bubble_chart Overview

An eye at rest focuses parallel light rays behind the retina, which is called farsightedness (hypermetropia, hyperopia). In such an eye, the optical focus lies behind the retina, resulting in a blurred image on the retina. To see distant objects clearly, the eye must use its focusing power to shift the focal point from behind the retina onto the retina. As a result, farsighted eyes are constantly in a state of adjustment, making them prone to eye strain.

bubble_chart Etiology

The most common type of farsightedness is axial farsightedness, where the anterior-posterior axis of the eye is shorter than that of an emmetropic eye. This is one of the more prevalent refractive errors. At birth, the average axial length of the human eye is about 17.3mm, and from the perspective of axial length, almost all infants are farsighted, making infantile farsightedness a physiological condition. As the infant's body develops, the anterior-posterior axis of the eye gradually lengthens, and by adulthood, the eye should become emmetropic or nearly emmetropic. However, during ocular development, some individuals may experience halted eyeball growth due to intrinsic (genetic) or extrinsic environmental factors, preventing the axial length from reaching the normal adult size. As a result, they retain the axial length of an infant or young child into adulthood, which is termed axial farsightedness. Conversely, excessive growth during development results in myopia. True emmetropia with zero refractive error is rare.

Generally, the degree of axial shortening in human farsighted eyes is not very significant, rarely exceeding 2mm. According to optical calculations, every 1mm reduction in axial length corresponds to approximately a 3D change in refractive error. Thus, farsightedness exceeding 6D is uncommon. However, high degrees of farsightedness do exist, and some eyes may exhibit farsightedness as high as 24D without any accompanying pathological changes. In cases of pathological developmental abnormalities, such as microphthalmos, the degree of farsightedness can even exceed 24D.

Shortening of the anterior-posterior axis can also occur in pathological conditions. For example, ocular tumors or inflammatory masses in the orbit may cause inward invasion of the posterior pole of the eye, flattening it. Additionally, retrobulbar neoplasms or edema of the ocular wall tissues can displace the macular region of the retina forward. A more severe scenario can arise from retinal detachment, where the displacement may be so extreme that the retina contacts the posterior surface of the lens, resulting in even more pronounced refractive changes.

Another cause of farsightedness is curvature-related farsightedness, which arises when the curvature of any refractive surface in the eye's optical system is flatter than normal. The cornea is particularly prone to such changes, as seen in congenital flat corneas or those altered by trauma or corneal diseases. From an optical perspective, every 1mm increase in the corneal radius of curvature corresponds to an increase of 6D in farsightedness. In such cases, very few corneas remain perfectly spherical, and most are accompanied by astigmatism.

The third type of farsightedness is refractive index-related farsightedness, caused by a reduction in the refractive power of the lens. This can result from physiological changes associated with aging or pathological changes induced by diabetes treatment. Posterior dislocation of the lens may also lead to farsightedness, which can be congenital or caused by ocular trauma or disease. Furthermore, the absence of the lens (aphakia) can result in high degrees of farsightedness.

