The Complex Relationship Between Cataract and Diabetic Eye Disease

Gain a better understanding of its consequences for cataract surgeons and their patients.

By Stephen G. Schwartz, MD, MBA and Harry W. Flynn, Jr., MD

The safety and success of cataract surgery has improved so dramatically in recent years that it can sometimes be difficult to bear in mind the unique needs of special patient populations that might necessitate a change in surgical approach. But the diabetic population in the US — 20 million strong and growing — are becoming an everyday occurrence in cataract surgery suites, and even the most highly skilled surgeon may have trouble fully grasping the consequences of diabetic eye disease.

To help, Ophthalmology Management enlisted the guidance of several eminent clinicians from Bascom Palmer Eye Institute in Miami. In the two articles to follow, retina and cornea specialists discuss the elevated risks and the possible modifications to consider when performing cataract surgery in this growing population. We are pleased to share their insights with readers.

Clinical Image Courtesy of Harry W. Flynn, Jr.
Illustration by Joel & Sharon Harris/Deborah Wolfe, Ltd.

Cataract is an important clinical problem affecting patients with diabetes mellitus. Both type 1 diabetes¹ and type 2 diabetes² are associated with an increased frequency of cataract surgery. The Wisconsin Epidemiologic Study of Diabetic Retinopathy reported that the cumulative incidence of cataract surgery in patients with type 2 diabetes is about 25% over 10 years.³

There is a complex relationship between diabetes mellitus and cataract progression. For example, the Beaver Dam Eye Study reported a statistically significant association between diabetes mellitus and cortical lens opacity.⁴ On the other hand, a recent prospective study reported a negative association between ischemic diabetic retinopathy and progression of nuclear sclerosis.⁵

Similarly, there is a cause-and-effect relationship between cataract formation and certain therapies used in the treatment of diabetic retinopathy. For example, clinical trials have documented that intravitreal triamcinolone acetonide is associated with cataract progression.⁶ However, the relationship between pars plana vitrectomy and cataract progression is less certain, at least in diabetic patients. There is a well documented association between PPV and cataract progression in non-diabetic patients,⁷ but several studies have found no association, or even a negative association, between PPV and cataract progression in diabetic patients.^8,9

Some studies have reported an association between cataract surgery and progression of diabetic retinopathy,¹⁰ but other studies have reported no significant association.^11,12 Further complicating our understanding is the fact that, in pseudophakic diabetic patients, it may be difficult to distinguish early diabetic macular edema from pseudophakic cystoid macular edema. Some diabetic patients may show features of both CME and DME following cataract surgery.

The Early Treatment Diabetic Retinopathy Study (ETDRS) published follow-up data on the subset of enrolled patients that subsequently underwent cataract surgery. The ETDRS reported that, at one year following cataract surgery, visual acuity improved by two or more lines in 64% of eyes randomized to early photocoagulation and in 59% of eyes randomized to deferral of photocoagulation.¹³

To better study these relationships, the Diabetic Retinopathy Clinical Research (DRCR) network is planning two trials. Protocol P is a non-randomized cohort study of patients with center-involved diabetic macular edema undergoing cataract surgery. Protocol Q is an observational study of patients with diabetic retinopathy without center-involved DME undergoing cataract surgery. Both studies are currently recruiting. With careful follow-up of these patients using standardized ETDRS visual acuity testing and optical coherence tomography, a better understanding of the association between cataract surgery and DME will be possible.

Considerations and Modifications

With these concepts in mind, certain recommendations become evident when faced with a patient with concomitant diabetic retinopathy and cataract.

First, the determination of a visually significant cataract in a patient with pre-existing diabetic retinopathy may be more difficult than in a patient with a normal posterior segment. Tests such as a potential acuity meter or potential acuity pinhole¹⁴ may be helpful in certain patients to determine what component of the visual loss is due to the cataract rather than the retinopathy. In addition, optical coherence tomography is widely employed before cataract surgery to assess the potential for coexisting retinal disease to limit postoperative visual performance. OCT may be particularly helpful in cases where visualization of the macula is hindered by dense lens opacity and in cases where the visual loss appears out of proportion to the degree of cataract.

