How is the eye examined?

The following information is taken verbatim from ophthobook.com

Vision, Pupil, and Pressure
Vision, pupil, and pressure are the “vital signs” of ophthalmology. After a brief history, I check these measurements before dilating the eyes. This is because dilating drops will effect vision, pupil size, and potentially elevate our pressure measurements so you need to check these signs first. If you ever consult ophthalmology, we will always ask you …

What’s the vision, pupil, and pressure?

It’s kind of a mantra. I don’t know how many times I’ve been told to “get the vision, pupil, and pressure, then dilate them.”

Visual Acuity
You measure visual acuity with a standard Snellen letter chart (the chart with the BIG E on it). If your patient can’t read the E on the top line, see if they can count fingers at different distances. Failing this, try hand motion and light. Poor distance vision usually occurs from refractive error (your patient needs better glasses).

You want to check a patient’s “best corrected vision” so have them wear their glasses. You’re going to be amazed at the number of people complaining of “blurry vision” who leave their glasses in their car. You’ll also be impressed by the number of consults you’ll get where the consulting doctor hasn’t bothered to check the patient’s vision. Remember: “I can’t see!” is a relative complaint – for some this means 20/25 vision and for others this means complete darkness.

Das Pinhole!
A quick and easy way to determine whether refraction is the culprit, short of actually testing different lenses, is with the pinhole test. Punch a small hole in a paper card, and have your patient reread the eye-chart while looking through this pinhole. This can actually improve vision by several diopters. It works because the paper blocks most of the misaligned rays that cause visual blur, and allows the central rays to focus on the retina. If your patient shows no improvement with pinholing, start thinking about other visual impediments like cataracts or other media opacities. Most occluders (the black plastic eye cover used during vision testing) have a fold-down pinhole device for this purpose.

Near Vision
Near vision can be assessed with a near-card or by having your patient read small print in a newspaper. Don’t try using the near-card to estimate distance acuity as distance vision is quite different than close-up acuity. That 20/20 marking printed on the near-card only checks “accommodated” near-vision. Remember that older patients can’t accommodate well and need a plus-power lens (reading glasses) to help them read the card. Carry a +2.50 lens with you when seeing older inpatients as most of these patients leave their reading glasses at home. We’ll cover accommodation and presbyopia in greater detail later in the optics chapter.

Pupils:
The pupils should be equally round and symmetric with each other. You can test reactivity to light with a penlight, but a brighter light like the one on the indirect ophthalmoscope will work much better. When testing the eyes, you will see a direct constriction response in the illuminated eye, and a consensual response in the other eye. These should be equal and synchronous with each other. Also, check the pupils with near-vision, as they should constrict with accommodation.

The Swinging Light Test
If one eye is injured, or not sensing light, then your patient may have an APD or “afferent pupillary defect.” Often these defects are only partial, making them difficult to detect on casual examination. To detect small APDs, you need to perform the “Swinging Light Test.” Here’s how it works:

When you shine a light back and forth between two normal eyes, you’ll find that the pupils constrict, then dilate a fraction as the light beam passes over the nose, and then constrict again. As you go back and forth you’ll see constriction, constriction, constriction, and constriction.

Things look different if one eye is partially blind. As before, when you shine the light in the good eye there is constriction. But, when you cross to the other bad eye, both eyes seem to dilate a little. The bad eye still senses light and constricts, but not as well. So you see constriction, dilation, constriction, and dilation. This phenomenon is also called a Marcus Gunn pupil.

Pressure:
We measure pressure by determining how much force it takes to flatten a predetermined area of the corneal surface. There are several ways to do this and in the ophthalmology clinic we use the “Goldman Applanation Tonometer” that is attached to the slit-lamp microscope.

In the ER, or with patients who are difficult to examine, we can check pressure using a handheld electronic Tono-pen. This little device can be tricky and in the wrong hands becomes a random-numbers generator. I’ll talk more about pressure and its importance within the glaucoma chapter.

Confrontational Fields
All patients should have their visual fields (peripheral vision) checked. A patient may have great central vision, with perfect eye-chart scores, but suffer from “tunnel vision” resulting from neurological diseases or glaucoma. Your patient may not even be aware of this peripheral visual loss if it has progressed slowly over time.

Confrontational fields are easy to perform but keeping your patient from “cheating” may be tougher. Have your patient cover one eye, and tell them to look straight at your nose. While fixating on your nose, have them count your fingers as you flash them in different quadrants. Be sure to cover your own eye and hold your hands equidistant between you and the patient. This gives you a better idea of what your patient ought to be able to visualize. If you can see your fingers, your patient should be able to see them as well.

EOMs (extraocular movements):
Check extraocular movements by having your patient follow your fingers into all quadrants. If the patient has decreased mobility in an eye from nerve paralysis or muscle entrapment, you may notice this from casual inspection or by more sophisticated cover/uncover tests. More often, though, you won’t see anything but your patient will, complaining of double vision.

Seeing Double?
When evaluating double vision, you must first determine whether the doubling is monocular or binocular.

