According to WHO statistics, hearing loss affects approximately 650 million people worldwide, corresponding to about 1 in 9 people on Earth. More than half have disabling hearing loss that interferes with daily life. In Russia, there are over 13 million people with hearing loss, of whom more than 1 million are children.
Visual impairment is observed in more than one-quarter of patients with hearing loss, with refractive errors being the most common. A study of 901 hearing-impaired children aged 4–21 years attending special schools in India found that about one-quarter (24%) had some ophthalmic problem, with refractive errors being the most frequent at 18.5%, of which 67.7% were myopia (Gogate et al., 2009). Another study of 302 hearing-impaired children aged 2–15 years in Saudi Arabia reported ophthalmic abnormalities in 61% and refractive errors in 48.7%, significantly higher than the hearing control group (23%) (Al-Abduljawad et al., 2005). Vision plays a central role in the development of newborns and children, and early visual impairment broadly affects motor skills, cognitive function, social communication skills, and social relationship building. The sharpness of central vision is one of the key diagnostic indicators.
Conventional visual acuity tests are based on subjective examinations in which the patient verbally responds to visual targets. In deaf or hard-of-hearing children, the lack or underdevelopment of verbal communication makes it extremely difficult to perform such tests.
Additionally, spatial perception in deaf or hard-of-hearing children tends to develop later than in hearing children. Attention to object size, color, shape, and spatial relationships develops about one year later than in hearing children. Since judging the direction of the gap in a Landolt C ring depends on spatial perception, this is particularly challenging for young deaf or hard-of-hearing children.
In children with hearing impairment, the frequency of hyperopia is significantly higher. A study conducted in Mashhad, Iran reported a hyperopia prevalence of 57.15% in hearing-impaired children, which was significantly higher than in hearing children (21.5%). The mean spherical equivalent was also significantly different: 1.7±1.9 D in hearing-impaired children versus 0.2±1.5 D in hearing children. Furthermore, the prevalence of amblyopia was 12.2% in hearing-impaired children and 1.2% in hearing children, with an odds ratio of 11.6, highlighting the critical importance of early detection and correction of refractive errors (Ostadimoghaddam et al., 2015).
In children with bilateral sensorineural hearing loss, it is important to differentiate Usher syndrome (a combination of sensorineural hearing loss and retinitis pigmentosa, often with vestibular dysfunction). Usher syndrome is the most common cause of deafblindness worldwide, with a reported prevalence of 4 to 17 per 100,000 people (Toms et al., 2020). Because visual symptoms due to retinitis pigmentosa appear later, screening before onset is recommended in children with hearing impairment. In recent years, genetic panel testing can identify causative mutations for Usher syndrome before visual symptoms appear. It has been reported that among 184 children with hearing impairment, 18 (9.8%) had biallelic mutations in Usher syndrome-related genes, and 29% of those evaluated had previously undiagnosed retinal abnormalities (Brodie et al., 2021). For children with severe to profound prelingual sensorineural hearing loss, a comprehensive ophthalmologic examination including electroretinography (ERG) is desirable.
Conventional vision tests are subjective examinations that require the patient to verbally or by pointing indicate the direction of the gap in a Landolt C ring, making them difficult to administer to deaf or hard-of-hearing children who have difficulty with verbal communication. Furthermore, spatial perception in deaf or hard-of-hearing children tends to develop about one year later than in hearing children, making it difficult for young children to discriminate the direction of the Landolt C ring gap.
When performing vision tests in deaf or hard-of-hearing children, it is important to select an appropriate method according to age, developmental stage, and language ability. The characteristics of each examination method are described below.
The normal visual acuity standards by age are as follows.
| Age | Normal Visual Acuity Standard |
|---|---|
| 3 months | 0.05 |
| 1 year | 0.1 to 0.2 |
| 2 years old | 0.3 to 0.5 |
| 3 years old | 0.5 to 0.8 |
| 6 years old | 1.0 |
Children’s vision is still developing, and results may vary depending on the testing method and the child’s mood. It is difficult to obtain accurate measurements in a single test, and it is advisable to consider multiple tests.
