Cataract Surgery Considerations in the Setting of Fuchs Dystrophy
Fuch’s dystrophy is a progressive disease of the endothelium that results in loss of endothelial cells, with associated corneal edema, loss of visual acuity, and ocular discomfort. Loss of endothelial cells is known to cause ineffective deturgescence, thereby affecting corneal transparency. The pathogenesis of the disease is also affected by a thickening of the Descemet membrane, presenting with guttae on exam.
Risk factors that have been previously implicated in endothelial cell loss include advancing age, lack of antioxidant enzymatic activity, as well as genetically decreased expression of anti-apoptotic genes such as in Fuch’s dystrophy. Endothelial loss is additionally affected by the very nature of ocular surgery and thus has important implications in cataract surgery in the setting of Fuch’s dystrophy.
Advanced Fuch’s corneal dystrophy is commonly associated with concurrent cataract presentation in patients, and thus decreased visual acuity is likely to be secondary to two causes, the cataract in addition to sequelae of the compromised endothelium.
Cataract surgery in the setting of Fuch’s dystrophy often presents a question of whether or not the cataract surgery should be performed alone, or in a combination with keratoplasty which is known as a ‘triple procedure’ (cataract surgery, lens implantation, and penetrating keratoplasty). Variants of the triple procedure include advances such as Descemet membrane endothelial keratoplasty and Descemet stripping endothelial keratoplasty.
A significant factor in considering cataract surgery in patients with Fuch’s dystrophy is the quantitative number of functioning endothelial cells.
Due to the traumatic nature of surgery, endothelial cells are compromised by ocular surgery, in addition to risk factors including history of prior ocular surgery, infections, trauma. Moreover, risk factors in decreased endothelial cell density include angle closure glaucoma, pseudoexfoliation syndrome, and a diabetes history of greater than 10 years. Regarding diabetes, diabetic patients are also known to have greater rates of endothelial cell loss after phacoemulsification procedures. Other reports of endothelial cell changes include sex playing a potential role, as a study found higher endothelial cell counts in women as compared to men.
Factors related to endothelial cell loss intraoperatively include mechanical, heat, hydrodynamic, heat, chemical, free radical formation, and also longer operating time. Protective factors for the endothelium include the use of viscoelastic material. The soft shell technique of layering cohesive viscoelastic underneath dispersive viscoelastic provides a synergistic protective effect in cases of Grade 4 or greater nuclear opacities.
A study found an endothelial cell density reduced by approximately 24% in guttate corneas that had undergone cataract surgery and lens implantation as opposed to an eye without surgery. A significant difference was also corroborated through analysis of unilateral cataract surgery in comparison to the contralateral eye.
IOL lens selection
Evidence shows that Fuch’s patients who undergo a Descemet stripping endothelial keratoplasty (DSEK) are likely to develop a hyperopic shift in refraction, which has been estimated throughout studies but has not been reproduced with reliability. Due to this lack of reliability, multifocal lenses are discouraged. Different factors have been implicated in this shift including graft dimensions as well as whether DSEK was performed combined or separate from cataract surgery. Studies showed refractive shifts of +0.71 diopters in patients who underwent DSEK after cataract surgery, whereas a shift of +1.15D had been seen in a combined surgery. In cases where a large thickness graft of 8.75mm-9.0mm was used, this shift was as great as +1.50D. Further discussion of refractive outcomes discussed in the Outcomes section.
Patients can be symptomatic with complaints of visual loss that is either a presentation of a cataract, the progressive disease process of Fuch’s or both. Glare, which can be a presenting symptom of cataracts, can be Fuch’s in etiology even without corneal stroma or edema, due to adhesed endothelial pigment and guttae.
Due to the nature of cataract surgery affecting the endothelium, it is important to consider the indication of cataract surgery alone versus a combination procedure. A study found that in 170 patients with Fuch’s dystrophy who underwent cataract surgery alone, 90% ultimately
underwent penetrating keratoplasty within a 30 year period. In patients who underwent bilateral penetrating keratoplasty and unilateral cataract surgery, penetrating keratoplasty was performed on average 3.2 years earlier in the eye in which cataract surgery had been performed. Therefore, it is important to counsel patients in surgical options and indications regarding availability of combination procedures (including DMEK, DSEK, penetrating keratoplasty) as well as surgical management of cataracts alone. Additional information regarding combination procedures compared to cataract management alone is discussed in the Surgical Technique and Outcomes section.
In regards to using pachymetry as a reference to indication for triple or combination procedure versus cataract surgery alone, it is recommended that a triple procedure be considered in corneas greater than 640 microns. Additionally, if epithelial edema is observed upon exam with topical anesthesia and gentle pressure with a cotton tip applicator, the triple procedure is indicated to prevent bullous keratopathy.
