In the acute zone, the eyes are flattened and the facets larger. The flattening allows more ommatidia to receive light from a spot and therefore higher resolution. The black spot that can be seen on the compound eyes of such insects, which always seems to look directly at the observer, is called a pseudopupil. This occurs because the ommatidia which one observes "head-on" (along their optical axes) absorb the incident light, while those to one side reflect it.There are some exceptions from the types mentioned above. Some insects have a so-called single lens compound eye, a transitional type which is something between a superposition type of the multi-lens compound eye and the single lens eye found in animals with simple eyes. Then there is the mysid shrimp, Dioptromysis paucispinosa. The shrimp has an eye of the refracting superposition type, in the rear behind this in each eye there is a single large facet that is three times in diameter the others in the eye and behind this is an enlarged crystalline cone. This projects an upright image on a specialised retina. The resulting eye is a mixture of a simple eye within a compound eye. Another version is a compound eye often referred to as "pseudofaceted", as seen in Scutigera. This type of eye consists of a cluster of numerous ommatidia on each side of the head, organised in a way that resembles a true compound eye.
Supine hypotensive syndrome

Causes
the causes for this condition are the following:
Obstruction by deep vein thrombosis or tumors (most commonly renal cell carcinoma)
Compression through external pressure by neighbouring structures or tumors, either by significantly compressing the vein or by promoting thrombosis by causing turbulence by disturbing the blood flow. This is quite common during the third trimester of pregnancy when the uterus compresses the vein in the right side position. Iatrogenic causes may be suspected in patients with a medical history of liver transplantion, vascular catheters, dialysis and other invasive procedures in the vicinity
Budd-Chiari syndrome

Diagnosis
The diagnosis can be made clinically by observing the patient when in the right sided position where you can see multiple dilated veins over abdomen due to collaterals. Ultrasound with Doppler flow measurement may be used to assess the IVC and circulatory system. Treatment
Treatment will vary depending on the cause of the vena cava compression or interruption. Often, treatment includes positional changes, avoidance of supine positioning, especially on the right side. In pregnancy, definitive management of the IVCS is to deliver the baby. In other conditions, medical or surgical treatment to remove or relieve the offending structure will relieve symptoms. Frequency
Epidemiological data is elusive owing to the wide variety of clinical presentation. In the U.S., incidence is estimated to be at 5–10 cases per 100,000 per year. Minor compression of the inferior vena cava during pregnancy is a relatively common occurrence. It is seen most commonly when women lie on their back or right side.