Managing Cataract with Corneal Disease

This overview highlights key clinical nuances associated with clinically significant cataracts found in the presence of corneal disease, the specific considerations of cataract surgery in these conditions, and the implications to postoperative management. Specific discussion centres on cataract in the presence of Fuchs’ dystrophy, keratoconus, previous corneal refractive surgery, dry eye, previous corneal transplantation, and pseudoexfoliation.

There is some discussion regarding the extent of endothelial cell loss in patients with existing low cell density

CATARACT AND FUCHS’ DYSTROPHY

Fuchs’ dystrophy is a relatively common condition affecting approximately 4 per cent of patients over the age of 40.¹ Patients classically present with endothelial cell loss and small excrescences of Descemet’s Membrane called guttata (Figure 1). As endothelial cell loss continues, the cornea becomes oedematous and eventually there can be the development of bullae and painful ulcers (Figure 2). Fuchs’ dystrophy is often found in the presence of cataract and it can be difficult to decide whether and when to perform surgery. The basic rule of thumb however, is that each condition should be treated on its merits. If the cataract is clinically significant and impacting on the patient’s vision and daily activities, then cataract surgery is indicated. Similarly, if the Fuchs’ dystrophy is impacting on the patient’s daily function then it too should be treated with an endokeratoplasty. The predominance of Fuchs’ dystrophy changes may manifest itself initially with poor night vision and a diurnal fluctuation in the vision.

If both conditions are clinically significant, then a combined cataract extraction, lens implant and keratoplasty will be performed.^2,3 Sometimes it can be difficult to ascertain whether or not the corneal endothelium will survive cataract surgery. There is some discussion regarding the extent of endothelial cell loss in patients with existing low cell density however even in the best of hands, every cataract operation leads to the loss of some corneal endothelial cells.⁴ In my opinion, the evidence based medicine is clear that the use of the femtosecond laser is less likely to cause endothelial cell loss.⁵ One of the best studies in this area was conducted locally by Brendan Vote’s group, which highlighted the fact that femtosecond laser preparation caused less endothelial cell loss, unless it was additionally used to create entry wounds.⁶ 

If I am unsure as to whether or not a cataract operation will cause endothelial decompensation in the presence of Fuchs’ dystrophy, I will warn the patient that there is a chance after cataract surgery that the cornea will not clear, in which case we will then proceed to a sequential endokeratoplasty (DSAEK, DMEK). During the cataract operation it is obviously important to protect the endothelium with an appropriate dispersive viscoelastic, such as Viscoat. This decision making is highlighted in the following case reports.

Case One 

A 60 year old fisherman with a best spectacle corrected visual acuity of 6/15 and no significant cataract, presents with corneal thickness of 650μm and a reduced endothelial cell count down to 850cells/mm2. There is a history of diurnal fluctuation and the cornea itself is showing some evidence of corneal epithelial oedema.

Given that there is no significant cataract, it would be appropriate to proceed to either an ultrathin DSAEK or DMEK procedure (Figure 3).

Case Two 

A patient presents with a best spectacle corrected visual acuity of R: 6/24 and L: 6/12. There is evidence of bilateral Fuchs’ dystrophy with an endothelial cell count of <1000cells/mm2. A clinically significant nuclear sclerotic cataract is present in the right eye.

The optimisation of the ocular surface is important because it may be leading to some of the patient’s visual disturbances

In this situation I would proceed to a combined cataract extraction and lens implant with a DMEK endokeratoplasty. Where combined surgery is undertaken, it is important to ensure appropriate follow-up and to explain to the patient that the visual recovery can vary and can take weeks to months before the optimal visual acuity is achieved. Most studies do not reveal a significant change in corneal astigmatism following uneventful DSEK or DMEK surgery and long term refractive outcomes can be excellent.⁷ Some surgeons have proposed the benefits of using Toric IOLs in these situations however this should be approached with caution, especially if there is a risk of IOL rotation.⁸ 

KERATOCONUS AND CATARACT

Keratoconus or forme fruste keratoconus is more common than is widely appreciated. With the advent of appropriate corneal topography and tomography, the incidence is probably approaching 3 per cent in some populations.⁹ It is therefore essential that any patient with astigmatism who is planning to have cataract surgery, has corneal imaging performed.¹⁰ It is not unusual for me to have patients referred for a second opinion following a less than satisfactory outcome after cataract surgery only to find that, in fact, they had evidence of forme fruste keratoconus.

