Obesity is a growing global health concern, often leading to various health complications like cardiovascular diseases, diabetes, and certain ophthalmic conditions. Conditions such as cataracts, age-related macular degeneration (AMD), diabetic retinopathy, and glaucomatous optic neuropathy have been linked to excess weight. This article examines the intricate relationship between weight loss, particularly through bariatric surgery, and its effects on ocular health, while also considering the potential risks associated with prescription weight loss drugs.
Bariatric Surgery and Ocular Health: An Overview
Bariatric surgery has emerged as an effective intervention for achieving significant and sustained weight loss. As body mass index (BMI) decreases post-surgery, various ocular changes occur, primarily impacting retinochoroidal microcirculation, glaucoma risk factors, and the ocular surface. This review aims to evaluate the impact of bariatric surgery-induced weight loss on ophthalmic parameters, focusing on intraocular pressure (IOP) and retinal nerve fiber layer (RNFL), retinochoroidal microcirculation, and the ocular surface.
Impact on Retinochoroidal Microcirculation
The fundus of the eye allows for the examination of retinal vascularity in vivo, enabling non-invasive observation and follow-up of post-bariatric surgery patients. Postoperative weight loss has a generally positive influence on retinochoroidal microcirculation. Studies indicate that arterial perfusion and vascular density improve, venules constrict, and the arteriole-to-venule ratio (AVR) increases after bariatric surgery.
Arteriole-to-Venule Ratio (AVR)
AVR is an indicator of endothelial function and reflects preclinical metabolic and cardiovascular risk in patients with obesity. Changes in AVR result from arterial narrowing, venular dilatation, or both. It decreases in the course of weight gain due to increased arteriolar resistance and systemic hypertension.
A study using digital fundus imaging found a significant dilatation of retinal arteries and decreased retinal vein calibers, increasing AVR. However, another study demonstrated no difference in AVR between patients with obesity who underwent bariatric surgery versus those who underwent conservative treatment (diet/exercise). Other research has detected factors predisposing to vein narrowing and increasing AVR. CRAE and CRVE give more repeatable and accurate results than separate measurements of the width of arterioles and veins of the retina.
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Choroidal Thickness (CT)
The CT reflects the total choroidal vasculature. Patients with extreme obesity often have decreased nitric oxide levels, which are responsible for vasodilatation. Furthermore, a positive association has been found between higher BMI and vasoconstrictor factors like endothelin-1 and angiotensin-II.
Research findings on the impact of bariatric surgery on CT are mixed. One study showed a statistically significant increase in subfoveal CT after bariatric surgery, while another observed increased CT in patients with obesity compared to those with normal BMI, although this difference did not reach statistical significance. Conversely, a study found a significant decrease in CT values postoperatively.
Retinal Thickness
Postoperative changes in retinal thickness have been an object of research. An inverse association between minimum foveal thickness (FT) values and BMI has been observed. Research has identified clinical predictors for retinal thickening after bariatric surgery. After the surgery, increased HbA1c and serum C-peptide drop were reportedly associated with retinal thickening in the foveal and parafoveal regions. Increased macular thickness in the fovea and parafovea but no significant increase in the perifovea.
Optical Coherence Tomography Angiography (OCTA)
OCTA is a new technology that provides non-invasive imaging and tracking of retinal capillaries. Researchers were the first to examine changes in SVP and DVP with OCTA before and after bariatric surgery, obtaining the capillary density index (CDI). A study found a significant statistical increase in macular VD in the DVP 3 months after the bariatric surgery. This observation aligned with another study, which reported a postoperative increase in perifoveal vascular density in the DVP.
Choroidal Vascularity Index (CVI)
A new imaging tool has been proposed to indicate the ratio of choroidal vessels to stroma-the choroidal vascularity index (CVI). CVI reflects the distinction between stromal and luminal vascular components. In another study, researchers analyzed the choroidovascular system and capillary density index (CDI).
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Total Macular Volume (TMV)
SD-OCT was used to measure total macular volume (TMV) in a study. Patients who underwent LSG presented a statistically significant increase in TMV postoperatively.
Foveal Avascular Zone (FAZ)
The foveal avascular zone (FAZ) is a circular capillary-free zone in the retina. Microvascular diseases reflect in the increase in size and loss of round contour of FAZ. Higher BMI is associated with narrower retinal arteriolar and wider venular calibers. These microcirculation changes contribute to cardiovascular and cerebrovascular diseases.
