Very scarce data exist regarding the possible effects of cataract surgery in the choroid. In our prospective study, we found that the choroid mean SFCT, as observed in EDI-OCT, significantly increased D7 after the surgery, reached a peak at M1, and started to decrease at M3. In 115 eyes, the greatest progression of SFCT was observed between the first and the seventh day after surgery. The SFCT of the fellow unoperated eyes remained unchanged during the follow-up period, excluding any systemic factor that could have affected choroidal measurements. All our patients were treated with antiinflammatory drops (dexamethasone and indomethacin eyedrops) prescribed from the completion of surgery and over a 1-month period. These antiinflammatory treatments are known to lower postcataract inflammation, and thus to diminish the postcataract retinal inflammatory response.
19 We can speculate that they could have lowered the choroidal response as well. However, it wouldn't have been ethical to study a control group without postoperative antiinflammatory agents to evaluate the true postcataract choroidal response. Falcao et al.
20 did not find, in 14 eyes of 14 patients, any statistically significant changes in choroidal thickness 1 week or 1 month after uneventful cataract surgery. However, the number of patients included in their study is too small to come to a conclusion or counterbalance our own results. Ohsugi et al.
21 evaluated the changes in choroidal thickness in 100 Japanese eyes after cataract surgery. They observed that the mean preoperative SFCT was 248.5 ± 82.7 μm. The mean SFCT significantly increased 3 days after surgery. The values of SFCT were comprised between 251 and 253 μm at D3, week 1, week 3, M3, and M6 after surgery.
21 The changes in choroidal thickness were negatively correlated with those in IOP early after surgery and later, negatively correlated with the axial length. In this study, the authors did not measure the CRT. In our study, the IOP was not measured at each time point. To our knowledge, no other study on choroidal thickness after cataract surgery is available.
Thus, phacoemulsification seems to be able to induce morphologic changes in the choroid layers. Recently, Xu et al.
13 have disclosed interesting results on the effect of cataract surgery in the choroid. They have investigated the expression of genes that might affect the blood–retinal barriers, including cytokine IL-1β, chemokines CCL2 and SDF-1, and growth factors FGF and VEGF, in the retina and the RPE/choroid of mice undergoing extracapsular lens extraction. They found that the expression of these genes was markedly upregulated in the retina and in the choroid. However, the level of upregulation was less elevated in the RPE/choroid than in the retina and was delayed in the RPE/choroid, occurring 24 hours post operation versus 30 minutes in the retina. Xu et al.
13 also found that the protein IL-1β, which is a pro-inflammatory cytokine, was strongly detected in the ganglion cell layer, inner cell layer, and in the choroid of operated mice eyes.
However, how cataract surgery induces retinal and choroidal inflammation is not understood. It is known that the surgical trauma induces releases of prostaglandins in the aqueous humor,
19 that causes a disruption of the blood–aqueous barrier. This results in the accumulation of other inflammatory mediators such as endotoxin, immune complex, and cytokines in the aqueous humor.
19 These inflammatory mediators diffuse into the vitreous cavity to reach the retina, where they are responsible for a rupture of the inner blood–retinal barrier resulting in another cascade of inflammatory mediators secretion together with an increased permeability from the perifoveal capillaries.
4,19 The outer blood–retinal barrier has also been shown to be disrupted as a consequence of postcataract surgery inflammation.
22 Thus, the inflammatory response of the anterior segment would lead to the occurrence of a posterior segment inflammation. Another explanation is that the surgical traumatism induces an inflammatory response with cytokine gene expression in all the structures of the eye at the same time, which would account for the acute (since 30 minutes after surgery) inflammatory gene transcription observed in the retina after cataract surgery.
13
In our series, we have observed that the mean SFCT at baseline was correlated with age and axial length. Our data are consistent with the published literature showing that the choroid thickness decreases with decades and millimeters of axial length.
23,24 We also found that, at baseline, the SCFT was thinner in diabetic patients versus nondiabetic patients. However, the difference did not reach statistical significance, probably due to the small number of diabetic patients in our study. The literature displays contradictory results on choroidal thickness in diabetic eyes. Some authors reported a choroidal thinning,
25 -27 while others found a thicker subfoveal choroid.
28
In our study, we encountered three cases of PCME (2.6%) despite the use of postoperative prophylactic antiinflammatory drops. For the three patients, no surgical complications occurred, the duration of the surgery was limited to less than 15 minutes and the amount of ultrasounds delivered was low. Two of the three patients had a risk factor for developing PCME. The first one had an epiretinal membrane.
2 The second patient suffered from well-controlled diabetes mellitus. Diabetic patients have a higher risk of PCME.
1 It usually develops in subjects with a prior history of diabetic macular edema,
29 which was not the case for our patient. For our third patient, no ocular or systemic risk factors for PCME were found. All three patients developed PCME at M2 after phacoemulsification while they encountered a decrease in their visual acuity. Surprisingly, the highest values of SCFT were observed for these patients at M1 after surgery, while no cystoid macular edema was present on the SD-OCT images. The CRT increased at M2 with a typical image of PCME on SD-OCT, while the SFCT was still elevated. It seemed that the increase of choroidal thickness preceded the occurrence of the PCME. These findings raise questions about the pathophysiological role of the choroid in the development of PCME.
One hypothesis would be a post inflammatory rupture in the outer blood–retinal membrane, which, in association with the rupture of the inner blood–retinal barrier, would enhance intraretinal accumulation of fluid. Experimental studies have suggested that the outer blood–retinal membrane plays a role in the pathogenesis of macular edema such as in diabetic patients.
30 A disruption of the outer blood–retinal membrane would lead to abnormal inflow of fluid into the retina resulting in accumulation of fluid in the retinal layers.
In other pathologies, it is believed that the choroid is primarily affected by the disease and leads to secondary retinal manifestations such as subretinal edema or RPE leaks. In serous central chorioretinopathy
31 or polypoidal choroidal vasculopathy,
32 the choroidal thickening precedes the occurrence of retinal abnormalities. In these pathologies, the increased choroidal thickness is associated with a choroidal vascular hyperpermeability, generally arising from the choriocapillaris.
31 In our study, angiographies were not performed in PCME patients, which enabled us to see whether the increased choroidal thickness was associated with an increased choroidal hyperpermeability.
Meanwhile, we are not aware of any reports of indocyanine green angiographies, laser Doppler flowmetry, or ultrasound performed or showing increased choroidal hyperpermeability in PCME patients.
Our study has shown that the SFCT increases after cataract surgery despite prophylactic antiinflammatory eye drops, showing that cataract surgery may induces inflammatory changes within the choroid. It is the first report of an increase of SFCT in patients prior to the development of PCME. However, the relationship between the extent of choroidal thickness and the development of PCME needs to be clarified. Further studies are needed to investigate if the choroid plays a role in PCME physiopathology.