Field Measures of Refractive Error

Presentation on theme: "Field Measures of Refractive Error"— Presentation transcript:

1 Field Measures of Refractive Error
Presented by Kyla Smith, BA New England College of Optometry

2 The problem at hand 161 million people worldwide are visually impaired
37 million blind 124 million visually impaired This measure is based on best corrected acuity and therefore ignores those who are visually impaired or blind due to uncorrected refractive error.

3 The problem of uncorrected refractive error…
Vision 2020: the Right to Sight Joint initiative between the WHO and the International Agency for Prevention of Blindness Goal is to eliminate the main causes of avoidable blindness. Refractive error is specifically named by this initiative. Dandona and Dandona (2006) showed that the total number of visually impaired persons worldwide when refractive error is considered is closer to 259 million, 61% higher than that quoted by the WHO.

4 The problem of uncorrected refractive error…
Can be severely debilitating. Simple to correct Provides a substantial improvement in an individual’s health, quality of life, and economic independence. However, providing this care is the real challenge.

5 Obstacles to providing refractive care
Lack of awareness Provision of affordable spectacles Cultural barriers to spectacle use Limited supply of eye care professionals Until Vision 2020, the problem of uncorrected refractive error was not recognized as a significant cause of blindness.

6 Measures of Refractive Error
Development and implementation of technology easy to use reliable affordable durable Several technologies have been invented to identify and in some cases correct refractive error in the absence of eye care professionals: AdSpecs Focometer Predetermined Lens Refraction Devices designed to address the problem of refractive error in the absence of an eye care professional include: AdSpecs Focometer Predetermined Lens Refraction (previously referred to as the flipper method) The AdSpecs, Focometer, and PLR method are referred to as field measures because they are primarily used outside of optometrists’ offices in areas where traditional equipment might not be available. All of these methods are currently used or have been proposed to be used by people in the developing world. Although all of the methods would require some degree of training, the AdSpecs in principle could be used without any supervision and double as eyewear.

7 AdSpecs Created by Joshua Silver, PhD (University of Oxford)
AdSpecs consist of a frame which contains lenses whose power is adjusted by injecting more or less fluid into the lenses. Advantages: May not require trained personnel Glasses are included in tool Disadvantages: Does not correct for astigmatism

8 AdSpecs in San Juan del Sur

9 Focometer Created by Ian Berger, MD, Dr.P.H., International Director of InFOCUS (Interprofessional Fostering of Ophthalmic Care for Underserved Sectors). The focometer is a monocular device that allows a patient to self test their by adjusting the focus of the tool while viewing an image. It corrects for astigmatism by means of a slit attached to the device. Advantages: Is able to correct for astigmatism One tool can be used for many people Can be used without an optometrist Disadvantages: Still have to supply eyewear More expensive tool to supply

10 Predetermined Lens Refraction
Implemented by Erik Weissberg, OD (New England College of Optometry) Local healthcare workers or trained laypersons undergo training to identify the simple spherical refractive error of a patient using a series of lenses. Patients’ refractive error was identified or the patient was referred Advantages: Optometrist not needed Layperson can continually provide care as well as train others. Disadvantages: Does not correct for astigmatism Limited range of spherical power

11 Subjective Refraction
A subjective refraction is the gold standard to which other methods are compared. Advantages: Best possible correction can be prescribed Prescription specific to patients’ needs Disadvantages: Shortage of optometrists in certain areas Cost of supplying correction and services to large numbers of people.

12 Study Design The study took place in two parts:
Part I consisted of a randomized clinical study comparing four methods of field refraction to a subjective refraction. Part II consisted of a field trial conducted in an area where these tools are intended to be implemented. The location was San Juan del Sur Nicaragua. This two part study consists of a clinical trial where the performance of each of these tools will be assessed under the best possible circumstances in a controlled environment and a field trial in San Juan del Sur, Nicaragua, a community that is representative of the many areas of the world where eye care is inaccessible or nonexistent. The field trial will allow us to evaluate the impact of cultural ideals and language barriers on the implementation of these tools in their target population whereas the clinical trial will allow us to assess the potential these tools posses in measuring and correcting refractive error in a best case scenario. This study will help to determine whether these refractive tools can perform reasonably well when compared with the accepted gold standard. It will also help us to determine whether or not it is realistic to use the Adspecs without the presence of a trained professional.

