| Entity/status | Inheritance / gene / variant | Hallmark phenotype and course | Strongest evidence / sample | Mechanism confidence | Management | Major gaps |
|---|---|---|---|---|---|---|
| Isolated/classic pre-Descemet corneal dystrophy (PDCD), historically overlapping with cornea farinata; IC3D 2024 treats PDCDs as a group and notes isolated PDCD remains poorly defined / category 4 | No established causal gene for isolated PDCD. Usually sporadic in modern imaging series; heredity unclear. IC3D notes prior overlap with cornea farinata/deep filiform/deep punctiform labels. DOI: https://doi.org/10.1097/ICO.0000000000003420 (2024); https://doi.org/10.1177/1120672119862505 (2020) (pqac-00000001, pqac-00000006, pqac-00000012) | Bilateral tiny gray/polymorphic punctiform opacities immediately anterior to Descemet membrane; generally asymptomatic with vision usually unaffected; nonprogressive to slowly progressive. Multimodal imaging suggests deposits throughout the stroma, maximal posteriorly. DOI: https://doi.org/10.1097/ICO.0000000000003420 (2024); https://doi.org/10.1177/1120672119862505 (2020) (pqac-00000001, pqac-00000006, pqac-00000011) | IC3D expert synthesis plus retrospective multimodal case series of 8 corneas from 4 unrelated male patients with bilateral disease; SD-OCT showed hyperreflective line anterior to Descemet membrane and IVCM showed extracellular stromal deposits plus enlarged posterior keratocytes. DOI: https://doi.org/10.1097/ICO.0000000000003420 (2024); https://doi.org/10.1177/1120672119862505 (2020) (pqac-00000001, pqac-00000006, pqac-00000010) | Moderate for a keratocyte-centered degenerative/deposition process; low for a single molecular cause. Evidence includes ultrastructural vacuoles with electron-dense/lipofuscin-like material and imaging evidence of stromal, not epithelial/endothelial, involvement. DOI: https://doi.org/10.1177/1120672119862505 (2020); https://doi.org/10.1097/ICO.0000000000003420 (2024) (pqac-00000001, pqac-00000011, pqac-00000012) | Usually observation/follow-up because vision is typically preserved; diagnosis supported by slit-lamp, IVCM, and anterior-segment OCT. No disease-specific therapy or trial identified. DOI: https://doi.org/10.1177/1120672119862505 (2020); https://doi.org/10.1097/ICO.0000000000003420 (2024) (pqac-00000001, pqac-00000011) | No prevalence/incidence estimates specific to isolated PDCD; no validated gene; little natural-history data; no penetrance estimates; no biomarker, trial, or pathology-standardized management pathway. Distinction from cornea farinata and secondary/systemic causes remains imperfect. (pqac-00000001, pqac-00000011, pqac-00000012) |
| Punctiform and polychromatic pre-Descemet corneal dystrophy (PPPCD); genetically supported distinct subtype; IC3D category 1 in 2024 | Autosomal dominant; PRDX3 is the leading causal gene. Recurrent heterozygous PRDX3 c.568G>C (p.Asp190His) identified in 4 of 5 reported families in the 2020 genetic study; PDZD8 c.872+10A>T segregated in 3 of 5 families but was not favored as the main cause. DOI: https://doi.org/10.1016/j.ajo.2019.11.024 (2020); https://doi.org/10.1097/ICO.0000000000003420 (2024) (pqac-00000000, pqac-00000003, pqac-00000004, pqac-00000005) | Posterior stromal/pre-Descemetic multicolored polychromatic punctiform opacities, usually bilateral; typically asymptomatic and without visual disturbance; cases reported from childhood to late adulthood, often nonprogressive or only mildly progressive. DOI: https://doi.org/10.1016/j.ajo.2019.11.024 (2020); https://doi.org/10.1097/ICO.0000000000003420 (2024) (pqac-00000000, pqac-00000001, pqac-00000016) | Strongest evidence is the 2020 family-based study: 12 affected individuals from 3 previously unreported families within a larger set of 5 PPPCD families; segregation plus recurrence of PRDX3 p.Asp190His across families. Imaging showed