10 Steps to a Better Slit Lamp Examination

10 Steps to a Better Slit Lamp Examination
Brush up on this essential part of every eye examination.
By Etty Bitton, OD, MSc, FAAO

Are you getting the most out of your slit lamp exam (SLE)? Like most, your slit lamp skills have no doubt improved with time. To maximize the use of your slit lamp, try adding the following 10 reminders to your routine.

1. Clean Up Your View

Whether or not you cover your slit lamp at the end of the day, dust and oils from your eyelashes will soil the oculars. Make sure you dust the mirror of the illumination column as well as the patient side of the oculars. You can use a small brush, which usually comes as part of the slit lamp accessories, to dust off the mirror. Adding a routine cleaning will keep your image sharp. 



 2. Adjust Your Oculars

This step may be more pertinent if you practice in a group or hospital
 setting whereby several individuals share the equipment. Verifying the
 interpupillary distance of the oculars prior to evaluation will maximize
 three dimensional (3D) viewing of the ocular tissues. In addition, you should
also adjust the objectives to your prescription by turning the knurled ring
 of the eyepiece. Daily handling can displace the interpupillary distance of the
 oculars, hence a small adjustment could make a big difference with respect to
 viewing comfort and rendering subtle
3D details more evident.

3. Follow the Anatomy A comprehensive SLE should follow a logical
sequence. It's best to begin with low magnification and observe the
 external structures first, such as lids, lashes, inner and outer canthi
 and tear meniscus. You can also evaluate the overall appearance of
the bulbar conjunctiva, cornea, iris and pupilBegin by sweeping the lid margin from the outer canthus towards the inner canthus. Of particular interest for contact lens (CL) wearers is a detailed examination of the lid margin, paying particular attention to the lids, lashes and tear film. Examine the lashes for signs of blepharitis, madarosis (loss of lashes) and trichiasis (misdirected lashes). Observing the tear meniscus should reveal a uniform structure with little debris and an inferior meniscus that's slightly larger than its superior counterpart. Note lid margin scars or deformities, especially if they obstruct the flow of the tears towards the punctum. Meibomian gland expression should require little force and reveal clear liquid secretions. Meibomian gland dysfunction is often underdiagnosed, leading to an unstable tear film and unexplained CL dropout. Make lid eversion a routine part of every anterior segment examination, even more so in CL wearers. Check the lids for signs of papillary response or hyperemia. Some silicone hydrogel lenses that have higher modulus have resulted in a papillary response in some patients. Switching to a lens with lower modulus may have beneficial effects. 

TABLE 1
llumination Techniques
ILLUMINATION	ILLUMINATION ANGLE (DEGREES)	MAGNIFICATION*	TISSUES
Diffuse	30-45	Low	External overall view, lid, lashes, CL fit
Direct:
• Broad beam	30-45	Low-med	Conjunctiva, cornea
• Parallelepiped	30-45	Med	Cornea, meniscus, iris, lens
• Optical Section	30-60	Med	Angle estimation, corneal layers, lenticular layers
• Conical Beam	30-45	Med	Anterior chamber (cells)
Indirect	45-60	Med	Cornea
Retroillumination	0	Low-med	Transillumination of the iris, lenticular opacities direct
Specular Reflection	90 from microscope	Med-high	Tear Layer, endothelium
Sclerotic scatter	60	Low	Corneal scars, central edema
Tangential	70-80	Med	Iris (freckles, suspicious nevi)
* Low: 6X to 10X, Med: 10X to 16X, High: 25X to 40X

A detailed examination of the corneal structures (epithelium, stroma and endothelium) is next, varying magnification and illumination as needed. Examine the iris, pupil and crystalline lens last because the direct illumination is more bothersome for the patient. A systematic SLE will improve efficiency, uncover reasons for CL intolerance, reduce chair time and limit omissions of tissue anomalies.

4. Know Your Illuminations

Can you differentiate between specular reflection and sclerotic scatter? Most practitioners vaguely remember learning about illuminations, but the specifics have developed cobwebs over time. Most of us perform SLE under a somewhat automated mode. We constantly switch from one type of illumination to another without realizing it.

A review of illuminations may be helpful in reminding us of those used less frequently but with inherent advantages. Table 1 offers a quick overview of different illuminations and which structures are best viewed under these illumination techniques. Some slit lamp models have the ability to tilt the illumination column (towards the patient) up to 20 degrees (in 5 degree increments). This oblique illumination is useful in reducing reflections during gonioscopy. In modern slit lamps, manufacturers have replaced most tungsten type bulbs, which have a redder light, with more efficient halogen illumination, which provides a bluer light. Fluorescein is also useful in performing the Seidel test, which identifies aqueous leaking.

5. Enhance Your View

Adding ophthalmic dyes to your SLE will improve your diagnostic evaluation. Sodium fluorescein highlights areas of corneal stress while lissamine green is best at highlighting conjunctival problems. Better tolerated than rose bengal, lissamine green is observed in white light and provides additional insight for patients presenting with dry eye symptomology or CL intolerance.

