The present research demonstrates a method to accurately examine dynamic visual acuity (DVA) in myopic subjects with eyeglass correction. Further analysis indicated that the closer the refraction state to emmetropia, the better the eyeglass-corrected binocular DVA is at both 40 and 80 degrees per second.
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Method Article
Binocular Dynamic Visual Acuity in Eyeglass-Corrected Myopic Patients
* These authors contributed equally
In This Article
Summary
Abstract
Current clinical visual assessment mainly focuses on static vision. However, static vision may not sufficiently reflect real-life visual function as moving optotypes are frequently observed daily. Dynamic visual acuity (DVA) might reflect real-life situations better, especially when objects are moving at high speeds. Myopia impacts static uncorrected distance visual acuity, conveniently corrected with eyeglasses. However, due to peripheral defocus and prism effects, eyeglass correction might affect DVA. The present research demonstrates a standard method to examine eyeglass-corrected DVA in myopia patients, and aimed to explore the influence of eyeglass correction on DVA.
Initially, standard subjective refraction was performed to provide the eyeglass prescription to correct the refractive error. Then, binocular distance vision-corrected DVA was examined using the object-moving DVA protocol. Software was designed to display the moving optotypes according to the preset velocity and size on a screen. The optotype was the standard logarithmic visual chart letter E and moves from the middle of the left to the right side horizontally during the test. Moving optotypes with randomized opening direction for each size are displayed. The subjects were required to identify the opening direction of the optotype, and the DVA is defined as the minimum optotype that subjects could recognize, calculated according to the algorithm of logarithmic visual acuity.
Then, the method was applied in 181 young myopic subjects with eyeglass-corrected-to-normal static visual acuity. Dominant eye, cycloplegic subjective refraction (sphere and cylinder), accommodation function (negative and positive relative accommodation, binocular cross-cylinder), and binocular DVA at 40 and 80 degrees per second (dps) were examined. The results showed that with increasing age, DVA first increased and then decreased. When myopia was fully corrected with eyeglasses, a worse binocular DVA was associated with more significant myopic refractive error. There was no correlation between the dominant eye, accommodation function, and binocular DVA.
Introduction
Current visual assessment mainly focuses on static vision, including static visual acuity (SVA), visual field, and contrast sensitivity. In daily life, either the object or the observer is often in motion rather than being stationary. Therefore, SVA may not sufficiently reflect visual function in daily lives, especially when objects are moving at high speeds, such as during sports and driving1. DVA defines the ability to identify the details of moving optotypes1,2, which might reflect real-life situations better and be more sensitive to visual disturbance and improvement3,4. Moreover, as magnocellular (M) ganglion cells located mainly in the peripheral retina primarily transmit high temporal frequency signals, DVA might reflect visual signal transmission differently from SVA5,6. The DVA test (DVAT) can be mainly divided into two types: static- and moving-object DVATs. While the static-object DVAT demonstrates the vestibule-ocular reflex7,8,9,10, the moving-object DVAT is commonly applied in clinical ophthalmology to detect visual acuity in the identification of moving targets3,4.
The prevalence of myopia has rapidly increased in recent decades, especially in Asian countries11. Myopia has an essential impact on static uncorrected distance visual acuity, which could be corrected with various lenses. Eyeglasses are mostly used among myopia patients due to accessibility and convenience. However, eyeglasses, especially high myopia lenses, have obvious peripheral defocus and prism effects that cause unclear and skewed images to be observed through the peripheral region12,13,14,15. For a static optotype, the subject commonly uses the central area of eyeglasses that could obtain a clear vision. However, the moving target could easily move out of the eyeglasses' clearest point. Thus, with eyeglass correction, myopic subjects might have normal SVA and affected DVA. However, no research has been performed to investigate the impact of myopia diopter on DVA in populations with eyeglasses.
This study demonstrates a method to examine DVA in eyeglass-corrected myopia patients and aimed to explore the impact of myopia diopter on moving-object binocular DVA in eyeglass-corrected patients. The research provides a basis for accurately interpreting DVAT in clinical ophthalmology considering the impact of eyeglasses and evidence on the influence of corrected myopia on motion-related activities.