hyperreflective posterior stromal/Descemet-level opacities; only measured biomechanical abnormality was increased corneal stiffness. DOI: https://doi.org/10.1016/j.ajo.2019.11.024 (2020) (pqac-00000000, pqac-00000003, pqac-00000004, pqac-00000013) | High confidence for a gene-disease relationship relative to other PDCD forms; moderate confidence for mechanism. PRDX3 encodes a mitochondrial antioxidant peroxidase regulating mitochondrial reactive oxygen species, but direct human corneal molecular profiling remains sparse. DOI: https://doi.org/10.1016/j.ajo.2019.11.024 (2020); https://doi.org/10.1097/ICO.0000000000003420 (2024) (pqac-00000003, pqac-00000005) | Observation and follow-up are usual because visual function is largely preserved; genetic counseling is reasonable given autosomal-dominant inheritance. No targeted therapy or registered clinical trial found. DOI: https://doi.org/10.1016/j.ajo.2019.11.024 (2020); https://doi.org/10.1097/ICO.0000000000003420 (2024) (pqac-00000000, pqac-00000001) | Extremely small literature base (about 10 families before 2020); prevalence unknown; penetrance and expressivity incompletely quantified; possible locus heterogeneity remains unresolved; uncertain whether extra-corneal crystals in isolated reports indicate a broader systemic process in some families. (pqac-00000000, pqac-00000005, pqac-00000013) |
| STS/X-linked ichthyosis-associated pre-Descemet opacities; better viewed as syndromic/secondary pre-Descemet corneal changes rather than primary isolated dystrophy | X-linked recessive STS deficiency. Case report demonstrated complete deletion of all 10 STS exons and flanking sequence failure by PCR in a 34-year-old man with known X-linked ichthyosis. DOI: https://doi.org/10.1186/s12886-017-0423-5 (2017) (pqac-00000007, pqac-00000008, pqac-00000009) | Bilateral tiny pleomorphic gray-brownish posterior stromal opacities anterior to Descemet membrane, with preserved corrected visual acuity (20/20 both eyes after refraction in the reported case); skin dryness/scaling from infancy; stable over 1 year in the published case. DOI: https://doi.org/10.1186/s12886-017-0423-5 (2017) (pqac-00000008, pqac-00000009) | Single detailed human case report with slit-lamp, IVCM, dermatologic exam, and molecular confirmation of STS deletion. IVCM showed enlarged activated posterior stromal keratocytes containing regularly distributed hyperreflective particles and additional anterior stromal particles; endothelial cell density remained normal. DOI: https://doi.org/10.1186/s12886-017-0423-5 (2017) (pqac-00000007, pqac-00000008, pqac-00000009) | Moderate for a secondary metabolic/deposition mechanism: authors proposed STS deficiency elevates cholesterol sulfate, causing lysosomal dysfunction and lipid accumulation in keratocytes; however this is based mainly on clinicopathologic inference and one genetically confirmed case. DOI: https://doi.org/10.1186/s12886-017-0423-5 (2017) (pqac-00000007, pqac-00000009) | Management centers on recognition of the ocular finding within X-linked ichthyosis, observation, and systemic/genetic counseling; no cornea-specific intervention was needed in the reported case. DOI: https://doi.org/10.1186/s12886-017-0423-5 (2017) (pqac-00000007, pqac-00000008) | Evidence limited to isolated cases; unclear prevalence among STS-deficient patients; natural history and treatment thresholds unknown; uncertain whether this should be classified with primary corneal dystrophies or as a manifestation of systemic disease. (pqac-00000001, pqac-00000007, pqac-00000009) |


*Table: This table contrasts the main evidence-supported forms of pre-Descemet corneal disease: poorly defined isolated PDCD, PRDX3-associated PPPCD, and STS/X-linked ichthyosis-associated pre-Descemet opacities. It summarizes what is established, what is inferred, and where major evidence gaps remain.*