Continuing Education Activity

Presbyopia is the most common optical error in the eye. It is characterized by a gradual and progressive reduction in the ability to see near. Systemic conditions that affect the integrity of the crystalline lens, like diabetes and chronic inflammatory disease requiring high doses of long-term cortisone therapy, can significantly affect testing and result in erroneous prescriptions. While this condition usually presents at about the age of 40, it may occur earlier or later, depending on the inherent refractive error of the patient. Proper refraction at a distance followed by near refraction can result in the correct power being obtained. This can be dispensed as single-vision lenses, multifocal, or contact lenses. A small percentage of people may opt for refractive surgery. Knowledge of the condition and related complications will help the healthcare team achieve better patient outcomes.

Objectives:

• Describe the pathophysiology of presbyopia.
• Review the embryology of the crystalline lens.
• Identify the signs and symptoms of presbyopia.
• Outline how comorbidities may interfere with proper prescriptions for presbyopia.

Introduction

The faculty and state of being able to qualitatively and quantitatively visualize or see, as well as fine spatial recognition regarding space, constitutes the major backbone of most activities. To achieve this, parallel light rays running via the entrance pupil are focused on the retina after undergoing fine refraction by the ocular refractive apparatus. Like every other tissue, the human crystalline lens undergoes an age-related regression in differentiation, replication, and function depreciation.[1] This subsequently manifests as the gradual reduction in the lens transparency, increased light scatter effect, denaturation of the lens crystallins, and loss of elasticity.[2] 

The human crystalline lens contributes about one-third of the dioptric power in the emmetropic eye. When the ciliary muscle contracts, the elastic nature of the lens fibers enables it to thicken and increase in steepness to produce a change in the dioptric power proportionate to the distance of regard. This ensures a clear, focused image of the object on the retina. This process is known as accommodation, and it is usually measured by assessing the change in the subjective response of a viewer when objects are moved from the far point to the near point (punctum proximum).

Theoretically, the punctum remotum of the eye can be considered as the point where vergence of incoming light results in a maximum of 0. 17 DS stimulus to accommodation. The vergence of light from the punctum remotum is usually considered negligible or zero. There is no blur produced by such vergence of light (in an emmetrope), and this subsequently causes the relaxation of the ciliary muscle and relaxation of accommodation. Dynamic accommodation gradually recedes with age.[3][4] 

The age-related variation of accommodative amplitude is mostly induced by age-related changes in the lens proteins, which mostly influence variation in refractive error in presbyopic adults.[5] Age-related loss of accommodation is a physiological process that accounts for a significant proportion of near-vision impairment in older adults.[6][7] This continuous deposition of lens fibers with time gradually leads to the hardening and loss of the elastic properties of the lens, which eventually culminates in nuclear sclerosis.[8][9]

Anatomy and Physiology

The lens is an avascular, transparent, biconvex structure held in place by the zonular fibers in the posterior chamber. It is located anteriorly to the vitreous and posteriorly to the iris. The crystalline lens is an elliptical structure with a steeper posterior surface than the anterior.[10] 

Embryologically, the development of the crystalline lens begins at the 4 mm stage, or two weeks of gestation, when the optic vesicle induces the differentiation of the surrounding surface ectoderm to form the lens placode. The lens placode is made up of single-layered columnar cells but may appear stratified due to variability in the location of the individual cell nuclei. As the embryonic lens further develops, a small depression appears in the developing lens placode, and at about four weeks, the lens placode begins to invaginate to form the lens vesicle.

The differentiating lens cells are oriented in such a way that the basal aspect of the cell is oriented externally while the apical aspect is directed to the lumen of the lens vesicle. This phenomenon provides for the formation of the lens capsule via the continuous deposition of the basal membrane. As the lens develops, the posterior vesicle cells grow forward into the lumen in such a way that between the 12 mm and 25 mm stages (5 to 7 weeks), the lumen is obliterated, and the previously posterior vesicle cells, which have now moved more anteriorly become the primary lens fibers.

While the posterior vesicle fibers elongate, the anterior vesicle fibers remain unchanged morphologically and eventually end up as the future lens epithelium. Continuous developmental changes include the loss of the primary lens fiber nuclei, the transition of the lens epithelium from columnar to cuboidal shape, and a burst in the lens epithelial proliferative activity ushers in the secondary lens fibers during the 7th week. After that, the continuous proliferative activity of the lens epithelium leads to crystalline lens maturation, which remains continuous after birth.

