Medical & Health // Case Study 3: Disorders of Visual Function
Case Study 3: Disorders of Visual Function
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Case Study 3: Disorders of Visual Function
1. How do visual disturbances arise from background and proliferative retinopathy?
Proliferative diabetic retinopathy (PDR) is characterized by growth of neovascular vessels, which are prone to leakage, bleeding, and the development of vitreoretinal membranes and tractional retinal detachment. They can also invade the anterior segment to cause neovascular glaucoma or ischemia. Risk of vision loss is significantly higher with PDR than non-proliferative diabetic retinopathy (NPDR). PDR is a microvascular disease, where relative retinal ischemia produces a pro-angiogenic environment. Martinez and Peplow (2019) noted that angiogenesis is mediated in large part that consists of multiple isoforms that are required for the normal development of the vasculature and lymphatics. Molecular studies have shown that it has promoted vascular permeability and angiogenesis through its interactions on vascular endothelial cells. Capillary endothelial tight-junction disruption and development of endothelial cell fenestration weakened blood vessels. It has also stimulated endothelial cell proliferation and migration – changes associated with early angiogenesis.
Visual impairment is experienced with older age at examination, longer duration of diabetes, presence of proliferative retinopathy, and presence of senile cataracts. Lartey and Aikins (2018) find that visual impairment was associated with older age at examination, longer duration of diabetes, presence of senile cataract, presence of macular edema, and proliferative diabetic retinopathy. The progression from non-proliferative diabetic retinopathy to a more advanced stage of moderate to severe non-proliferative diabetic retinopathy and proliferative diabetic retinopathy occurs very quickly after diagnosis of mild non-proliferative diabetic retinopathy. The etiology of diabetic retinopathy is unclear, and present treatments have limited effectiveness. Currently diabetic retinopathy can only be diagnosed by a trained specialist, which reduces the population that can be examined. A screening biomarker of diabetic retinopathy with high sensitivity and specificity would aid considerably in identifying those individuals in need of clinical assessment and treatment.
2. How might blindness occur with a prolonged detached retina? Explain using your knowledge of pathophysiology.
Retinal detachment is defined as the separation of the neurosensory retina from
the underlying retinal pigment epithelium (RPE). In its rhegmatogenous form, liquefied.
vitreous detaches the retina by passing through a retinal tear or hole. Its incidence is around 1 in 10,000 persons per year (Danese & Lanzetta, 2022). According to the macular involvement, it may be classified as “macula on” or “macula off” retinal detachment. Especially when it is of recent onset and without macular involvement, it is considered a surgical emergency. Potential risks of delayed surgery are a progression of the detached retina, development of proliferative vitreoretinopathy, and worse functional outcomes if the macula becomes involved. It may lead to blindness of the affected eye unless surgical treatment is promptly performed.
A diversity of artificial vitreous has been long investigated as substitutes for the native counterparts to repair retinal tear and detachment. Emphasis has been placed on improving the optical and mechanical properties, as well as the biocompatibility and biodegradability (Danese & Lanzetta, 2022). Synthetic hydrogels, because of the versatile programmability and intrinsic resemblance to the native vitreous, are emerging as promising alternatives. Recently, prolonged substitution is achieved by curtailing degradation-caused changes in the intraocular pressure, whereas a novel thermogel is presented that elicits the reformation of vitreous-like-body during the degradation process.
The prolonged detachment of macula-off retinal showed that the baseline visual acuity and time to surgical repair are among the best predictors of vision outcomes. The number of detached quadrants and the stage of proliferative vitreoretinopathy are also related to poor postoperative anatomical results and poor visual prognosis. In addition, the integrity of the ellipsoid zone and the external limiting membrane is useful to predict postoperative visual acuity. However, per studies where two patients with macula-off retinal detachment experienced a postoperative improvement in visual acuity secondary to ellipsoid zone restoration.
3. What are the similarities and differences between traction retinal detachment and rhegmatogenous detachment?
Traction retinal detachment (TRD) have long been the most common indication for Proliferative diabetic retinopathy (PDR) related vitreoretinal surgery (Danese & Lanzetta, 2022). Vitrectomy surgery is indicated for recent TRD involving the macula, progressive TRD that threatens the macula, and recent data suggest that chronic macula involving TRDs may also benefit. Patients having extramacular traction retinal detachments may need de novo or supplemental PRP to reduce neovascular activity, wall-off the detached area, and thereby reduce the probability of spread of detachment into the macula.
Meanwhile, rhegmatogenous retinal detachment typically presents with the perception of light flashes, floaters, or a “dark curtain.” In most cases, the retinal tear is a consequence of degeneration of the vitreous body. Epidemiologic studies have identified myopia and prior cataract surgery as the main risk factors. Persons in the sixth and seventh decades of life are most affected. Rhegmatogenous retinal detachment is an emergency, and all patients should be seen by an ophthalmologist on the same day that symptoms arise. The treatment consists of scleral buckle, removal of the vitreous body (vitrectomy), or a combination of the two. Anatomical success rates are in the range of 85% to 90%. Vitrectomy is followed by lens opacification in more than 70% of cases. The earlier the patient is seen by an ophthalmologist, the greater the chance that the macula is still attached, so that visual acuity can be preserved.
Feltgen and Walter (2014) explained that the most common cause of rhegmatogenous retinal detachment is degeneration of the vitreous body. The vitreous is made up almost entirely (98%) of water and is stabilized by collagen fibrils that extend into the superficial (internal) layers of the retina (Feltgen & Walter, 2014). Physiological degeneration of this vitreous scaffold has been demonstrated as early as the first few years of life. In the course of time the collagen fibrils harden, sometimes leading to perception of the mobile dots and threads known as muscae volitantes or “floaters”. The progressive loss of elasticity eventually results in separation of the vitreous from the retina. This process is described as “posterior vitreous detachment.” In this context, the risk that a tear will arise in the retina is most acute when the vitreous body is still attached to the retina at one or more points and its weight exerts traction. Because the vitreous usually begins to separate from the retina at the posterior pole of the eye, extending to the so-called equator, the tension on the retina is particularly strong in this region. The equator marks the transition of the central to the peripheral retina and is the point where the retina is at its thinnest, which explains the predilection for tension-related holes in the retina.
References
Feltgen, N., & Walter, P. (2014). Rhegmatogenous retinal detachment—an ophthalmologic emergency. Deutsches Ärzteblatt International, 111(1-2), 12.
Lartey, S. Y., & Aikins, A. K. (2018). Visual impairment amongst adult diabetics attending a tertiary outpatient clinic. Ghana Medical Journal, 52(2), 84-87.
Martinez, B., & Peplow, P. V. (2019). MicroRNAs as biomarkers of diabetic retinopathy and disease progression. Neural regeneration research, 14(11), 1858.
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