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. 2001 Jan;85(1):40–46. doi: 10.1136/bjo.85.1.40

Influence of laser photocoagulation on choroidal capillary cytoarchitecture

R Guymer 1, G Hageman 1, A Bird 1
PMCID: PMC1723689  PMID: 11133710

Abstract

AIM—To identify if laser photocoagulation induces morphological changes specifically related to the choroidal capillary endothelial processes that protrude into Bruch's membrane.
METHODS—Two human eyes and one adult macaque monkey eye received retinal laser photocoagulation that was just suprathreshold, before enucleation or exenteration. They were examined by electron microscopy to determine the length of the endothelial processes emanating from the choroidal capillaries in the region around the laser burn. One human and two monkey untreated eyes were used for comparison.
RESULTS—In human eyes, there was no increase in the number of processes 15 hours after laser treatment but at 5 days the processes were more numerous and longer within 400-500 µm of the burn than in the untreated half of the same eye. The processes were longer 9 days after photocoagulation in the monkey, when compared with untreated monkeys, and some breached the elastic lamina, a phenomenon not seen in the untreated eyes. Qualitative differences were also noted in the endothelial cell processes following photocoagulation. Neovascularisation was not observed.
CONCLUSIONS—Protrusion of choroidal endothelial cell processes into Bruch's membrane is a normal anatomical feature but the number, length, and morphology of the processes change following mild photocoagulation. It is plausible that these processes may play a part in the clearance of debris from Bruch's membrane, and represent an early stage of angiogenesis. If the latter is true prophylactic laser photocoagulation at just suprathreshold levels may carry a risk of inducing choroidal neovascularisation.



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Figure 1  .

Figure 1  

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Fundus photographs of a patient who received prophylactic photocoagulation treatment for high risk drusen. (A) Before treatment with 12 spots ×200 µm ×0.2 seconds at a power to just whiten the retina. The lesions are placed in a ring 1000 µm from the fovea; (B) 3 months after photocoagulation; (C) 6 months after photocoagulation; (D) 20 months after photocoagulation. Note that the clearance starts around the area of the laser burns and spreads out circumferentially and that the effect is continuing at 20 months.

Figure 2  .

Figure 2  

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Electron micrograph of choriocapillaris and Bruch's membrane in human eyes. (A) An untreated area of patient 3 (final magnification 48 000), and (B) an 71 year old man (final magnification 50 000). These show focal thickening of basal lamina (small arrow) around the base of a cell process (curved arrow) associated with long spacing collagen (LSC) (thick arrow) in the outer collagenous zone (OCZ). (C) 22 year old man (final magnification 100 000), (D) an 82 year old woman (final magnification 80 000); these show a magnified appearance of the processes (thick arrow).

Figure 3  .

Figure 3  

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Patient 2 treated 15 hours before exenteration. (A) Colour fundus photograph of the laser burns taken minutes after they were created. (B) Histology of the laser burn. The burn is localised to the photoreceptors (small arrow) and RPE (curved arrow), with Bruch's membrane (thick arrow) still intact and most of the choriocapillaris surviving.

Figure 4  .

Figure 4  

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Patient 3 lasered 5 days before exenteration. (A) Colour fundus photograph of the laser burns taken minutes after they were created. (B) Histology of the laser burn. The burn is localised to the photoreceptors (small arrow) and RPE (curved arrow), with Bruch's membrane (thick arrow) still intact and most of the choriocapillaris surviving.

Figure 5  .

Figure 5  

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Graph of the average number of processes per 100 µm of Bruch's membrane against the distance from the laser burn in patient 2. Patient 2 received laser treatment 15 hours before exenteration. The shaded area represents the range in the number of processes seen in the untreated half of patient 2's retina. The broken line is the average number seen per 100 µm.

Figure 6  .

Figure 6  

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Graph of the average number of processes per 100 µm of Bruch's membrane against the distance from the laser burn in patient 3. There were 5 days between photocoagulation and exenteration. The shaded area represents the range in the number of processes seen in the untreated half of patient 3's retina. The broken line is the average number seen per 100 µm. Note the increase in number of processes 400-500 µm from the laser burn.

Figure 7  .

Figure 7  

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Monkey eye after photocoagulation. Histology of the laser burn. The burn is localised to the photoreceptors (small arrow) and RPE (curved arrow), with Bruch's membrane still intact (thick arrow) and most of the choriocapillaris surviving.

Figure 8  .

Figure 8  

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(A) Electron micrograph of a monkey's Bruch's membrane and choriocapillaris showing endothelial processes (small arrow) (final magnification 40 000) and (B) electron micrograph showing a process (small arrow) protruding through the elastic lamina of Bruch's membrane (thick arrow) (final magnification 80 000). (C) Electron micrograph in which the endothelial cell appears to have an increase in cytoplasmic organelles (small arrow) (final magnification 48 000), and (D) electron micrograph with processes displacing the basal lamina (small arrow) of the endothelial cell (final magnification 32 000).

Selected References

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