BASICS

DESCRIPTION

Presbyopia, literally “old eyes,” is the condition where the ability to see clearly at near is lost due to the gradual loss of accommodation in the aging eye.

EPIDEMIOLOGY

Incidence

100% of population older than 50 years with average age of onset at 45 years.

Prevalence

38% of U.S. population (115 million people).

GENERAL PREVENTION

No evidence that onset of presbyopia can be prevented or delayed with exercises, lenses, vitamins, or diet.

PATHOPHYSIOLOGY

Accommodative amplitude (AA) gradually decreases from childhood to adulthood. From approximately 12 diopters (D) at age 10 years to 10 D at 20 years, 8 D at 30 years, 5 D at 40 years, 2 D at 50 years, and 1 D at 60 years (1), (2), (3)[C].

ETIOLOGY

• Helmholtz theory of accommodation—The long accepted hypothesis, published in 1855, attributes increased focusing power of the lens during accommodation to relaxation of the zonules during ciliary body contraction allowing the lens to assume a more spherical shape. At rest, the ciliary body ring expands increasing zonular tension on the lens equator flattening the lens and decreasing the power for distance vision. Presbyopia is attributed to the hardening of the crystalline lens with age preventing it from changing shape.

• Schachar theory of accommodation—Introduced in 1992, attributes accommodation to relaxation of the anterior and posterior zonules, but increased equatorial zonular tension during ciliary body contraction resulting in peripheral flattening and central steepening of the lens. Presbyopia is attributed to the gradual equatorial growth of the lens with aging effectively decreasing the working distance of the ciliary body (4).

DIAGNOSIS

HISTORY

Patients complain of gradual onset of blurred near vision, especially with small print, dim lighting, after prolonged near work or when fatigued. May also note difficulty changing focus from near to far. The classic complaint is “my arms are not long enough to read anymore.”

PHYSICAL EXAM

• Distance and near acuity depends on presence of any refractive error.

– Emmetropes (patients with no refractive error) and corrected ametropes (patients with refractive error)—clear distance vision with blurred near vision

– Myopes-–clear near vision at a near point determined by the amount of myopia

– Hyperopes—better distance vision than near vision

– Myopic astigmatism—may have some improvement in near vision over distance vision

DIAGNOSTIC TESTS & INTERPRETATION

Diagnostic Procedures/Other

• Goal is to determine the amount of plus power, the “add,” over the distance correction needed to give comfortable clear near vision.

• Age-appropriate adds: Near adds are commonly prescribed without clinical measurement. Prescribing the average add power appropriate for the patient’s age will usually allow clear comfortable near vision for most patients. As a rule, patients are more comfortable with an add that is undercorrected compared with an add that is overcorrected. When prescribing age-appropriate adds consider the patient’s habitual near add and any symptoms. The following is a guide for prescribing age-appropriate adds:

• Near refraction: With near test card at habitual reading distance and distance refraction in place the amount of plus power needed for clear near vision is determined. Range of clear near vision can also be measured and adjusted as needed. More plus moves focus closer, but collapses range of clear near vision. Reducing plus moves near point further away and expands range of clear vision.

• Fused Jackson cross cylinder (JCC) test: With distance correction in place and near target of vertical and horizontal crossed lines at habitual reading distance, JCC lenses introduced binocularly with red axis vertical. Add plus lenses +0.50 D greater than expected age-appropriate add. Patient should report vertical lines are darkest. Reduce plus until reversal and horizontal lines darkest. Midpoint where lines are equal is the amount of plus needed in combination with patient’s accommodation that places focus on target.

• Measuring AA:

– Push up method—Measured monocularly with distance correction in place. Near point of clear vision is determined and converted to diopters (D = 1/M)

– Minus lens to blur—Monocularly with distance correction in place and near card at 40 cm, minus lenses slowly added until 20/40 line blurs. Amount of minus added, +2.5 D for accommodating to 40 cm, equals AA

TREATMENT

MEDICATION

First Line

• As a rule, one half of AA can be used comfortably for extended periods. Total amount of plus power needed to read is determined by the patient’s working distance, usually 40 cm (16”), requiring +2.50 D of power. When AA drops below 5 D, presbyopic symptoms can occur and additional plus power will be needed for near work. For example, if AA is 3 D then 1.5 D can be comfortably provided toward the 2.50 D needed for extended reading. Theoretically, a +1.00 D add together with +1.50 D accommodation would provide the +2.50 D needed to allow comfortable extended near work. This additional plus power can be provided in several ways:

• Glasses:

– Over-the-counter readers—Good for patients without significant astigmatism or anisometropia.

– Single vision near Rx—For patients with good distance vision or unable to adjust to bifocals. Calculated by adding the distance Rx and near add together.

– Bifocals—Advantage of allowing clear distance and near vision without two pairs of glasses. Even advantageous for emmetropes allowing clear distance vision without need to remove reading Rx.

– Lined bifocal—One near focal power limits intermediate vision. Cosmetically less desirable.

Progressive bifocal—Add power increases gradually from distance to full near power at bottom. Provides clear vision at all distances. Cosmetically more acceptable. Can be harder to adjust to, especially for previous lined bifocal wearers. Expensive.

Second Line

• Contacts:

– Monovision—Dominant eye corrected for distance and nondominant eye corrected for near. Compromised clarity and depth perception. High percentage of failures.

– Bifocal contacts—Compromised clarity and depth perception. High percentage of failures although improved newer lens designs result in greater number of satisfied patients.

SURGERY/OTHER PROCEDURES

• All surgical options for presbyopia correction require careful patient selection and patient education.

– LASIK: Monovision correction possible in previously successful monovision contact lens wearers or after successful monovision trial (5)[C].

– Intraocular lenses: With cataract surgery patients have multiple options for presbyopic correction

Monovision—For previously successful monovision contact lens wearers traditional IOLs can be used to achieve monovision correction.

Multifocal and accommodating IOLs—Clear distance, intermediate, and near vision possible. Some dissatisfied patients require lens exchange. Significant cost to patient (6)[C].

• Scleral expansion bands: Increases distance from ciliary body to lens equator to reverse effect of presbyopia. Inconsistent results. Not generally accepted.

ONGOING CARE

PROGNOSIS

Once presbyopic symptoms begin, the process progresses until all accommodation is lost, usually above 65 years of age. At this point, a full add of +2.50 is required for the average reading distance of 40 cm. Adds greater than +2.50 will only decrease the working distance and should not be used unless a reading distance of less than 40 cm is desired due to acuity less than 20/40, occupational needs, or patient has a shorter habitual reading distance.

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