bubble_chart Pathogenesis

Farsightedness Optical State of the Eye: {|###|} Regardless of whether farsightedness is caused by a shortened axial length of the eye, reduced curvature of the refractive surfaces, or a decrease in refractive index, the optical effects are the same. Parallel light rays from infinity converge behind the retina, forming a blurred image on the retina [Figure 1(2)]. Due to the shortened axial length, the retina moves closer to the nodal point, resulting in a smaller image compared to an emmetropic eye (Figure 2). In an emmetropic eye, light emitted from the macula on the retina becomes parallel after refraction by the eye's optical system. In other words, the macula of an emmetropic eye and infinity are conjugate focal points, so an emmetropic eye requires no accommodation to see distant objects. In contrast, light emitted from the macula of a farsighted eye diverges, and its conjugate focal point lies behind the eyeball, forming a virtual focus. Since converging light does not exist naturally, a farsighted eye at rest cannot see any object clearly (Figure 3). To converge the light, two methods can be employed: first, by the eye's own accommodative effort [Figure 1(3)], and second, by wearing convex lenses [Figure 1(4)]. {|###|} {|###|} {|###|} Figure 1 Farsightedness Eye {|###|} (1) Emmetropic eye: Parallel light converges on the retina; (2) Farsighted eye: Parallel light converges behind the retina; (3) Farsighted eye: Due to lens accommodation, parallel light converges on the retina; (4) Farsighted eye: Placing a convex lens in front of the eye substitutes for accommodation, allowing parallel light to converge on the retina. {|###|} {|###|} {|###|} Figure 2 Image Size in Farsighted, Emmetropic, and Myopic Eyes {|###|} AB is the object; N is the nodal point; ab is the inverted image formed on the retina by light rays from A and B passing through N; H is farsightedness, E is emmetropia, M is myopia; 3 > 2 > 1. {|###|} {|###|} {|###|} Figure 3 Light Emitted from a Farsighted Eye Extends Behind the Eyeball, Forming a Virtual Focus R {|###|} Accommodation in Farsightedness: {|###|} Accommodation is the eye's evolutionary adaptation for viewing near objects or fine details. An emmetropic eye at rest forms a clear image of distant objects on the retina. For near objects, the incoming light diverges and forms an image behind the retina, resulting in a blurred retinal image. This blur stimulates the visual cortex, triggering a visuomotor response that excites the ciliary muscle (innervated by the third cranial nerve), the pupillary sphincter, and the medial rectus muscle, leading to the triad of accommodation, convergence, and miosis—collectively known as the near reflex. Among these, accommodation is the primary mechanism. In farsightedness, the eye's shorter axial length or weaker refractive power causes even parallel light from infinity to focus behind the retina, producing a blurred image. This blur, similar to that in an emmetropic eye viewing near objects, generates a visuomotor stimulus in the visual cortex, inducing accommodation to shift the image forward and achieve clarity on the retina. The accommodation used by an emmetropic eye for near vision is termed physiological accommodation, while that used by a farsighted eye is called non-physiological accommodation. A farsighted eye must accommodate to see any object, linking accommodation closely to farsightedness. Based on the role of accommodation, farsightedness can be classified into latent farsightedness and manifest farsightedness, with the latter further divided into facultative farsightedness and absolute farsightedness.

bubble_chart Pathological Changes

Generally speaking, the eyeball of a farsightedness eye is smaller. This reduction in size is not only evident in the anteroposterior axis but also in all other axes. The corneal membrane of highly farsighted eyes is also small. Since the shape of the lens does not change significantly, the lens appears relatively larger compared to the shrunken eyeball, leading to a shallower anterior chamber. This makes such eyes more prone to glaucoma, a point that should be noted when using mydriatics. Highly farsighted eyes may exhibit developmental deformities, such as microphthalmos. However, a small eyeball does not necessarily indicate farsightedness; the key factor is the alignment between the anteroposterior axis of the eyeball and its refractive system. If the refractive power of the eye's optical system increases while the eyeball shrinks, it may not necessarily result in farsightedness.

Fundus examination of a typical farsighted eye may reveal a distinctive retinal membrane, characterized by a special sheen caused by reflection, known as the retinal sheen ring. The optic disc may exhibit a unique appearance resembling optic neuritis, hence termed pseudopapillitis. The disc appears dark red with slightly blurred and irregular edges. Outside the blurred area, it may sometimes be surrounded by a gray halo or by radiating streaks extending from the margins, further obscuring the edges. A crescent-shaped change is often observed below the optic disc. These changes are generally considered congenital and do not significantly impair vision. In addition to enhanced vascular reflections, abnormal vascular tortuosity and irregular branching may also be observed. Such ocular changes should be carefully examined to avoid misdiagnosis. When unilateral high farsightedness occurs, the ipsilateral side of the face often exhibits poor development, resulting in facial asymmetry. Asymmetrical development is also commonly observed in the eye itself, and most such farsighted eyes are accompanied by astigmatism.

