Research Interests and Achievements

The eye is not just an extension of the brain. It’s a window to neurological health and a complex organ that drives and modulates many non-visual cerebral functions such as the pupillary light reflex, circadian entrainment, cognition, alertness, sleep and mood. I’m interested in the neurobiological interactions between the eye and the brain and in processes by which light can regulate ocular and neurological functioning and development. My goal is to translate fundamental findings in visual neurosciences into screening and therapeutic clinical interventions.

Understanding non-visual photoreception and using light to treat chronobiological disorders.

Over the past 15 years, my research focused not only on understanding the non-visual impact of light on physiology and behaviour in humans, but also on technical applications related to this matter. Within that framework, I contributed to the contemporary understanding of the non-image forming impacts of light detected by the retina, and led studies at the Concordia Polar Station, Stanford University, and INSERM/France, to successfully implement spectrally and temporally tailored lighting regimens, to treat chronobiological and sleep disorders, and alleviate associated health decrements. Main publication / Media coverage

Developing novel handheld devices and deep learning algorithms for the detection of sight and life-threatening conditions

Handheld chromatic pupillometry for ocular disease screening: At the Singapore Eye Research Institute (SERI), I tapped on the contemporary understanding in non-visual photoreception, and led the development of a novel handheld chromatic pupillometer allowing an objective, fast and accurate functional evaluation of ocular integrity. This handheld device, potentially useable in a non-clinical setting or even at home, yielded a high accuracy for the detection of ocular diseases such as glaucoma and diabetic retinopathy. Main publication / Media coverage #1 / Media coverage #2

Deep learning on ocular fundus photographs for the detection of intra-cranial hypertension: Together with Prof Dan Milea (SERI), I co-led the creation of the BONSAI Consortium and the development of the BONSAI deep learning system (DLS), in collaboration with the Institute of High Performance Computing (A*STAR). This DLS, trained on 14,341 fundus photographs collected from 19 sites in 11 countries worldwide, yielded a high accuracy for the classification of normal discs, discs with papilledema (a swelling of the optic disc that is due to intra-cranial hypertension – a life-threatening condition), and discs with other abnormalities (e.g., non-artretic ischemic optic neuropathy, optic disc atrophy, optic disc drusens) with AUCs of 0.98, 0.96 and 0.90, respectively. These findings, published in the most prestigious journal in Medicine, The New England Journal of Medicine, provide non-ophthalmology trained healthcare personnel with the means to identify sight and life-threatening conditions automatically on digital fundus images. Main publication

Optimizing the lighting environment for better myopia-control.

Myopia is a highly prevalent refractive error characterized by the blurred vision of objects when viewed at a distance. Myopia is projected to affect 50% of the world population by 2050 and is commonly due to excessive ocular axial growth leading to images being focused in front of the retina. Epidemiological studies have shown that time spent outdoors is protective against myopia. This can be due to the high intensity and peculiar spectral composition of sunlight. My team is conducting research in animal models and humans to better understand the impact of light on ocular growth and identify optimal features (i.e., intensity, pattern and spectrum) of light for better myopia-control. Our most recent findings in a chicken model of myopia, emphasize that ocular growth and metabolomics are dependent upon the spectral composition of ambient indoor white light. These novel findings, if translatable to humans, open new horizons for effective light-based and/or pharmacological therapy for myopia. Main publication / Media coverage

My group, in collaboration with A/Prof VA Barathi (SERI), is also one of the few groups in the world to have developed the Rhesus macaque model for myopia. Rhesus macaques constitute one of the most suitable models for vision research. Our preliminary findings using this model, show that form-deprived monkey eyes, reared under standard indoor light levels (150 lux) replicate all the features of myopia development in humans including axial elongation, negative refractive error, and choroidal thinning. Such changes are circumvented when animals are raised under an intermittent pattern of high illuminance light. Abstract

Some ongoing research projects:

• Handheld chromatic pupillometry with embedded machine learning for the classification of inner vs outer retinal dysfunction.
• Beyond Sight - Elucidating the Non-visual Consequences of Ocular Diseases.
• Identifying novel eye movement and pupillometric biomarkers in ocular and neurological diseases.
• The Spectral Tuning of Light for MyOPia-control (STOP).
• Intermittent bright light for myopia-control: pathways and implementation strategies

Open Research Positions:

• Postdoctoral Research Fellow (Visual Neuroscience, Vision Science)
• PhD Students

For more details, please contact:

Asst/Prof Raymond P. Najjar (rpnajjar@nus.edu.sg)

