Author: 

Dr.Satabdi Nanda, MBBS, DNB 2nd YEAR RESIDENT

Dr.Anuradha Chandra, MBBS, M.S., FAICO

EFFECT OF AGE ON ADULT STEREOACUITY AS MEASURED BY DISTANCE RANDOT TEST- A COMPARISION BETWEEN STEREOACUITY IN PRE-PRESBYOPIC AND PRESBYOPIC AGE GROUPS

INTRODUCTION-

Stereopsis implies the ability to obtain an impression  of depth by superimposition of two pictures of the same object taken from different angles. It is measures in seconds of arc. Lower the value, better the stereoscopic vision.

PURPOSE-

To observe the change in stereoscopic acuity over a age span of 20-80 years in patients with vision better than or equal to 6/12. We aimed at finding normative data for Distant Randot stereoacuity in 3 age groups, 20-40, 40-60, 60-80 yrs and look for age related depression of values. Also, effect of presbyopia on stereopsis was observed. Comparision of stereoacuity in early cataractous and pseudophakic patients was done.

SETTING-

Cross-sectional study at a tertiary care hospital       

METHODS-

The Distant Randot is a Polaroid vectographic book, presenting 2 shapes each of 4 disparities- 400, 200, 100 and 60 secs of arc viewed at 3m through polarizing glasses. The smallest disparity level at which the patient identifies the shapes is recorded as stereoacuity.

We administered the test to 125 patients with good vision (>=6/9), 50 in 20-40yrs, 50 in 40-60 yrs, 25 in 60-80yrs, and tabulated the results.

RESULTS-

Distance Randotscores from normal subjects have low variability within each age group. In the 20-40 age group, 54% had stereoacuity of 60”, 28% had 100” whereas in 40-60 age group, 46% had 60”, 24% had 100”, and 20% had 200”. Above 60yrs, stereoacuity declined to 200” in 60% patients.

CONCLUSION-

Age-related deterioration in stereoacuity is reflected not only by a linear correlation between age and threshold but also by a catastrophic factor that produces more marked deterioration after age 60. Both factors are probably cerebral. The Distance Randot Stereotest is a sensitive measurement of binocular sensory status that may be useful in monitoring progression of strabismus and/or recovery following strabismus surgery. Due to lack of any normative data for distance stereopsis in the Indian population, this study can be taken forward with a larger sample.

INTRODUCTION-

                       Many studies have been conducted in the past to describe the stereopsis in the elderly, using a variety of tests like the TNO test, Frisby Davis test etc.  A high incidence of deficient stereopsis has been described in population studies of elderly subjects, but this was often associated with poor vision in one eye.[1] These studies have not generally measured stereopsis across the full adult age range in normal subjects.

 

                       The Distant Randot is a Polaroid vectographic book with 8 pages, presenting 2 shapes each of 4 disparities- 400, 200, 100 and 60 secs of arc viewed at 3m through polarizing glasses. The smallest disparity level at which the patient identifies the shapes is recorded as stereoacuity. The advantages of the Distant Randot over the Frisby-Davis Distance test is that it doesn’t offer any monocular clues discouraging guessing. The FD2 is also large is size and cumbersome to handle.

                        A number of studies have described reduced stereoscopic function in older people,with one study describing a ‘‘catastrophic’’ drop in stereoacuity in some subjects over the age of 60 years.[2] This study aims at procuring normative data for distance stereopsis for age group 20-80 along with observing if there is any such rapid depletion of stereoscopy due to presbyopia or cataractous changes in the lens.

 

 

AIMS AND OBJECTIVES

  • AIM– To study the Distant Randot Stereoacuity values in 100 patients of 20-60 years.
  • PRIMARY OBJECTIVE-

To obtain normative data for 20-60yr olds in Distant Randot Test

     To compare stereopsis values in pre-presbyopic and presbyopic population.

  • SECONDARY OBJECTIVE-

     To compare stereopsis values in phakic and pseudophakic population.

 

METHOD-

It is a cross-sectional study of observational type with the entire data collected over the span of 2 months from 1st of March  to 1st of May 2017. Sample size initially taken as 200 including patients with vision better than 6/12 which was later trimmed to 125 because the minimum visual acuity as brought down to 6/9. There are 50 patients each in 20-40, 41-60 yr agegroups and 25 in 61-80 yrs age group. The study as conducted at a tertiary eye care hospital. The study parameter taken is distance stereoacuity measured in seconds of an arc , by the standard Distant Randot Stereotest.

 

Distance Randot Stereotest Protocol[3]

The Distance Randot Stereotest is a Polaroid vectographic book (21 × 17

cm), presenting 2 geometric shapes at each of 4 disparities: 400, 200, 100, and 60 arcsec. Subjects viewed the books at 3 meters in a normally illuminated room while wearing polarizing glasses (Stereo Optical Polarized Viewer). If the subject wore corrective spectacles, polarizing glasses were worn over his/her corrective lenses.

