lens practice pearls
Slit Lamp Examination: Back to Basics
BY THOMAS G. QUINN, OD, MS, FAAO
Proper examination procedures are vital to assess a patient's response to contact lens wear. The slit lamp examination is undoubtedly the most accessible and powerful means of assessment.
Are you getting the most out of your slit lamp examination?
Ask patients to wear their contact lenses for at least 4 hours before a follow-up examination. Many adverse physiological phenomena, such as corneal edema and mechanically induced staining, become evident only after patients have worn their lenses for several hours.
Give It Some Thought
Perform a thoughtful examination rather than mindlessly trudging
through the motions and waiting for something to "jump out" at you. Consider the
patient's contact lens wearing modality and how the lenses are fitting, then look
for problems most likely to arise in the presence of these factors. For example,
what problems could a low- riding GP lens cause? The answer, of course, is staining
at 3 o'clock and 9 o'clock, so actively look for this in patients wearing this modality.
A +3.00 hyperope who is wearing a low water content soft contact lens 16 hours a
day may show signs of hypoxic stress, such as corneal striae,
microcysts and neovascularization. If a patient wears continuous wear silicone hydrogel lenses, you should look for possible mechanical problems, such as superior epithelial arcuate lesions and contact lens-induced papillary conjunctivitis.
Figure 1. High-magnification view of microcysts. Note indirect illumination.
To prevent overlooking unanticipated physiological changes, establish a pattern to your slit lamp examination. Consider starting with a low-magnification overview of the ocular surface, lid margins and adjacent tear prism. Add more magnification to inspect the iris and the anterior chamber before observing the exposed cornea and bulbar conjunctiva. Ask the patient to look up as you pull down the lower lid to inspect the lower cornea, limbus, bulbar conjunctiva, palpebral conjunctiva and eyelid margin.
Next, ask the patient to look down so you can lift his upper lid and inspect the upper cornea, limbus, bulbar conjunctiva and upper eyelid margin. While the patient is still gazing downward, evert the upper eyelid to inspect the superior tarsal plate. Repeat the sequence to examine the other eye.
Everting and examining the superior tarsal plate is still an important part of the slit lamp examination. Although many new continuous wear contact lenses offer exceptional oxygen transmission, they also have a higher modulus of elasticity, increasing the potential for mechanical irritation of the corneal surface and the upper palpebral conjunctiva. Some patients with these changes will be asymptomatic until the condition has progressed to the point where they must discontinue lens wear.
Be proactive. Evert the upper lid during every examination so you can identify changes early and avoid unnecessary inconveniences to the patient.
Microcysts and Mucin Balls
|Figure 2. High-magnification view of mucin balls.|
Microcysts form when the cornea is under chronic hypoxic stress, which is thought to adversely affect basal cell formation. These defects are best visualized using indirect illumination and relatively high magnification (Figure 1). Microcysts can be a valuable "red flag," indicating the patient needs a lens with higher oxygen transmissibility.
Don't be alarmed if you observe an initial increase in microcysts after refitting a patient with a more oxygen-permeable contact lens. The additional oxygen will "flush out" microcysts from deeper epithelial layers over the first month or two after switching lens materials.
Continuous wear contact lenses made of stiffer (high modulus) materials have a somewhat greater propensity than lower modulus materials to develop mucin balls between the corneal surface and the base curve of the contact lens (Figure 2).
Usually, mucin balls are considered clinically insignificant, but the dimple staining they create in the epithelial surface are sometimes confused with microcysts. These two phenomena can be differentiated by size (mucin balls are generally larger than microcysts) and appearance under indirect illumination. Unlike mucin balls, microcysts appear darker against the brighter background illumination.
I always instill fluorescein when assessing a patient's ocular response to contact lenses, sometimes using a yellow Wratten filter to enhance the view. When viewed through the slit lamp, fluorescein staining can show subtle epithelial disruption caused by solution toxicity, mechanical rubbing or surface drying.
Another interesting phenomenon to look for is conjunctival staining in the limbal region. The significance of this finding still isn't clear, but this particular type of staining appears to be increasing among contact lens wearers and warrants continued monitoring.
Lissamine green is another diagnostic dye that can enhance slit lamp examinations. Applying this dye before white light slit lamp examination can reveal signs of dry eye (Figure 3). You are likely to see more staining if you wait 2 to 3 minutes after instilling diagnostic dye.
Figure 3. Lissamine green staining of the bulbar conjunctiva showing dry eye.
Talk to the Patient
Information is powerful. As you perform your slit lamp examination, let the patient know what you're doing and explain why. While everting the patient's eyelid, you can say, "I'm making sure your contact lens isn't irritating the underside of your eyelid when you blink. I want to identify changes like this before they hurt your eyes." This brief exchange puts patients at ease and shows you're working on their behalf.
Significant advances in contact lens design and material chemistry benefit more patients than ever before, offering higher levels of visual clarity, comfort and safety. A quality slit lamp examination helps us identify potential problems early and make changes that ensure continued safe, successful contact lens wear.
Dr. Quinn is in group practice in Athens, Ohio, and has served as a faculty member at The Ohio State University College of Optometry.