Step 1: Prepare Corrected Vision
Perform the check while wearing your usual glasses or contact lenses. Doing it with bare eyes may mix in difficulty seeing due to refractive errors, preventing accurate evaluation.
Self-Check for Vision Loss (Importance of Checking One Eye at a Time)
Key points at a glance
Section titled “Key points at a glance”1. What is a self-check for vision loss?
Section titled “1. What is a self-check for vision loss?”Among self-check methods for detecting vision loss, the most important is checking each eye individually (monocular check).
In daily binocular vision (seeing with both eyes open), the better eye compensates for the worse eye. Therefore, diseases that progress unilaterally are often not noticed, leading to delayed consultation. Glaucoma, age-related macular degeneration, and retinal detachment often start and progress in one eye, and are easily missed due to the compensatory effect of binocular vision.
According to a nationwide survey of causes of new visual impairment certifications in Japan (Morizane 2019), glaucoma, diabetic retinopathy, and age-related macular degeneration are the leading causes of acquired blindness1). All of these have few subjective symptoms in the early to middle stages, and early detection through self-checks and regular eye examinations is key to preserving visual function.
Glaucoma prevalence and undiagnosed rate
Section titled “Glaucoma prevalence and undiagnosed rate”The Tajimi Study (Iwase 2004) reported that the prevalence of primary open-angle glaucoma in Japanese people aged 40 and over is about 5%2). Of these, normal-tension glaucoma accounts for about 72%, and visual field defects progress even when intraocular pressure is within the statistically normal range2). The majority of affected individuals remain undiagnosed and untreated, and regular examinations including evaluation of the optic nerve and visual field, not just intraocular pressure measurement, are necessary.
Q
How often should I perform a monocular check?
A
It is desirable to make it a habit about once a week. For example, it is easier to continue if you get into the habit of checking each eye when looking at a calendar or before going to bed. For those aged 40 and over, an annual eye examination is also recommended3). If there is a family history of glaucoma or age-related macular degeneration, consider more frequent self-checks and earlier ophthalmology visits.
2. Specific Methods for the One-Eye Check
Section titled “2. Specific Methods for the One-Eye Check”The one-eye check can be performed without special equipment. Follow these 4 steps.
Step 2: Gently Cover One Eye
Gently cover one eye with the palm of your hand. Be careful not to press on the eyeball. Check each eye alternately.
Step 3: Check Distance and Near Vision
Distance: Check the text on a TV screen, calendar, or wall clock with each eye individually. Near: Check text in a book or smartphone with each eye individually.
Step 4: Evaluate Differences Between Eyes
Check for obvious differences in visual acuity, visual field, or distortion between the left and right eyes. Pay attention to changes such as “text appears missing when viewed with one eye,” “straight lines appear distorted,” or “the edge of the visual field is dark.”
Check Points
Section titled “Check Points”- Distance check: Use TV captions, wall calendars, clock hands, advertisement text, etc., as targets with straight lines or fine print.
- Near check: Reading, smartphone text, graph paper, chess notation, etc. Grid-like materials make distortion easier to detect.
- Visual field check: While facing forward, check for any missing areas in the peripheral vision (nasal side, ear side, top, bottom).
- Checking the difference between the left and right eyes is the most important criterion.
Q
Can I check while wearing contact lenses or glasses?
A
It is recommended to check with your usual correction (wearing glasses or contact lenses). Checking with bare eyes makes it impossible to distinguish difficulty seeing due to refractive errors (myopia, hyperopia, astigmatism) from that due to eye disease. By checking with corrected vision, you can evaluate differences between eyes based on your true vision.
3. Self-check of the macula using the Amsler chart
Section titled “3. Self-check of the macula using the Amsler chart”
Nowak JA, et al. Multimodal Imaging in Age-Related Macular Degeneration. Medicina (Kaunas). 2023;59(4):647. Figure 2. PMCID: PMC10144202. License: CC BY 4.0.
Color SLO fundus photograph (A) shows numerous small to medium-sized yellow drusen deposits in the macula, typical of early AMD. This corresponds to age-related macular degeneration discussed in the section “Self-check of the macula using the Amsler chart.”
