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

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



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.


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.


Cross-sectional study at a tertiary care hospital       


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.


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.


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.


                       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.




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

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

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


     To compare stereopsis values in phakic and pseudophakic population.



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.



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


  1. No ocular surgery other than cataract surgery


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


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.


                               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”).


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.





[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



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



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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Computer Vision Approach to Diabetic Retinopathy Screening

Computer Vision Approach to Diabetic Retinopathy Screening

Author: Dr Aniruddha Maiti

Co-authors: Dr ChandanChakraborty, Dr Maitreya Maiti,Dr Kanika Agarwal,Dr RahulBahekar , Dr Chirag Bhatt, Dr R C Paul

Key words : Diabetic Retinopathy Screening , Computer assisted, Quantitative characterization

Abstract : It is estimated that diabetes mellitus affects 4 per cent of the world’s population, almost half of whom have some degree of DR at any given time. DR occurs both in type 1(Juvenile Diabetes or Childhood Diabetes )and type 2 (adult onset) diabetes mellitus and has been shown that nearly all type 1 and 75 per cent of type 2 diabetes will develop DR after 15 yr duration of diabetes . In collaboration with IIT Kharagpur a software has been developed which is used for the early detection and risk categorisation of diabetic retinopathy (DR). The software uses data analytics capabilities to automatically compare and analyze retina images of the patient. It can tell if the patient has DR and also provides risk categorization ranging from low to medium and high. Results with the software shows accuracy level of 77-93 percent when real patient screening for diabetic retinopathy.


Diabetic retinopathy (DR) or retinal damage caused by diabetes is a predominant reason for loss of vision. In 2007, International Diabetes Federation estimated that 40.9 million people in India were diabetic and speculated that this number would rise to 69.9 million by 2025. However, DR can be prevented if diagnosed early. With the increasing tendency of diabetes in Indian population, there should be a retinal screening protocol for follow-up on routinely basis. This calls for an immediate development of DR screening tool for Indian (diabetic) population to prevent it on regular basis. Computer assisted screening of diabetic patients using fundus images is highly relevant not only to provide mass screening service but also to act as a clinical decision support system in order to provide ‘Affordable’, ‘Accessible’ DR screening facilities.

Purpose :

To conduct a feasibility study of computer-aided screening for diabetic retinopathy by developing a computerized program to automatically detect retinal changes from digital retinal images.

Material and method:

The study was carried out in three steps. Step 1 was to collect baseline retinal image data of  eyes of normal subjects with normal fundus and data  of diabetic patients with diabetic retinopathy. All data were recorded by digital fundus camera. Step 2 was to analyze all retinal images for normal and abnormal features. By this method, the automated computerized screening program was developed inIndian Institute of Technology Kharagpur  in the department ofSchool of Medical Science & TechnologyThe program preprocesses color retinal images and recognizes the main retinal components (optic disc, fovea and blood vessels) and diabetic features such as exudates, haemorrhages, and microaneurysms. All of the accumulated information is interpreted as normal, abnormal, or unknown. Step 3 was to evaluate the sensitivity and specificity of the computerized screening program by testing the program on diabetic patients and comparing the program’s results with the results of screening by retinal specialist in Susrut eye hospital and research centre.

In digital world, an image can be described as two-dimensional matrix where each unit (pixel) contains a numeric value (intensity).  The dimension of the matrix is equal to the original image size. Color image like RGB has three channel viz. Red, Green and Blue. So the pixel value of any point of an image is sum of RED, GREEN and GREEN value.  In a image we can consider some group of entities like background and foreground (blood vessels, microaneurysms etc). Each entity or group contain similar pixel value.

Digital Image processing follows  the steps: Acquisition, Pre-processing , Segmentation, Feature Extraction

Fig-1 – Image Acquisition

We needed pre-processing to make the image more noise free and accurate. Neighborhood sampling algorithm makes the image more robust to identify the vessel by selecting the pixel with values lies between 0.025 -0.55 μm.