Identifying the keratoconus is critical so that the patient can be appropriately counselled about the likely final visual outcome. In patients who have keratoconus and then develop cataracts, the cataract surgery itself is not significantly different to a standard cataract operation. However, advanced keratoconus can make precise visualisation of the lens difficult, which is especially true if there is apical scarring (Figure 4). The presence of keratoconus also has implications for the intraocular lens calculations. Obtaining accurate keratometry and axial length in moderate to severe cases can represent a significant challenge. Apart from the increasingly irregular keratometry, marked cases often have longer axial lengths and deeper anterior chambers compared to normal eyes, which may impact the use of standard IOL power calculations. Currently, using the actual keratometry values will often lead to a hyperopic surprise and therefore a target of low myopia represents a valid option to optimise final uncorrected vision and minimise the risk of overcorrection.^11,12 An increased ability to accurately chart the posterior corneal astigmatism in patients with keratoconus is likely to further improve the accuracy of power calculations although keratometry repeatability remains a concern, particularly with moderate to marked keratoconus.¹³ The majority of moderate to severe keratoconus patients will rely on rigid gas permeable (RGP) contact lenses for best vision. In order to maximise the final refractive outcomes, a period of corneal adjustment without the lenses is ideal prior to biometry. This can be difficult for the patient and may require a staged process. Removing the RGP lens in one eye only, for a period of three weeks leading to biometry, may be possible although an alternative may be the use of an equivalent soft contact lens for several weeks prior to the test procedures. This may help normalise the residual effects of RGP wear and allow the reduction of time without contact lens wear to only three to five days prior to assessment, as required with soft contact lens wear traditionally.

One of the key decisions to consider in patients undergoing cataract surgery with keratoconus, is whether or not to use a toric intraocular lenses. I use a toric intraocular lens in 90 per cent of my standard cataract patients. The Alcon toric platform in conjunction with Barrett formulae in my opinion, provides the most precise refractive outcomes following cataract surgery (Figure 5). The decision to use a toric IOL will be partly governed by both the ability and desire of the patient to return to a gas permeable contact lens following surgery. If gas permeable lenses remain an option, the use of a

toric IOL is contraindicated as the correction of astigmatism in the corneal plane represents an extremely difficult task.

A toric intraocular lens can be used for cataract surgery in keratoconus when:

1. The manifest astigmatism is similar to the keratometric astigmatism,
2. The astigmatism is not too irregular. This can be deduced by the fact that the patient has had a reasonable spectacle corrected visual acuity prior to the development of cataracts,
3. The ectasia is stable.

The cataract surgery itself in patients with pseudoexfoliation is often more difficult

CATARACT IN PREVIOUS CORNEAL REFRACTIVE SURGERY

A significant part of my practice now is dealing with cataracts in patients who have had previous corneal refractive surgery. The key issue here is IOL power selection and predictability of outcome. The real question is: What is normal? Warren Hill has published figures on 260,000 consecutive eyes using the Haigis formula and has found that only 1 per cent of surgeons are able to obtain a predictability of +/- 0.50 dioptres in 92 per cent of cases. Six per cent of surgeons can achieve that level of predictability in 84 per cent of cases, and 55 per cent in 78 per cent of cases.¹⁴ With appropriate adjustments for the posterior corneal curvature, similar results can now be obtained in patients who have had corneal refractive surgery. It was thought that the problem in these patients was initially an inability to measure the central keratometry accurately, but in fact, there are a number of floored assumptions in the original IOL formula.¹⁵ The first assumption is related to corneal imaging. Current keratometry units assume a fixed ratio between anterior and posterior surfaces. Although this remains reasonable in standard eyes, corneal refractive surgery significantly alters the relationship. In myopic surgery patients this results in artificially flatter keratometry leading to eventual overestimation of the IOL power and subsequent hyperopic surprise. Keratometry is used in standard IOL power formulas in two ways; to determine the power of the IOL and the placement of the IOL itself. Using the incorrect keratometry in determining lens placement further amplifies the potential postoperative surprise. In significant errors, the removal of corneal tissue may reduce the refractive index of the cornea, thereby providing additional concerns with the accuracy of measurements and subsequent calculations.