The Amsler grid is a standardized self-test tool consisting of grid lines and a central point. It is used to detect abnormalities in the macula (the central part of the retina).
Guide to test results
Section titled “Guide to test results”| Amsler finding | Suspected condition | Action guide |
|---|---|---|
| All grid lines appear straight | Likely normal | Continue regular checks |
| Lines near the center appear wavy or distorted | Possible macular disease (e.g., age-related macular degeneration, epiretinal membrane)4) | See an ophthalmologist within a few days |
| A dark spot (blind area) in the center | Possible macular lesion | See an ophthalmologist promptly |
| Part of the grid is missing or cannot be seen | Possible retinal disease or glaucoma | See an ophthalmologist promptly |
| Lines appear blurry or hazy | Possible cataract or refractive error | Get a thorough eye exam |
Sensitivity and Limitations of the Amsler Grid
Section titled “Sensitivity and Limitations of the Amsler Grid”A systematic review of the Amsler grid for age-related macular degeneration (AMD) screening (Faes 2014) reported a sensitivity of approximately 70% for detecting metamorphopsia within the central 5 degrees 4). While useful for detecting metamorphopsia (distorted vision), false negatives can occur with small lesions or atypical AMD 5).
The Amsler grid is not perfect, and it is important to note that a negative result does not rule out problems 5). Especially in high-risk individuals (e.g., family history of AMD, history of drusen), it is important to combine it with regular eye examinations.
For quantitative assessment of metamorphopsia, M-CHARTS (metamorphopsia quantification charts) are useful, allowing objective measurement of metamorphopsia in epiretinal membrane, macular hole, and age-related macular degeneration 6).
Q
Where can I get an Amsler grid?
A
They are often distributed at ophthalmology clinics. Printable templates are also available on the official websites of the Japan Ophthalmologists Association, ophthalmology societies, and eye disease awareness sites. Some smartphone apps include Amsler grids for self-checking. However, since screen resolution and display size can affect test accuracy, it is preferable to use a standard printed chart.
4. Main Eye Diseases That Can Be Detected by Self-Check
Section titled “4. Main Eye Diseases That Can Be Detected by Self-Check”The following are major eye diseases that may be detected through monocular checking and the Amsler grid.
| Symptoms/Findings | Suspected Main Disease | Urgency |
|---|---|---|
| Blurred vision (hazy) / glare | Cataract | Low (regular checkup) |
| Visual field defect (gradual) | Glaucoma 2) | Moderate (early visit) |
| The center appears distorted or dark | Age-related macular degeneration, epiretinal membrane4) | Moderate (early visit) |
| Sudden increase in floaters | Posterior vitreous detachment, retinal tear | Moderate to high (early to same-day visit) |
| Curtain-like shadow or visual field defect | Retinal detachment | High (same-day visit) |
| Sudden vision loss | Central retinal artery occlusion, ischemic optic neuropathy, etc. | High (same-day visit) |
| Vision loss + floaters (diabetic patients) | Diabetic retinopathy, vitreous hemorrhage7) | Moderate to high |
| Strong myopia with visual field defects | Myopic glaucoma / myopic macular degeneration8) | Moderate (early visit recommended) |
Characteristics of Major Diseases
Section titled “Characteristics of Major Diseases”Cataract: The most common cause of vision loss in people over 50. Clouding of the lens is perceived as blurred vision or glare. Often bilateral but may have asymmetry.
Glaucoma: Visual field defects progress gradually. Central vision is preserved until the late stage, so detection is delayed without monocular testing2). About 72% of glaucoma in Japanese people is normal-tension glaucoma, which can develop and progress even with normal eye pressure.
Age-related macular degeneration: Main symptoms are metamorphopsia (straight lines appear wavy) and central scotoma. Often unilateral, making metamorphopsia difficult to notice with binocular vision4). The Amsler chart is effective for early detection.
Diabetic retinopathy: Regular fundus examinations are essential for diabetic patients7). Initially asymptomatic; when vision loss is noticed, the disease is often advanced.
