Eczema and the Eye
Donald Rudikoff, Steven R. Cohen, Noah Scheinfeld in Atopic Dermatitis and Eczematous Disorders, 2014
Glaucoma occurs as a complication of elevated intraocular pressure. Normal intraocular pressure depends on a balance between the production and outflow of the aqueous humor in the anterior segment of the eye. The function of aqueous humor is to maintain the shape of the eye and to provide nourishment to the lens and cornea. Aqueous humor is formed by the ciliary body in the posterior chamber. From there, it flows through the pupil to the anterior chamber. It leaves the anterior chamber through a sponge-like system of pores called the trabecular meshwork, located at the junction of the cornea and the root of the iris. The trabecular meshwork causes a resistance to flow and elevation of pressure. From the trabecular meshwork, fluid moves into the canal of Schlemm and then to the venous system. Under physiological conditions, a balance exists between fluid production and fluid outflow such that enough internal pressure is present to maintain the overall round shape of the eye. The normal intraocular pressure is 15 mmHg (Lens et al. 1999, Kaufman and Alm 2003). An elevation of intraocular pressure with no other abnormalities is known as ocular hypertension. Ocular hypertension associated with visual field defects or observable damage to the optic nerve is considered glaucoma.
Rheology of Retinal Disorders
Gordon D. O. Lowe in Clinical Blood Rheology, 2019
The intraocular pressure is normally high compared to other tissue pressures, presumably for maintenance of eyeball shape and normal refraction. This high pressure tends to cause the retinal veins to collapse, which is prevented by their high flow resistance, particularly at the level of the lamina cribrosa, where the central retinal vein egresses from the eye and where the central retinal artery and vein are in close contact.9,10 McGrath et al.11 have pointed out that the high flow resistance and anatomical peculiarities of the retinal venous circulation severely limit its ability to adapt to increased blood viscosity, and have suggested that this may be the principal reason for the frequent involvement of the retinal circulation in blood hyperviscosity states.
Vision Impairment and Its Management in Older Adults
K. Rao Poduri in Geriatric Rehabilitation, 2017
Glaucoma is an optic neuropathy thought to be related to the relative value of the intraocular pressure, which is felt to be too high for the health of optic nerve tissue in those with the disease. Intraocular pressure can increase when the passage of aqueous fluid out of the eye is blocked. Globally, glaucoma, both open-angle and angle closure, is the second leading cause of blindness. The term angle refers to the space between the iris and cornea at which the entrance to the trabecular meshwork that drains the aqueous fluid is found. Approximately, 8.4 million people are blind due to glaucoma worldwide, and 2% of the US population over 40 years of age has open-angle glaucoma (OAG).82,83 Afro-Caribbean and African Americans are most at risk for developing OAG.84 Most people with angle closure glaucoma (ACG) are of Asian descent with 20.2 million people being affected globally and 15.5 million of these living in Asia.85 Cases of OAG will increase from 2.2 to 3.3 million by 2020 and this is larger because of the aging population86–87 as aging is both a risk factor for OAG and ACG.88–95
Mechanistic links between systemic hypertension and open angle glaucoma
Published in Clinical and Experimental Optometry, 2022
Ying-kun Cui, Li Pan, Tim Lam, Chun-yi Wen, Chi-wai Do
In the eye, the intraocular pressure exerts pressure on the retina. Since there are no venous valves to control the direction of blood flow in ocular veins, the compression caused by intraocular pressure would hinder rather than enhance ocular circulation. It is suggested that venous pressure in the eye is roughly equivalent to the intraocular pressure. As shown in Figure 1B, the arterial pressure pushes the blood to flow downstream against the venous pressure, and the pressure in the veins before leaving the eye slightly exceeds the intraocular pressure under normal conditions.41 In the eye, the ocular perfusion pressure is the difference between arterial pressure and intraocular pressure. In principle, the higher the ocular perfusion pressure, the higher the ocular blood flow to the tissue.42
Classification of Seasonal Hyperacute Panuveitis (SHAPU)
Published in Ocular Immunology and Inflammation, 2022
Ranju Kharel Sitaula, Anadi Khatri, Pratap Karki, Sagun Narayan Joshi, Haramaya Gurung, Eliya Shrestha, Indraman Maharjan, Ananda K Sharma, Madan Prasad Upadhyay
Moderate SHAPU cases have more severe anterior chamber reaction with ≥1+ cell and ≥1+ flare (based on SUN’s Classification11). The fibrinous exudates may be seen in front of the pupil and iris crypts with or without the presence of hypopyon. The hypopyon is mobile, predominantly yellow in color, plano or convex in shape (Figure 2a). The lens is clear but the pupillary light reflex may be altered due to the exudates present in the vitreous leading to subtotal leucokoria in a red eye. But the fundal glow is still appreciable and the visible portion of retina appears apparently normal. The B scan ocular ultrasonography shows hyperechoic shadows in anterior and mid vitreous with attached retina but increased thickness of retinochoriodal complex (Figure 2b). Intraocular pressure can be (i) normal, (ii) lower due ciliary shutdown, or (iii) raised due to the outflow obstruction in the trabecular meshwork by the cells/exudates or pupillary block secondary angle closure glaucoma. Hence, moderate SHAPU cases have features predominantly of anterior and intermediate uveitis, which may start involving the retina if appropriate interventions are not taken at this stage.
Inter-Eye Comparison in Highly Myopic Patients with Unilateral Myopic Traction Maculopathy
Published in Current Eye Research, 2022
Jiaxin Tian, Yue Qi, Yinghan Zhang, Caixia Lin, Ningli Wang
From January 2021 to May 2021, 54 eyes of 27 patients (ID: PM01-PM27) with unilateral MTM, including 22 females and 5 males, were enrolled in the study. Three patients lost the OCT images of 3D Widefield MCT, so the protrusion of the sclera was assessed by radial line scans in OCT. The mean age was 48.89 ± 12.78 years with a range of 18 to 65 years. The average intraocular pressure was 15.85 ± 3.22 mmHg. The AXL positively correlated with the mean PSH, horizontal height and vertical height (r = 0.610, P < .001; r = 0.559, P < .001; r = 0.588, P < .001). Among the eyes with MTM, 10 eyes were classified as T1, 10 eyes were classified as T2, 6 eyes were classified as T3, and 1 eye with macular hole retinal detachment was classified as T5. All the eyes had outer retinoschisis, 6 eyes had S1, 4 eyes had S2, 4 eyes had S3, and 13 eyes had S4. The inter-eye comparison showed the affected eyes had worse BCVA and longer AXL than the fellow eyes (P < .001; P < .001). Moreover, the eyes with MTM had greater PSH no matter in the horizontal plane, the vertical plane, or the total mean. The inter-eye PSH difference in nasal was most obvious in four quadrants (P = .004). Besides, higher rates of posterior staphylomas, vitreovascular traction and ERMs were observed in the affected eyes (P = .010; P = .002; P < .001). While there was no significant inter-eye difference in the location of the protrusion of the sclera in the horizontal and vertical plane (P = .525; P = .650; Table 1).
Related Knowledge Centers
- Eye
- Glaucoma
- Trabecular Meshwork
- Vitreous Body
- Ciliary Body
- Ocular Tonometry
- Eye Care Professional
- Aqueous Humour
- Posterior Segment of Eyeball
- Eye Examination