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The most common ocular complication in homocysteinuria is lens subluxation.1 We present a patient with homocysteinuria who developed subhyaloid haemorrhages during pars plana vitrectomy/lensectomy for a subluxated lens in the right eye. She had also developed preretinal and intraretinal haemorrhages in her fellow eye 6 months earlier, after phacoemulsification of the subluxated lens. No preoperative or intraoperative anticoagulation was used for either eye surgeries.
A 12 year old girl with homocysteinuria presented with decreased vision in the right eye as a result of an anteriorly luxated lens causing pupillary block glaucoma with an intraocular pressure (IOP) of 50 mm Hg. The posterior segment was normal. She had undergone phacoemulsification and anterior vitrectomy for pupillary block glaucoma caused by subluxated lens in the fellow eye 6 months earlier. Retinal examination postoperatively revealed preretinal and intraretinal haemorrhages in the mid-periphery (fig 1), which cleared spontaneously over the next 5 months.
Since medical therapy was ineffective in the right eye, she underwent pars plana lensectomy and vitrectomy. As the core vitrectomy was initiated, small subhyaloid haemorrhages were noted to develop in the mid-periphery. The vitrectomy settings were changed to a high cutting speed and low aspiration but the haemorrhages continued to form. Induction of the posterior vitreous detachment was aborted when peripapillary intraretinal haemorrhages were noted to develop.
On the first postoperative day, a 2 disc diameter subhyaloid haemorrhage (not seen at the end of the surgery) was noted in the macula (fig 2). All haemorrhages resolved spontaneously over the next 10 weeks.
The precise mechanism of action of homocysteine on the vascular tree is not well understood. Elevated homocysteine levels can cause endothelial disruption, structural damage by toxic effects on the intima and media, increased oxidation of low density lipoproteins, and alterations of clotting factors leading to a hypercoagulable state.2
Histopathological data derived primarily from animal models demonstrate smooth muscle cell hypertrophy and hyperplasia of the arteries.3 Postmortem studies of hyperhomocysteinaemic patients have shown intimal and medial thickening with disruption of the internal elastic lamina of small and large vessels.4 Histopathology of small arteries reveal focal proliferation of connective tissue with increased fibroblasts, collagen, and irregular elastic fibres.4 These changes may contribute to the fragility of small arteries and capillaries.
Valsalva retinopathy sometimes occurs with general anaesthesia. We do not believe this patient experienced this mainly because Valsalva retinopathy is bilateral. The retinal haemorrhages occurred only in the operated eye and not the fellow eye each time the patient underwent surgery.
The haemorrhages noted postoperatively in the left eye may have occurred because of ocular decompression retinopathy. An acute lowering of IOP can decrease the resistance of the retinal and choroidal circulation, temporarily overwhelming the capacitance of the capillary bed and resulting in multiple endothelial leaks and intraretinal haemorrhages.5 Hyperhomocysteinaemia can affect the autoregulation of small arteries.2,3 This may have contributed to the development of retinal haemorrhages in the left eye. The subhyaloid haemorrhages in the right eye, however, were unlikely to be related to ocular decompression retinopathy since no haemorrhages were seen during pars plana lensectomy, but these developed soon after vitrectomy was initiated. Minimal traction transmitted to the internal limiting membrane and nerve fibre layer by the vitrectomy may have caused the extremely friable superficial capillaries to rupture. Indeed, defects in retinal vascular autoregulation due to homocysteinuria, may have contributed to the development of the observed haemorrhages.
We hypothesise that individuals with chronic hyperhomocysteinaemia are at an increased risk for retinal haemorrhages because of homocysteine mediated destructive changes in small vessel walls and an autoregulatory defect that results in extreme capillary fragility.
This work was supported by Research to Prevent Blindness Inc, the Lions Eye Research Foundation of New Jersey, and the Eye Institute of New Jersey.