Retinal detachment: Typical symptoms include a sudden increase in floaters, photopsia (flashes of light), curtain-like shadow, and visual field defect. May require emergency surgery; same-day consultation is necessary.
5. Timing of Consultation and Urgency Criteria
Section titled “5. Timing of Consultation and Urgency Criteria”The following are criteria for deciding when to seek medical attention based on self-check results.
Three-level classification of urgency for consultation
Section titled “Three-level classification of urgency for consultation”| Urgency level | Examples of symptoms and findings | Recommended action |
|---|---|---|
| Same-day consultation | Sudden vision loss, curtain-like shadow, rapid increase in floaters, photopsia, severe eye pain | Visit an ophthalmology emergency or specialist clinic on the same day |
| Early consultation (within a few days) | Difference in vision between eyes, distortion or missing area on Amsler grid, worsening chronic blurred vision or glare | Visit an ophthalmologist within a few days |
| Regular consultation (planned) | No subjective symptoms but age 40 or older, risk factors, or family history | Eye examination at least once a year1)2) |
Recommended Candidates for Regular Checkups
Section titled “Recommended Candidates for Regular Checkups”- General adults aged 40 and older: The prevalence of glaucoma, cataracts, and age-related macular degeneration increases with age. Annual eye examinations are recommended2).
- Family history of glaucoma: Having a first-degree relative with glaucoma increases the risk by approximately 3 to 9 times1). Consider regular checkups starting before age 40.
- Patients with diabetes: Undergo a fundus examination immediately after diagnosis and continue at least once a year thereafter4).
- High myopia (≥ -6 D): Pathological myopia increases the risk of glaucoma, retinal detachment, and macular degeneration; regular checkups are recommended5).
Q
I notice a difference in vision between my eyes when using one eye at a time, but there is no pain. Should I see a doctor immediately?
A
Even without pain, a difference in visual acuity or visual field between eyes is an important sign. Glaucoma, age-related macular degeneration, and retinal diseases all progress painlessly. If you notice a difference between eyes, we strongly recommend seeing an ophthalmologist within a few days. Do not assume that “no pain means no problem”—early detection is directly linked to better treatment outcomes.
6. Why Monocular Check Is Important (Pathophysiological Background)
Section titled “6. Why Monocular Check Is Important (Pathophysiological Background)”
Hommer N, et al. Visual field defects in glaucoma with and without normal-tension. BMC Ophthalmol. 2021;21:343. Figure 2. PMCID: PMC8459489. License: CC BY 4.0.
Visual fields of a glaucoma patient showing localized defects on central static perimetry (left) and peripheral kinetic perimetry (right). These correspond to the nasal visual field defects in glaucoma discussed in the section “Why Monocular Check Is Important (Pathophysiological Background).”
The importance of monocular checking stems from the neurophysiological compensatory mechanism of binocular vision.
Compensatory Mechanism of Binocular Vision
Section titled “Compensatory Mechanism of Binocular Vision”The human visual system integrates information from both eyes in the brain (primary and higher visual cortices). Even if the visual acuity or visual field of one eye declines, input from the other eye compensates, so mild to moderate monocular abnormalities often go unnoticed during daily binocular vision.
This compensation leads to oversight especially in the following situations:
- Nasal visual field defects in glaucoma: Unless the visual field defects in both eyes perfectly overlap, the other eye compensates for the defect in one eye. Central visual acuity is preserved until the late stages, so awareness is significantly delayed1).
- Metamorphopsia in age-related macular degeneration: Even if there is distortion in the center of one eye, the other normal eye takes over central vision, making it difficult to notice metamorphopsia in daily life3).
- Superior retinal detachment: When the upper part of the retina detaches, the lower visual field is lost, but this is compensated by binocular vision. Monocular checking when noticing a sudden increase in floaters or photopsia contributes to early detection.
Risk of missing normal-tension glaucoma
Section titled “Risk of missing normal-tension glaucoma”According to the Tajimi Study, approximately 72% of glaucoma in Japanese people is normal-tension glaucoma (progression even with intraocular pressure ≤21 mmHg)1). Detection is difficult with intraocular pressure measurement alone; regular examinations combining optic disc observation, OCT RNFL evaluation, and visual field testing are necessary. Even if intraocular pressure is normal, visual field defects progress, leading to a false sense of security that “pressure is normal so there is no problem.” Regular monocular checking to notice differences or changes in visual field between eyes can trigger a visit to the doctor.
