Mini Museum 3- The Eye and the Intricacies of Visual Perception by

LASIK: developing precise vision

subramanian193 — 2024-04-22 20:23:07 UTC

In the late 20th century, LASIK (Laser-Assisted In Situ Keratomileusis) surgery has become an advancement in ophthalmology. It serves in vision correcting procedures. Before LASIK, surgery required procedures like radial keratotomy (RK) and photorefractive keratectomy (PRK). These techniques weren't extremely effective and came with potential dangers. The concept of reshaping the cornea using a laser to correct refractive errors had been explored readily. The technology and techniques necessary for safe and precise corneal reshaping were developed in the late 20th century. The key technological advancement, the development of the excimer laser, allowed for the development for LASIK surgery. This specialized laser emits a cool ultraviolet light that can remove microscopic quantities of tissue from the cornea without damaging surrounding structures. Ophthalmologists refined surgical protocols and parameters to achieve optimal outcomes while minimizing risks and side effects. LASIK strives for the correction of myopia (nearsightedness), hyperopia (farsightedness), and astigmatism. It gained popularity among patients since it is safe, effective, and minimally invasive. LASIK surgery offered was the outcome of incredible understanding of the eye and vision. Patients experienced rapid improvement in vision and reduced daily need for glasses or contact lenses.

Source:

https://en.wikipedia.org/wiki/LASIK

https://www.webmd.com/eye-health/lasik-laser-eye-surgery

The Early Questions of Vision: Extramission Theory

subramanian193 — 2024-04-22 20:24:26 UTC

Galen who was a Greek physician in Europe in 130-200 AD made significant contributions to the understanding of the human body, including the eye. In relevance ophthalmology, Galen developed theories that influenced the understanding of vision which is relevant today in neuroscience and understanding our senses. He believed that the eye was composed of membranes and different fluids that allowed us to exude vision. The extramission theory of vision was one of Galen's relevant theories. Galen theorized that vision occurs when the eye emits rays of light that touch objects, allowing perception. This concept was contradictory with the later-established intromission theory, which states that objects emitted light that opposingly entered the eye. Galen's interest in understanding the body and anatomy served as an incredible neuroscientific pillar to help us with early understanding of senses and particularly vision. Furthermore, Galen had an understanding of the eye to be able to function with the anatomical understanding of the lens which projected images to the human body. As many people from his time did, he perceived sight as a process involving an optical pneuma, a vital spirit flowing from the brain to the eyes through hollow optic nerves. This pneuma was believed to convey sensory information from the external world to the brain, providing the eye with instructions for vision. Galen studied the work of anatomists like Rufus of Ephesus, and enhanced the structures. He made the retina, cornea, iris, uvea, tear ducts, and eyelids, more detailed, providing a comprehensive understanding of the eye's composition. Galen also identified two important fluids within the eye: the vitreous humor and the aqueous humor. These fluids were thought to play crucial roles in maintaining the eye's shape and facilitating vision.

Sources:

https://pubmed.ncbi.nlm.nih.gov/16052835/

Photoreceptors, Color, and Helmholtz' theory of color vision

subramanian193 — 2024-04-22 20:28:00 UTC

In the mid-19th century, Helmholtz proposed the trichromatic theory of color vision, which revolutionized our understanding of how humans perceive color. Thomas Young's thepory bled into Helmholtz' understanding of the eye and color. This theory suggested that the human eye has three types of receptors, each sensitive to a different range of wavelengths corresponding roughly to red, green, and blue. Helmholtz's trichromatic theory stated that combined activity of three types of cone cells in the retina, allowed for vision in color to be possible and furthermore, we have the ability to view different wavelength of visible light. These cones are now known as short-wavelength (S-cones), medium-wavelength (M-cones), and long-wavelength (L-cones) cones. The activation of these cones in different combinations allows humans to perceive a wide range of colors. Helmholtz supported his theory with experimental evidence, including psychophysical experiments in which he observed color mixing and color matching. He also used mathematical modeling to explain how the responses of the three types of cones could account for the perception of a diverse array of colors. Helmholtz's trichromatic theory laid the foundation for modern understanding of color vision. It provided a framework for subsequent research into the neural mechanisms underlying color perception, including the discovery of opsins and the organization of color-sensitive cells in the retina and visual cortex. Neuroscience studies have investigated how cone photoreceptors in the retina work and it’s incredible to understand their sensitivity, wide spectrum and synaptic connections with downstream neurons.