The crystalline lens is divided into a capsule, cortex, and nucleus.[11] The lens capsule is a thin, transparent enclosure that carries the crystalline lens. It houses the entire lens structure and takes the shape of the lens due to its elasticity. The lens capsule acts as a basement membrane and regulatory passage. It allows the movement of mostly low molecular weight nutrients into the lens body. The suspensory ligaments attached to the pre-equatorial and post-equatorial zones anchor the lens at the equator to the ciliary body. The lens epithelium consists of cuboidal cells which continually differentiate under mitotic scenarios throughout life.[12] 

The lens epithelial cells undergo continuous elongation to reach the anterior and posterior suture, where the apical aspect joins the anterior suture and the basal aspect of the cells joins the posterior suture. Lens fibers are matured epithelial cells which have lost their organelles. Lens fibers are continuously deposited at the center and push older fibers outwards. As measured nasal to temporally, the diameter ranges from 9 mm to 10 mm in adults with an average annual growth of 0.023 mm. The anteroposterior thickness of the adult lens is between 3 mm to 5 mm.[11][13]

The transparency of the crystalline lens is maintained by its avascularity, protein content, nature of the crystalline, and lens fiber arrangement. The crystalline lens obtains its oxygen and glucose supply from the surrounding ocular fluids. Aerobic glycolysis is mostly achieved in the superficial layers of the crystalline lens because the deeper layers contain lens fibers that have lost their cell organelles. Adequate communication between the deeper lens fibers (lens nucleus) and superficial lens cells (capsule, epithelium, and lens cortex) is necessary to ease the flow of nutrients to the deeper lens layers. This communication is mediated via gap junctions formed by the interdigitation of the lens fibers.  

The sodium-potassium ATPase system maintains ionic transport in and out of the crystalline lens. This system, along with water channels known as aquaporins, maintains water homeostasis in the crystalline lens. The systems are influenced by factors such as long-standing hyperglycemia and age. Poor hyperglycemic control puts significant metabolic stress on the lens via intra-lenticular sorbitol build-up, leading to the formation of lens vacuoles with subsequent lenticular opacification.

Indications

Presbyopia is a progressive age-related loss of the ability to focus near objects.[14] The aging crystalline lens is characterized by a gradual progressive loss of transparency, fiber elasticity, and subsequent loss of accommodation.[15] The prevalence and degree of age-related accommodative deficits increase with age, with an estimated 85% of individuals over the age of 40 years developing some degree of age-related accommodative deficits.[14] In 2015 the prevalence of age-related accommodation loss was estimated to be about 1.8 billion globally, which is expected to grow by a sixth of that in 2030.[15][14]

Symptoms such as headache, tearing, ocular discomfort, diplopia, asthenopia, and loss of concentration are usually associated with uncorrected presbyopia.[16] Presbyopia can greatly affect the quality of life.[17] The indication for presbyopic correction can be affected by various factors. Although aging is known as the most important risk factor for presbyopia, other risk factors may include environment, gender, and refractive status.[18][19] It has been shown that women above 40 years present with a higher prevalence of presbyopia compared to men of similar age.[18] 

Refractive errors can affect the age of onset of presbyopic symptoms, prompting intervention and correction. The degree of age-related accommodative deficit varies greatly with the type and degree of refractive error. An uncorrected hyperope of a moderate degree may present with symptoms earlier than an individual with uncorrected myopia of the same degree and age. Consequently, early presbyopia, which refers to the onset of presbyopic symptoms before 40 years of age, tends to be most likely associated with uncorrected hyperopia. Thus, adequate correction of the underlying refractive error is fundamental in the management of presbyopia.

Contraindications

Presbyopia management and prescription glasses can call for reassessment or postponement in conditions that can alter the natural refractive status of the eye. These conditions include metabolic diseases such as diabetes mellitus; long-term chronic use of steroids; ocular trauma and/or surgery; high-order aberrations resulting from cornea ectasias and keratoconus; cornea plana, etc.[20]

Individuals with irregular high astigmatism must first be addressed before any consideration is made for presbyopic correction. Preexisting ocular conditions need to be thoroughly diagnosed and addressed, which include trauma, infection, uveitis, inflammatory conditions, keratitis, glaucoma, surgery, etc. These conditions may require thorough management before the initiation of presbyopic intervention. There may also be other chronic neurological conditions affecting a patient's ability to function visually at near, and these should be considered.[21]

Equipment

The equipment required for the evaluation, examination, and diagnosis of presbyopia includes standard ophthalmic instruments normally used in a routine clinical setting. Generally, visual acuity is first assessed during the ophthalmologic examination, which is defined as the degree to which the visual system resolves fine details.[22]

Visual acuity is an invaluable ophthalmological assessment tool and should be measured for far and near vision.[23] Charts such as the Sloan chart, LogMAR, and even contrast sensitivity chart can be employed to assess visual acuity.[24][25] 

Systemic and ocular health evaluations are necessary clinical procedures that should be performed before any refractive procedure. The slit-lamp biomicroscope is an essential ophthalmic instrument when evaluating and examining ocular health status. The slit lamp tends to be used with accessory instruments such as a Volk lens, goniolens, and Goldmann tonometer, giving the practitioner a good idea of the ocular health status.[26]

After completing the systemic and ocular health evaluation, clinical instruments such as a phoropter, trial lens box, retinoscope, and auto-refractor can be used to determine the refractive status of the eye.[27]

Selecting Frames

The frame selection is an important aspect of ophthalmic dispensing corrective glasses since the frames can be face and prescription specific. When dispensing ophthalmic frames, the lens power, shape of the face, type of lens, pantoscopic tilt, wrap angle, weight, and height of the frame are important factors to address for the best visual performance, optimum fit, and adequate aesthetics.