Bilateral symmetry in age-related macular degeneration
Section titled “Bilateral symmetry in age-related macular degeneration”Exudative AMD generally starts in one eye, and the affected eye may precede the fellow eye. Since both eyes rarely develop simultaneously, monocular Amsler grid checking is recommended to detect metamorphopsia or scotoma early in one eye3).
7. Latest perspectives and self-monitoring tools
Section titled “7. Latest perspectives and self-monitoring tools”Smartphone-based self-check of visual acuity and visual field
Section titled “Smartphone-based self-check of visual acuity and visual field”Development and validation of a visual acuity test app (Peek Acuity) using smartphones is progressing. Its usefulness as an ophthalmic screening tool in rural areas or regions with limited medical resources has been reported, and clinical validation shows good correlation with conventional methods6). However, managing smartphone screen resolution, brightness, and measurement distance is difficult, and accuracy is inferior to facility-based testing. The current recommendation is to use it only as a supplementary reference tool.
Home monitoring device (ForeseeHome)
Section titled “Home monitoring device (ForeseeHome)”ForeseeHome is a home visual monitoring device for patients with age-related macular degeneration. In the HOME study (Chew 2014) RCT, the group using ForeseeHome detected conversion to exudative AMD earlier and significantly suppressed vision loss compared to conventional outpatient monitoring7). It is FDA-approved, and research for its adoption in Japan is ongoing.
AI-assisted fundus screening
Section titled “AI-assisted fundus screening”Automated diagnosis of fundus images using deep learning is rapidly moving toward practical application. In a 2016 Google study by Gulshan, a deep convolutional neural network was shown to detect diabetic retinopathy with sensitivity and specificity equal to or greater than that of ophthalmologists 8). In the future, simple fundus photography systems combined with smartphone cameras and self-screening using AI interpretation are expected to become a reality.
Importance of Awareness Activities
Section titled “Importance of Awareness Activities”The Japan Ophthalmologists Association conducts awareness activities centered on “Eye Care Day” (October 10), recommending regular eye examinations for people aged 40 and older 9). To encourage ophthalmology visits even when patients are unaware of vision loss, continuous patient education and social awareness activities are essential.
8. References
Section titled “8. References”- Iwase A, Suzuki Y, Araie M, et al. The prevalence of primary open-angle glaucoma in Japanese: the Tajimi Study. Ophthalmology. 2004;111(9):1641-1648.
- 日本眼科医会. 40歳を過ぎたら目の定期検査を（啓発資料）. 2020.
- Faes L, Bodmer NS, Bachmann LM, et al. Diagnostic accuracy of the Amsler grid and the preferential hyperacuity perimetry in the screening of patients with age-related macular degeneration: systematic review and meta-analysis. Eye (Lond). 2014;28(7):788-796.
- 日本糖尿病眼学会. 糖尿病網膜症診療ガイドライン（第1版）. 日眼会誌. 2020;124(12):955-981.
- Ohno-Matsui K, Lai TY, Lai CC, et al. Updates of pathologic myopia. Prog Retin Eye Res. 2016;52:156-187.
- Bastawrous A, Rono HK, Livingstone IA, et al. Development and validation of a smartphone-based visual acuity test (Peek Acuity) for clinical practice and community-based fieldwork. JAMA Ophthalmol. 2015;133(8):930-937.
- Chew EY, Clemons TE, Bressler SB, et al. Randomized trial of the ForeseeHome monitoring device for early detection of neovascular age-related macular degeneration. The HOME Study. Ophthalmology. 2014;121(2):535-544.
- Gulshan V, Peng L, Coram M, et al. Development and validation of a deep learning algorithm for detection of diabetic retinopathy in retinal fundus photographs. JAMA. 2016;316(22):2402-2410.
- 日本眼科医会. 目についての健康情報（公式サイト）. https://www.gankaikai.or.jp/