With a worldwide prevalence of 1 in 4,000, retinitis pigmentosa (RP) is the most common form of hereditary retinal degeneration. More than 30 genes and loci have been implicated in nonsyndromic autosomal-recessive (ar) RP. Genome-wide homozygosity mapping was conducted in one Dutch and one Israeli family affected by arRP. The families were found to share a 5.9 Mb homozygous region on chromosome 2p23.1-p23.3. A missense variant in one of the genes residing in this interval, C2ORF71, has recently been reported to be associated with RP. C2ORF71, encoding a putative protein of 1,288 amino acids, was found to be specifically expressed in human retina. Furthermore, RT-PCR analysis revealed that in the mouse eye, C2orf71 is expressed as early as embryonic day 14. Mutation analysis detected a 1 bp deletion (c.946 del; p.Asn237MetfsX5) segregating with RP in the Dutch family, whereas a nonsense mutation (c.556C > T; p.Gln186X) was identified in the Israeli family. Microsatellite-marker analysis in additional Israeli families revealed cosegregation of a C2ORF71-linked haplotype in one other family, in which a 13 bp deletion (c.2756_2768 del; p.Lys919ThrfsX) was identified. Clinically, patients with mutations in C2ORF71 show signs of typical RP; these signs include poor night vision and peripheral field loss, typical retinal bone-spicule-type pigment deposits, pale appearance of the optic disk, and markedly reduced or completely extinguished electroretinograms. In conclusion, truncating mutations in C2ORF71 were identified in three unrelated families, thereby confirming the involvement of this gene in the etiology of arRP.

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The orbital apex is an undefined but well understood concept of Orbital Surgeons. We sought to determine the surgical apex area specifically where the volume ratio decreases significantly impacting on the optic nerve. A retrospective analysis using PACS program processing, measured the right retrobulbar space volume changes in 100 randomly selected cases without orbital pathology where CT was performed for non-ophthalmic indications. Volume of the retrobulbar space was measured between two recognizable landmarks. The first landmark being the point of exit of the optic nerve from the eye and the second landmark the optic nerve's point of exit from the orbit. The measured length between these two points was divided into five equal segments, V1-V5. The volumes of all 5 segments were compared and the most significant area of volume depletion was established. The mean numeric value of measured orbital volumes was compared. A ratio difference of V1/V2 was less than 2, V2/V3 was 2.32 (± 0.27), V3/4 was 3.24 (± 0.39), and V4/V5 was 5.67 (± 1.66). The most remarkable difference in ratio was between V4 and V5 (mean 5.67 ± 1.66 with p < .0001). The V3 segment (the posterior 3/5 of the retrobulbar space volume) is the location where decrease in orbital volume impacts, and measured ratios are statistically significant. We defined the surgical apex as the posterior 3/5 of the retro-bulbar orbital space. It is consequently the area of higher risk for optic nerve compression. This definition could be routinely utilized by ophthalmologists and neuroradiologists when evaluating masses affecting the orbit.