Source:

https://study.com/academy/lesson/young-helmholtzs-trichromatic-theory-of-color-vision.html#:~:text=The%20trichromatic%20theory%20of%20color%20vision%20says%20that%20human%20eyes,tested%20by%20Hermann%20Von%20Helmholtz.

Varsalius eyes meet the depiction of anatomy

subramanian193 — 2024-04-22 20:29:54 UTC

Vesalius's anatomical illustrations of the eye depicted its various components, such as the cornea, iris, lens, retina, and optic nerve, with remarkable precision. His work contributed to a comprehensive understanding of ocular anatomy, which is essential for studying vision and visual processing. While Vesalius's primary focus was on gross anatomy, his descriptions of the eye and surrounding structures provided insights into the organization of the visual pathways within the brain. Although the finer details of neural connectivity were not fully elucidated until later centuries, Vesalius's work laid the groundwork for subsequent studies on the visual system. "De Humani Corporis Fabrica" became a cornerstone of medical education, influencing generations of anatomists and neuroscientists. Vesalius's detailed illustrations of the eye and other anatomical structures remain invaluable resources for teaching and learning about the nervous system and sensory organs. Vesalius's work marked a departure from the traditional teachings of anatomy, which relied heavily on the writings of ancient authorities like Galen. By emphasizing the importance of direct observation and empirical study through human dissection, Vesalius revolutionized anatomical science and paved the way for modern neuroscience research.

Sources:

https://www.nature.com/articles/521160a

George Wald's light-sensitive component: Vitamin A, discovery in rhodopsin

subramanian193 — 2024-04-23 01:53:36 UTC

George Wald, an American scientist, played a central role in the discovery of rhodopsin. Rhodopsin is a light-sensitive pigment found in the rod cells of the retina, which are specialized photoreceptor cells responsible for low-light and night vision. Before its discovery, the molecular mechanism underlying the sensitivity of rod cells to light was not fully understood. Along with his colleagues, Wald conducted pioneering research aimed at elucidating the biochemical processes involved in vision. Wald and his team conducted a series of experiments using biochemical techniques to isolate and characterize the light-sensitive pigment present in rod cells. They analyzed the chemical composition and spectral properties of the pigment to unravel its role in visual perception. Through their research, Wald identified rhodopsin, which is the pigment responsible for light sensitivity in rod cells. Rhodopsin is a protein complex consisting of a protein called opsin and a light-sensitive molecule called retinal (a derivative of vitamin A). Rhodopsin plays a crucial role in the initial stages of the visual transduction cascade, where it absorbs photons of light and undergoes a series of molecular changes, which leads to electrical signals being generated. This gets transmitted to the brain, resulting in the perception of images. George Wald was awarded the Nobel Prize in Physiology or Medicine in 1967, along with Haldan Keffer Hartline and Ragnar Granit, for discovering physiological and chemical visual processes of rhodopson in the eye. We now know molecular mechanisms regarding vision. It laid the foundation for further research into the biochemistry of vision and has allowed development of therapies for vision disorders related to rhodopsin malfunction.

SOURCE:

https://www.nobelprize.org/prizes/medicine/1967/wald/facts/

The Accidental Discovery of Inversions in our Retina

subramanian193 — 2024-04-23 01:55:10 UTC

Johannes Kepler was a German scientist, philosopher, mathematician and astronomer, who lived from 1571-1630. He was incredibly significant in connection philosophical and histography in science which has been monumental in our understanding of the laws of nature and science. Kepler published his book, Ad Vitellionem Paralipomena which was the earliest in 1604, to explain the closest understanding to optical anatomy and optics of the eye. This was very closely related to his scientific knowledge or mirrors and lens which is reflected in his review of the inverse square law of light intensity. One particularly specific discovery is that he understood how images were inversely reflected on the retina and it's recognition and information processing. This was not in his specific field of study, and didn't gain deep study from Kepler as it didn't pertain to his scientific interests. Although he has not been entirely correct in the connection pathways, his understanding of the eye correlation to the brain and visual processing is foundational for modern optics. He Kepler also goes into detail regarding conic sections and foci to reflect the continuous change of the projective geometry.