 

Pretest—The subject was asked to identify black-and-white pictures of the 4 geometric shapes (circle, triangle, square, and star) to confirm that they were able to name or match the shapes used in the test. The test proceeded only if the subject was able to name or match the shapes.

 

Test—Testing always began with the 400 arcsec level. If the subject passed

the pretest but could not identify or match both shapes at the 400 arcsec level, the test was scored as nil. If both responses were correct, testing proceeded to 200 arcsec, and so on, untilthe subject made an error. The smallest disparity atwhich the subject identified or matchedboth shapes correctly was recorded as stereoacuity.

 

PATIENT SELECTION-

  • INCLUSION CRITERIA
  1. Age 20-80yrs
  2. BCVA >= 6/9

EXCLUSION CRITERIA-

  1. No ocular surgery other than cataract surgery

DATA TABULATION

The  data was tabulated basing upon the following-

  • 3 age groups -20-40yrs, 41-60yrs, 61-80yrs
  • Lens status- phakic, cataractous or pseudophakic
  • Presbyopic correction whether or not needed
  • Distant Randot Stereoacuity value
  • Any other significant existing ocular pathology

STATISTICAL ANALYSIS

In the 20-40 age group, the mean value was found to be 86.4 arcsec with standard error(SE) of 6.45 arcsec. 95% of values range from 73.75 to 99.04 arcsec. There was 1 outlier. 

  In the 41-60 age group, the mean was 103.90 arcsec with SE of 7.56”. 95% values lie between 84.56-114.12 arcsec with 3 nil values.

In the 61-80 age group, the mean was calculated to be 140.13 arcsec with SE of 13.25 arcsec. 95% values lie between 119.10- 162.71” with 2 nil values.

DISCUSSION

                               Stereopsis is the ability to fuse images that have horizontally disparate retinal elements within Pannum’s fusional area resulting in binocular appreciation of object in depth.It implies the ability to obtain an impression of depth by super imposition of two pictures of the same object which have been taken from different angles[4].It is measured in seconds of an arc. Stereopsis emerges early on in development at 3 to 6 months of life ,continues to mature until about 10 years of age and declines in later life[5].

                                 Distance stereoscopy, the central topic of the study has been found to be sensitive to refractive error changes, hetereophoria and strabismus[6].It is particularly important clinically, because clinical groups such as intermittent exotropes are more impaired on distance than near stereoacuity.[7] There are various tests for its measurement, Frisby- Davis test and Distant Randot test being the most commonly used. There is no use of monocular clues in Distant randot like in Frisby Davis test, hence the false positives are reduced. AO Vectographic method and Mentor B-VAT II video acuity tester are no longer put to use.[8]

                              In the light of the currently undergoing demographic shift in the Indian population, there will be a growing proportion of the middle aged to elderly individuals. Also, in the present age, the levels of activity in these age groups has considerably increased because of greater consciousness. The elderly now have many more options for outdoor activities for which stereopsis and accurate depth perception is of prime concern.

                        Other than that, the Distant Randot stereoacuity test is a relatively new test which is underutilized in our country. No normative data is available for the indian population. No such study has been found to have been conducted in West Bengal. So, lack of normative data makes it difficult to put the test to use. There are a few studies for normative data in children , but hardly any for adults across all age groups. Also, most of the previous studies fail to control for vision, considering that low vision will undeniably cause a drop in stereoacuity. For this reason, age-related changes in depth discrimination could reflect either ocular optical changes, changes in general neural pathways mediating many aspects of vision, or brain mechanisms restricted to depth discrimination or possibly just stereopsis. 

                    In one of the earliest studies on stereopsis and ageing conducted by Wright and Wormald[9], it was concluded that of 728 individuals over the age of 65 ,only 27% has full stereopsis and 29% had no stereopsis, even without any significant ocular morbidity as measured by Frisby stereotest. The prevalence of decreased stereopsis increased with age.

                       In a study published in 2006, Garnham and Sloper[10] compared various stereoacuity test (TNO, Frisby Near, Frisby Davis Distance,Titmus) values to check for variability. In all tests, results showed mild decline of stereoacuity with age, with more marked reduction in subjects above 55(only TNO test). Wang et. al[11] published a study on normative data based on Distant Randot Test considering 156 volunteers(6-40yrs) and 77 strabismic patients (<65yrs). They opined that 96% of normal population had a stereoacuity of less than 100 arcsec, hereas in strabismic patients, 62.3% had abnormal values. Also, there seemed to be low variability of stereoacuity within each group.

In our study, 125 subjects have been considered, 50 each in 20-40 and 40-60 yrs age group, and 25 in 60-80years age group. It is a cross sectional study of an observational nature. In the study, we consider subjects of acuity better than or equal to 6/9, hence controlling for vision. All patients who have been taken as subjects have never undergone any ocular surgery other than cataract surgery. Presbyopia has also been considered as a factor to compare stereoscopy. The lens status of the patient as noted as early cataract, normal or pseudophakic.