13 Study Design The four different measurements described above were implemented in a randomized order The subject’s best possible visual acuity was be determined using the AdSpecs first without instruction and then with instruction. The focometer was used to determine the subject’s best visual acuity. A trained layperson refracted the subject with simple lenses The subject was also be refracted by an optometrist with a trial frame.

14 Part I Boston, MA

15 Part I Descriptive Statistics of Sample Population
Age 24.3 ±1.5 Gender 34 (76%) Female Refractive Error Mean -2.56 ± 3.179 Emmetropes 3 (6%) Hyperopes 10 (20%) Myopes 37 (74 %) Table 1: Demographics regarding subjects recruited in Boston

16 Part I Refractive Error
Figure 1. Average difference from mean RE determined by SR.

17 Part I Visual Acuity Figure 2. Percent of subjects able to achieve 20/20 with each measure of RE.

18 Results In this population both the AdSpecs and Focometer demonstrated potential and were able to determine similar refractive error (within 0.30D) when compared to the gold standard subjective refraction. The Focometer and AdSpecs held a statistically significant and clinically significant advantage over the PLR in determining RE. The AdSpecs and Focometer also held an advantage over the PLR in their ability to achieve 20/20 VA. From this we can conclude that in a population which is predominately myopic such as this one, the Adspecs and Focometer are at least comparable to an SR and are more practical than the PLR.

19 Part II San Juan del Sur, Nicaragua

20 Part II Descriptive Statistics of Sample Population
Age 40.0 (±13.7) Gender 34 (76%) Female Refractive Error Mean 0.51D (+/- 0.72) Emmetropes 6 (12%) Hyperopes 37 (74%) Myopes 7 (14 %) Table 2: Demographics regarding subjects recruited in Nicaragua

21 Part II Refractive Error
Figure 3. Average difference from mean RE determined by SR.

22 Part II Visual Acuity Figure 4. Percent of subjects able to achieve 20/20 with each measure of RE.

23 Discussion All three techniques demonstrated potential and were able to determine similar refractive error (within 0.25D) when compared to the gold standard subjective refraction. The Focometer and AdSpecs held a statistically significant but clinically insignificant advantage over the PLR in determining refractive error. The highest percentage of patients able to read 20/20 was achieved by the PLR.

24 Conclusions Both the AdSpecs and Focometer showed promise when applied to two very different populations – both when determining refractive error and ability to achieve maximal visual acuity. The PLR appropriate for use in areas where the norms of refractive error are also limited. This is the first and promising report of the AdSpecs being used as a refractive tool. All things being equal, the AdSpecs may have advantages due to versatility of design –they can be used as a refractive tool as well as provide continuous refractive correction. The AdSpecs held up very well throughout the study.

25 Further research Replication of the study
Larger sample size More hyperopic distribution of refractive error. Use of these tools in other populations Children Presbyopes Implementation of these tools by trained lay people from the community in which they are intended to be used. However, the next challenge is identifying steps to implement these tools in the real world.

26 Questions?

27 References Thylefors, B., et al., Global Data on Blindness. Bulletin of the World Health Organization, : p State of the world's sight vision 2020 : the right to sight , Geneva: WHO. Dandona L, D.R., What is the global burden of visual impairment? BMC Med. , 2006 Mar 16. 4(6). Berger, I.B., et al., Testing the FOCOMETER-a new refractometer. Optometry and Vision Science, : p Du Toit, R., et al., Quantification of Refractive Error: Comparison of Autorefractor and Focometer. Optometry & Vision Science, (8): p Douali, M.G. and J.D. Silver, Self-optimised vision correction with adaptive spectacle lenses in developing countries. Ophthalmic and Physiological Optics, (3): p