Fig-2 – Pre-processing

Each color channel generate different pixel intensity value for the entities of the image. From study, we got that, the green color channel based image (pixel value only containing green intensity) gives the more suitable pixel set where different entity can be distinguished like exudates from image background.

Later we simply identify the set of pixels for different entities and segment them from the image based on thresholding (choose only those pixel  values lesser/greater than a particular value) and some mathematical morphological reconstruction.

Fig-3- Segmentation

Fig- 4

Hence, high intensity regions were segmented by thresholding for morphological reconstruction. Quantitative features were extracted as counts, total area due to microaneuryms, haemorrhages, exudates, blood vessels, number of bifurcation points. Features were statistically analyzed to find most significant ones. Finally, DR screening module has been developed based on neural network and fuzzy-rule based approaches.

Results :

The developed software provided around 85%, 77%, and 93% accuracy using the 100 images, respectively, for hemorrhages and microaneurysms, hard exudates . (Fig-5)

The specificity was 72 %


Fig -5

Conclusion :

The automated screening program was able to differentiate between the normal fundus and the diabetic retinopathy fundus. The program may be beneficial for use in screening for diabetic retinopathy. Further development of the program may provide higher sensitivity.

References :

  1. Singalavanija A, Supokavej J, Bamroongsuk P, Sinthanayothin C, Phoojaruenchanachai S, Kongbunkiat VFeasibility study on computer-aided screening for diabetic retinopathy.Jpn J Ophthalmol. 2006 Jul-Aug;50(4):361-6
  2. References :

    1. Singalavanija A, Supokavej J, Bamroongsuk P, Sinthanayothin C, Phoojaruenchanachai S, Kongbunkiat VFeasibility study on computer-aided screening for diabetic retinopathy.Jpn J Ophthalmol. 2006 Jul-Aug;50(4):361-6
    2. Automated analysis of retinal images for detection of referable diabetic retinopathy.Abràmoff MD, Folk JC, Han DP, Walker JD, Williams DF, Russell SR, Massin P, Cochener B, Gain P, Tang L, Lamard M, Moga DC, Quellec G, Niemeijer M. JAMA Ophthalmol. 2013 Mar;131(3):351-7. doi: 10.1001/jamaophthalmol.2013.1743.
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Complete visual recovery following intervention within critical period in a case of central retinal artery occlusion

Complete visual recovery following intervention within critical period in a case of central retinal artery occlusion

Abstract: A 55-year-old male presented to us within one and a half hour of sudden painless loss of vision in left eye on waking up in the morning. A diagnosis of central artery occlusion (CRAO) was made after complete ophthalmic examination and fundus fluorescein angiography revealed an atheromatous plaque in the inferotemporal branch of central retinal artery. Patient underwent immediate anterior chamber paracentesis, was given two tablets of 250 mg acetazolamide stat, two tablets of 5 mg of isosorbide dinitrate sublingually and was asked to rebreath in a paper bag. Fundus examination on fifth day of follow up revealed completely dislodged plaque with normal appearing retina. The final visual acuity two weeks later was 20/30. The case report highlights the importance of conservative management focused upon decreasing the intraocular pressure and vasodilation during the window period which might cause dislodgement of plaque or thrombus leading to complete visual recovery.

In this case study we reported that the patient had Central retinal artery occlusion (CRAO) in the left eye and appropriate intervention within critical period (around 90 minutes) salvaged his vision.


Key-words: Central retinal artery occlusion, AC paracentesis, Vasodilation, Critical period.



CRAO is an ophthalmic emergency with incidence of 1.3 in 100,000 reporting to clinics.[1] It causes irreversible damage to retina due to ischemic necrosis. Atherosclerosis related embolism and thrombus are thought to be responsible for majority of cases of CRAO. The length of time, the human retina can tolerate ischemia before irreversible damage occurs remains uncertain, however the window period for recovery is around 90 minutes.[2] Most of these patients present late when ischaemic necrosis has already settled in, and till date there is no proven treatment for such cases. Various modalities (AC paracentesis, ocular massage, oral acetazolamide) have been described for cases presenting in the window period. The efficacy of these modalities either as monotherapy or as combination therapy varies between 6 to 49%, with a mean visual improvement rate of 15 to 21%,[3] but overall these therapies do not alter the outcome more than the natural course of the disease. We herewith describe a rare case of CRAO managed by AC paracentesis and oral acetazolamide following which patient had complete visual recovery.