Personnel

Individuals with presbyopia considering multifocal lenses should choose frames large enough to accommodate distant and near powers. The clinical personnel involved in evaluating, diagnosing, and managing presbyopia may vary across different countries. Eye care practitioners like optometrists and ophthalmologists are usually responsible for the evaluation and management of presbyopia.[19] The services these two professionals provide, however, may differ significantly from country to country.[28]

The national services provided can be greatly influenced by economic status.[29] The improved standard of health care delivery and the rapid technological advancement in the 21st century has heralded longer life expectancy worldwide. Consequently, chronic diseases like glaucoma and age-related macular degeneration are on the rise. Diabetic and hypertensive retinopathy, as well as presbyopia, is expected to increase.[30] Therefore, near visual impairment resulting from uncorrected presbyopia may affect daily activities and quality of life, which may lead to decreased productivity among individuals.[31]

The need for eye care professionals has constantly been increasing in the modern era of aging populations in a digital world. These specialists are needed for timely evaluation, examination, and diagnosis, in addition to the management of presbyopia.[32][33] Age-related accommodative deficits may be more pronounced in hyperopic and emmetropic individuals whose occupations require a high near vision demand. These individuals may experience presbyopia-associated asthenopic symptoms earlier and present to the eye care practitioner earlier than those whose occupation requires minimal acuteness of near vision.

Preparation

The evaluation and examination of the ocular and systemic health prior to refractive procedures is usually the gold standard in clinical care because the age of most presbyopic subjects increases the risk for chronic age-related ocular and systemic morbidities.[34][35]

Some presbyopic subjects may not know their systemic and ocular health status and may be presenting for the first time to the hospital.[36]

Thorough clinical history, which normally initiates the rapport between the patient and the practitioner, can aid in determining the last patient check-up, essential underlying clinical conditions, and ocular risk factors, as well as giving insight into ulterior testing that may be needed for proper diagnosis and treatment.[37]

Technique or Treatment

Various treatment options exist for the treatment and management of presbyopia.[38] The treatment option is determined by the patient's preference, needs, economic status, educational status, accessibility to healthcare facilities and practitioners, occupation, and aesthetics.[14] Spectacles are the commonest employed treatment option, considering availability, cost efficiency, and ease of use.[39]

Contact lenses can be an option based on individual needs and can be considered for patients with preexisting ocular conditions, such as high-order aberrations resulting from cornea ectasias, penetrating keratoplasty, trauma, and healed deep lamellar corneal ulcers. In these cases, therapeutic contact lenses can neutralize a significant degree of astigmatism to improve vision. Contact lenses may also be a personal preference in individuals who do not like using spectacles, in which case thorough patient education is necessary before use.[40] Other options include pharmacological agents such as pilocarpine and multifocal intra-ocular lenses.[41]

The distance refractive correction should be obtained prior to determining the effective dioptric equivalent needed for the presbyopic correction.[42] Proper refractive processes, including fogging during subjective steps and cylindrical refinement, are important.[43] The ADD can be determined by: i) the patient's age (gives a gross value), ii) the positive relative accommodation (PRA) and negative relative accommodation (NRA) test (gives a net value), and iii) the fused cross-cylinder.

Individuals may begin to suffer from presbyopia at about the age of 40 years. Studies have shown that the prescription ADD is about 0.25 diopters every two years from 40 to 50 years old.[44] Presbyopic ADD after the age of 50 years tends to slow down, showing an approximate rate of 0.03 diopters/yearly or about 0.25 diopters/8 years.

Complications

Unexpected negative results associated with presbyopia management usually arise from inadequate clinical work-up, incorrect frame selection, poor optical work and fitting, and wrong treatment options. Systemic conditions may also interfere with the success of presbyopia management and should be properly investigated. These may include systemic and ocular evaluations such as blood pressure, fasting blood sugar, HbA1c, exophthalmometry, intra-ocular pressure, pupil assessment, and anterior and posterior segment assessment.

Patients who may require contact lenses must have optimum blink amplitudes, no existing ocular infection or inflammation, no existing cornea, and conjunctival inflammation, possess adequate tear function, no existing dry eye disease, and, more importantly, be willing to adhere to all clinical instructions including hours of use and proper hygiene. Frames that meet the optical and aesthetic needs of the patient should be selected; however, the optical requirements of a frame should supersede its aesthetic need when selecting an ophthalmic frame.

Clinical Significance

The prevalence of presbyopia is expected to increase steadily due to improved health care and a global increase in life expectancy. Adequate presbyopic correction can address the patient's visual symptoms and improve the quality of life and productivity. It is, therefore, necessary to consider the timely evaluation, examination, treatment, and management of presbyopia, as this could help reduce dependence and improve the overall standard of living.

Enhancing Healthcare Team Outcomes

The widespread prevalence of presbyopia suggests that conventional clinical setting-based examinations may not be able to cater to the magnitude of the need. Large-scale screening programs to address the issue of uncorrected presbyopia are common in both rural and urban settings worldwide. Every participant is therefore important in improving the outcomes of such programs, right from the allied health and support staff, to the dispensing opticians and the clinical teams.[45] 

The protocols must be such that other refractive errors are not ignored in the quest to improve reading abilities in patients.