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Protocol
The present study enrolled consecutive myopia patients in the Department of Ophthalmology of Peking University Third Hospital. The research protocol was approved by the Peking University Third Hospital Ethics Committee, and informed consent was obtained from each participant.
1. Patient preparation
- Use the following initial inclusion criteria to enroll subjects: myopia subjects aged 17-45 years old.
- Use the following exclusion criteria: any history of ocular diseases, including keratitis, glaucoma, cataract, retinal and macular diseases, that significantly impact corrected distance visual acuity (CDVA). Evaluate uncorrected distance visual acuity (using the standard logarithmic VA chart), dominant eye, intraocular pressure, slit lamp, corneal topography, fundus photography, automatic computer optometry, cycloplegic subjective refraction, and CDVA. Exclude participants with keratoconus, cloudy cornea, or retinal abnormalities, including retinal breaks, retinal vascular inflammation, congenital retinal and macular diseases, or monocular CDVA worse than zero (based on the standard logarithmic VA chart).
- Set up the DVA test components, including test distance, environment, hardware, software, movement mode, and rules as follows:
- For test distance and environment, set the test distance according to the size of the screen and examination requirements.
NOTE: Here, DVA was assessed at 2.5 m in a quiet and bright room (luminance 15-30 lux). - For hardware, present the optotype with a 24 inch in-plane switching (IPS) or twisted nematic (TN) screen (refresh rate, 60 to 144 Hz; response rate less than 5 ms).
- Ensure that the software is designed to display the optotype according to the preset velocity and size. Use the dynamic optotype as the letter E designed according to the standard logarithmic visual chart with four opening directions: upper, left, lower, and right. Ensure that the visual angle of the motion optotype presented at the test distance equals the optotype with the decimal size in the standard logarithmic visual chart. Set the color of the letter E to black, with a white background. Express the velocity of motion as the viewing angle changes per second.
- Movement mode: during the test, ensure that the optotype with a specific size and velocity appears in the middle of the screen's left side, moves horizontally to the right side, and then disappears.
- Test rule: Ask the subjects to identify the opening direction of the visual target. Test the minimum visual target at a certain speed that the subjects can recognize.
- For test distance and environment, set the test distance according to the size of the screen and examination requirements.
2. Subjective refraction
NOTE: The result of subjective cycloplegic refraction is the basis for the eyeglasses prescription to correct the refractive error in myopia subjects.
- Perform automatic computer optometry as the primary data for subjective cycloplegic refraction and measure the pupil distance.
- Examine one eye at a time and occlude the other eye.
- First, achieve the maximum plus to maximum visual acuity: fogging with +0.75 - +1.0 D lens, inducing a visual acuity of 0.3-0.5 (decimal visual acuity). Next, gradually decrease the positive lens in a 0.25 D step. Use a Lancaster red-green test to tune the accurate spherical diopter. Add more negative/positive lens if the patients report that the letter seen against the red/green background is clearer.
NOTE: The primary spherical diopter is obtained after the above step.
- First, achieve the maximum plus to maximum visual acuity: fogging with +0.75 - +1.0 D lens, inducing a visual acuity of 0.3-0.5 (decimal visual acuity). Next, gradually decrease the positive lens in a 0.25 D step. Use a Lancaster red-green test to tune the accurate spherical diopter. Add more negative/positive lens if the patients report that the letter seen against the red/green background is clearer.
- Refine the cylinder axis.
- Place the Jackson cross cylinder device in the "axis" position so that the thumb-wheel's connecting line is parallel to the axis of the astigmatism. Rotate the thumb-wheel and ask the subject to compare the clearness between both sides. Turn the cylinder axis toward the red dots on the cross cylinder in the side with clearer vision. Repeat the binary comparison until the endpoint.
- Refine cylinder power.