Document staining, noting the form, depth and extent. The shape of staining can be micropunctate (resembling small dots), macropunctate (larger dots) or coalescent staining (a patch). Its depth can be limited to the epithelium or it may enter the stromal layers. You can approximate the extent in percentage of the surface area affected by the staining. Improving your documentation of staining will facilitate your observation for any progression or regression at follow-up visits.

Table 2
Effect of Magnification on Field of View*
MAGNIFICATION	FIELD OF VIEW
6X	35.1mm
10X	22.5mm
16X	14.1mm
25X	8.8mm
40X	5.6mm
* Using a 12.5X eyepiece

6. Filters

We perform most of a SLE using white light. When using fluorescein, use a yellow (Wratten #12) barrier filter in conjunction with a cobalt (blue) filter to maximize viewing of the fluorescence. Positioning the yellow barrier filter in the path of the returning light and not in the path of the incident light will enhance the contrast significantly. Newer slit lamps have integrated the yellow barrier filter in the ocular housing, as its use is becoming more commonplace.

You can use the red-free (green) filter to differentiate vascular from pigmented lesions. Blood vessels and small hemorrhages will take on a dark appearance with the use of the red-free filter, whereas pigmented lesions will remain dark. Some slit lamps can also be equipped with a neutral density filter and/or a heat-absorbing filter to increase patient comfort.

7. Magnification

Most slit lamp models offer 10X, 16X and 25X magnification, although some models extend to 40X. Most use eyepieces of 10X or 12.5X. As magnification increases, it limits the depth of focus, hence small adjustments with the joystick of the slit lamp will keep the image in sharp focus. Furthermore, increased magnification reduces the field of view (Table 2), allowing for greater detail of structures. Depending on the model, magnification drums can have specified click stops or be continuous. The continuous option, also called zoom system, has the advantage of a smoother transition with no image loss.

If upgrading your biomicroscope is not in your immediate plans, then try extending the magnification by simply purchasing an additional set of oculars (for example, 20X). Returning the magnification to the lowest setting at the end of the examination will reduce prep time for the next patient.

8. Illumination Intensity

Novice users have a tendency to use the highest illumination intensity during the entire examination. The problem is that these habits are hard to break. The examination should begin under the lowest intensity to examine external tissues and to allow the patient to adapt to the illumination, which is even more important if the patient has undergone pupillary dilation. The slit width is often decreased to examine details of ocular tissues under higher magnification. Reserve higher intensity illumination for examining details and use it for a shorter amount of time to conserve energy. You can equally reduce the slit beam height to increase patient comfort during the use of higher illumination intensity.

9. Viewing Angle

During most of the SLE, the observation arm of the slit lamp is directly in front of the patient. You can move the illumination arm to obtain different illumination angles to assess different tissues. Large illumination angles allow you to determine the depth of corneal and lenticular lesions with greater accuracy because the distance between layers of these tissues is increased under these conditions.

To increase the distance between layers even further, make the illumination angle even larger. One way of achieving this is to displace the observation arm from its habitual central position to a more nasal one while extending the illumination column more temporal (Figure 2b). This will enhance your view of the individual layers of the cornea or lens and allow you to determine the depth of lesions with enhanced accuracy.

10. Measuring Eyepiece

Practitioners have traditionally made a subjective evaluation of the height and width of lesions, nevi, staining, meniscus and neovascularization. A measuring eyepiece or graticule can replace a traditional eyepiece to considerably improve this measurement. The eyepiece has a linear and an angular scale, the latter being useful for evaluating toric lens rotation with improved accuracy. With the advent of ocular photography, many offices photograph lesions to properly document problems and to allow for future comparisons. If this capability isn't available in your office, then a measuring eyepiece may considerably enhance your documentation. You can subsequently store the eyepiece for safekeeping and future use.

Final Pearls

SLEs are dynamic. You should have one hand on the joystick and the other available to adjust the illumination arm, magnification, lighting intensity, slit width or even to hold an accessory instrument.

Locking your biomicroscope following examination will prevent unnecessary swinging and possible damage to the mechanics of the slit lamp during positioning towards or away from the patient. Using a dust cover over the slit lamp at the end of the day will help protect your investment.

Knowing the different options (filters; illumination width, height and intensity; magnification) your slit lamp has to offer, coupled with proper maintenance, will ensure a high image quality and help you perform a more efficient SLE. 

Interesting Article About Eye Health

Our eyes, like the rest of us, inevitably change with time. And almost everyone is going to need some help seeing the computer screen or the morning paper as middle age rolls around.
Other problems can be prevented, stalled or fixed if you get the proper medical attention and take care of your vision, experts say.
Too many people wait until they fail the vision test when they go to renew their driver’s licenses before seeking help, said a professor of clinical optometry.