Can be performed in children aged 3 years and older. The child responds to the direction of the gap by speaking, pointing, or using a steering wheel.
Used for 2- to 3-year-old children who have difficulty with the Landolt ring test. Silhouettes of butterflies, fish, birds, dogs, etc., are drawn in sizes corresponding to visual acuity values. Children can respond verbally or by pointing to or picking up the same picture from a set of cards. This test can be performed enjoyably in children aged 2.5 to 3.5 years. Note that a visual acuity of 0.7 measured with picture optotypes is evaluated as lower than a visual acuity of 0.7 measured with the Landolt ring.
The child responds by pointing to the eyes (dots) in pictures of rabbit or bear faces. This measurement is based on the minimum visible threshold (not the minimum separable threshold), with a testing distance of 30 cm (near vision). It can be used from around 2 years of age and is useful for infants aged 1 to 3 years. The card itself is small and portable, making it suitable for use outside the clinic.
An examination method that utilizes the tendency of infants to prefer looking at striped patterns over uniform screens.
A simplified clinical application of the FPL method. Can be performed in a bright room and takes about 10 minutes. Note that TAC visual acuity tends to show better values than Landolt C visual acuity.
Based on the same principle as the PL method, this can be easily performed in an outpatient setting. There are several methods, including TAC, grating acuity, Lea grating paddles, and the Cardiff acuity test. The Cardiff acuity test uses line drawings (fish, duck, car, train, etc.) and easily attracts children’s attention. It is possible to estimate visual acuity even in older children with intellectual disabilities who cannot perform picture optotypes or Landolt rings.
An objective test that measures potential changes in the occipital visual cortex in response to visual stimuli. Using pattern VEP, the threshold is determined by gradually reducing the size of checkerboard or grating patterns.
Nystagmus induced by vertical stripes on a rotating drum is recorded. This method is effective from around 2 months of age and can also be used in adults suspected of feigning illness.
Used in children under 3 years of age or those with developmental delay. Visual response development: at 1 month, monocular fixation and pursuit to midline; at 2 months, binocular fixation and pursuit beyond midline. If the child resists occlusion of one eye (“aversion reflex”), it indicates a difference in visual acuity between the eyes.
Infancy (under 2 years)
Blink reflex, fixation, and pursuit: Basic visual response assessment.
Aversion reflex: Resistance to occlusion of one eye to estimate interocular visual acuity difference.
OKN・PL method (FPL): Objective measurement based on preference response to striped patterns.
VEP: From 3 to 4 years old with skin electrodes. Under general anesthesia, any age.
Early childhood (2–5 years)
Morizane dot card: From around 2 years old. Pointing response. Near vision at 30 cm.
Picture optotypes: 2.5 to 3.5 years old. Can be performed using a picture-matching method.
TAC method / stripe visual acuity cards: A clinically simplified version of the FPL method. Measurement takes about 10 minutes.
Landolt C (single optotype): Recommended for ages 3 and older. Success rate: 60% at age 3, 95% at age 4.
School-age (6 years and older)
Landolt C (crowded) : Standard visual acuity test. Crowded optotypes are recommended.
LEA SYMBOLS・HOTV : Suitable for infants to early elementary school children as responses are 4-choice.
Sloan letters : Standard visual acuity chart recommended for older children.
In Russia and other former Soviet countries, the following visual acuity charts have been used.
A similar version of the Lea chart. It uses black pictograms (star, mushroom, Christmas tree, circle, chicken, car, horse, airplane, elephant, motorcycle) on a white background. It consists of two sheets: the left 5 rows correspond to visual acuity 0.1–0.3, and the right 7 rows correspond to 0.4–1.0. The number of optotypes is 3 each for 0.1–0.2, 4 for 0.3, 5 for 0.4–0.5, 6 for 0.6–0.7, 7 for 0.8–0.9, and 8 for 1.0.
The most commonly used visual acuity measurement method for patients with hearing and speech disorders. Developed in 1923 by Soviet ophthalmologists Sergei Golovin and D.A. Sivtsev. The left column consists of Cyrillic letters (Ш・Б・М・Н・К・Ы・И), and the right column consists of Landolt C rings, each with 12 rows. Visual acuity values from 0.1 to 2.0 can be measured. The testing distance is 5 meters. Because it requires judging the direction of the gap in the Landolt C ring (up, down, left, right), it is difficult for deaf and hard-of-hearing children.