Forms of keratoplasty
Of the common surgical techniques, DSEK has been found to have numerous benefits over the traditional penetrating keratoplasty technique in patients with Fuch’s corneal dystrophy. DSEK offers faster visual rehabilitation, less complications including those of suture abscess, wound dehiscence, and irregular astigmatism, as well as greater reliability in predicting visual outcomes. This procedure has also been attributed to less pain and ultimately sharper vision. Indications for penetrating keratoplasty can include cases presenting with significant corneal scarring for which DSEK may not be sufficient to restore vision.
Use of viscoelastics
There has been previous concern regarding the use of viscoelastics in the case of endothelial keratoplasty such as DSAEK, to which previously surgeons have used air to fill the anterior segment or BSS in order to prevent donor dislocation. In a study assessing DSAEK alone compared to DSAEK in combination with phacoemulsification in a series of 315 Fuch’s dystrophy eyes, there were no dislocations that could be attributed to the use of Healon. That being said, all 8 of the dislocations had been corrected with an air bubble application and remained intact.
While literature has analyzed differences in use of Healon vs Duovisc, results showed significantly greater central corneal thickness in the Healon group at 6 month followup, but this has not been yet correlated to implications in endothelial cell density.
In regards to methodology of cataract removal, literature suggests that extracapsular cataract extraction is safer for endothelium in dense nuclear sclerosis, but in all other cases, phacoemulsification is safer with decreased endothelium loss.
Cataract surgery alone is a shorter and faster surgery, with less anesthesia, less cost, has a faster recovery time in achieving best corrected visual acuity, fewer postoperative follow-up visits, and does not require long term topical immunosuppression. This is at the potential risk of corneal decompensation and postoperative corneal edema in a patient with Fuch’s. Additionally, visual outcomes may be affected by increased corneal thickness and corneal structure abnormalities present in Fuch’s dystrophy.
On the other hand, a triple or combination procedure allows for a definitive treatment of both conditions, the cataract and Fuch’s dystrophy, avoiding risk of decompensating cornea at the expense of a longer and more invasive surgery, with a more significant follow up course.
The technique involved in the combination surgery generally has been removing the cataract once trephination of the cornea has been performed in an ‘open sky’ manner, after which the intraocular lens is placed. If performing a DSEK, and the view through the corneal stroma or edema is impaired, then the DSEK can be performed first before performing the cataract extraction in order to allow for a clear window. Of note, graft adherence has not been found to be affected by the use of viscoelastic agents in the process of cataract surgery.
When comparing a combination surgery as opposed to a cataract surgery and DSEK sequentially, endothelial cell counts at 6 month follow up were not significantly different. Literature also demonstrated that in cases of DSAEK in combination with cataract surgery versus sequential surgery groups, visual outcomes varied significantly. In the DSAEK only group, 91% of patients were within 2 Diopters of emmetropia as opposed to 97% of patients within emmetropia in the combination surgery group at 12 months follow-up. This suggests that the DSAEK combination surgery has predictable, successful visual acuity outcomes as opposed to the discussion of a different study in the next section.
In a separate study, this outcome of endothelial cell counts was corroborated in that penetrating keratoplasty in combination with cataract surgery was compared to sequentially performing keratoplasty followed by cataract surgery. There was no significant difference in endothelial cell loss in the two groups, but a finding was that refractive error from the targeted refraction varied significantly more so in the simultaneous, combination surgery group compared to the sequential surgery group. While the sample size was limited to 62 eyes, limited to 1 year follow up, and was performed as penetrating keratoplasty as opposed to DSEK, this effect is noteworthy. Results from the study demonstrated that 39% of patients were within 2 D of target refraction in the simultaneous group, while 70% remained within 2 D of targeted refraction. Variability in the simultaneous group led to up to a 8.5D change in refractive error.
These outcomes are important for a surgeon to consider in the setting of individual circumstances on a patient to patient, case by case basis considering factors of methodology, patient circumstances, and optimizing risks for a favorable outcome.
Three of the possible complications that can occur in the setting of DSAEK in Fuch’s include dislocations, graft failure, and pupillary block glaucoma. In a study assessing patients who underwent either a triple/combination procedure versus DSAEK surgery alone in Fuch’s patients, there was no significant difference in dislocations between the two groups. The rate of dislocations in this population was 2.5%, of which all were successfully resolved with an air bubble application, after which the grafts remained clear. In regards to a separate complication of primary graft failure, there were no cases of iatrogenic graft failure in the population of 315 Fuch’s eyes. A third complication assessed in the study was pupillary block glaucoma. One case of pupillary block glaucoma occurred in which an air bubble was identified attached to the pupil margin, and was subsequently resolved with no recurrence.
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