You should also remember that all corneal refractive surgery patients are not the same. A photorefractive keratectomy procedure performed in 1992 does not produce the same cornea as a Wavefrontoptimised LASIK procedure done in 2002, or a SMILE procedure done in 2015. These procedures vary in terms of their predictability, the ablation zone size, and the induction of corneal aberrations. It is essential that all patients who have previously undergone refractive surgery have their higher order aberrations measured with an appropriate aberrometer. Lens selection may need to be adjusted based on whether or not there is any significantly inducted spherical aberrations.¹⁶ The use of multifocal or trifocal IOLs in previous corneal laser refractive patients represents an ongoing debate. The presence of significant aberrations will reduce the patient’s quality of vision. Although this does not represent a strict contraindication to the use of multifocal or trifocal IOLs, it does require caution to avoid a further decrease in overall quality, which may additionally impact patient satisfaction and the ability to carry out standard activities, particularly at night. If the patient is significantly motivated, customising the lens choice in terms of design and reading addition is essential.

Finally, it is essential that patients undergoing cataract surgery after previous refractive surgery do have a discussion as to the likely predictability. These patients have previously chosen to undergo a form of surgery to reduce their dependency on glasses and are unlikely to be satisfied unless they can get a similar result when they have their cataract surgery. The bar, in terms of refractive and visual outcome, is therefore very high. Enhancement options following the lens procedure may include a secondary IOL or further laser refractive surgery, albeit if anatomically appropriate due to existing aberration profile and corneal thickness.

One specific situation that we often see in Sydney is patients presenting with cataract who have had previous radial keratotomy. Although I never performed radial keratotomy, it was a relatively common procedure in the 1980s, in Sydney and other parts of Australia. These patients often develop a slow hyperopic shift and, while the IOL selection is not as complex as in patients who have had LASIK surgery, these patients often have some irregular astigmatism.^17,18 The final key point is that these patients can have quite a slow visual recovery and will often have a latent hyperopia for one to two months after the operation. It is essential that the patients are therefore counselled about this and that no knee-jerk reaction to address the pseudo-hyperopic surprise is performed (Figure 6).

CATARACT IN PATIENTS WITH DRY EYE

Ocular surface dysfunction in patients presenting for cataract surgery is common, however many present undiagnosed which represents a potential confounding factor in surgery outcomes.¹⁹ This makes it essential to investigate and optimise the ocular surface in any patient undergoing cataract surgery.²⁰ Every one of my patients who undergoes cataract surgery, whether they have had corneal problems or not in the past, will have tear film osmolarity and undergo an OSDI questionnaire (Figure 7). If there is any suggestion of ocular surface disease, this is managed aggressively prior to keratometry or biometry measurements with a regimen of artificial lubricants, topical anti-inflammatory medication, and fish oil tablets. This is customised to clinical findings.

The optimisation of the ocular surface is important because it may be leading to some of the patient’s visual disturbances. It may cause inaccurate keratometry and therefore poor IOL predictability. Epitropoulos and co-authors found significant greater variation in keratometry readings in patients with abnormal tear film osmolarity compared to patients with normal values in a test-retest series. This study in particular highlighted the potential impact of subtle dry eye disease upon cataract surgery power calculations.²⁰ Additionally, dry eye can complicate postoperative recovery leading to suboptimal patient satisfaction.²¹ I have no doubt that recent improvements in my corneal refractive and cataract practice, in terms of predictability, have been due to aggressive management of dry eye and ocular surface disease.

CATARACT SURGERY IN CORNEAL TRANSPLANTATION

Corneal transplant outcomes were previously judged by the survival of a clear graft however, with the development of lamellar techniques, visual, and refractive results appear to represent the new measure of success.³ Patients who have had corneal transplants and then develop cataracts pose a number of specific challenges.² The cataract can be treated on its merits and the technical aspects of the surgery are not particularly complex. A decision to use a toric intraocular lens is reasonable if the corneal transplant itself has limited regular and irregular astigmatism. If that is the case, and the corneal transplant subsequently fails, then an endokeratoplasty (DSAEK or DMEK) can be performed. However, if the cornea has evidence of significant astigmatism (>5.00 dioptres) or significant irregular astigmatism, then a toric intraocular lens should be avoided, anticipating that a further transplant may be necessary at some time down the track. An endothelial cell count should be performed in all patients undergoing cataract surgery and corneal transplantation, as it is likely to be lower than that in a normal patient. If it is sufficiently low, then the patient should be warned about the possibility of endothelial dysfunction during the operation.