bubble_chart Clinical Manifestations

High hyperopia eyes, because they cannot clearly see any external objects, exhibit more pronounced visual symptoms. Grade I hyperopia eyes can overcome their refractive defects using accommodative power and may show no visual symptoms at all. Adolescents have strong accommodative power, so even moderate hyperopia may not cause any visual symptoms. Hyperopic eyes not only require accommodation to correct refractive defects for distance vision but also need additional accommodative power for near vision. Therefore, the subjective visual disturbances in hyperopic eyes often first manifest when viewing near objects. For example, while an emmetropic eye uses 3.00D of accommodation to focus on an object at 33cm, a 2.00D hyperopic eye requires 5.00D of accommodation to achieve the same optical effect. When the degree of hyperopia is very high and the accommodative power is insufficient to correct the refractive error, another scenario may arise: the eye compensates by enlarging the image to enhance object recognition. Occasionally, hyperopic patients may hold reading materials very close to their eyes, which, if not carefully observed, might be mistaken for myopia—a phenomenon termed "hyperopic myopic behavior." Such excessive use of accommodation can quickly lead to fatigue. Even with mild hyperopia, advancing age or physical and mental exhaustion can impair accommodative ability, resulting in blurred vision, especially after prolonged near work. Temporary cessation of visual tasks and short breaks for the ciliary muscles are necessary to restore clear vision. Asthenopia is the most common symptom of hyperopia, often accompanied by headaches, dizziness, and physical or mental discomfort. If asthenopia persists for too long, temporary ciliary muscle paralysis may occur, causing significant visual impairment. Alternatively, spasmodic contraction of the ciliary muscles may induce pseudomyopia. The dissociation between accommodation and convergence can manifest in two ways: accurate accommodation paired with excessive convergence, or insufficient accommodation paired with appropriate convergence. However, the former tends to be the general trend in hyperopia, as it provides more satisfactory vision—sacrificing binocular vision to achieve clarity in one eye. Consequently, the habit of relying on the better eye while neglecting the other may develop, leading to esophoria or esotropia.

bubble_chart Treatment Measures

Generally speaking, grade I farsightedness does not require correction if it does not cause visual impairment, asthenopia, or strabismus, and if overall health is good. Conversely, if any of these conditions are not met, appropriate glasses should be worn for correction. In principle, refraction should be performed under cycloplegia, and convex lenses should be prescribed to correct the refractive error. This is particularly necessary for young children and adolescents. For children under 7 years old, grade I farsightedness is a physiological phenomenon and does not require glasses. However, if the degree is too high, vision is reduced, or strabismus is present, glasses should be prescribed for correction. For students aged 7 to 16, even low degrees may warrant glasses, and correction is mandatory if asthenopia, reduced vision, or strabismus occurs. For adults with farsightedness, initial prescriptions should not fully correct the condition, as the ciliary muscles, due to long-term overuse, may have developed hypertrophy. Complete relaxation in a short period is often difficult, so gradual correction is advisable. When retinoscopy is performed under cycloplegia, the corrective lenses should be slightly weaker than the actual measured degree to accommodate the physiological tension of the ciliary muscles. There is no fixed rule for the degree of reduction, but a reasonable approach is to add one-fourth of the latent farsightedness to the measured degree as the correction standard. However, each case should be handled individually, taking into account factors such as the patient's tolerance of the prescribed lenses (based on visual acuity), age, clinical symptoms, balance of extraocular muscle function, general physical and mental state, and occupation. Ultimately, the goal is to ensure the glasses provide the most comfortable vision. For elderly individuals, when all farsightedness becomes fixed, glasses are needed for both distance and near vision, but retinoscopy under cycloplegia is unnecessary.