Neuro-ophthalmology is a subspecialty that deals with the relationship between the eyes and the brain. The visual pathway that carries vision is made up of a complex route that runs from the optic nerve to the optic chiasm, optic tract, lateral geniculate body, optic radiations, and then to the visual cortex in the occipital lobe. Depending on where a lesion occurs in this system, characteristic visual field defects and eye movement disorders can appear.
The history of this field begins with ancient theories of vision. It is a lineage of knowledge spanning about 2,500 years, leading from Renaissance anatomical discoveries, through 19th-century specialization, to the establishment of the subspecialty in the 20th century and into the present day.
It is a subspecialty of ophthalmology that deals with the relationship between the eyes and the brain. It specializes in diseases where the nervous system and the eyes overlap, such as disorders of the visual pathway including the optic nerve, optic chiasm, and visual cortex, eye movement disorders, and pupil abnormalities. It was established through the accumulation of anatomical discoveries, beginning with the study of ancient theories of vision.
Philosophers of ancient Greece were the first to discuss the nature of vision in a systematic way.
The table below shows the main figures and how the theories changed over time.
| Person / period | Origin / era | Main claim |
|---|---|---|
| Socrates (469-399 BC) | Greece | Perception can be altered by filters |
| Plato (427-347 BC) | Greece | Formulated the emission theory (the eye emits rays) |
| Aristotle (384-322 BC) | Greece | Questioned the emission theory |
| Euclid (325-265 BC) | Greece | Performed ray tracing and gave the emission theory mathematical credibility |
Socrates is considered one of the first to argue that perception can change under the filter of the mind, referring to the allegory of the cave. Plato formulated the emission theory, the idea that the eye sends out finger-like protrusions that touch the environment. Aristotle questioned this theory, asking how such protrusions could reach distant mountains. Euclid carried out the first ray tracing, giving the emission theory mathematical credibility.
Herophilos of Alexandria (344–289 BCE) noted that sensory function passes through something that connects the brain and the eye, and left the first descriptions of the optic nerve and the optic chiasm.
Galen of Pergamon (129–216) described cranial nerves III, IV, and VI (the oculomotor, trochlear, and abducens nerves) through his studies of gladiators. The oculomotor nerve (CN3) supplies the medial rectus, superior rectus, inferior rectus, inferior oblique, and levator palpebrae superioris; the trochlear nerve (CN4) supplies the superior oblique; and the abducens nerve (CN6) supplies the lateral rectus. Galen believed the optic nerve was hollow and carried resonant waves to the brain’s three ventricles for sensation, reasoning, and memory, establishing the basic idea of a physical connection between the eye and the brain.
Al-Kindi (800–870) supported a theory that combined emission and intromission. In this view, the eye sends light out to the object being observed, and that light reflects back into the eye.
The beginning of neuro-ophthalmology is marked by Ibn al-Haytham (Alhazen, 965–1040). He created early visual representations of the eye and visual pathways, depicting the lens as the light receptor and the optic nerve as a hollow tube. He explained that the image is first formed by the lens, then travels through the optic nerve to meet at the optic chiasm, where the images from both eyes are integrated. He also argued that both eyes recognize a single image because each eye has one corresponding point within corresponding points. However, he did not recognize the inverted image on the retina.
In ancient Greece, the emission theory—the idea that the eye emits rays that touch the surrounding world—was long supported. Euclid gave it a mathematical basis. Later, the Arab scholar Ibn al-Haytham created diagrams of the visual pathway and explained image formation by the lens and image integration at the optic chiasm. The shift from emission theory to intromission theory was an intellectual process that took about 1,000 years.
During the Renaissance, understanding of vision changed dramatically. The work of the main contributors is shown below.
Da Vinci
Leonardo da Vinci (1452-1519): Rejected the emission theory. Proposed the revolutionary idea that the eye works like a camera obscura.
Diagram of the ventricles: Drew the pathways to the lateral ventricles and the third and fourth ventricles, showing a deeper understanding of anatomy.
Vesalius
Andreas Vesalius (1514-1565): Disproved Galen’s claim that the optic nerve was hollow and showed that it is a solid bundle of fibers.
Termination in the thalamus: Correctly showed that the optic nerve ends in the thalamus, paving the way for a more accurate understanding of the visual pathway.
Kepler and Newton
Johannes Kepler (1571-1630): Discovered the path of light to the retina. Raised the fundamental question of whether we see with the brain or with the eye.
Isaac Newton (1643-1727): In 1704, hypothesized partial crossing of optic nerve fibers at the optic chiasm.
Thomas Willis (1621-1675) and William Briggs (1650-1704) showed that the eye provides input to the brain through the optic nerve.
At the optic chiasm, crossing fibers from the nasal retina enter the optic tract on the opposite side, while uncrossed fibers from the temporal retina enter the optic tract on the same side. This partial decussation theory, proposed by Newton in 1704, was later confirmed in 1880 by pathological examination by Bernhard von Gudden (1824-1886).
In the 19th century, understanding of brain anatomy advanced greatly, and neurology and ophthalmology emerged as independent specialties.
Francesco Gennari (1752-1797) identified a distinctive extra layer in the visual cortex. This is the structure now known as the Gennari line.
Marie-Jean-Pierre Flourens (1794-1867) showed through animal experiments that removing the visual cortex leads to loss of vision.