it is essential that patients undergoing cataract surgery after previous refractive surgery do have a discussion as to the likely predictability

The decision to undertake a triple procedure (combined cataract removal, IOL insertion and corneal transplant) requires individual consideration. The ability to undertake concurrent endothelial lamellar surgery will depend on the depth of the anterior chamber and replacing the natural cataractous lens with a thin IOL may create more space for the surgeon. Lamellar techniques also have an advantage of being largely refractively neutral, although there is some variation.²²

ADDITIONAL INTRAOCULAR LENS OPTION IN DIFFICULT CASES

In some cases, the existing options discussed may likely provide minimal benefit to patients, particularly those with complex corneal histories. Recently, surgeons have been provided with the additional option of a pinhole IOL device which is implanted as a secondary IOL within the sulcus (XtraFocus IOL, Morcher, Germany) (Figure 8). The pinhole effect remains an old and established principle within optometry and ophthalmology. In patients where re-establishment of a perfect or at least manageable optical system is difficult, the pinhole device may minimise the effect of significant corneal aberrations or irregular astigmatism. Increasing the patient’s depth of focus may provide additional lee-way in terms of IOL power calculation, effectively bypassing several of the existing concerns with calculations. Patients with central scarring that impinges the pinhole location will not receive any benefit from the IOL however and insertion should be avoided in these cases. The artificial pupil may also impact the patient adjusting through different light conditions, which represents an important aspect for preoperative patient counselling. This is often considered a relatively minor trade-off against significantly improved unaided visual acuity at both distance and near. Bilateral implantation of the secondary IOL would require more cogent consideration preoperatively.

Case Three 

A 59 year patient had bilateral radial keratotomy procedures over 25 years prior. In the years following the procedure, he developed significant hyperopia and irregular astigmatism with bilateral best corrected visual acuity of 6/9 using an RGP lens. The patient has encountered significant glare and star bursts since the procedure. Examination shows radial keratotomy cuts impacting the central 4mm (Figure 9). Mild lens changes are also noted in the left eye. After discussion, the decision to proceed with cataract removal and implantation of an aspheric IOL and secondary pinhole IOL in the left eye was undertaken. The patient removed the RGP from this eye for three weeks prior to biometry. Topography at this point still indicated a measure of corneal irregularity however the imaging appeared stable. Following surgery, unaided visual acuity was 6/7.5 part and N6 in the treated eye. The patient described a significant reduction in symptoms and was very happy with the outcomes. On further questioning, he described some additional difficulty with night driving, however he did not feel this impacted vision or safety.

CATARACT SURGERY IN PSEUDOEXFOLIATION

Some people might be surprised to see pseudoexfoliation listed as a corneal condition. Pseudoexfoliation, as most people are aware, can cause issues with secondary open angle glaucoma, poor iris dilatation and lens instability.²³ It is less widely appreciated, however, that all patients with pseudoexfoliation also have an endotheliopathy and their preoperative endothelial cell counts tend to be lower than normal.²³ The cataract surgery itself in patients with pseudoexfoliation is often more difficult and if there is need for excessive manipulation, such as the use of capsular tension rings or iris retraction, this can have a further negative impact on the endothelial cell count. Again, my preference is always to use the femtosecond laser in cataract surgery for patients with pseuodexfoliation, as it is less likely to cause endothelial cell loss and requires less intraoperative lenticular manipulation.

Modern cataract surgery is an extremely successful operation that is able to give patients visual freedom and has been shown to significantly reduce comorbidities in elderly patients

CONCLUSION

Modern cataract surgery is an extremely successful operation that is able to give patients visual freedom and has been shown to significantly reduce comorbidities in elderly patients, such as hip fracture, social isolation and depression. Cataract surgery in the presence of corneal disease poses additional challenges, but with appropriate awareness, planning and surgical skill, these patients can also enjoy excellent visual outcomes.

Professor Gerard Sutton is internationally recognised as an expert in cataract surgery, laser vision correction and corneal transplantation. He has performed over 20,000 surgical procedures, and is the Sydney Medical School Foundation Professor of Clinical Ophthalmology and Eye Health. Prof. Sutton consults at Vision Eye Institute Chatswood and is the Medical Director of the Lions NSW Eye Bank. He remains actively involved in research. 

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