sometimes. These lenses also provide chromatic aberration. Simultaneous vision sometimes poses difficulty in adaptation and may take weeks to months for adaptation sometimes.[19] These lenses are difficult to design and require greater precision. These are made up of low Dk materials; these lenses must center well to function well. These lenses also have a small optic zone of 5 mm.[20]

Concentric Simultaneous Lenses

These lenses demonstrate a sharp distinction between distant and near powers. They can be concentric near or concentric distance. The zones can be located on the front and back surface but are primarily designed on the anterior surface. The zone can be between 3 to 4 mm, and the lens functioning depends on the pupil size.[21]

Aspheric Bifocal Simultaneous Vision Lenses

This is a progressive type of contact in which the anterior and posterior surface curvature is altered to allow simultaneous distance and near vision. The zones can be on the front surface as well as the back surface. There can be a center distance (C-D) and center near (C-N) surfaces.[22]

The back aspheric surface allows distance fixation, and the front aspheric surface allows near fixation. The power of these lenses increases or decreases uniformly. These lenses are not true bifocal lenses; they improve the depth of perception and field depth of the retina associated with the near range of the subject. These lenses also provide a modified monovision mechanism approach.[23]

Diffractive Lenses

These lenses have concentric rings, as seen in Fresnel prisms. These lenses are made up of multiple increasing-size zones arranged concentrically. These are the best fit for moderate myopia. These lenses provide high-resolution and sharp images. The pupil size has minimal to no effect on the lens performance. These are good quality lenses that are easier to fit.[24]

Disadvantages

These lenses give poor visual acuity in low ambient illumination, and night driving also becomes difficult.

Alternating or Translating Bifocal Contact Lenses

These lenses can be rigid gas-permeable or soft contact lenses and have a reading segment located away from the center. These patients should look above for distance and below for near, as they have alternate sections. These lenses usually translate so that the vision alternate between distant and near.[25]

Considerations For Fitting Alternating Bifocals

These lenses require a predetermined power for near addition. The size, shape, and height of the near segment above the lens's lower edge are considered. The thickness of the lowest edge of the lens, prism ballast, vertical meridian thickness, and lens stability are other factors in consideration.[14]

Advantages

These lenses are ideal for patients who require higher addition for near, those who need better stereopsis at both distance and near, those with less tolerance for blur, and those who have failed the simultaneous lenses trial.[1]

Disadvantages

The head position, patient attitude, and movement may require a change for the patient. The bifocal lenses should change without significant rotational power. There is an issue with the image jump. The translational movement must be good enough to relocate the near zones of the majority of the pupils. The translational change and re-centration must be faster. The non-ideal translational movement may result in reduced visual acuity.[26]

Requirements

• Pupil coverage
• Translational movement from down to near in down-gaze
• The fitting of the lens to the anterior surface of the cornea must be acceptable
• The post-blink recovery should be rapid
• The orientation should be correct
• The centration must be inferior in downgaze[27]

Contraindications

• Ptosis
• Lax lids
• High riding of the lower lid
• Large pupil
• Low blink rate
• High riding of lenses
• Poorly motivated patients
• Lower power needed
• Intolerance to RGP
• Near-vision activities performed close to the eye in the primary gaze[28]

Rules of Fitting Rigid Gas Permeable Bifocal Lenses

• The lens is made to sit in the flattest K
• The back optical zone diameter (BOZD) must be larger
• The total diameter must be selected carefully
• The lens should move sufficiently over the eye to ensure that the correct area of the lens should be able to cover three-quarters of the pupil area for both distance and near.[29]

Monovision

Monovision is a technique where one eye is corrected for distance, and another is corrected for near. It is based on the principle that the visual apparatus can reduce the central image of focus, and the intended object is seen clearly. In this fitting technique, there occurs some disruption in binocularity.[30]

Eye Dominance Test

The prime requirement for this test is the arms and hands of the subject, and an object kept 3 meters from the subject. In this test, the subject's arms are extended in front of the body, and the hands are clubbed to make a small triangle between the thumbs and the knuckle. With both eyes wide open, the subject looks through the triangle and focuses on a small object. Next, the left eye of the examiner is closed. If the object remains in view, the subject is right-eye dominant, and if the hand moves away from the object and to the left, the subject is left-eye dominant.[31]

Contraindications

• One-eyed patients (corneal scar, amblyopia, Phthisis bulbi, etc.)
• Absence of binocularity
• Reduced stereopsis
• Less or no adaptation to monovision
• Confusion
• Imbalance
• Reduced quality of vision
• Reduced contrasts sensitivity
• Suppression[32]

Difficulties Encountered in Monovision

• Stronger ocular dominance
• Large pupil size poses difficulty
• Intermediate vision reduction if the power is more than two dioptres
• Difficulty in night driving
• Tasks needing smoother shifting of gaze
• Blurred, small, and bright stimulus against a dark background[33]

Advantages

• These are simple lenses to fit
• These lenses are well suited for presbyopes
• The success rate of monovision lenses is approximately 73%
• These lenses are cheaper similar to simultaneous vision lenses
• In uncomplicated cases usually, less time is required
• The monovision lens fitting is simple
• The monovision lenses can also be optimized for distance as well as near
• These lenses are best suited for social or occasional users
• These lenses are accepted or rejected quickly[34]

Disadvantages

• Reduction in stereoacuity
• Reduction in contrast sensitivity
• Reduction in distant acuity
• Loss of clarity for intermediate visual acuity[34]
• The speed of near work is reduced
• These are not a suitable option for amblyopic patients
• These are also not suitable for patients with binocular visual anomalies
• These lenses may cause night vision problems
• These lenses may result in sustained refractive error after a long period of use.[35]