                    In our sample, 23 patients has early cataract (nuclear sclerosis grade 1 and/or cortical cataract), 19 patients were pseudophakic and 83 had completely normal lens status. Subjects with early cataractous lens has a slight decrease in the stereoacuity, mean being 127” as compared to early and pseudophakic population, which had nearly similar mean stereoacuity values.(98-102”)

 

 

Similarily, the entire group was divivded into presbyopes (86) and pre-presbyopes(39). Mean value of stereoacuity as measured in presbyopes was 122 “, which was almost 25-30% below the mean of the other group(82”).

CONCLUSION

In 20-40 age group , 84% had Stereoacuity <100 arcsec. There was a gradual but mild decline in older age, but still enough to be called as sufficient for daily work (most values<200) . Presbyopes show a small fall in stereopsis. Early cataract with good vision causes a fall in stereopsis (~25%), but pseudophakia doesnt affect stereopsis.The normal distance stereopsis in Indian population >40 can be considered to lie between 100-200”.

The study also has a few limitations. One major limitation is the small sample size because of which the values show larger degree of variability. Had the sample size been larger, there could have been lesser variability. Also, our study doesn’t take into consideration the near stereoacuity.

 

 

 

REFERENCES

[1] Fawcett, S., Stager, D. and Felius, J. (2004). Factors influencing stereoacuity outcomes in adults with acquired strabismus. American Journal of Ophthalmology, 138(6), pp.931-935.

2 Jani SN. The age factor in stereopsis screening. Am J Optom Arch Am Acad

Optom 1966;43:653–7.

3  WANG, J. (2010). The Final Version of the Distance Randot Stereotest: Normative data, reliability, and validity. JAAPOS, 14(2), p.1.

4 BHOLA, R. (2006). BINOCULAR VISION. [online] Available at: http://webeye.ophth.uiowa.edu/eyeforum/tutorials/Bhola-BinocularVision.htm [Accessed 16 Nov. 2017].

5 Bohr I, Read JCA (2013) Stereoacuity with Frisby and Revised FD2 Stereo Tests. PLoS ONE 8(12): e82999. doi:10.1371/journal.pone.0082999

6 BOHR, I. and READ, J. (2013). Stereoacuity with Frisby and Revised FD2 Stereo Tests. PLOS, p.2.

7  Sharma, P. (2008). Strabismus simplified. New Delhi: CBS Publishers & Distributors.

8 Sharma, P. (2008). Strabismus simplified. New Delhi: CBS Publishers & Distributors

9 WRIGHT, L. and WORMALD, R. (1992). STEREOPSIS AND AGEING. p.1.

 10 GARNHAM, L. and SLOPER, J. (2006). EFFECT OF AGE ON STEREOACUITY. BR J OPHTHALMOLOGY.

11 WANG, J. (2010). The Final Version of the Distance Randot Stereotest: Normative data, reliability, and validity. JAAPOS, 14(2), p.1.

 

[1] Fawcett, S., Stager, D. and Felius, J. (2004). Factors influencing stereoacuity outcomes in adults with acquired strabismus. American Journal of Ophthalmology, 138(6), pp.931-935.

[2] Jani SN. The age factor in stereopsis screening. Am J Optom Arch Am Acad

Optom 1966;43:653–7.

 

[3] WANG, J. (2010). The Final Version of the Distance Randot Stereotest: Normative data, reliability, and validity. JAAPOS, 14(2), p.1.

[4] BHOLA, R. (2006). BINOCULAR VISION. [online] Available at: http://webeye.ophth.uiowa.edu/eyeforum/tutorials/Bhola-BinocularVision.htm [Accessed 16 Nov. 2017].

5 Bohr I, Read JCA (2013) Stereoacuity with Frisby and Revised FD2 Stereo Tests. PLoS ONE 8(12): e82999. doi:10.1371/journal.pone.0082999

6 BOHR, I. and READ, J. (2013). Stereoacuity with Frisby and Revised FD2 Stereo Tests. PLOS, p.2.

7  Sharma, P. (2008). Strabismus simplified. New Delhi: CBS Publishers & Distributors.

8 Sharma, P. (2008). Strabismus simplified. New Delhi: CBS Publishers & Distributors

[9] WRIGHT, L. and WORMALD, R. (1992). STEREOPSIS AND AGEING. p.1.

   10 GARNHAM, L. and SLOPER, J. (2006). EFFECT OF AGE ON STEREOACUITY. BR J OPHTHALMOLOGY.

11 WANG, J. (2010). The Final Version of the Distance Randot Stereotest: Normative data, reliability, and validity. JAAPOS, 14(2), p.1.

 

 

 

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