Case Report:

A 55-year-old male presented to us with sudden, painless loss of vision in the left eye, for the past one and a half hour. On examination, vision in right eye was 20/20, while it was just perception of light in the left eye. Pupil of left eye was non reacting, mid dilated with relative afferent pupillary defect (RAPD). Rest of the anterior segment examination in both eyes was unremarkable. Fundus examination of the right eye was within normal limits, while the left eye revealed peripapillary edema, severe arteriolar attenuation and boxcarring of vessels. A diagnosis of left central retinal artery occlusion was established. On systemic examination his pulse rate was 78 beat min-1 and regular, blood pressure 130/78 mmHg, respiratory rate 18 breaths min-1 , and he was afebrile. Patient was a chronic smoker, however was no history of diabetes mellitus, stroke, hypertension, or any cardiac disorder.

Immediate anterior chamber paracentesis was done with a 30 guage needle under aseptic precautions under topical anaesthesia and patient was give two tablets of 250 mg acetazolamide, and two tablets of 5 mg sublingual isosorbide dinitrate. Patient was allowed to rebreath in a paper bag for around 15 minutes. Repeat paracentesis was done thrice at  30 minutes interval by enlarging the previous port with 15⁰sideport blade and pressing the posterior lip of sideport by letting a gush of aqueous flow out. Fundus fluorescein angiography was done in the intervening period which revealed an atheromatous plaque in the infero temporal branch of central retinal artery at second bifurcation [Fig.1a] with delayed retinal arterial filling by 20 seconds [Fig. 1b]. Patient was advised to take tablet 5 mg  nitroglycerine thrice a day, and to continue rebreathing in the paper bag. Patient was also advised consultation with a cardiologist for a complete cardiao vascular evaluation.

Following this intervention, the patient noticed marked improvement in vision and the very next day visual acuity in left eye improved to finger counting at 3 meters. Two days later the best corrected visual acuity improved to 20/80 and pupil was sluggishly reacting. In the meantime echocardiography and electrocardiography revealed no abnormality. Complete hemogram, coagulation profile, and other systemic investigations were within normal limits .Serum lipid profile was mildly deranged with total cholesterol level being 278 mg/dl, LDL 194 mg/dl and Triglyceride 197 mg/dl. Carotid Doppler revealed focal calcified plaque at posterior bulb of both common carotid arteries with focal thickening.  He was advised Capsule Ecosprin AV 75/14 ( Aspirin and Atorvastatin) once daily and to stop smoking. On fifth day vision improved to 20/60 and repeat fundus photography revealed that the plaque had been dislodged [Fig. 2]. Two weeks later his best corrected vision improved to 20/30. The minimal residual visual loss was attributable to early nuclear sclerosis. Patient was advised regular monthly follow up.



CRAO is an ophthalmic emergency and more than 240 minutes of occlusion produces near total optic nerve atrophy and nerve fiber damage.[4] Good visual recovery has been reported as long as three days after CRAO.[5]  Though there is no consensus regarding treatment regimen for CRAO, a number of therapeutic interventions have been proposed. The optimal management of CRAO should be aimed at dislodging the vaso-occlusive cause (thrombus or plaque) allowing reperfusion and preventing secondary ischemic injury of  the retina.

The retinal tolerance time had been evaluated in experimental studies suggesting that the retina in elderly, hypertensive and atherosclerotic rhesus monkeys suffer no retinal damage to CRAO for 97 minutes.[2] Thereafter, partial recovery is possible if the ischemia is reversed within this period. Hence, for any treatment to be effective, it is essential to implement within the correct time window.