Source:

https://en.wikipedia.org/wiki/Johannes_Kepler#Optics

Marriott's Spot: Discovery of the blind spot of the eye

subramanian193 — 2024-04-23 12:46:13 UTC

Mariotte techniques with as grid patterns and recorded measurements to map out the visual field and identify any areas where perception of the observed object seemed to be lacking. Mariotte conducted an experiment using a small white circle on a dark background as a fixed point for his vision. He placed another circle next to it, slightly lower and to the right, about two feet away. Keeping his right eye focused on the first circle, he gradually moved away. When he reached a distance of ten feet, the second circle, approximately four inches wide, disappeared from view. He repeated the experiment with his left eye, closing the right one, and achieved the same result. This was incredible to see that the loss of vision as due to the optic nerve rather than a disordered visual field. Mariotte was additionally the first to measure the size of the blind spot, which he did by observing that the largest circle of paper, and measuring when it disappeared from vision. According to Mariotte, the blind spot had a diameter ranging from 1/9 to 1/10 of the experiment's distance. Using established optical principles, he deduced that the blind area in the eye matched the entrance of the optic nerve. Additionally, he proposed a technique to illustrate the blind spots caused by large blood vessels near the papilla's edge. These are all incredible discoveries for neuroscience and the progression of our understanding of the eye and the neurological connections to daily life.

Sources:

https://pubmed.ncbi.nlm.nih.gov/17574069/#:~:text=Edme%20Mariotte%2C%20a%20Roman%20Catholic%20priest%20and,perception%20is%20less%20well%20remembered.%20In%20%E2%80%A6

Electricity of the Eye: Discovering Resting Potential

subramanian193 — 2024-04-23 12:48:26 UTC

Du Bois Reymond discovered the resting potential of the eye. He was a German physiologist and physicist born in 1818 and passing away in 1896. He analyzed via electro-oculography (EOG) which is a technique that measures eye movement by detecting changes in the corneoretinal potential. This potential is generally within the range of 0.4 to 1.0 mV. Horizontal eye movements are measured using electrodes placed at the outer canthi of the left and right eyes. When the eye moves, a potential difference is recorded between the electrodes. One direction of movement becomes positive and the other negative. Calibration involves having the patient look at two known fixation points a set angle apart to determine signal accuracy. EOG is generally accurate with a solid range of analysis but the linearity decreases after approaching 30°. There are advantages of of EOG which include the ability to record in darkness or with closed eyes. He also debated the understanding of eye movement, Through his studies we have a better understanding of the difference between 'pursuit' movements of only the eye moving, and 'compensatory' movements are by body and/or head movement. He also allowed us to further understand that eye movements are adjacent with the head positioning and allowed the eyes to move in parallel. Eye movement is also analysed via the jumping of one eye focus spot to the next called saccadic movements.

Sources:

https://www.bem.fi/book/28/28.htm#:~:text=Emil%20du%20Bois%2DReymond%20(1848,of%20as%20a%20resting%20potential.

The Optic Chiasm

subramanian193 — 2024-04-23 12:48:38 UTC

The optic chiasm has been of our interest since 460 BC and has been studied my a plethora of physicians and neuroscientists over a period of time. The optic chiasm is a crucial intersection in the visual sensory system, involving 2.4 million afferent axons, and intersects neurosurgery, ophthalmology, neurology, and endocrinology. To start, Hippocrates made early approximations of the chiasm's function and structure, noting its involvement in vision. Anatomists in such as Herophilus and Erasistratus, furthered understanding through dissections of humans and animals.

Rufus of Ephesus furthered our understanding through study and research in neuroanatomy and described the optic chiasm's role in vision. Galen of Pergamon had theories on vision and the optic chiasm, though it was hard to truly know due to the lack of human dissections. Arab physicians like Rhazes and Avicenna built upon Galen's work, suggesting the decussation of optic nerves at the chiasm and its role in binocular vision. Anatomical dissections happened later in Europe in the thirteenth century, with scientists like Mondino de Luzzi producing the first modern manuals of anatomy, which described the optic chiasm in relation with optic nerves. Isaac Newton, in the late seventeenth century, suggested partial crossing of the optic nerves in the chiasm, which was later confirmed. The nineteenth century saw experimental studies confirming chiasmal semi-decussation and understanding the consequences of optic chiasm compression, leading to advancements in neuro-ophthalmology. Now we are able to have a deepened understanding of the importance, sensitivity, and neuronal logic behind the optic chiasm with centuries of study to reinforce.