Examining retinal and choroidal vessels in vivo provides a window to the human microvasculature. AVR was the first parameter to be studied. With the development of new technologies, it has become possible to explore new links between BMI and microcirculation. OCT quickly became an essential tool in retinal diagnosis, enabling choroidal thickness measurements and vascular density indices. OCT angiography gives an insight into the perfusion in retinal microvasculature.
Postoperative AVR improvement, increased choroidal and retinal thickness in the macula, and increased macular VD in the DVP prove that obesity-induced microvasculature alterations might be reversible after weight loss. Current research focuses on advanced technologies, including software for automatic vessel density measurement in DVP and SVP.
Glaucoma Risk Factors
Glaucoma is an ocular disorder leading to optic neuropathy and the first cause of irreversible blindness worldwide. Increased IOP is a leading risk factor in the pathogenesis of glaucoma. IOP can be elevated mechanically with fat accumulated intraorbital and elevated pressure in episcleral veins. Disrupted vascular homeostasis and endothelial dysfunction are reasons for the vascular etiology of glaucomatous changes. Changes in the RNFL and visual fields are objective parameters used to diagnose and evaluate the progression.
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Weight loss is positively correlated with IOP decrease when the surgery succeeds. Studies have observed a significant IOP decrease postoperatively. In these studies, IOP remained reduced at the 1-year follow-up visit.
After the bodyweight dropped, systolic blood pressure (SBP) significantly decreased. One study concluded that blood pressure is inversely related to RNFL thickness, supporting the assumption of vascular pathogenesis of RNFL changes in subjects with obesity. However, contrary results have also been presented, with one study showing that RNFL thickness was significantly reduced postoperatively. The authors hypothesize that postoperative decrease of fat tissue or vascular changes might impact RNFL.
A positive correlation between IOP and BMI is indisputable. The lower the body weight after the bariatric surgery, the lower the risk of glaucoma. Although the authors agree on the outcome, the mechanism of these findings needs to be investigated.
Ocular Surface and Vitamin A Deficiency
Dry eye is a multifactorial disease of the tears and ocular surface that results in symptoms of discomfort, visual disturbance, and tear film instability. Postoperatively, most patients reported mild to severe dry eye symptoms. No statistically significant correlation was found between variables such as visual function, ocular surface condition, and vitamin A serum level. On the contrary, other researchers noticed no dry eye symptoms in bariatric surgery patients. The fact that 20% of patients maintained a BMI > 35 mg/m2 postoperatively may have contributed to this.
Studies focused on assessing confocal microscopy parameters such as corneal nerve fiber density (CNFD), corneal branch density (CNBD), corneal nerve fiber length (CNFL), and keratocyte density (KD) before and 12 months after bariatric surgery. CNFL, CNBD, and keratocyte density from all three stroma layers were significantly lower in patients with obesity compared to controls.
After Roux-en-Y gastric bypass surgery, some patients presented decreased vitamin A levels. Six of them presented decreased visual acuity, xerosis, night vision deterioration, and suffered from eye pain or foreign body sensation. Vitamin A is one of the fat-soluble vitamins that cannot be synthesized by the human body and must be ingested to preserve tissue storage.
Several case reports highlight the importance of vitamin A supplementation after bariatric surgery. Cases of corneal ulceration, Bitot’s spots, and visual deterioration due to decreased vitamin A serum levels have been reported. Inadequate vitamin A supplementation following bariatric surgery can lead to severe bilateral dry eye and visual deterioration.
Studies on ocular surface disturbances following bariatric surgery have many limitations, including small, poor sex-diversified samples without a control group. In most studies, no significant change in ocular surface parameters was observed. Clinical presentation of vitamin A deficiency may imply many different ocular morbidities. Ocular complications of hypovitaminosis A are potentially reversible; however, in some cases, the recovery was significant but incomplete. Vitamin A supplementation after bariatric surgery is crucial to prevent severe visual impairment.
Prescription Weight Loss Drugs and Eye Health
Prescription weight loss drugs, particularly those that mimic the action of the GLP-1 hormone, have grown in popularity. While these drugs can speed weight loss and offer benefits like improved blood sugar control and reduced cardiovascular disease risk, patients should be aware of potential ocular side effects.
Blurred Vision
One of the side effects that some patients may experience is blurred vision. Changes to blood glucose levels can affect the shape of the eye’s lens that may cause blurred vision. Older adults are more likely to experience blurred vision when they start taking the medication because the eye’s lens is less flexible as we get older, and it takes the body longer to adjust to changes in blood sugar levels. Therefore, it takes longer to stabilize vision.