Selected Publications

• Sia, J.T., Lee, E.P.X., Cheung, C.M.G., Fenwick, E.K., Laude, A., Ho, K.C., Fenner, B.J., Wong, T.Y., Milea, D., Lamoureux, E.L., Man, R.E.K., Najjar, R.P., 2022. Associations between age-related macular degeneration and sleep dysfunction: A systematic review. Clin Exp Ophthalmol. 2022 Dec;50(9):1025-1037. https://doi.org/10.1111/ceo.14146
• Tan, T.-E., Finkelstein, M.T., Tan, G.S.W., Tan, A.C.S., Chan, C.M., Mathur, R., Wong, E.Y.M., Cheung, C.M.G., Wong, T.Y., Milea, D., Najjar, R.P., 2022. Retinal neural dysfunction in diabetes revealed with handheld chromatic pupillometry. Clin Exp Ophthalmol. 2022 Sep;50(7):745-756. https://doi.org/10.1111/ceo.14116
• Muralidharan, A.R., Low, S.W.Y., Lee, Y.C., Barathi, V.A., Saw, S.-M., Milea, D., Najjar, R.P., 2022. Recovery From Form-Deprivation Myopia in Chicks Is Dependent Upon the Fullness and Correlated Color Temperature of the Light Spectrum. Invest Ophthalmol Vis Sci. 2022 Feb 1;63(2):16. https://doi.org/10.1167/iovs.63.2.16
• Najjar, R.P., Rukmini, A.V., Finkelstein, M.T., Nusinovici, S., Mani, B., Nongpiur, M.E., Perera, S., Husain, R., Aung, T., Milea, D., 2021. Handheld chromatic pupillometry can accurately and rapidly reveal functional loss in glaucoma. Br J Ophthalmol. 2021 Dec 1:bjophthalmol-2021-319938. https://doi.org/10.1136/bjophthalmol-2021-319938
• Vasseneix, C., Najjar, R.P., Xu, X., Tang, Z., Loo, J.L., Singhal, S., Tow, S., Milea, L., Wei Sw Ting, D.S., Liu, Y., Wong, T.Y., Newman, N.J., Biousse, V., Milea, D., BONSAI Group, 2021. Accuracy of a Deep Learning System for Classification of Papilledema Severity on Ocular Fundus Photographs. Neurology. 2021 Jul 27;97(4):e369-e377. https://doi.org/10.1212/WNL.0000000000012226
• Biousse, V.*, Newman, N.J.*, Najjar, R.P.*, Vasseneix, C., Xu, X., Ting, D.S., Milea, L.B., Hwang, J.-M., Kim, D.H., Yang, H.K., Hamann, S., Chen, J.J., Liu, Y., Wong, T.Y., Milea, D., BONSAI (Brain and Optic Nerve Study with Artificial Intelligence) Study Group, 2020. Optic Disc Classification by Deep Learning versus Expert Neuro-Ophthalmologists. Ann Neurol. 2020 Oct;88(4):785-795. https://doi.org/10.1002/ana.25839 *Co-first author
• Milea, D.*, Najjar, R.P.*, Jiang, Z., Ting, D., Vasseneix, C., Xu, X., Aghsaei Fard, M., Fonseca, P., Vanikieti, K., Lagrèze, W.A., La Morgia, C., Cheung, C.Y., Hamann, S., Chiquet, C., Sanda, N., Yang, H., Mejico, L.J., Rougier, M.-B., Kho, R., Tran, T.H.C., Singhal, S., Gohier, P., Clermont-Vignal, C., Cheng, C.-Y., Jonas, J.B., Yu-Wai-Man, P., Fraser, C.L., Chen, J.J., Ambika, S., Miller, N.R., Liu, Y., Newman, N.J., Wong, T.Y., Biousse, V., 2020. Artificial Intelligence to Detect Papilledema from Ocular Fundus Photographs. N Engl J Med. 2020 Apr 30;382(18):1687-1695. https://doi.org/10.1056/NEJMoa1917130 *Co-first author
• Prayag, A.S., Najjar, R.P., Gronfier, C., 2019. Melatonin suppression is exquisitely sensitive to light and primarily driven by melanopsin in humans. J Pineal Res. 2019 May;66(4):e12562. https://doi.org /10.1111/jpi.12562
• Najjar, R.P., Sharma, S., Atalay, E., Rukmini, A.V., Sun, C., Lock, J.Z., Baskaran, M., Perera, S.A., Husain, R., Lamoureux, E., Gooley, J.J., Aung, T., Milea, D., 2018. Pupillary Responses to Full-Field Chromatic Stimuli Are Reduced in Patients with Early-Stage Primary Open-Angle Glaucoma. Ophthalmology. 2018 Sep;125(9):1362-1371. https://doi.org/10.1016/j.ophtha.2018.02.024
• Najjar, R.P., Zeitzer, J.M., 2016. Temporal integration of light flashes by the human circadian system. J Clin Invest. 2016 Mar 1;126(3):938-47. https://doi.org/10.1172/JCI82306

Collaborations

View more details on the collaborations here