“People are living longer, so they need to use their eyes longer. If we look at World War II (population) statistics and project those onto baby boomers, we’re going to see a doubling in the rates of legal blindness,” .
“The sad thing is, it’s preventable. Don’t wait until your vision is blurry. Come on in.”
After age 65, people need a dilated eye exam once a year.

   “There are changes that take place in the eyes and all of the tissues around the eyes that occur with aging,” said  an ophthalmologist. “Eyelids become more puffy, more droopy, and they may not make good contact with the eye. Eyes become drier with time.”

   On top of that, a muscle inside the eye that controls the focusing mechanism weakens over time (hence the reading glasses or bifocals), and the lens starts to turn cloudy, leading to cataracts.

   “If you live a normal-length life, you will develop cataracts,”. Most people have cataract surgery around age 71.

   Cataract surgery used to be much more complex, and patients were prone to infections and had to wear thick glasses after surgery. Now, most people do well with a quick operation in which their clouded lens is replaced with an artificial lens.

   Common cataract symptoms include trouble seeing at night or while driving in the rain, seeing halos around lights and needing more light to read.

   Annual eye exams are important for a number of reasons, particularly for screening for glaucoma, which does not have any symptoms. Those with glaucoma, cataracts or macular degeneration might need to be seen more frequently.

   Besides scheduling an annual exam with an optometrist or ophthalmologist, people can help protect their vision by wearing sunglasses that guard against ultraviolet rays, avoiding cigarettes and living a generally healthy life.

   “I tell patients: ‘Try to adhere to good general health practices. Control your blood sugar, control your blood pressure, control your cholesterol. Take a multivitamin usually. Do not smoke,’”.

   Protection from the sun helps prevent and slow the development of cataracts and macular degeneration, a disease of the center of the retina that can lead to blindness.

   Treatment for macular degeneration has come a long way. “There used to be very little we could do except diagnose it early.”

   Now, eye doctors understand that nutritional supplements, including antioxidants and lutein, can slow the progression of dry macular degeneration, in which the retina wastes away.

   In the rarer and more-severe form, which is called wet macular degeneration, new blood vessels form, impairing vision. Doctors can inject a cancer drug  to stop the growth of blood vessels.

   The procedure often has to be done repeatedly and is costly and burdensome, but “ the alternative is to go totally blind,”.

   Other potentially blinding diseases that increase with age are diabetic retinopathy (caused by a thickening of the arteries and high blood pressure) and glaucoma, a condition in which fluid pressure inside the eye increases because of slowed drainage from the eye.

   “Particularly with diabetes or glaucoma, the treatment goal is to keep it from getting worse, but you can’t get vision back once it’s gone,” .

   Good control of diabetes is the key to preventing diabetic retinopathy, or stalling the disease once it has already shown up, he said.

   Glaucoma can be found early only through pressure tests and by examining the optic nerve to see if there’s change over time. People with high blood pressure, heart disease or diabetes are at higher risk of developing the disease, as are African-Americans and Latinos.

   Glaucoma can be treated with drops, but if they don’t control the pressure, a doctor might recommend a laser procedure or surgery.

 A 66-year-old , was in for his annual eye exam a few years ago and learned that the pressure was up in both eyes. He went to an ophthalmologist and found out he had a precursor to glaucoma. Now, eyedrops are preserving his vision.

   “I don’t know of any family history, so it caught me by surprise,”.

   More primary-care physicians should do vision screening and talk about risks with patients. Even just reminding patients that they should go to an eye-care provider could help, he said.

   “They could very well be wearing glasses they got 15 years ago.”


 Age and eyes

   Age-related macular degeneration damages sharp, central vision. It’s the leading cause of vision loss in older adults.

   PARTS OF THE EYE

   Cornea: clear, outer layer of the focusing system at the front of the eye

   Iris: colored part of the eye that regulates amount of light that enters the eye

   Pupil: opening at the center of the iris, which adjusts to control the amount of light that enters.

   Lens: clear part behind the iris that helps to focus light and images on the retina

   TYPES OF DEGENERATION

   If you notice symptoms of age-related macular degeneration, contact an eye-care professional to schedule a dilated-eye exam.

   WET

   What it is: Abnormal blood vessels behind the retina grow under the macula and leak blood and fluid, which can displace and damage the macula.

   What you see: Straight lines appear wavy.

   Retina: light-sensitive tissue lining the back of the eye; converts light into electrical signals for the brain

   Optic nerve: millions of bundled nerve fibers that transmit signals from the retina to the brain

   Macula: sensitive area at the center of the retina that gives central vision

   Fovea: macula’s center that gives the sharpest vision

   DRY

   What it is: Cells in the macula break down gradually, causing blurred central vision in the affected eye. Yellow spots under the retina, known as drusen, are detected; it occurs in stages.

   What you see: As it progresses, a blurred spot might appear and grow in the center of vision; extra light might be needed to focus; faces can be difficult to recognize.

Sources: Columbus Dispatch Article 03/01/12
Sources: National Eye Institute; National Institutes of Health; American Academy of Opthalmology