Non-Arteritic Anterior Ischemic Optic Neuropathy (NAION)
Some studies suggest a potential link to a condition called non-arteritic anterior ischemic optic neuropathy (NAION), which can lead to vision loss. NAION is a type of “eye stroke” where blood flow to the optic nerve is reduced or blocked, causing sudden, painless vision loss, often in one eye. The risk of occurrence of NAION is low with this class of medication. Patients with smaller optic discs are at higher risk of developing NAION. The risk for NAION is also higher the first year of use of this class of medication.
Age-Related Macular Degeneration (AMD) and Diabetic Retinopathy
More research is being done to investigate whether GLP-1 medications affect blood flow or oxygen levels in the eye, which could increase a patients’ risk of developing age-related macular degeneration (nAMD) and/or have a negative implication for patients who already have nAMD. The implications of long-term use of GLP-1 medication and diabetic retinopathy progression requires further study. Diabetic retinopathy involves damage to small blood vessels in the retina. For most patients, the cardiovascular and blood sugar control benefit of these drugs outweigh the small risk of retinopathy progression. In the long term, the diabetic retinopathy will be better controlled with improved diabetic control.
Recent Study Findings
A new study discovered that people prescribed semaglutide, sold as Ozempic and Wegovy, have a higher risk of developing NAION. People with diabetes who had been prescribed semaglutide were more than four times more likely to be diagnosed with NAION.
NAION is relatively rare, occurring up to 10 out of 100,000 people in the general population. NAION is the second-leading cause of optic nerve blindness (second only to glaucoma) and it is the most common cause of sudden optic nerve blindness. NAION is thought to be caused by reduced blood flow to the optic nerve head, with the consequence of permanent visual loss in one eye. The visual loss caused by NAION is painless and may progresses over many days before stabilizing, and there is relatively little potential for improvement.
The researchers analyzed the records of more than 17,000 patients treated over the six years since Ozempic was released and divided the patients in those who were diagnosed with either diabetes or overweight/ obesity. The researchers compared patients who had received prescriptions for semaglutide compared to those taking other diabetes or weight loss drugs.
There are several limitations to the study. The study population is majority white, and the number of NAION cases seen over the six-year study period is relatively small. The researchers also couldn't determine if the patients actually took their medication or if they started and then stopped taking semaglutide at some point and how this might have impacted their risk.
Lifestyle Factors and Eye Health
Beyond weight loss interventions, several lifestyle factors significantly impact eye health.
Smoking
Smoking is a well-established risk factor for various eye diseases. Smokers are more likely to develop cataracts and AMD than those who never smoked. The risk remains high even up to 20 years after quitting.
Diet and Exercise
Maintaining a healthy diet and engaging in regular physical activity are crucial for overall health, including eye health. A long-term study found that people who were physically active and drank occasionally experienced less vision loss over 20 years than those who didn’t exercise or drink at all.
Sun Exposure
Exposure to ultraviolet (UV) light increases the risk of cataracts and AMD. The structures in the eye absorb UV from natural sunlight, which is thought to damage the cells and change their metabolism. Wearing sunglasses that protect against UVA and UVB wavelengths is essential.
Regular Eye Exams
Regular eye exams are crucial for detecting early signs of eye conditions. It is recommended that adults have comprehensive eye exams every one to two years, depending on their needs and overall health.
The Link Between Obesity and AMD
Studies have shown that higher body mass index increases the risk for progression to the advanced forms of macular degeneration. Higher waist circumference was associated with a 2-fold increased risk for progression, and continued increased risk with greater waist circumference. Higher waist to hip ratio (WHR) also increased risk for progression to later stages of age-related macular degeneration.
A review of the literature found little evidence for being overweight and onset of early AMD, but did find a 32% increase in the risk of developing late macular degeneration among obese individuals. A review found that half of the studies they reviewed showed an increased risk of AMD with higher BMI, while other studies found no association. As with previous studies, the findings showed that obese individuals have an increased risk for developing late AMD. Other measurements of body weight such as waist circumference (WC) and waist-hip ratio (WHR) were also confirmed the association between body weight and disease progression. For example, one longitudinal population cohort found that a decrease in WHR is associated with a lower incidence rate of any form of AMD.
Inflammation and Nutrient Absorption
Excess weight can lead to increased inflammation in the body, including the eyes. When you’re overweight, your body stores more nutrients, including the carotenoids essential for eye health, in fat cells.
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