We tried to dislodge the emboli by inducing hypercarbia through rebreathing into paper bag and increasing retinal perfusion through paracentesis in combination with oral acetazolamide and ocular massage. A maximum increase in retinal artery volume flow of only 20% has been estimated from animal studies and a rise in perfusion pressure of less than 15% is expected when intraocular pressure falls from 15 to 5 mmHg.[6] Along with this, tablet sublingual nitroglycerine dilates the retinal vessels by relaxing vascular smooth muscle to improve the blood flow, although its efficacy is not proven.[7]

There are few reports means to lyse or dislodge the emboli by Nd-YAG Laser and pars plana vitrectomy,[8] but it is uncertain whether  these technique can be applied within the window period along with their own complications like vitreous hemorrhage, false aneurysm. Two large review[9,10]  have suggested that thrombolysis might improve the vision, however the rate of  adverse effects  was far higher  in the thrombolysis group than standard therapy group (37% vs 4.3%).[11]  The therapeutic uncertainty and the potential risk involved with thrombolyis prevented us from opting thrombolysis as a management option.

Hyperlipidemia, hypertension and diabetes are recognized risk factors for carotid stenosis.[12] All patients of central retinal artery occlusion need a complete systemic workup to rule out these conditions and proper management. Our patient was diagnosed with hyperlipidemia along with carotid plaque on Doppler. He was started on blood thinner and anti- hyperlipidemic drugs by the cardiologist. 

This present case highlights the importance of carrying out office measures (AC paracentesis, ocular massage, induced hypercapnia) in all cases of CRAO. Rapid lowering of intraocular pressure and induced vasodilatation by above means might improve retinal circulation sufficient enough to cause complete visual recovery as in the present case.

Written By: Dr Madhurima


  1. Jacqueline A. Leavitt, Theresa A. Larson. The incidence of Central Retinal Artery Occusion in Olmsted County, Minnesota; Ophthalmology 2011; 152: 820-3.
  2. Hayrey SS, Kolder HE, Weingeist TA. Central retinal artery occlusion and retinal tolerance time. Ophthalmology 1980; 87:75-78.
  3. Margo CE, Mack WP. Therapeutic decisions involving disparate clinical outcomes: patient preference survey for treatment of central retinal artery occlusion. Ophthalmology 1996; 103: 691.
  4. Hayreh SS, Jonas JB. Optik disk and retinal nerve fibre damage after transient central retinal artery  occlusion: an experimental study in rhesus monkeys. Am J Ophthalmology 2000; 129: 786-795
  5. Duker JS, Brown GC. Recovery following acute obstruction of retinal and choroidal circulations. A case history. Retina 1988; 8:257-260.
  6. Atebara NH, Brown GC, Cater J. Efficacy of anterior chamber paracentesis and Carbogen in treating acute nonarteritic central retinal artery occlusion.Ophthalmology. 1995; 102:2029-34.
  7. Rumelt S, Dorenboim Y, Rehany U. Aggressive systemic treatment for central artery occlusion. Am J Ophthalmology 1999; 128:733-8.
  8.  Tang WM. Topping TM. Vitreous surgery for central retinal artery occlusion. Arch Ophthalmol 2000; 118:1536-7.
  9. Biousse V, Calvetti O. Bruce BB, Newman NJ. Thrombolysis for central retinal artery occlusion. J Neuro Ophthamol  2007; 27:215-30.
  10. Noble J, Weizblit N, Baerlocher M, Enkk. Intra-arterial thrombolysis for central retinal artery occlusion: a systemic review. Br J Ophthalmol 2008; 92:588-93.
  11. Schumacher M, Schmidt D, Jurklies B, Gal C,Wanke I, Schmoor C et al. Central retinal artery occlusion: local intra-arterial fibrinolysis versus conservative treatment, a multicenter randomized trial. Ophthalmology 2010; 117: 1367-1375; e1361.
  12. Rudkin A, Lee A, Chen C. Vascular risk factors for central artery occlusion  Eye 2009; 24: 678-681.
Ten Things You Should Know about 3D Viewing System in Ophthalmology