- Turn the Jackson cross cylinder device so that the thumb-wheel's connecting line is at 45° to the astigmatism axis. Rotating the thumb-wheel, ask the subject to compare the clearness between both sides. If the patient reports clearer placement of the cross cylinder red/white dots connecting line along the cylinder axis, add a negative/positive lens, respectively. Repeat the binary comparison until the endpoint.
- For the second maximum plus to maximum visual acuity, repeat the Lancaster red-green test to tune the accurate spherical diopter.
- For binocular balance, apply a vertical prism of 6Δ before one eye to dissociate the binocular vision. Balance the clearness of the optotypes between both eyes.
3. Dynamic visual acuity test
NOTE: DVA was measured binocularly with refractive errors fully corrected with eyeglasses in the present study.
- Test settings
- Adjust the test distance according to the requirements. Adjust the seat to make the subject's sight at the screen's midpoint level. Ensure the subject wears the distance vision corrected eyeglasses binocularly.
- Test parameter configurations
- Set the optotype moving velocity and the initial optotype size.
- For the pretest, display five optotypes with a randomized opening direction to guide the subjects to understand the test mode.
- Formal test
- Start the test at the size 3-4 lines bigger than the best-corrected distance visual acuity. Display the optotype with randomized opening directions.
- Ask the subject to identify the opening direction of the moving optotype. Present the next optotype after the subject's response. Present eight optotypes for a certain size. If five out of eight optotypes are identified correctly, adjust the optotype to one size smaller. Repeat the above procedures until the size for which the subject can identify less than five optotypes is obtained.
- Record the minimum size (A, decimal VA) that subjects can recognize (five out of eight optotypes are identified correctly) and the number (b) of optotypes recognized for one size smaller than A.
- DVA calculation
- Present eight optotypes for each size so that each identified optotype gains 0.1/8 visual acuity. Calculate DVA according to the algorithm of logarithmic visual acuity, as shown by Eq (1); see step 3.5 for an explanation of A and b:
(1)
NOTE: In the present study, optotypes of 40 and 80 dps were examined in order. Previous studies have reported that people could apply smooth pursuit when observing dynamic objects moving at 30-60 dps, whereas observing objects moving faster than 60 dps involves head movement and saccade16,17. Thus, two motion speeds of 40 and 80 dps were selected.
- Present eight optotypes for each size so that each identified optotype gains 0.1/8 visual acuity. Calculate DVA according to the algorithm of logarithmic visual acuity, as shown by Eq (1); see step 3.5 for an explanation of A and b:
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Results
Subject examinations
For the enrolled subjects, accommodation function, including negative relative accommodation (NRA), accommodation response (binocular cross-cylinder (BCC)), and positive relative accommodation (PRA), were examined in the mentioned order. Binocular DVA at 40 dps and 80 dps was tested with distance visual acuity-corrected eyeglasses based on subjective refraction.
Statistical analysis
Statistical analysis was performed using scientif...
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Discussion
DVA is a promising indicator to assess visual function, which might better reflect actual vision in daily life. Myopic patients could have corrected, normal SVA, but their DVA might be affected. This study demonstrates a method to examine the DVA in myopic subjects with eyeglass correction accurately and analyzes its correlation with optometric parameters, including refraction, accommodation, and the dominant eye. The results indicated that DVA at 40 dps was superior to that at 80 dps. The closer the refraction state is ...
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Disclosures
The authors declare that they have no competing interests.
Acknowledgements
This work was supported by Natural Science Foundation of Beijing Municipality (7202229).
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Materials
| Name | Company | Catalog Number | Comments |
|---|---|---|---|
| Automatic computer optometry | TOPCON | KR8100 | |
| Corneal topography | OCULUS | Pentacam | |
| Dynamic visual acuity test design software | Mathworks | matlab 2017b | |
| Fundus photography | Optos | Daytona | |
| Matlab | Mathworks | 2017b | |
| Noncontact tonometry | CANON | TX-20 | |
| Phoropter | NIDEK | RT-5100 | |
| scientific statistical software | IBM | SPSS 26.0 | |
| Slit lamp | Koniz | IM 900 |
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