How Eye See It Photography is a Rapid City, South Dakota based modern wedding photographer. Owner Maysa Oakly is passionate about adventurous and natural photography styles, and will work with you to ensure that your photos truly reflect your unique connection with each other. After the iris, the next area of the eye is the lens.
What is the iris?
The iris is the part of the eye that regulates the amount of light that enters the eyes. It also determines the color of the eyes. The iris is located in the anterior portion of the lens and controls the size of the pupil, which opens and closes to let or block light rays from entering the eyes.
The iris has two layers: the front pigmented fibrovascular layer known as the stroma and pigmented epithelial cells beneath it. The stroma contains melanocytes, which produce the brown or black pigment that determines the eye’s color.
During normal development, the iris is symmetrically shaped. However, in some individuals the iris has asymmetrical shapes. This is called iridoplegia. It usually occurs due to physical impact on the iris or inflammation.
In some cases, asymmetrical structures can cause problems with the iris’s function. For example, the sphincter pupillae (structures at the iris’s borders that help control its movement) may not work properly. This can make it difficult to focus on objects that are close by or blurred vision due to divergent light rays accessing the eye.
Other conditions that affect the iris include iritis and heterochromia. Iritis is an infection of the iris that can cause red, painful eyes and symptoms like headache and sensitivity to light. This condition can also cause vision loss, cataracts and glaucoma.
Heterochromia is when one or both irises are a different color than the other. This condition can occur in people who have genetic problems and is a common congenital condition.
Variegation of the iris is also common in some animals, including Siberian Huskies and some white cat fancies. Some herding breeds, such as Australian Shepherds and Border Collies, can have well-defined blue areas within a brown iris.
Iris color is determined by a combination of the stroma’s melanin content and its cellular density. There are various other pigments in the iris that can be absorbed or reflect light. These include melanin, eosinophilic pigments and lipofuscin.
The iris is a very thin, pigmented structure that controls the diameter and size of the pupil. This control helps the iris regulate the amount of light that enters the eyes and the retina.
What is the lens?
The lens is an important part of the eye that focuses light. It’s located behind the iris and in front of the vitreous body, and is a transparent biconvex structure that refracts light, or bends it, so that it can reach the retina.
The human lens is about 10 mm across and 4 mm from front to back. It’s usually transparent, but it can be yellow or green in some people.
It’s a very thin tissue that’s made up of proteins. This tissue allows light to enter the eye and focus directly on the retina, creating a clear picture.
There are three main parts to the lens: the lens capsule, the lens epithelium, and the lens fibers. The lens fibers are long, thin cells that form the bulk of the lens.
In humans, the lens fibers are typically about 12 mm long and 4-7 micrometres in diameter. They are tightly packed, similar to onion layers, and they stretch lengthwise from the posterior poles to the anterior poles.
A single layer of cells, the lens epithelium, sits between the lens capsule and the lens fibers. These cells provide nutrients to the fibers, remove waste from them, and regulate lens homeostasis. They also produce aqueous humor, the clear fluid that carries water and ions throughout the eye and keeps the lens healthy.
The ciliary body helps the lens to change its shape and to focus on different objects. It’s a series of tiny muscles that bend and thin the lens when it needs to focus on far away objects, and thicken and expand when it needs to focus on near objects.
When the ciliary body isn’t working properly, it can cause a variety of problems, including cataracts, presbyopia, ectopia lentis, and aphakia. Some of these problems can be treated by a surgical procedure, and others require regular visits to the eye doctor.
The lens is a very complex structure that’s shaped differently in each of the four major classes of animals: land vertebrates, aquatic vertebrates, birds, and reptiles. In most land vertebrates, the lens changes its shape to allow it to focus on distant objects. This adjustment is known as accommodation.
What is the vitreous humor?
The vitreous humor is a clear, gel-like substance found in the eye between the retina and the lens. It makes up 80% of the total volume of your eyeball and is responsible for assisting vision.
It also helps withstand shock and maintains the shape of your eyeball. Its main ingredient is water, but it contains a wide range of other materials. It contains proteins, salts (electrolytes), sugars (glycosaminoglycan) and collagen fibers.
Vitreous humor is made by your ciliary body in the posterior chamber of your eye. It travels through your pupil and then drains out of your eye into the scleral venous sinus, where it enters your bloodstream.
The ciliary body also produces the aqueous humor in the anterior chamber, between your cornea and iris. This fluid is responsible for providing nutrients to your eye, draining out any excess fluid, and lubricating the lens.
Your aqueous humor is mainly water and contains a variety of other substances, including amino acids, electrolytes, ascorbic acid, glutathione and immunoglobulins. Its presence in the eye can help diagnose and treat some conditions.
As you get older, changes to the aqueous humor can cause some serious problems. This is why it’s so important to have regular eye exams. Your provider can check for any signs or symptoms and offer treatment.
If your aqueous humor is cloudy, your doctor may recommend a procedure called a vitrectomy. This surgery removes your vitreous humor and replaces it with a synthetic substitute that will help restore your vision.
This is a common operation for patients with certain diseases and disorders of the eyes. It can improve your sight, but it is a very delicate and complex operation that may have many complications.
Your doctor will use a special device to measure your pressure in your eye. This is done by blowing a small puff of air into your eye and measuring the pressure with an instrument called a tonometer.
A 2022 review explains that your doctor will be looking for any signs or symptoms of conditions affecting the aqueous humor and/or the vitreous humor, such as blurry vision, halos around things you’re seeing and floaters in your vision. Your doctor may suggest medications, laser therapy or surgery to fix your condition.
What is the retina?
The retina is the thin lining of cells within the eye that converts light into nerve impulses to be processed by the brain. The retina is a vital part of the eye and disease of the retina can lead to vision loss and blindness.
The cellular components of the retina are composed of photoreceptors (photosensitive cells), the ganglion cell layer and the retinal pigment epithelium. The photoreceptors convert light into electrical and chemical signals that are sent to the brain through a network of neurons, which includes bipolar and ganglion cells, to be used for visual perception.
Each of the photoreceptors in the retina contain disk-shaped segments filled with a molecule called opsin that absorbs photons. Each of these discs is then connected to a connecting cilia that bridges the inner and outer segments of the photoreceptors.
These cilia and opsins also protect the photoreceptors from damage by light. When a photon strikes 11-cis-retinal in the rod or cone disks, it triggers changes in opsins that activate the surrounding RPE cells to pump the retinal back into the cis- form.
This opsin recycling process is an important function of the RPE and it allows the photoreceptors to remain functional for decades without becoming damaged by light.
In order to accommodate the limited space of the optic nerve, the retina spatially encodes or compresses neural impulses that represent an image to fit in this small area. This is done by what are known as centre-surround structures, implemented by bipolar and ganglion cells. The centre-surround structures can be on-centres or off-centres, depending on the position of each photoreceptor in relation to the surround.
When these axons are triggered by an image-representing neural signal, they pass from the retina to the visual centres in the brain via the optic nerve. The axons from both eyes are vertically divided, so that the axons of the nasal half cross the brain at the optic chiasma to join with axons from the temporal half of the other eye before crossing into the lateral geniculate body.
A specialist in retina is an ophthalmologist who has undergone additional training in the medical and surgical management of diseases and injuries to the posterior segment of the eye. They can perform treatments such as laser treatment to reduce leakage from retinal blood vessels and to reduce the risk of macular hole formation and scar tissue. Other procedures include pneumatic retinopexy, scleral buckle, cryotherapy and laser photocoagulation.