Ten Things You Should Know about 3D Viewing System in Ophthalmology

1. Evolution of this latest state of the art technology in ophthalmology:

Three-dimensional (3D) display systems were first developed for aircraft and military use. The term “heads-up surgery” derived from the so-called “head-up display”, a display system first used in aircraft flight decks that projects an image into the normal field of view. This display system allows visualization in a “heads-up” position. In this procedure, the operating surgeon does not perform by looking at the eyepieces of the microscope, but by viewing the microscopic image on a panel display sent from a 3D camera[1]. After the creation of the TrueVision 3D Visualization System for Microsurgery, this innovative, ground-breaking technological boon has entered the operating room.

2. Major types of 3D visualization technique:

Conventional 3D systems are classified as either active or passive systems.

  • In active systems, the 3D image is obtained by showing high-speed consecutive images for the right and left eyes alternatively, while a special pair of electronic glasses actively suppress the image in the other eye.
  • In passive 3D systems, the three-dimensional image is acquired by mixing two images horizontally and then passively separating them into polarized 3D glasses.

3. Active systems:

Head mounting systems (HMS) are active systems. There are many HMS are available like, –

  • Sony Head-Mounted System HMS-3000 MT device
  • Avegant Glyph retinal projection system (Avegant Corp., Belmont, CA, USA)
  • Clarity™ (Beyeonics Surgical, Haifa, Israel).

Ivan Sutherland first started working on HMS in 1960. Its main purpose was to be used in military, police, firefighting, and civilian-commercial use, namely in video gaming and sports. HMS has been used by authorities to display tactical information such as maps or thermal imaging data while viewing a real scene.

HMS was first adapted in the operating room by Sony in 2012. They developed HMS-3000MT [2], which is a personal viewing system that provides a 3D colour video display of images from 3D surgical camera systems. Not only for the operating surgeon, but this system can also connect to a second head-mounted monitor, giving other theatre staff a simultaneous 3D view.

Mechanism of action for HMS: HMS device requires different images for the left and right eyes for depth perception. It differs from the conventional 3D system by showing two simultaneous images, one for each eye, avoiding the ghosting image effect caused by cross-talk in active 3D systems. The system of dual video inputs using two independent organic light-emitting diodes (OLED) panels offers a complete separate video signal to each eye, which provides the maximum resolution for each image [2].

Dutra-Medeiros et al performed several ophthalmic surgeries using the Haag-Streit Surgical microscope HS Hi-R NEO 900 (Haag-Streit Surgical GmbH, Wedel, Germany) connected to the Sony Head-Mounted System HMS-3000 MT device. They have done pars plana vitrectomy, phacoemulsification with intraocular lens (IOL) implantation, subluxated IOL extraction, epiretinal membrane peeling, internal limiting membrane peeling, endolaser photocoagulation, and tamponade with silicone oil and sulphur hexafluoride gas [3].

4. Passive systems:

Different passive systems in ophthalmology are,

  • TrueVision 3D Visualization System
  • NGENUITY® 3D Visualization System (Alcon, TX, USA)
  • Sony HD Medical Display system (Sony, Tokyo, Japan)
  • MKC 700 HD and CFA 3DL1 (Ikegami, Tokyo, Japan)
  • Panoramic RUV viewing system for vitreoretinal surgery (Leica, Wetzlar, Germany)
  • Artevo 800 by Zeiss

The TrueVision 3D Surgical System is a camera unit that attaches to standard surgical microscopes, sending stereoscopic images and video to a 3D, high-definition (HD), large-screen monitor positioned a few feet from the surgeon, providing visualization in real-time. The US Food and Drug Administration (FDA) has granted clearance for the TrueVision Refractive Cataract Toolset, an application that provides 3D graphical overlays for image-guided cataract surgery. More recently, TrueVision has developed the TrueGuide and the TruePlan applications, which have been designed for intelligent surgical planning to aid in achieving targeted refractive outcomes, as in toric IOL.

