Eye disordersA look at eye disorders

About eye disorders, 70% of all sensory information reaches the brain through the eyes. Eye disorders can interfere with a patient’s ability to function independently, perceive the world, and enjoy beauty. No matter where you practice nursing, you’re likely to encounter patients with eye problems. Some patients may report an eye problem as their chief complaint; others may tell you of a problem while you’re evaluating another complaint or performing routine care.

Eye disorders: Anatomy and physiology

The eye is the sensory organ of sight. It’s a hollow ball filled with fluid (vitreous humor) and consists of three layers:

  1. fibrous outer layer — sclera, bulbar conjunctiva, and cornea
  2. vascular middle layer — iris, ciliary body, and choroid
  3. inner layer — retina

A close look at the eye

This cross section details important anatomic structures of the eye.

 

Eye disorders

 

Eye disorders: Lens and liquids

Between the iris and retina lies the lens, suspended by ligaments from the ciliary body. The vitreous and aqueous humors are separated by the lens. The vitreous humor lies behind the lens, and the aqueous humor, in front of the lens.

Eye disorders: Muscles for movement

Six extraocular muscles, innervated by the cranial nerves, control the movement of the eyes. The coordinated actions of those muscles allow the eyes to move in tandem, ensuring clear vision.

Eye disorders: Lashes and lacrimals

Outside the eye, the bony orbits protect the eye from trauma. Eyelids (palpebrae), lashes, and the lacrimal apparatus protect it from injury, dust, and foreign bodies. (See A close look at the eye.)

Sclera, bulbar conjunctiva, and cornea

The sclera is the white coating on the outside of the eyeball. Together with the vitreous humor on the inside, the sclera helps maintain the retina’s placement and the eyeball’s nearly spherical shape. The bulbar conjunctiva, a thin, transparent membrane that lines the eyelid, covers and protects the anterior portion of the white sclera. The cornea is a smooth, avascular, transparent tissue located in front of the iris that refracts (bends) light rays entering the eye. A film of tears coats the cornea, keeping it moist. The cornea merges with the sclera at the corneal limbus.

Eye disorders: Here’s mud in your eye

The ophthal mic branch of cranial nerve V (trigeminal nerve) innervates the cornea. Stimulation of this nerve initiates a protective blink called the corneal reflex.

Iris and pupil

The iris is a circular, contractile diaphragm that contains smooth and radial muscles and is perforated in the center by the pupil. Varying amounts of pigment granules within the iris’s smooth muscle fibers give it color. Its posterior portion contains involuntary muscles that control pupil size to regulate the amount of light entering the eye.

Eye disorders: Grand opening

The pupil, the iris’s central opening, is normally round and equal in size to the opposite pupil. The pupil permits light to enter the eyes. Depending on the patient’s age, pupil diameter can range from 3 to 5 mm.

Ciliary body and choroid

Suspensory ligaments attached to the ciliary body control the lens’s shape for close and distant vision. The pigmented, vascular choroid supplies the outer retina’s blood supply, then drains blood through its remaining vasculature.

Lens and vitreous chamber

Located behind the iris at the pupillary opening, the lens consists of avascular, transparent fibrils in an elastic membrane called the lens capsule. The lens refracts and focuses light onto the retina. The vitreous chamber, located behind the lens, makes up fourfifths of the eyeball. This chamber is filled with vitreous humor, the gelatinous substance that, along with the sclera, maintains the shape of the eyeball.

Posterior and anterior chambers

The posterior chamber, which lies right in front of the lens, is filled with a watery fluid called aqueous humor. As it flows through the pupil into the anterior chamber, this fluid bathes the lens capsule. The amount of aqueous humor in the anterior chamber varies to maintain pressure in the eye. Fluid drains from the anterior chamber through collecting channels (trabecular meshwork) into Schlemm’s canal.

Retina

The retina is the innermost layer of the eyeball. It receives visual stimuli and transmits images to the brain for processing. Vision of any kind depends on the retina and its structures. The retina contains the retinal vessels, the optic disk, the physiologic cup, rods and cones, the macula, and the fovea centralis.

The retina has four sets of retinal vessels. Each of the four sets contains a transparent arteriole and vein that nourish the inner areas of the retina. As these vessels leave the optic disk, they become progressively thinner, intertwining as they extend to the periphery of the retina.

Eye disorders: No light here

The optic disk is a well-defined, round or oval area measuring less than 1/8 (0.3 cm) within the retina’s nasal portion. The ganglion nerve fibers (axons) exit the retina through this area to form the optic nerve. This area is called the blind spot because it contains no light-sensitive cells (photoreceptors). The physiologic cup is a light- colored depression within the temporal side of the optic disk where blood vessels enter the retina. It covers a quarter to a third of the disk.

Eye disorders: Now I see the light!

Photoreceptor neurons called rods and cones make vision possible. Rods respond to low-intensity light and shades of gray. Cones respond to bright light and are responsible for sharp, color vision.

Eye disorders: Look sharp!

Located near the center of the retina lateral to the optic disk, the macula is slightly darker than the rest of the retina. The macula provides the sharpest vision, allowing us to read and recognize faces, for example. The fovea centralis, a slight depression within the macula, contains the heaviest concentration of cones and provides the clearest vision and color perception.

Eye disorders: Assessment

Now that you’re familiar with the anatomy and physiology of the eyes, you’re ready to assess them.

Eye disorders: History

To obtain an accurate and complete patient history, adjust your questions to the patient’s specific complaint and compare the answers with the results of the physical assessment.

Current health status

Begin by asking the patient some basic questions about his vision:

  • Do you have any problems with your eyes?
  • Do you wear or have you ever worn corrective lenses? If so, for how long? Are they glasses or hard or soft contact lenses?
  • For what eye condition do you wear corrective lenses? Do you wear them all the time or just for certain activities, such as reading or driving?