Sources:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5644697/

Sushruta: the father of Indian ophthalmology, a look into Cataracts

subramanian193 — 2024-04-23 12:53:26 UTC

Sushruta was a surgeon in India in 5 BC and was celebrated for his incredibly forward thinking surgical techniques and contributions to diseases that are still being developed today in modern medicine. He authored the Sushruta Samhita, a text with information about medicine, surgery, treatments, and had an extensive understanding of ayurvedic medical treatments. Sushruta delved into the surgical methods behind plastics and ophthalmology as a pioneer of his time. He developed extracapsular cataract surgery which utilized a pointed instrument with a trough like-end to access the tissue. This is incredibly useful for neuroscience as a field, and neurosurgery, because the eyes and surgical methods are crucial to brain surgery and any type of analysis of damage in the eyes or connection to the brain. Sushruta analysed different disorders that are extremely insightful in our growth to understanding of the proper and improper functionalities of the brain. His understanding of Ayurvedic principles emphasized the importance of treating the individual as a whole, considering both physical and spiritual well-being in the pursuit of health, which our medical practices today otherwise lack.

Source:

https://pubmed.ncbi.nlm.nih.gov/9476614/#:~:text=In%20particular%2C%20Sushruta%20describes%20what,a%20testament%20to%20his%20virtuosity.

Optical coherence tomography: A modern visualization method of the retinal intricacies

subramanian193 — 2024-04-23 12:53:51 UTC

Optical Coherence Tomography, or OTC allows ophthalmologists to see each layer of the retina and measure their thickness. This has helped diagnose and guide treatment for glaucoma, age-related macular degeneration (AMD), and diabetic eye disease. With an angiography, we are able to take pictures of blood vessels in and under the retina without using dyes to understand any issues that are occuring.This procedure is relatively quick, lasting about 5 to 10 minutes, in which a patient will sit with their head rested which eye drops dilate their eyes. This method and machine is used to understand the presence of macular holes, puckers, edemas, glaucomas, and diabetic retinopathy. Since we have the analysis of fluid in the retina, vitreous traction and abnormal blood vessels are detected as well. The optic nerves are observed clearly which is a clear example of the progression of neuroscientists in the past and present affecting the work and growth of the field and science. The relevance dates all the way back to the first artifact regarding cataracts. OCT utilizes light waves though, which means it cannot be used with dense cataracts or significant vitreous bleeding.

Source:

https://www.aao.org/eye-health/treatments/what-is-optical-coherence-tomography

Revival after partial blindness: rewiring the visual system

subramanian193 — 2024-04-23 19:50:50 UTC

A study funded by the National Institute of Health studied mice for induced stimulation. It shows high-contrast visual stimulation aids damaged retinal neurons regrow optic nerve fibers. As it was studied alongside chemical neural stimulation, this approach resulted in more significant axon growth than previous strategies, leading to partial visual function restoration in mice. Investigators observed the ability to track moving objects, pupillary reflex, depth perception, and ability to detect a predator, which showed mice with combination therapy to perform better in. Adult regenerated central nervous system axons can navigate to the correct brain targets, which is an incredible step for the understanding of cell growth, and restoration in neuroscience. Generally, optic nerve damage causes vision loss and as we’ve observed, retinal ganglion cell axons typically don't regrow in adults. Mice with induced optic nerve damage exposed to high-contrast visual stimulation showed unexpected axonal regrowth. The process of combining increased mTOR activity with visual stimulation allowed for axon regeneration, promoting brain visual centers to be restored when sutured close. The regenerating axons were able to perform and navigate properly in the brain after the combination. The research holds promise for therapies targeting retinal diseases, which is a big step for optics.

Sources:

https://www.nih.gov/news-events/news-releases/use-it-or-lose-it-visual-activity-regenerates-neural-connections-between-eye-brain