The NGENUITY 3D Visualization System is an FDA-regulated platform for digitally assisted vitreoretinal surgery with a 3D display, comprising four key elements: a high-dynamic-range 3D digital camera that provides superb resolution, image depth, clarity and colour contrast; a high-speed graphics processing unit that processes and optimizes stereoscopic images of anatomy and pathology during microsurgery; a 55-inch immersive 3Ddisplay that renders real-time images with 4K organic light-emitting diode(OLED) ultra-HD technology; and passive, circularly polarised 3D glasses, with augmented reality capability.

The NGENUITY® 3D Visualization System provides improved visualization at high magnification compared to traditional analog microscopy.

  • Provides 19% greater magnification
  • Delivers 2.7 times better depth of field
  • Produces 19% finer depth resolution

Surgeon benefit: 

  • Provides increased magnification of anatomical structures, instruments, implants, etc.
  • The need to refocus is less affected by typical patient movements
  • More anatomical structures, instruments, implants, etc. contained within voluminous surgical space remain in focus while performing surgical tasks
  • Improved delineation of anatomical structures such as ILM, ERM, detached retina, etc.

ARTEVO 800 was unveiled in 2019 at ASCRS. It produces a stereoscopic 3D image that is viewed using passive polarized glasses on a 55 inch 4K monitor, with 25% higher resolution and brightness. The field of vision is exceptional, no need to refocus the microscope; minor adjustments can be done with the foot pedal. Auto-Adjust technology anticipates workflow and change settings automatically when switched between the anterior and posterior segment providing a great depth of focus. Data, such as intraoperative OCT, cataract assistance functions, phaco vitrectomy values, patient information even operating room settings can be overlaid on to the screen without blocking the surgical view. The Hybrid technology allows the surgeon to use oculars at any point, a sterile knob can redirect a portion of the light to them while rest of the crew watches on screen, making it a powerful teaching tool.

5. Experience in cataract surgery:

Weinstock et al introduced a 3D viewing system in ophthalmology and first performed cataract surgery in 2010 with TrueVision. He reported a minimal time difference between the binocular microscope and 3D surgery. Interestingly, the rate of unplanned vitrectomy was three times higher in the standard microscope group compared with the TrueVision group. Hypothetically, superior depth perception, and higher magnification of the image may be factors associated with reduced risk of posterior capsular rupture and improved anterior vitrectomy[4,5].

In one study, Solomon J reported toric IOL implantation using TrueGuide® resulted in 83.3% of eyes were corrected to < 0.50 D of cylinder, and 100% were corrected to < 1.00 D cylinder. In addition, 80% of the eyes had final vision 20/20, 100% of the eyes achieved 20/25 or better [6,7]

6. Experience in cornea surgery:

In the year 2017 Mohamed et al first reported a non-Descemet Stripping Automated Endothelial Keratoplasty (nDSAEK) for post-traumatic bullous keratopathy and reported great visual experience and ergonomics. However, the authors state that frequent adjustment of focus was needed for a clear stereoscopic view of the flap[8]. Galvis et al in 2017 performed  DMEK. They reported good postoperative outcomes, easy learning curve, enhanced depth of field, colour contrast, and size/quality ratio compared to the traditional microscope, also Moutsouris’ sign was much more evident in the 3D screen[9].

7. Experience in strabismus surgery:

Hamasaki et al in 2019 published a small case series of strabismus surgery with NGENUITY® 3D Visualization System. They opined Strabismus surgery could be performed without special illumination, the potential to reduce phototoxic injury but there is some degree of assistant’s discomfort [10].

8. Experience in vitreoretinal procedures:

In the year of 2011 Riemman[11] performed a pilot study in VR surgery. Subsequently, Eckardt C and Paulo EB (2016) used TrueVision and reported superior ergonomics, similar speed, and ease of use of instruments. Adam et al in 2017 performed the surgery at 10% luminance level and concluded reduced requirements of illumination power [12].