Developed by Uzbek ophthalmologist Eldor Jonnazarov, MD. Patented in the Russian Federation under RU 2,703,697 C1 (September 3, 2018). The official name is Just Evident Images / Jonnazarov Eldor Ikhtiyorovich (JEI/JEI).
Uses 13 types of color and black optotypes (sun, flower, Christmas tree, house, chicken, child, star, horse, bear, car, kitten, ball, rabbit). Optotypes with equal width and height are used.
The testing distance is 2.5 m (shorter than the conventional 5 m). The child is given a card with duplicate optotypes and holds up the corresponding card when an optotype is indicated on the chart (no verbal response required).
Each image has equal height and width (first column = 35 mm, second column = 17.5 mm, tenth column = 3.5 mm), and the bottom of the chart is placed 60 cm above the floor so that the symbols in the middle row are at the child’s eye level.
Examination procedure:
Calculation formula for visual acuity less than 0.1 or greater than 1.0:
V2 = (d × V1) / D
(V1: normal visual acuity, D: distance at which a child with normal vision can identify that line, d: distance at which the test child can see, V2: visual acuity of the test child)
Vision testing with Landolt C rings is considered feasible from age 3 and above. However, the success rate varies significantly by age: 60% at age 3 and 95% at age 4. In particular, deaf and hard-of-hearing children tend to have delayed spatial awareness development compared to hearing children of the same age, so results may not be equivalent to those of hearing peers.
Several testing methods that do not rely on verbal responses are available. Representative examples include the Morizumi Dot Card (pointing response, from around age 2), picture optotypes (shadow picture matching, from age 2.5), the PL method (preferential looking at striped patterns), and VEP (objective measurement using brain waves). For deaf or hard-of-hearing children, the JEI/JEI test chart (card-matching method, testing distance 2.5 m) is also effective and can be performed from age 2.
The JEI/JEI test chart uses a card-matching method, so no verbal response is required. The testing distance is short at 2.5 m, and it can be performed without contraindications for all deaf or hard-of-hearing children from age 2. It can also be used in different language environments and can be administered outside the examination room (at home or in facilities). Unlike the Golovin–Sivtsev table, it does not require judging the orientation of Landolt C gaps, making it suitable for deaf or hard-of-hearing children who may have delayed spatial perception development.
In children with developmental delays, visual acuity may be lower than that of healthy children of the same age, but when adjusted for developmental age, it often shows equivalent visual acuity. The choice of examination method should be based on developmental age rather than chronological age. Additionally, since children’s vision is still developing, it is often difficult to obtain accurate measurements in a single examination, and it is important to comprehensively evaluate the results of multiple examinations. If a visual impairment is confirmed, early refractive correction (prescription of glasses) is important for visual development.
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Ostadimoghaddam H, Mirhajian H, Yekta AA, Sobhani Rad D, Heravian J, Malekifar A, Khabazkhoob M. Eye problems in children with hearing impairment. J Curr Ophthalmol. 2015;27(1-2):56-59. doi:10.1016/j.joco.2015.10.001. PMID: 27239577; PMCID: PMC4877721.
Al-Abduljawad KA, Al-Hussain HA, Dasugi AA, Zakzouk SM. Ocular profile among hearing impaired children. Saudi Med J. 2005;26(5):738-740. PMID: 15951860.
Toms M, Pagarkar W, Moosajee M. Usher syndrome: clinical features, molecular genetics and advancing therapeutics. Ther Adv Ophthalmol. 2020;12:2515841420952194. doi:10.1177/2515841420952194. PMID: 32995707.
Brodie KD, Moore AT, Slavotinek AM, Meyer AK, Nadaraja GS, Conrad DE, Weinstein JE, Chan DK. Genetic Testing Leading to Early Identification of Childhood Ocular Manifestations of Usher Syndrome. Laryngoscope. 2021;131(6):E2053-E2059. doi:10.1002/lary.29193. PMID: 33111992.