If, after covering an eye, the vision stays doubled, you know you’re dealing with monocular diplopia. Monocular diplopia isn’t a neurological problem, but likely from a refractive error such as astigmatism, cataract, or corneal surface wrinkling.

Binocular diplopia indicates a misalignment between the eyes … and this is likely due to neuromuscular paralysis or muscle entrapment (if after trauma). To tease out what muscle groups and nerves are involved, you should determine what gaze direction improves and worsens the doubling. We’ll discuss cranial nerve palsies in greater detail in the neuro chapter.

The Slit-Lamp Exam:
It takes several months to get good at using the slit-lamp microscope. A lot of pathology can be found under the microscope and it’s easy to miss crucial findings. This makes it important to keep yourself organized and describe your findings in the same order with every patient, starting from the outside skin and working your way to the back of the eye. Here’s how we do it:

External Exam (EXT):
With the external exam, make sure the eyes look symmetric and that the patient doesn’t exhibit ptosis (drooping of the eye) or proptosis (extruding eyes or “bug-eyes”). If the patient has a conjunctivitis, check for a swelling of the pre-auricular nodes (in front of the ear) and sub-mandibular/mental nodes.

Lids and lacrimation (L/L):
Always look at the lid margin and lashes for signs of blepharitis. Evert the lids to look for follicles or papillary bumps on the inside of the lids that might indicate infection or irritation.

Conjunctiva and Sclera (C/S): Check to make sure the sclera is white and non-icteric, and the conjunctival blood vessels aren’t injected (red and inflamed). If they are injected, see if the blood vessels blanch when you dilate the patient with phenylephrine.

Cornea (K):
Look at the corneal surface for erosions and abrasions that might indicate trauma. Does the stroma look clear? Look at the back endothelial surface for folds or gutatta bumps. Fluorescein dye will make surface abrasions easier to spot.

Anterior Chamber (AC):
Look for cell and flare, which could indicate inflammation or intraocular bleeding. Individual cells are hard to see - you need to turn the lights down and shoot a “ray of light” into the eye. If you compare this light to a projector beam at a movie theater, then “cells” will look like dust flecks while “protein flare” is diffuse and looks like smoke floating in the aqueous. Also, comment if the anterior chamber is deep and well-formed, or shallow and thus a setup for angle-occlusion glaucoma.

Iris (I):
Make sure the iris is flat and the pupil round. If the patient has diabetes or an old retinal vascular occlusion you should comment whether you see any signs of neovascularization of the iris.

Lens (L):
Is the lens clear, or hazy with cataract? Are they phakic (they have their own lens), pseudophakic (prosthetic lens), or aphakic (no lens at all)?

Vitreous (V):
You can look behind the lens into the dark vitreous cavity. If you suspect a retinal hemorrhage or detachment, you may see cells floating here.

Fundus Exam:
The fundus is the only place in the body where you can directly visualize blood vessels and nerves. In our notes we typically comment on four retinal findings: You’re probably going to be terrible at the retina exam during your first few months, but do your best. There are several methods we use to view the retina:
 * 1) Macula – Does it look flat? Is there a good light reflex off the surface?
 * 2) Vessels – Any signs of AV nicking? Attenuation of the arterioles?
 * 3) Periphery – Any lattice, cobble-stoning, or tears?
 * 4) Disk – What’s the cup-to-disk ratio? Do the rims look pink and healthy?

The Direct ophthalmoscope
For non-ophthalmologists the most common way to examine the fundus is with the direct ophthalmoscope. This hand-held device is not easy to use, especially in an undilated eye. The key to success with this instrument is to get yourself as CLOSE to the patient as possible.

Get really close! Dilating the eye also helps.

Using that darn direct scope
Switch the light to the highest setting, and rotate the beam to the medium-sized round light. I set my focus ring to “0,” but you may need to adjust this to compensate for your own refractive error. Place your hand on your patient’s shoulder or head.

Starting far away, find your patient’s red-reflex and follow that reflection in as you close in to the eye. Be sure to switch eyes so that you don’t end up face-to-face with the patient (unless they are extremely attractive and you remembered to brush your teeth). Just kidding.

It may take you a while to visualize the fundus with the direct scope, especially in undilated eyes, because the field-of-view you get is very small, making it hard to even recognize what you are seeing.

I find it easiest to find a blood vessel and then follow this vessel back to its origin at the optic disk. Inspect the disk margins and the size of the disk cupping. You may be able to pick up AV nicking from high blood pressure and retinal hemorrhages in the form of dot-blot spots or flame hemorrhages.

At the slit-lamp
The best way to look at the posterior fundus in magnified detail is with a lens at the slit-lamp. This is how we look at the optic nerve and macula in the clinic, but it takes practice. We use smaller, more powerful lenses such as a 90-diopter lens.

The Indirect Ophthalmoscope
This is how we look at the peripheral retina in the ophtho clinic. The eye needs to be dilated to get a good image, but the field of view is excellent. We use a larger, 20-diopter lens, for this.

Other Tests Specific to Ophthalmology
There are many other exam techniques specific to ophthalmology such as gonioscopy and angiography that you probably won’t be exposed to unless you go into the field. I’ll cover these topics in later chapters as they become relevant.