6.1 Slit Lamp Biomicroscopy, Illumination & Fundus Lenses

Slit Lamp, Penlight, and Fundus Lenses

The technician prepares the instrument and patient so the authorized examiner or photographer can obtain reproducible views. Before contact, verify patient and eye, explain the task, clean patient-contact surfaces, inspect optics, set the table and chair safely, and ask about pain, trauma, infection precautions, mobility, and ability to maintain position.

Instrument setup

Focus each eyepiece using the instrument's calibration method before examining the patient. Adjust interpupillary distance, begin at low illumination and magnification, and align the patient's lateral canthus with the device reference when the model uses one. The forehead should remain against the band and the chin stable without neck strain. Do not force a patient with kyphosis, tremor, respiratory distress, or recent surgery into an unsafe posture; use an approved alternate setup or ask for help.

Inspect the bulb or LED, filters, slit width and height controls, joystick, locks, fixation target, chin rest, forehead band, and power cord. A cracked ocular, unstable table, contaminated surface, flickering lamp, or failed movement control is an out-of-service concern.

Illumination methods

• Diffuse illumination provides an external survey of lids, conjunctiva, sclera, cornea, and gross anterior-segment appearance.
• Direct focal illumination uses a parallelepiped or thin optical section to localize a finding within cornea, anterior chamber, iris, lens, or anterior vitreous.
• Retroillumination outlines opacities or defects against reflected iris or fundus light.
• Specular reflection aligns illumination and observation to inspect a reflective interface, such as corneal endothelium, when the examiner's method calls for it.
• Cobalt-blue illumination excites fluorescein for ordered surface evaluation or Goldmann tonometry. Filter and dye do not themselves establish a diagnosis.
• Sclerotic scatter introduces light at the limbus so loss of corneal transparency can scatter it into view.

Record eye, structure, technique, magnification or lens when relevant, and limitations. A technician describes opacity, cells, blood, irregularity, or poor view and routes it for interpretation.

Anterior-chamber screening

Van Herick estimation compares the peripheral aqueous interval with corneal thickness using a narrow temporal slit. It is a screening estimate affected by beam position, illumination angle, corneal shape, examiner technique, and anatomy. Record the observed grade or ratio using the clinic method. A very shallow or absent interval, corneal haze, pain, nausea, irregular fixed pupil, or prior angle-closure history is a stop-and-notify finding before dilation under protocol. Gonioscopy remains the clinician's method for direct angle assessment.

A penlight can provide a gross oblique-illumination screen and can support pupil, external, and motility assessment. It does not measure an angle. Avoid pressure on a traumatized eye, compare both eyes under similar conditions, and disinfect the device as required.

Noncontact fundus lenses

A handheld condensing lens forms a real, inverted, laterally reversed aerial image for slit-lamp posterior-segment viewing. Lens power, diameter, pupil, working distance, media clarity, and examiner technique affect field and magnification. A 78 D lens commonly provides somewhat greater magnification and narrower field than a 90 D lens; exact specifications come from the product.

Center the patient and microscope, use low light initially, hold the clean lens steadily without touching lashes or cornea, and move lens and microscope as a coordinated system until the aerial image appears. For peripheral viewing, the patient follows the requested gaze while the examiner re-centers through the pupil. Do not claim that a normal posterior-pole view excludes a peripheral tear.

Contact and mirrored lenses

Contact fundus or gonioscopy lenses require an authorized order or examiner, topical anesthesia when ordered, compatible coupling fluid, intact cornea, and a lens free of chips or deposits. Mirror size, angle, retinal region, and image orientation differ by design. Use the exact lens diagram rather than memorizing one angle-to-region table for every model.

After removal, inspect the ocular surface as directed and reprocess the lens using its current instructions and facility infection-control policy. Cleaning removes soil; the compatible disinfection method, concentration, contact time, rinse water, drying, and storage depend on lens material and manufacturer validation. Do not improvise bleach, alcohol, heat, or an enzymatic product across all lenses.

Quality and escalation

Poor focus can come from eyepiece error, patient refraction, tear film, media opacity, dirty optics, pupil edge, or alignment. Recheck setup before increasing light. Stop for severe pain, sudden vision change, vasovagal symptoms, corneal contact injury, a broken sterile or clean field, or equipment failure. The technician produces a safe, documented view; the licensed clinician determines diagnosis and dilation or treatment decisions.

Penlight screening

A penlight supports a gross external, pupil, motility, and anterior-chamber screen when a slit lamp is not yet available. Verify eye and ambient conditions, inspect lids and conjunctiva, compare pupil size and reaction, and use an oblique temporal beam to look for an iris shadow that may suggest a shallow chamber. This is a screening observation, not a measured angle and not a substitute for slit-lamp Van Herick estimation or gonioscopy. Marked asymmetry, pain, corneal haze, irregular pupil, shallow appearance, or an unexpected light response is documented and routed to the clinician before dilation under protocol. Avoid pressing on a traumatized eye or using a shared device without approved disinfection.