The ora serrata is the most anterior edge of the sensory retina, continuing posteriorly from the pars plana (posterior ciliary body). It is located approximately 5 mm anterior to the equator of the eye and is about 2 mm wide.
It is the boundary where the single-layer non-pigmented epithelium of the pars plana transitions into the multilayered sensory retina, and its appearance is serrated. The serrated shape results from alternating retinal projections and bays of the pars plana.
The location differs between the nasal and temporal sides. On the nasal side, it is easily identifiable at 5.5–6 mm from the limbus, while on the temporal side it is slightly more posterior at 6.5–7 mm. The area from the vortex veins to the ora serrata is called the peripheral retina.
Location
Approximately 5 mm anterior to the equator: The most anterior edge of the retina adjacent to the pars plana.
Nasal side: 5.5–6 mm from the limbus. The bays are wide and easily identifiable.
Temporal side: 6.5–7 mm from the limbus. Located slightly posterior.
Structure
Serrated border: Retinal projections and ciliary body indentations alternate.
Approximately 2 mm wide: Transition zone from non-pigmented epithelium to multilayered sensory retina.
Undifferentiated photoreceptor band: The transition zone is about 280 μm wide and contains undifferentiated photoreceptors lacking outer and inner segments.
Functional Significance
Anchor point for vitreous attachment: The vitreous base firmly attaches across the ora serrata for 360°.
Weak point for retinal detachment: The contact area between undifferentiated photoreceptors and the retinal pigment epithelium is small, resulting in low adhesion.
Surgical landmark: Anatomical reference for determining incision sites in vitrectomy.
The ora serrata is located inside the eye (intraocular), just posterior to the pars plana, approximately 5.5–6 mm nasal to the limbus and 6.5–7 mm temporal to the limbus. It is the most anterior part of the sensory retina and can be observed during fundus examination using indirect ophthalmoscopy with scleral depression.
The ora serrata is an anatomical structure and does not itself cause subjective symptoms. Symptoms appear when lesions near the ora serrata (such as retinal dialysis, tears, or cystoid degeneration) occur.
Histological features of the ora serrata are as follows.
The main lesions occurring near the ora serrata and their risk factors are shown below.
Ora Serrata Tear
Definition: A crescent-shaped peripheral retinal tear (retinal dialysis). It takes the form of a detachment of the vitreous-retinal adhesion at the posterior border of the ora serrata1).
Predilection site: More common in the inferotemporal quadrant. Asymmetry between nasal and temporal sides is considered a factor.
Cause: Often associated with trauma. Juvenile cases are bilateral and progress slowly.
Giant Tear
Definition: A tear of 90° or more. It may extend posteriorly from the ora serrata.
Predisposition: Common in highly myopic eyes with lattice degeneration.
Tears at the posterior border of the vitreous base: Small characteristic tears may occur along the posterior border of the vitreous base in highly myopic eyes or eyes with intraocular lenses.
Degeneration and Tears
Cystoid degeneration: Present in almost all normal individuals. Involved in juvenile retinal dialysis and retinoschisis.
Lattice degeneration: Frequency 5–10%. Lattice degeneration is present in about 40% of retinal detachment cases, but the rate of progression from degeneration to detachment is only 0.3–0.5%.
Undifferentiated photoreceptors near the ora serrata have a small contact area with the retinal pigment epithelium, and capillary attraction and the number of attachment complexes are reduced. This provides an anatomical background that makes peripheral retina more prone to detachment than the macula (see Pathophysiology section).
Retinal dialysis is a condition where the posterior border of the ora serrata, where the vitreous and retina are firmly attached, is torn by trauma or other causes. A crescent-shaped tear forms, commonly occurring in the inferotemporal quadrant 1). Many cases are associated with trauma, but in young individuals, it may be bilateral and slowly progressive.
For observation of the ora serrata and its surrounding lesions, a detailed examination of the peripheral retina using indirect ophthalmoscopy with scleral indentation is essential.
In symptomatic posterior vitreous detachment (PVD), 5–14% of cases in which a break is found at the initial examination develop additional breaks during follow-up 1). Therefore, follow-up for a certain period after the initial examination is necessary.
In photocoagulation or cryocoagulation of peripheral horseshoe tears, it is important to confirm that the treatment surrounding the tear reaches the ora serrata 1). The most common cause of treatment failure is insufficient treatment of the anterior border 1).
Vitrectomy using liquid perfluorocarbon (PFCL) is selected. PFCL is a heavy liquid that helps unfold the detached retina and is useful for repositioning in giant tear cases.
In vitrectomy, trocar ports are placed posterior to the corneal limbus. The safe port position guidelines are as follows.
| Eye condition | Distance from the limbus |
|---|---|
| Phakic eye | 3.5–4.0 mm |
| Pseudophakic/aphakic eye | 3.0–3.5 mm |
Incision sites should avoid the 3 and 9 o’clock positions, as the long posterior ciliary arteries and nerves run there, posing a risk of injury.
In vitrectomy, the incision (trocar placement) is determined based on the anatomical location of the ora serrata. If the incision is too anterior, it may damage the ciliary body and lens; if too posterior, manipulation of the vitreous base becomes insufficient. Understanding individual variations of the ora serrata (nasal vs. temporal differences, presence of the lens) is essential for safe surgery.
The vitreous base is a 360° band approximately 6 mm wide that straddles the ora serrata. Collagen fibers run perpendicular to the retinal surface, forming strong adhesions. These firm attachment sites become focal points for tear formation when subjected to traction.
The positional relationship between the ora serrata and the ciliary body is summarized below.
| Structure | Distance from the ora serrata |
|---|---|
| Posterior edge of the ciliary processes | 2–2.5 mm anterior |
| Pars plana (anteroposterior width) | 3–4.5 mm |
| Anterior border of the vitreous base | 5 mm anterior |
In the macula, rod photoreceptors contact the retinal pigment epithelium over a large surface area, resulting in strong adhesion. In contrast, near the ora serrata, the outer and inner segments of undifferentiated photoreceptors are underdeveloped, and the contact area with the pigment epithelium is significantly smaller. Consequently, both capillary attraction and the number of adhesion complexes are reduced, making retinal detachment more likely even with minimal traction.
In addition, the asymmetry between the nasal and temporal sides (the temporal side is located more posteriorly than the nasal side) is thought to explain why ora serrata tears are more common in the inferotemporal quadrant.
Photoreceptors near the ora serrata are undifferentiated and lack outer and inner segments, so the contact area with the pigment epithelium is small. Capillary attraction and the number of adhesion complexes are reduced, making this area vulnerable to traction. Additionally, because the vitreous base is firmly attached across the ora serrata, this region is most susceptible to vitreous traction.
In minimally invasive vitreous surgery (MIVS) using 25-gauge or 27-gauge instruments, the trocar system allows for smaller, self-sealing incisions. This reduces invasiveness to the ciliary body and vitreous base, lowering the risk of postoperative inflammation and hypotony.
A definitive correlation between the anatomical morphology of the ora serrata (individual differences in the number and shape of dentate processes) and pathological changes has not been established at present. The association between bilateral retinal dialysis without a history of trauma and developmental abnormalities of the ora serrata remains a topic for future research.
