Iris transillumination defects are areas where the normally light-blocking posterior iris pigment epithelium has thinned or been lost, and because different underlying conditions produce transillumination defects in characteristically different locations and patterns, this simple bedside technique, shining a focused light through the pupil or sclera and watching where light escapes through the iris itself, can meaningfully narrow the differential diagnosis in seconds.
How Transillumination Works
The technique involves directing a focused light source, either through the pupil (retroillumination) or through the sclera, and observing the iris from the front: where the posterior pigment epithelium is intact and healthy, it blocks the transmitted light effectively, while areas of pigment epithelial thinning or loss allow light to pass through, appearing as a bright red or orange glow against the surrounding normally dark iris.
Pattern-Based Differential Diagnosis
Pigment Dispersion Syndrome
Produces characteristic mid-peripheral, spoke-like or radial transillumination defects, resulting from mechanical rubbing of the posterior iris pigment epithelium against the anterior zonular fibers as the iris flexes with normal pupillary movement, a mechanism specific enough that this pattern is considered classic for the condition and directly relevant to its associated pigmentary glaucoma risk.
Albinism
Produces diffuse transillumination throughout the entire iris, reflecting the generalized reduction in ocular pigmentation characteristic of albinism, in clear contrast to the more localized, patterned defects seen in pigment dispersion syndrome or trauma, and is typically accompanied by other characteristic ocular findings, including foveal hypoplasia and nystagmus (see albinism and foveal hypoplasia).
Trauma
Produces focal, often irregular transillumination defects at the specific site of prior injury, sometimes corresponding to a visible iris sphincter tear or other structural disruption, and typically unilateral and asymmetric with the fellow eye, distinguishing it from the more symmetric, bilateral patterns of pigment dispersion syndrome or albinism.
Pseudoexfoliation Syndrome
Produces transillumination defects typically concentrated at the pupillary margin, related to chronic mechanical rubbing between the iris and the pseudoexfoliative material deposited on the anterior lens capsule, a distribution pattern distinct from the mid-peripheral pattern of pigment dispersion syndrome.
Herpetic Iridocyclitis
Can produce patchy, sector-shaped transillumination defects following an episode of herpes simplex or herpes zoster-related anterior segment inflammation, reflecting focal iris ischemia and pigment epithelial damage from the inflammatory process itself.
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From Choroida — the team behind this siteClinical Significance
- Confirming pigment dispersion syndrome supports appropriate monitoring for pigmentary glaucoma, given the meaningful proportion of affected patients who go on to develop elevated intraocular pressure
- Recognizing a traumatic pattern supports a more complete assessment for other, sometimes more visually threatening, consequences of the same injury, including angle recession and lens subluxation (see angle recession glaucoma)
- Diffuse transillumination in an infant or young child prompts full evaluation for albinism, including assessment of visual acuity, nystagmus, and foveal development
- A sector-shaped pattern following a red eye episode supports a herpetic cause even when the acute presentation has already resolved and the patient no longer recalls the details clearly
Examination Technique
Both transillumination methods, retroillumination through the pupil and scleral transillumination, are performed at the slit lamp with the room lights dimmed for optimal visualization, and both eyes should be examined and compared, since bilaterality, symmetry, and the specific pattern observed all contribute meaningfully to the differential diagnosis.
Clinical Value
Iris transillumination defects are a straightforward, always-available bedside finding that, evaluated with attention to pattern and distribution rather than simply noted as present or absent, meaningfully narrows the differential diagnosis for a range of anterior segment conditions, from a common, glaucoma-relevant pigment dispersion process to a distinctly rarer, systemic pigmentary disorder.
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From Choroida — the team behind this siteReferences
- Campbell DG. Pigmentary dispersion and glaucoma. A new theory. Arch Ophthalmol. 1979;97:1667-1672.
- Summers CG. Albinism: classification, clinical characteristics, and recent findings. Optom Vis Sci. 2009;86:659-662.
- Ritch R. A unification hypothesis of pigment dispersion syndrome. Trans Am Ophthalmol Soc. 1996;94:381-405.
- Liesegang TJ. Herpes zoster ophthalmicus natural history, risk factors, clinical presentation, and morbidity. Ophthalmology. 2008;115:S3-12.
Test yourself
A few questions straight from this article.
-
Iris transillumination defects represent which underlying change?
The posterior iris pigment epithelium normally blocks transmitted light; where it has thinned or been lost, light passes through the iris and a defect becomes visible. -
On transillumination, an area of iris pigment epithelial loss appears as what?
Light escaping through an area of pigment epithelial thinning glows bright red or orange against the surrounding normally dark iris. -
Which iris transillumination pattern is classic for pigment dispersion syndrome?
Pigment dispersion syndrome produces characteristic mid-peripheral, spoke-like or radial defects, a pattern considered classic for the condition. -
What mechanism produces the iris transillumination defects of pigment dispersion syndrome?
As the iris flexes with normal pupillary movement, its posterior pigment epithelium rubs mechanically against the anterior zonular fibres and is worn away. -
Diffuse transillumination of the entire iris in a young child should prompt evaluation for which condition?
Albinism causes generalized diffuse iris transillumination and is typically accompanied by foveal hypoplasia and nystagmus, so acuity, nystagmus and foveal development are all assessed. -
Which iris transillumination pattern points to prior ocular trauma as the cause?
Trauma produces focal, often irregular defects at the site of injury, typically unilateral and asymmetric with the fellow eye, sometimes alongside a visible sphincter tear. -
In pseudoexfoliation syndrome, iris transillumination defects are typically concentrated where?
Chronic rubbing between the iris and pseudoexfoliative material on the anterior lens capsule concentrates the defects at the pupillary margin, unlike the mid-peripheral pattern of pigment dispersion. -
A patchy, sector-shaped iris transillumination defect after a past red eye episode suggests which cause?
Herpes simplex or zoster anterior segment inflammation leaves patchy, sector-shaped defects from focal iris ischaemia and pigment epithelial damage, recognisable long after the acute episode. -
Confirming pigment dispersion syndrome on transillumination mainly supports monitoring for what?
A meaningful proportion of patients with pigment dispersion syndrome go on to develop raised intraocular pressure, so confirming it supports monitoring for pigmentary glaucoma. -
How should iris transillumination be performed for optimal visualization?
Both retroillumination and scleral transillumination are done at the slit lamp with the lights dimmed, and both eyes are examined and compared because bilaterality and symmetry inform the diagnosis.
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