With the help of NGENUITY 3D system, Skinner et al (2018) performed VR surgery in severe kyphotic patients with good pain control[13]. Coppola et al in 2017 proved triamcinolone staining is not required in 3D HUD[14]. There are numerous studies that concluded the 3D heads-up display system is not inferior to conventional surgery and, despite there being an 80-ms latency time compared with the standard microscope, it is not noticeable during intraocular procedures. In addition, 3D systems may reduce copiopia and asthenopia [15,16].

9. Advantages of 3D viewing system:

Traditional microsurgery can lead surgeons to deleterious neck and back postures that cause musculoskeletal fatigue and injuries, which has been associated with reduced surgical longevity. The prevalence of neck, upper body, or lower back symptoms among ophthalmologists has been reported to be as high as 62%. Superior ergonomics and good posture during the 3D surgery can provide a solution to this age-old hazard.

The brightness of the surgical field can be superior to that of traditional surgery, without exposing the retina to additional light. Electronic amplification of the camera’s signal to increase brightness might be helpful in situations of vitreous hemorrhage, opaque media, or dark pigmented fundus. Furthermore, the digital enhancement of the image might allow for the lesser application of vital dyes during surgery, reducing potential toxic side effects of such products. In addition, the NGENUITY 3D allows the simultaneous display of OCT scans and fluorescein angiograms that might facilitate and shorten procedure times. The rapid learning curve of the NGENUITY system has been confirmed in a recent prospective study assessing the learning curve in macular hole surgery[17].

10. Pitfalls of 3D viewing system:

Although three-dimensional display systems are increasingly demonstrating good results in ophthalmology, there are some noteworthy pitfalls. Most notably assistant discomfort and operating theatre logistics, visual disturbance by media opacities, and surgeon headache and nausea after prolonged laser photocoagulation. Some HMS devices will require becoming wireless before being more widely adopted. In conclusion, the 3D viewing system is showing ever more promising results in the field of ophthalmology. Despite few minor drawbacks, it’s probably the next sensation in ocular microsurgery offering benefits to both experienced surgeons and trainees.


  • References:
  1. Eckardt C, Paulo EB. Heads-up surgery for vitreoretinal procedures: an experimental and clinical study. Retina 2016;36:137–147.
  2. Sony’s HMS-3000MT brochure, available at https://pro.sony.com/bbsccms/assets/files/mkt/med/brochures/HMS-3000MT_brochure.pdf
  3. Dutra-Medeiros M , Nascimento J, Henriques J, Barrão S, Fernandes-Fonseca A, Aguiar-Silva N, Moura-Coelho N, Ágoas V. THREE-DIMENSIONAL HEAD-MOUNTED DISPLAY SYSTEM FOR OPHTHALMIC SURGICAL PROCEDURES Retina. 2017 Jan 16. doi: 10.1097/IAE.0000000000001514.
  4. Weinstock RJ, Desai N. Heads up cataract surgery with the TrueVision 3D Display System. In: Garg A, Alio JL, eds. Surgical Techniques in Ophthalmology—Cataract Surgery. New Dehli, India: Jaypee Medical Publishers; 2010:124–127.
  5. Weinstock RJ. Operate with your head up. Cataract Refract Surg Today. 2011;8:66, 74
  6. TrueGuide brochure, available at http://www.truevisionsys.com/TVS_TrueGuideBrochureN032515.final.pdf
  7. Jonathan Solomon at ACOS/CXL Congress Deer Valley 2014 – information available in the TrueGuide brochure
  8. Mohamed YH, Uematsu M, Inoue D, Kitaoka T. First experienceof nDSAEK with heads-up surgery: a case report. Medicine(Baltimore). 2017;96:e6906.
  9. Galvis V, Berrospi RD, Arias JD, et al. Heads up Descemet membrane endothelial keratoplasty performed using a 3D visualization system. J Surg Case Rep. 2017;rjx231.
  10. Hamasaki I, Shibata K, Shimizu T, et al. Lights-out surgery for strabismus using a heads-up 3D vision system. Acta Med Okayama. 2019;73:229–33.
  11. Riemann CD. Machine vision and vitrectomy: three-dimensional high definition (3DHD) video for surgical visualization in vitreoretinal surgery. Proceedings of the SPIE Volume 7863. Stereoscopic Displays and Applications XXII. 25 January 2011, San Francisco, CA, USA.
  12. Adam MK, Thornton S, Regillo CD, et al. Minimal endoillumination levels and display luminous emittance during three-dimensional heads-up vitreoretinal surgery. Retina. 2017;37:1746–9.
  13. Skinner CC, Riemann CD. “Heads up” digitally assisted surgical viewing for retinal detachment repair in a patient with severe kyphosis. Retina Cases Brief Rep. 2018;12:257–9.
  14. Coppola M, La Spina C, Rabiolo A, et al. Heads-up 3D vision system for retinal detachment surgery. Int J Retin Vitr. 2017;3:46.
  15. Weinstock RJ, Diakonis VF, Schwartz AJ, Weinstock AJ. Heads-up cataract surgery: complication rates, surgical duration, and comparison with traditional microscopes. J Refract Surg. 2019;35:318–22.
  16. Palácios RM, de Carvalho ACM, Maia M, et al. An experimental and clinical study on the initial experiences of Brazilian vitreoretinal surgeons with heads-up surgery. Graefes Arch Clin Exp Ophthalmol. 2019;257:473–83.
  17. Palácios RM, Maia A, Farah ME, Maia M. Learning curve of three-dimensional heads-up vitreoretinal surgery for treating macular holes: a prospective study. Int Ophthalmol. 2019; doi: 10.1007/s10792-019-01075-y
  18. Moura-Coelho, Nuno,l, José Henriques, Gama Pinto João Nascimento, et al. “Three-Dimensional Display Systems in Ophthalmic Surgery – A Review.” European Ophthalmic Review 13, no. 1 (2019): 31. https://doi.org/10.17925/EOR.2019.13.1.31.


