Heavy Eye Syndrome (HES) is a type of acquired strabismus that develops in association with high myopia. It is also called strabismus fixus convergence, myopic strabismus fixus, or highly myopic strabismus.
It is characterized by progressive esotropia and hypotropia with limited abduction and elevation. Atypical cases of exotropia and hypertropia have also been reported.
Epidemiological features:
Differentiation from Sagging Eye Syndrome (SES):
HES and SES are similar strabismus conditions. SES occurs in non-myopic elderly individuals and differs from HES in that it involves esotropia that worsens at distance, bilateral ptosis, and deepening of the eyelid sulcus. For details, see the “Diagnosis and Examination Methods” section.
HES is caused by dislocation of the posterior globe outside the muscle cone due to axial elongation in high myopia, resulting in large-angle esotropia and hypotropia with severe abduction and elevation limitation. SES is caused by age-related degeneration of the LR-SR band in non-myopic elderly individuals, with relatively mild esotropia and minimal movement restriction. The LR-SR angle on MRI is significantly different: 121±7 degrees in HES versus 104±11 degrees in SES 4).
HES is an acquired disease that first becomes symptomatic in adulthood and is not usually seen in childhood.
Axial elongation due to high myopia is the fundamental cause. As the axial length increases, the posterior part of the eye exhibits staphylomatous changes, and the connective tissue band between the superior rectus (SR) and lateral rectus (LR) muscles (SR-LR band) ruptures 1)2).
Disruption of the SR-LR band leads to a cascade of extraocular muscle misalignment.
Not all high myopia leads to heavy eye syndrome. If the elongation of the eyeball is only axial and does not cause superotemporal dislocation, the condition does not develop 4).
Even with high myopia, if the elongation of the eyeball is only axial and does not cause superotemporal dislocation, HES does not develop 4). The development requires morphological changes such as disruption of the SR-LR band and superotemporal dislocation of the posterior eyeball, and cannot be predicted by simple refractive power alone.
Orbital MRI (coronal section) is the most important imaging test for diagnosing HES 1)2). It confirms inferior displacement of the lateral rectus muscle, medial displacement of the superior rectus muscle, and superotemporal dislocation of the eyeball.
The following shows MRI quantitative comparisons (LR-SR angle, globe dislocation angle) among HES, SES, and normal controls.
| HES | SES | Normal control | |
|---|---|---|---|
| LR-SR angle | 121±7 degrees4) | 104±11 degrees4) | — |
| Globe dislocation angle | 179.9±30.8 degrees5) | — | 102.9±6.8 degrees5) |
It is necessary to differentiate HES from diseases that present similar abduction and elevation deficits.
Imaging Findings of HES
Lateral rectus muscle: Deviated downward, with the muscle course shifted inferiorly
Superior rectus muscle: Deviated medially, with the muscle course shifted nasally
Posterior globe: Dislocated from the superotemporal quadrant outside the muscle cone. LR-SR angle 121±7 degrees4)
Imaging findings of SES
Lateral rectus: downward deviation (due to LR-SR band degeneration)
Superior rectus: medial deviation is minimal or absent
Posterior globe: dislocation is minimal. LR-SR angle 104±11 degrees4)
The main differential diagnoses are characterized as follows.
| Disease | Distinguishing features |
|---|---|
| Sagging eye syndrome (SES) | Non-myopic elderly, only lateral rectus inferior displacement, mild esotropia4) |
| Thyroid eye disease (TED) | Eyelid retraction, proptosis, extraocular muscle hypertrophy on MRI4) |
| Sixth cranial nerve palsy | Monocular abduction deficit, no extraocular muscle displacement on MRI4) |
| Duane syndrome | Congenital, globe retraction on adduction, narrowing of palpebral fissure |
| Myasthenia gravis | Fatigability, diurnal variation |
The essence of HES is the deviation of extraocular muscle paths and globe dislocation, which can only be confirmed on coronal MRI. Imaging findings are also essential for differentiating from other causes such as SES and thyroid eye disease. In mild cases, the degree of dislocation varies with eye position, so imaging in multiple directions is recommended.
Once diagnosed by MRI, even if ocular motility limitation is mild and the strabismus angle is small, superior and lateral rectus muscle suturing (Yokoyama procedure) is the first choice.