Previous health status

To gather information about the patient’s past eye health, ask these questions:

  • Have you ever had blurred vision or lost your vision in one eye temporarily? Have you ever seen spots, floaters, or halos around lights?
  • Have you ever had eye surgery or an eye injury?
  • Do you have a history of high blood pressure or diabetes?
  • Are you taking prescription medications for your eyes or other conditions? If so, which medications and how much and how often do you take them?

Family health status

Next, ask the patient if anyone in his family has an eye disorder. Also ask if anyone in the patient’s family has ever been treated for myopia, cataracts, glaucoma, retinal detachment, or loss of vision.

Lifestyle patterns

To explore daily habits that might affect the patient’s eyes, ask these questions:

  • Does your occupation require intensive use of your eyes, such as long-term reading or prolonged use of a video display terminal?
  • Does the air where you work or live contain anything that causes you to have eye problems?
  • Do you wear goggles when working with power tools, or when engaging in sports that might irritate or endanger the eye, such as swimming, fencing, or playing racquetball?

Eye disorders: Physical examination

An eye assessment involves inspecting the conjunctivae, assessing the pupils, assessing eye muscle function, and examining intraocular structures with an ophthalmoscope.

Inspecting the conjunctivae

To inspect the conjunctivae, ask the patient to look up. Gently pull the lower eyelid down to inspect the bulbar conjunctiva. It should be clear and shiny. Note excessive redness or exudate. Also observe the sclera’s color, which should be white to buff. In black patients, you may see flecks of tan.

Eye disorders: In the pink

To examine the palpebral conjunctiva (the membrane that lines the eyelids), have the patient look down. Then lift the upper lid, holding the upper lashes against the eyebrow with your finger. The palpebral conjunctiva should be uniformly pink.

Assessing the pupils

The pupils should be equal in size, round, and reactive to light. In normal room light, the pupil will be about one-fourth the size of the iris. Unequal pupils generally indicate neurologic damage, iritis, glaucoma, or therapy with certain drugs.

Eye disorders: The direct approach

Test the pupils for direct and consensual response. In a slightly darkened room, hold a penlight about 20 (51 cm) from the patient’s eyes, and direct the light at one eye from the side. Note the reaction of the pupil you’re testing (direct response) and the opposite pupil (consensual response). They should both react the same way. Also note sluggishness or inequality in the response. A pupil that doesn’t react to light (a “fixed” pupil) can be an ominous neurologic sign. Repeat the test with the other pupil.

Memory jogger

Here’s a pearl of wisdom for you: When examining the patient’s pupils, remember the acronym PERRL:

Pupils Equal Round and Reactive to Light

Eye disorders: So accommodating

To test the pupils for accommodation, place your finger approximately 4 (10 cm) from the bridge of the patient’s nose. Ask the patient to look at a fixed object in the distance and then to look at your finger. His pupils should constrict and his eyes converge as he focuses on your finger.

Assessing eye muscle function

Testing the six cardinal positions of gaze evaluates the function of each of the six extraocular muscles and the cranial nerves responsible for their movement (cranial nerves III, IV, and VI).

Eye disorders: Roving eyes

To perform the test, ask the patient to remain still while you hold a pencil or other small object directly in front of his nose at a distance of about 18 (46 cm). Ask him to follow the object with his eyes without moving his head. Then move the object to each of the six cardinal positions, returning to the midpoint after each movement. The patient’s eyes should remain parallel as they move. (See Cardinal positions of gaze.)

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Eye disorders

 

Examining intraocular structures

The ophthalmoscope allows you to directly observe internal structures of the eye. To see those structures properly, you should adjust the lens disc several times during your examination. Use the black, positive numbers on the disc to focus on near objects, such as the patient’s cornea and lens. Use the red, negative numbers to focus on distant objects such as the retina. (See Seeing eye to eye.)

 

Eye disorders

 

Eye disorders: Looking at the lens

First, set the ophthalmoscope’s lens disc to zero and hold the ophthalmoscope about 4 (10 cm) from the patient’s eye. Direct the light through the pupil to elicit the red reflex, a reflection of light off the choroid.

Now, move the ophthalmoscope closer to the eye. Adjust the lens disc so you can focus on the eye’s anterior chamber and lens. If the lens is opaque, indicating cataracts, you may not be able to complete the examination.

Eye disorders: Rotating to the retinal structures

To examine the retinal structures, start with the dial turned to zero. Rotate the lens-power disc to keep the retinal structures in focus. The first retinal structures you’ll see are the blood vessels. Rotating the dial into the negative numbers will bring the blood vessels into focus. The arteries will look thinner and brighter than the veins.

Follow one of the vessels along its path toward the nose until you reach the optic disk, where all vessels in the eye originate. Examine arteriovenous crossings for arteriovenous nicking (localized constrictions in the retinal vessels), which might be a sign of hypertension.

Eye disorders: Diggin’ the disk

The optic disk is a creamy pink to yellow-orange structure with clear borders and a round-to-oval shape. The disk may fill or exceed your field of vision. If you don’t see it, follow a blood vessel toward the center until you do. The nasal border of the disk may look somewhat blurred.

Eye disorders: Riveted on the retina

Completely scan the retina by following four blood vessels from the optic disk to different peripheral areas. As you scan, note lesions or hemorrhages. (See A close look at the retina.)

A close look at the retina

This illustration shows the complex anatomy of the retina and its structures.

 

Eye disorders

 

Eye disorders: Movin’ in on the macula

Finally, move the light laterally from the optic disk to locate the macula, the part of the eye most sensitive to light. It appears as a darker structure, free from blood vessels. If you locate it, ask the patient to shift his gaze into the light.

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