  • Writers of the content: 
Dr Aniruddha Maiti. MBBS, DO, DNB, MNAMS,FRVS, FICO, MRCSED(Ophth)
Senior Vitreo Retinal consultant in Susrut Eye Foundation & Research Centre
Dr Aniruddha Maiti is a senior Vitreo Retinal consultant in Susrut Eye Foundation & Research Centre in Kolkata. After MBBS from Calcutta National Medical College in 2000 completed Diploma in Ophthalmology from Regional Institute of Ophthalmology ,Kolkata. This was followed by DNB & long term vitreo retinal fellowship from Mumbai. He has multiple publications and presentations in International & National forums along with instruction courses in ASRS ,AIOS & OSWB Conferences. His list of awards includes Dr Anutosh Dutta Gold Medal, 2005 for DO, AIOS Quiz winner 2008, the Young Researchers Award in AIOS 2010, IJO Gold Award for best publication in Indian Journal of Ophthalmology 2012, Fellow of International Council of Ophthalmology(FICO),2012, Dr K P Roy Memorial Award and Dr B K Mitra Memorial Award for best paper presentation in State Annual Conference 2012 & 2013 and AIOS APOS K Vengala Rao Award for best paper in Comprehensive Ophthalmology in All India Ophthalmological Society (AIOS) Annual Conference, 2015, best poster in 2017 State annual conference. Recipient of HONOR Award & Senior HONOR Award from American Society of Retina Specialists in 2018 & 2019 for outstanding academic contribution in ASRS. Received International Ophthalmic Heroes of India given by AIOS in 2019& 2020. He was the PG Education Committee Chairman and Joint Secretary of Ophthalmic Society of West Bengal. Presently is the Scientific Committee Chairman of OSWB from 2019-2020.


Dr Joydeep Majumdar,MBBS,DNB.
Vitreoretina Fellow, Susrut Eye Foundation & Research Centre
Dr Joydeep Majumdar passed MBBS from Calcutta national Medical College in 2015, completed DNB from JPM rotary eye hospital cuttack in 2019, currently pursuing retina fellowship from Susrut Eye foundation and research center, Kolkata.