Contraindications

• Issues with binocular vision
• Amblyopia patients
• Low lighting conditions
• Patients with finer visual tasks who require more stereopsis[36]

Guidelines for Monovision Lens Application

• The first step is to identify the dominant eye.
• Correct the maximum distance visual acuity and correct astigmatism of more than 0.75D
• Use disposable contact lenses for a less costly trial
• Change the trial of the eye if required
• The lens should be discontinued if not acceptable[35]
• The correction should start with the least plus lens that provides a clear near vision.
• The aim should be to maximize the spectrum of clear vision
• Newer presbyopes have difficulty in suppressing the power if the difference between the eyes is smaller
• Older patients have difficulty if addition is very high[36]

Factors Considered While Monovision Fitting and Prescription

• Binocular visual acuity testing to assess the effect of the monovision phenomenon on stereopsis
• A good eye for near visual acuity must be selected
• The near power add should be explained to the patient
• Don't compare the two eyes of the patient
• The patient should be educated about vision improvement with time
• Night driving should be avoided
• The patient may require up to 2 to 6 weeks to fully adapt to monovision.[37]

Modified Monovision Strategy

In this technique, the first eye is added with distant correction, and another eye is added with a bifocal lens. The binocularity is improved, and stereo acuity is reduced in these patients. This technique is also of greater use in highly sensitive patients to distant vision.[38]

Preparation

Evaluation

• Uncorrected and corrected distant visual acuity at distance, intermediate, and near 
• Different vergences
• Contrast sensitivity
• Stereopsis
• Binocular single vision
• Dysphotopsia[39]

Visual Acuity

High and low contrast visual acuity in log Mar units is the standard method to assess clinical visual performance. Fernandes et al., in their analysis, showed that the high contrast visual acuity was better compared to earlier studies with proclear multifocal lenses. However, the high contrast near visual acuity was comparable to other studies by Ferrer-Blasco and Madrid-Costa. Consider simultaneous vision bifocals in cases with small pupils, and in patients with large pupils, choose to translate lenses.[40]

A detailed anterior and posterior segment examination must be performed to rule out any ocular pathology that may hamper contact lens applications.

Fitting Strategy Based On Degree of Presbyopia

Technique or Treatment

Contact Lens Fitting Strategies in Presbyopia

The presbyopic contact lenses must be disposable lenses. The trial period of the lenses must be extended and realistic and should be based on patient feedback. The trial lens power must be close to the required power. The manufacturer fitting suggestions should be followed during the trial period. The tinted lenses assist in handling. The near, intermediate, and distant visual performance should be reconciled with the patient's needs.[41] Lens suggested power selections appear in the chart below.[42]

Quattro Suggested the Power Selection for Dominant as well as Non-Dominant Eye

Complications

• Punctate epithelial erosions
• Epithelial abrasions
• Epithelial defect
• Foreign body defects
• Dellen
• Mucin bells
• Microcysts
• Vacuoles
• Dimple veiling
• Corneal edema
• Acute and chronic hypoxia
• Corneal anesthesia
• Contact lens-induced keratitis (Microbial - staphylococcal, Pseudomonas, Acanthamoeba, etc.)
• Sterile infiltrates
• Corneal neovascularization
• Limbal stem cell deficiency
• Corneal scarring
• Corneal warpage
• Corneal endothelial damage
• Blindness[43]

Clinical Significance

In presbyopia contact lenses, both foci are formed simultaneously, so the lens does not have to move. The lens designs are also axially symmetrical, so axial rotation is not a problem. The fitting of the contact lenses can be remembered by the acronym RISONS.

• R- Refraction
• I- Initial trial of lenses depending on the refraction and fitting number
• S- Setting time of a minimum of 15 to 20 minutes
• O- Overrefraction, if needed
• N- Near assessment
• S- Send away after a trial[2]

The patient should undergo an assessment for binocular vision. The fitting recommendation should be followed. The patient should undergo a trial of extended-wear lenses. The balance between near and distance should be maintained. An adequate adaptation time should be allowed to adapt for the patient to have an excellent visual performance. The patients should be carefully screened for single-lens wearers and bifocal lenses. Monovision should be kept as a second option.[30]

The patient should have realistic expectations before starting a trial fitting. The success of the patient depends on understanding the patient's needs, using a wide range of contact lens fitting options, understanding and listening to patient feedback, and the enthusiasm of the treating ophthalmologist or the optometrist.[44]

Enhancing Healthcare Team Outcomes

Any patient presenting to the clinic with complaints of defective near vision should be meticulously evaluated to rule out any other ocular pathology. The patient must be made to understand what presbyopia is and what are the management options.[1]

Patients willing to use contact lenses should be counseled in detail regarding the contact lenses available and the benefits of one lens over the other. Patients should be explained about contact lens complications and the need to maintain ocular hygiene while applying contact lenses. The examining ophthalmologist, optometrist, and nursing team play a key role in the meticulous management of these patients. The patient should understand that they will require a change of presbyopic correction with age, and there will be a need for contact lens change in the future.[43]

Nursing, Allied Health, and Interprofessional Team Interventions

The nursing, allied health staff, and interprofessional team help in patient management by counseling, recruiting the patients to contact lens clinics, and explaining the pros and cons of contact lens wear.[45]

Nursing, Allied Health, and Interprofessional Team Monitoring

The nursing, allied health staff, and interprofessional team help monitor the patients to determine whether they are wearing contact lenses correctly, explain and check for contact lens hygiene, and check for contact lens fit and cornea condition.[45]