Iris Anatomy and Uveitis Overview

Iris Coloboma

• Iris colobomas are caused by incomplete closure of the choroidal fissure
• This results in a keyhole-shaped defect in the inferonasal region of the iris
• The rest of the iris is typically normal
• Atypical colobomas can occur in other areas, though less common
• The collarette is the thickest part of the iris

Uveitis and Legal Blindness

• Uveitis is a significant cause of blindness in the US
• Approximately 30,000 new cases of legal blindness from uveitis occur annually in the US
• This accounts for roughly 10-20% of all blindness cases in the US
• Uveitis can affect people of any age, but is most frequent in people in their 40s
• There is a higher prevalence of uveitis in women

Anatomy of Iris and Ciliary Body

• The non-pigmented epithelium of the ciliary body is continuous anteriorly with the posterior pigmented epithelium of the iris
• It is continuous posteriorly with the neurosensory retina
• The non-pigmented epithelium is the innermost layer of the ciliary body and contacts the aqueous humor
• The apexes of the non-pigmented epithelium cells in the ciliary body face outwards, while the apexes of the pigmented epithelium cells face inwards; thus the cells of these two layers are adjacent

Slit-lamp Examination Findings in Patients with Down Syndrome

• Brushfield Spots are whitish or greyish lesions found circumferentially around the peripheral iris
• They represent focal areas of stromal hyperplasia, surrounded by areas of relative hypoplasia
• More common in patients with lightly pigmented irides
• Strongly associated with Down syndrome, but can be present in some normal individuals

Keratic Precipitates (KPs)

• KPs are aggregates of inflammatory cells found in the aqueous humor, typically on the inferior half of the cornea
• Their appearance varies based on the severity, duration, and type of uveitis
• Non-granulomatous KPs appear as small, discrete, fleck-like, linear, or stellate corneal opacities
• Granulomatous KPs ("mutton-fat" KPs) have a fluffy, greasy, or waxy appearance and are composed of macrophages and epithelioid cells

Pupil Size

• Patients who are nearsighted, young, or have lighter-colored irises typically have larger pupils than patients who are hyperopic, older, or have darker-colored irises.

Ciliary Muscle Muscle Groups

• All three muscle groups (longitudinal, radial, and circular) originate from the ciliary tendon.
• Only the longitudinal muscle terminates at the suprachoroid
• Radial muscles attach to the ciliary processes
• Circular muscles attach to the ciliary processes, but their termination point is at the anterior end of the processes

Panuveitis

• Panuveitis involves inflammation of all anterior and posterior structures of the eye
• According to the International Uveitis Study Group, the anatomical classification of uveitis is:
  • Anterior uveitis
  • Intermediate uveitis
  • Posterior uveitis
  • Panuveitis

Anterior Chamber Cells Grading with SUN Scheme

• The SUN grading scheme for anterior chamber cells is:
  • Grade 4+: 50+ cells in a 1mm slit beam field