Self-Check for Vision Loss (Importance of Checking One Eye at a Time)

Key points at a glance

Summary of this article

• In binocular vision, the better eye compensates, making it easy to overlook diseases that progress unilaterally (age-related macular degeneration, glaucoma, retinal detachment). It is important to develop the habit of checking each eye alternately.
• The prevalence of glaucoma in people aged 40 and over is about 5% (Tajimi Study)²⁾, and the majority of cases remain undiagnosed. Since it progresses without subjective symptoms, regular self-checks and eye examinations are virtually the only means of early detection.
• Use the Amsler chart at a distance of 30 cm with corrected vision, testing one eye at a time. Distortion or missing areas of straight lines may indicate macular disease.
• Among 12,505 people aged 18 and over newly certified with visual impairment in fiscal 2015, the causative diseases were glaucoma (28.6%), retinitis pigmentosa (14.0%), diabetic retinopathy (12.8%), and macular degeneration (8.0%), in that order¹⁰⁾. Early detection of eye diseases is important for preserving visual function.
• Sudden vision loss, curtain-like shadows, or severe eye pain are emergency signs that require same-day medical attention.
• If there is a difference in vision between the two eyes when checking one eye at a time, even without pain, it is recommended to see an ophthalmologist within a few days.
• After age 40, an annual eye examination is recommended³⁾. If there is a family history of glaucoma, consider regular checkups from an earlier age.

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.

In a complete survey of 12,505 people aged 18 and over newly certified with visual impairment in fiscal 2015 (Morizane 2019), the causative diseases were glaucoma (28.6%), retinitis pigmentosa (14.0%), diabetic retinopathy (12.8%), and macular degeneration (8.0%), in that order¹⁰⁾. These include diseases with few subjective symptoms during some stages, making early detection through self-checks and regular eye examinations key to preserving visual function.

Glaucoma prevalence and undiagnosed rate

The Tajimi Study (Iwase 2004) found a prevalence of primary open-angle glaucoma of 3.9% among Japanese people aged 40 and over, and 92% had an intraocular pressure of 21 mmHg or less¹⁾. This was a cross-sectional prevalence study, not a study showing the progression rate of visual field defects. Because glaucoma can exist even with intraocular pressure in the normal range, regular examinations including optic nerve and visual field evaluation, rather than intraocular pressure measurement alone, 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

The one-eye check can be performed without special equipment. Follow these 4 steps.

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.

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

• 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

Ranetti AE, Stanca HT, Tăbăcaru B, et al. Retromode Imaging in Age-Related Macular Degeneration. Medicina (Kaunas). 2023;59(4):647. Figure 2. PMID: 37109604; PMCID: PMC10144202; Source: https://pmc.ncbi.nlm.nih.gov/articles/PMC10144202/ DOI: 10.3390/medicina59040647. License: CC BY 4.0 (https://creativecommons.org/licenses/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).

How to use the Amsler chart

1. Perform the test with your usual correction (wearing glasses or contact lenses).
2. Place the chart 30 cm from your eyes.
3. Perform the test one eye at a time. Cover the other eye completely.
4. Stare at the central point and check the condition of the grid lines.
5. If you notice any abnormalities such as wavy, distorted, or missing lines, see an ophthalmologist early.

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

A systematic review of the Amsler grid for age-related macular degeneration (AMD) screening (Faes 2014) reported a sensitivity of approximately 78% for detecting metamorphopsia within the central 5 degrees ³⁾. 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

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

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 may be delayed without monocular testing²⁾. In the Tajimi Study, 92% of people aged 40 and over with primary open-angle glaucoma had an intraocular pressure of 21 mmHg or less¹⁾. Glaucoma can exist even with intraocular pressure in the normal range, and visual field defects may progress in normal-tension glaucoma.

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

The following are criteria for deciding when to seek medical attention based on self-check results.

Signs Requiring Emergency Consultation

If any of the following apply, visit an ophthalmologist on the same day.

• Sudden vision loss (rapid deterioration within hours)
• A curtain-like or veil-like obstruction in part of the visual field
• Sudden increase in floaters
• Recurrent photopsia (seeing flashes of light in the dark)
• Vision loss or blurred vision accompanied by severe eye pain or headache

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

• 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)

Ma X, Tang L, Chen X, et al. Periphery kinetic perimetry: clinically feasible to complement central static perimetry. BMC Ophthalmol. 2021;21(1):343. Figure 2. PMID: 34551740; PMCID: PMC8459489; Source: https://pmc.ncbi.nlm.nih.gov/articles/PMC8459489/ DOI: 10.1186/s12886-021-02056-5. License: CC BY 4.0 (https://creativecommons.org/licenses/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

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

In the Tajimi Study, the prevalence of primary open-angle glaucoma among people aged 40 and over was 3.9%, and 92% had an intraocular pressure of 21 mmHg or less¹⁾. Detection is difficult with intraocular pressure measurement alone; regular examinations combining optic disc observation, OCT RNFL evaluation, and visual field testing are necessary. Visual field defects can progress even in normal-tension glaucoma, which may lead to the false reassurance that “pressure is normal so there is no problem.” Regular monocular checking to notice differences or changes in the visual field between the eyes can trigger a visit to the doctor.

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

Research stage / Reference information

The following content includes information at the research stage or early implementation. It is not currently available in all facilities or situations, and is positioned as reference information for future development.

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)

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

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

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

1. Iwase A, Suzuki Y, Araie M, Yamamoto T, Abe H, Shirato S, et al. The prevalence of primary open-angle glaucoma in Japanese: the Tajimi Study. Ophthalmology. 2004;111(9):1641-8. doi:10.1016/j.ophtha.2004.03.029. PMID:15350316.
2. 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.
3. Faes L, Bodmer NS, Bachmann LM, Thiel MA, Schmid MK. 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 (London, England). 2014;28(7):788-96. doi:10.1038/eye.2014.104. PMID:24788016; PMCID:PMC4094801.
4. 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.
5. Ohno-Matsui K, Lai TY, Lai CC, Cheung CM. Updates of pathologic myopia. Progress in retinal and eye research. 2016;52:156-87. doi:10.1016/j.preteyeres.2015.12.001. PMID:26769165.
6. Bastawrous A, Rono HK, Livingstone IA, Weiss HA, Jordan S, Kuper H, Burton MJ. 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. doi:10.1001/jamaophthalmol.2015.1468. PMID:26022921; PMCID:PMC5321502.
7. Chew EY, Clemons TE, Bressler SB, et al. Randomized trial of a home monitoring system for early detection of choroidal neovascularization home monitoring of the Eye (HOME) study. Ophthalmology. 2014;121(2):535-544. doi:10.1016/j.ophtha.2013.10.027. PMID:24211172; PMCID:PMC3918479.
8. Gulshan V, Peng L, Coram M, Stumpe MC, Wu D, Narayanaswamy A, 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. doi:10.1001/jama.2016.17216. PMID:27898976.
9. 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/
10. Morizane Y, Morimoto N, Fujiwara A, et al. Incidence and causes of visual impairment in Japan: the first nation-wide complete enumeration survey of newly certified visually impaired individuals. Jpn J Ophthalmol. 2019;63(1):26-33. doi:10.1007/s10384-018-0623-4. PMID:30255397.