The Basic Anatomy of the Eye

When you have an eye exam, the doctor is evaluating two things, your ocular health you’re your refractive error. Most people think of their eye health in terms of refractive error (if you need glasses/contacts and how big your prescription is), but your glasses prescription does not indicate the state of eye health.

Basic Eye Anatomy & Common Conditions

First let’s talk about the basic eye anatomy and common conditions associated with each structure. We will start towards the front and work our way towards the back.

  • Lids, lashes, conjunctiva: these structures protect and lubricate the eye to keep it healthy and also maintain good vision.
    • These structures can be irritated in dry eye disease, chronic allergic conjunctivitis and contact lens over wear
  • Cornea: this is the clear part that sits in front of the iris (colored part). It has many nerve endings and is highly sensitive to pain
    • This structure can be affected by a host of conditions; most commonly contact lens over wear which can lead to corneal inflammation, swelling and sight-threatening ulcers
  • Sclera: the white part of the eye
    • Although, not common, the sclera can become painfully inflamed. Usually this only occurs in people with autoimmune conditions
  • Anterior chamber:
    • Contains fluid that drains out through the ‘angle’ of the eye
    • Can become inflamed in Uveitis
  • The angle: where the iris and the cornea meet.
    • Sometimes these structures get damaged in certain conditions or trauma
    • Malformations or damage of this structure is will increase your risk for glaucoma
  • Pupil: the hole in the middle of the colored part. The innervation that regulates pupil size is connected to the brain.
    • Abnormalities in the pupil could indicate optic nerve disease or an issue with the brain
  • Iris: this is the colored part of the eye. It contains two muscles that control the pupil size
    • Can grow new and dangerous blood vessels in diabetes, called iris rubeosis
  • Lens: clear disc-shaped structure that changes thickness to help us transition from looking at a distance, to at arms-length and up close.
    • After 40 years of age, changes in the cause difficulty focusing at arms-length and up close, also called presbyopia.
    • Color changes here naturally happen with age, called cataracts
  • Vitreous: this is a clear jelly that fills the inside of the eye
  • Retina: neural tissue that lines the back of the eye. Supported by blood vessels, some of which can be easily seen when the doctor looks inside your eye
    • Cardiovascular disease can manifest as bleeding or changes in the retinal blood vessels which can be viewed by your eye doctor
  • Optic Nerve: all the axons from the photoreceptors that make up the retina gather at the optic disc and exit the eye ball and connect to the brain
    • This is the structure that is damaged in glaucoma
  • Macula: this is the central part of the vision and is responsible for giving you 20/20 vision
    • This part is affected in a condition called macular degeneration

Secondly, let’s discuss some of the factors that influence your refractive error (glasses/contacts prescription). The need for glasses is almost always independent of eye health. In other words, perfectly healthy eyes could need glasses or be able to see great without glasses. Alternatively, eyes with pathology could also not have a refractive error.

There are two major factors that contribute to prescription:

  • Eyeball length (aka axial length): abnormally long or short eyeballs are more likely to need glasses. In general, longer eyeballs tend to be nearsighted and need a minus lens whereas shorter eyeballs tend to be farsighted and need a plus lens to correct them.
  • Lens strength: if your lens inside your eye is unusually powerful, particularly too powerful for your eyeball length, you will be nearsighted and need a minus lens. Likewise, if your lens is weaker, you will be farsighted and need a minus lens.
  • How spherical the lens and cornea are: If either the cornea or lens (or both) are not perfectly spherical, the image will focus in two separate planes rather than one. This is what causes astigmatism.

What determines if someone is farsighted or nearsighted is if the lens strength and the eye length coincide. For example, you can have a very strong lens but if you have a matching shorter eye, you will not have much of a refractive error, if any at all.

So the take home message is that whether or not you have a refractive error, we all have the same ocular structures that work intricately to allow us to see 20/20 (some of us may need glasses to do so). Therefore, the eye exam will examine all of these structures and make sure they are healthy to allow you to have good vision for your lifetime.

A Little Bit About…

A Little Bit About…

Ashley Iketani-Castillo, OD, MS

Dr. Iketani is a Florida native who has a passion for managing ocular disease. She views each patient as a whole person and believes the eyes are a window to a patient’s systemic health. She also has a passion for fitting rigid lenses on patients with corneal disease to help them obtain their best vision.

Dr. Iketani graduated from the University of Alabama at Birmingham School of Optometry where she completed internships at the Hefner Veteren’s Affairs hospital in Charlotte, NC and The Metrolina Association for the Blind which focused on Low Vision rehabilitation. Prior to pursuing optometry, she obtained a Masters of Science which focused on developmental genetics and worked as a technician in a lab that researched breast cancer.

Dr. Iketani currently resides in Charlotte with her husband, a pediatric resident, their two cats and they are welcoming a baby boy in December 2018.

Disclaimer

Information contained within this Web site is intended solely for educational purposes and is neither intended nor implied to be a substitute for professional medical advice relative to your specific medical condition or question. Always seek the advice of your physician or other health care provider for any questions you may have regarding your medical condition. Only your physician can provide specific diagnoses and therapies. By using this Web site, you agree to this Medical Disclaimer.

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205 E Council Street, Suite B
Salisbury, North Carolina 28144

Phone: (704) 310-5002
Fax: (704) 310-5003
kristin@salisburyeyecareandeyewear.com

 

205 E Council Street, Suite B
Salisbury, North Carolina 28144

Phone: (704) 310-5002
Fax: (704) 310-5003
kristin@salisburyeyecareandeyewear.com

 

Hours:
Monday: 8:30 AM – 5:00 PM
Tuesday: 10:00 AM – 7:00 PM
Wednesday: 8:30 AM – 5:00 PM
Thursday: 8:30 AM – 5:00 PM
Friday: 9:00 AM – 1:00 PM

Hours:
Monday: 8:30 AM – 5:00 PM
Tuesday: 10:00 AM – 7:00 PM
Wednesday: 8:30 AM – 5:00 PM
Thursday: 8:30 AM – 5:00 PM
Friday: 9:00 AM – 1:00 PM

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