This is a surgical technique in which the bellies of the superior rectus and lateral rectus muscles are sutured together to reposition the posterior half of the globe, which has dislocated outside the muscle cone, back into the muscle cone.
Suture site
Suture position: 15 mm posterior to the insertion of each rectus muscle
Suture method: Pass the suture twice at different distances from the muscle edge to firmly fix the muscle
Suture material
使用糸：5-0ポリエステル糸
選択理由：不要な組織反応を避けるため、吸収糸は使用しない
追加手術
内直筋後転の適応：眼球が筋錐内に整復されても外転制限が残る場合に追加する
手術順序：上外直筋縫着の後に内直筋後転を検討する
横山法の術後成績： Yamaguchiらは23例でループ筋固定術（±内直筋後転）を施行した5)。術前23例全員で牽引試験陽性→術後陽性は1例のみ。眼球脱位角の減少、最大外転・上転角度の改善、斜視角の減少を確認。平均48.8ヶ月追跡で再発を認めなかった5)。
Additional conjunctival recession: Performed simultaneously if the nasal conjunctiva is contracted.
Medial rectus recession alone provides only temporary effect, and esotropia with hypotropia recurs in the long term. It should be positioned as a procedure added after the Yokoyama procedure as needed.
If MRI does not confirm abnormal muscle course, conventional recession-resection (R&R) is effective, and loop myopexy is unnecessary 4).
Consider referral to a retinal specialist before surgery to check for active retinal pathology in progressive myopic degeneration.
Medial rectus recession alone provides only temporary effect, and esotropia recurs in the long term. The fundamental cause of HES is posterior dislocation of the eyeball and deviation of extraocular muscle paths; superior and lateral rectus suturing (Yokoyama procedure) to reposition them is the first choice. Medial rectus recession is positioned as an additional procedure only when abduction limitation remains after the Yokoyama procedure.
The pathology of HES is formed by a chain reaction: axial elongation → disruption of the SR-LR band → extraocular muscle deviation → eyeball dislocation.
Axial elongation and disruption of the SR-LR band:
In high myopia, as the axial length increases, the posterior part of the eye becomes deformed like a staphyloma. During this process, the SR-LR band is stretched and eventually ruptures1)2). Disruption of the band occurs preferentially in the superotemporal quadrant, where age-related connective tissue degeneration is common.
Quantitative evaluation by MRI:
The ocular dislocation angle is defined by the angle formed by the center of the globe, the lateral rectus muscle, and the superior rectus muscle, and can quantify the degree of dislocation5).
Yamaguchi et al. (2010) measured the ocular dislocation angle in 23 patients with HES5). The mean ocular dislocation angle in HES patients was 179.9±30.8 degrees, significantly larger than 102.9±6.8 degrees in normal controls. This value quantitatively indicates the severity of ocular dislocation in HES.
The degree of inferior displacement of the lateral rectus and medial displacement of the superior rectus can also be measured by MRI, and are used for diagnosis of HES and evaluation of treatment efficacy1)2).
Dual mechanism of mechanical restriction:
Mechanical restriction of abduction and elevation in HES is caused by two factors. The first is anatomical restriction due to deviated extraocular muscle paths, and the second is secondary contracture of the medial rectus muscle due to long-standing strabismus4).
Muscle path and complication risk:
Mechanical stretching and torsion of the optic nerve can block blood flow, leading to ocular ischemia, optic atrophy, and CRAO. The importance of muscle path is emphasized from the perspective of these complication risks3).
The Yokoyama procedure has established efficacy, but improvements toward simpler and more reliable surgical techniques continue.
Several modifications have been reported. An improved method using two sutures to connect the muscle bellies has been reported. A technique applying the Jensen procedure, splitting the upper half of the lateral rectus and the temporal half of the superior rectus for separate suturing, has also been proposed. A method moving the upper half of the lateral rectus and the temporal half of the superior rectus to an intermediate point along Tillaux’s spiral has been reported. Zip-up loop myopexy, a silicone sleeve binding method, and a three-suture SR-LR binding method have also been proposed.
複数の変法が報告されている。ループ筋固定術単独（内直筋後転を同時に行わない）で72%の症例で良好な結果が得られたとの報告がある。同時に内直筋後転を行うアプローチは2回目の手術を不要にする利点があり、術後の斜視角を確認してから内直筋後転を追加する段階的アプローチは全体の手術量を抑制できる利点がある。いずれが優れるかは現在も検討中である。