Pierre Gratiolet (1815-1865) clarified the connections of the optic tract (Gratiolet radiation, that is, the optic radiation) and its connections to the lateral geniculate body and the pretectal area. The lateral geniculate body has six layers, with crossing fibers entering layers 1, 4, and 6, and uncrossed fibers entering layers 2, 3, and 5. These discoveries defined the visual pathway as a complex, multilayered system.
In 1851, Hermann von Helmholtz (1821-1894) invented the ophthalmoscope. This allowed clinicians to directly observe the optic disc and retina, making it possible for the first time to correlate specific eye findings with neurological diseases.
Albrecht von Gräfe (1828-1894) used the ophthalmoscope and was the first to detect bilateral papilledema in patients with brain tumors.
Hughlings Jackson (1835-1911) strongly advocated the importance of routine ophthalmoscopic fundus examination. He even said that neurological disease cannot be diagnosed without an ophthalmoscope, and noted that severe headaches require an ophthalmic examination.
Hermann Wilbrand (1851-1935), together with Alfred Zenger, wrote the nine-volume work Neurology of the Eye and linked clinical findings and pathological specimens in detail. This was a landmark achievement that first documented that a lesion anywhere in the visual pathway beyond the optic chiasm can cause homonymous hemianopia.
Johann Friedrich Horner (1834-1886) and the physiologist Claude Bernard (1813-1878) described ocular sympathetic denervation, later known as Horner syndrome.
Santiago Ramón y Cajal (1852-1934) created detailed drawings based on the retina and proved that the nervous system is made up of individual neurons. For this work, he received the Nobel Prize in Physiology or Medicine in 1906.
Cyrus Weir Mitchell (1829-1914) studied nerve injuries in soldiers during the American Civil War. Gordon Holmes (1876-1965) studied the relationship between gunshot wounds to the occipital lobe and specific visual deficits during World War I, clarifying the functional organization of the visual cortex.
Also, Alfred Graefe and Franciscus Cornelis Donders (1818-1889) were pioneers who discussed convergence, accommodation, and strabismus, and William C. Posey (1866-1934) and William C. Spiller (1863-1940) edited the coauthored book The Eye and the Nervous System, laying the literary foundation for American neuro-ophthalmology.
The ophthalmoscope invented by Helmholtz in 1851 made it possible for clinicians to directly observe the optic disc and retina for the first time. This first established the link between eye findings and neurological disease, and laid the foundation for the clinical practice of neuro-ophthalmology, for example with von Graefe detecting bilateral papilledema in brain tumors.
Modern neuro-ophthalmology was fundamentally defined by Frank Burton Walsh (1895-1978).
Walsh at the Wilmer Eye Institute at Johns Hopkins Hospital meticulously documented extensive clinical cases and worked closely with neurologists and neurosurgeons. The result of systematizing observations that had been only loosely related was Clinical Neuro-Ophthalmology (first edition, 1947), often called the bible of the field. This book became the definitive reference that summarized and defined the field.
Walsh later coauthored with William F. Hoyt at the University of California, San Francisco, expanding the book into the revised three-volume Walsh and Hoyt’s Clinical Neuro-Ophthalmology (1969). Hoyt trained more than 70 fellows, many of whom became leaders in neuro-ophthalmology.
Walsh
Frank Walsh (1895-1978): At Johns Hopkins, he documented clinical cases in detail and promoted collaboration with neurology and neurosurgery.
Clinical Neuro-Ophthalmology (1947): The decisive reference that established the direction of neuro-ophthalmology as the field’s bible.
Cogan
David G. Cogan (1908-1993): Renowned for research on eye movement disorders caused by lesions of the central nervous system.
Main works: Neurology of the Ocular Muscles (1948) and Neurology of the Visual System (1966). His leadership role at the National Eye Institute strengthened the field’s scientific credibility.
Hoyt and Successors
William F. Hoyt: Trained more than 70 fellows. At Bascom Palmer, J. Lawton Smith, Glaser, Schatz, and David formed a center of neuro-ophthalmology.
Simmons Lessell (1933-2016): Described toxic optic neuropathy, visual persistence, and cerebral achromatopsia. He wrote more than 200 papers and received the Hoyt Award in 2003.
Other Hoyt Award recipients include Jonathan Trobe (University of Michigan, honored pioneers in the field in the Legacy Series), Neil Miller (who took over Walsh’s chair at the Wilmer Eye Institute), Nancy Newman (Emory University), and Alfred Sadun (research on hereditary optic neuropathy and mitochondrial disease).
At Johns Hopkins, Walsh carefully documented a wide range of clinical cases and actively promoted multidisciplinary collaboration with neurologists and neurosurgeons. He systematized observations that had previously been loosely connected, and his 1947 book, “Clinical Neuro-Ophthalmology,” became the definitive reference in the field. He is called the “founder” because he brought individual observations together as one discipline.
The establishment of neuro-ophthalmology as an independent subspecialty was the result of the tireless efforts of many distinguished predecessors and was achieved through a gradual process.
The following are the technological innovations that greatly changed diagnosis in modern times.
Advances in genetics and molecular biology have fundamentally changed our understanding of complex disease mechanisms. A field once defined by description and careful observation has become one characterized by intervention, innovation, and multidisciplinary collaboration. At the same time, fidelity to its clinical roots—careful history taking, examination, and mentorship—remains unchanged.
One challenge facing modern neuro-ophthalmology is that demand for neuro-ophthalmologists is growing faster than the supply of the workforce. Training, sustainability, and access to care are urgent issues.