Second, when possible, it appears prudent to treat preexisting diabetic retinopathy prior to scheduling elective cataract surgery. This may appear obvious, but several caveats must be considered. Depending on the density of the cataract, it may be difficult to properly diagnose or treat retinopathy prior to cataract surgery. In addition, diabetic retinopathy may persist despite appropriate treatment. For example, the DRCR has reported that at least 50% of patients with DME will have persistent edema two years following focal/grid photocoagulation.^15,16 In another series, 52% of eyes with persistent DME following focal/grid photocoagulation manifested definite signs of vitreomacular interface abnormalities, including anomalous vitreomacular adhesions, epiretinal membrane, or both.¹⁷ Therefore, it may not be feasible to delay cataract surgery until the macular edema has completely resolved.

Third, certain modifications to the surgical strategy become important in patients with advanced diabetic retinopathy, or in patients judged likely to progress in the future. For example, silicone intraocular lenses are associated with visually significant moisture condensation during fluidair exchange¹⁸ and may be a suboptimal choice in a patient deemed likely to require subsequent pars plana vitrectomy. Additionally, presbyopia-correcting intraocular lenses may be problematic for many reasons in the diabetic population. Patients with pre-existing macular diseases, such as DME, have impaired contrast sensitivity and may be particularly dissatisfied with their visual quality following implantation of a premium IOL, particularly a diffractive multifocal lens, owing to the light-splitting nature of the refractive correction provided.¹⁹

Although spectral domain OCT has greatly improved our ability to evaluate the macula prior to cataract surgery, some eyes will have a guarded visual prognosis, and this should be explicitly discussed with the patient and family members during the informed consent process. With these recommendations in mind, most diabetic patients will achieve favorable anatomic and visual outcomes following cataract surgery. OM

References

1. Klein BE, Klein R, Moss SE. Prevalence of cataracts in a population-based study of persons with diabetes mellitus. Ophthalmology 1985;92:1191-1196.
2. Klein BE, Klein R, Wang Q, Moss SE. Older-onset diabetes and lens opacities. The Beaver Dam Eye Study. Ophthalmic Epidemiol 1995;2:49-5.
3. Klein BE, Klein R, Moss SE. Incidence of cataract surgery in the Wisconsin Epidemiologic Study of Diabetic Retinopathy. Am J Ophthalmol 1995;119:295-300.
4. Klein BE, Klein R, Wang Q, Moss SE. Older-onset diabetes and lens opacities. The Beaver Dam Eye Study. Ophthalmic Epidemiol 1995;2:49-5.
5. Holekamp NM, Bai F, Shui YB, Almony A, Beebe DC. Ischemic diabetic retinopathy may protect against nuclear sclerotic cataract. Am J Ophthalmol 2010 Aug 3 [Epub ahead of print].
6. Chu YK, Chung EJ, Kwon OW, Lee JH, Koh HJ. Objective evaluation of cataract progression associated with a high dose intravitreal triamcinolone injection. Eye 2008;22:895-899.
7. Panozzo G, Parolini B. Cataracts associated with posterior segment surgery. Ophthalmol Clin North Am 2004;17:557-568.
8. Smiddy WE, Feuer W. Incidence of cataract extraction after diabetic vitrectomy. Retina 2004;24:574-581.
9. Holekamp NM, Bai F, Shui YB, Almony A, Beebe DC. Ischemic diabetic retinopathy may protect against nuclear sclerotic cataract. Am J Ophthalmol 2010 Aug 3 [Epub ahead of print].
10. Chung J, Kim MY, Kim HS, Yoo JS, Lee YC. Effect of cataract surgery on the progression of diabetic retinopathy. J Cataract Refract Surg 2002;28:626-630.
11. Henricsson M, Heijl A, Janzon L. Diabetic retinopathy before and after cataract surgery. Br J Ophthalmol 1996;80:789-793.
12. Romero-Aroca P, Fernandez-Ballart J, Almena-Garcia M, et al. Nonproliferative diabetic retinopathy and macular edema progression after phacoemulsification: prospective study. J Cataract Refract Surg 2006;32:1438-1444.
13. Chew EY, Benson WE, Remaley NA, et al. Results after lens extraction in patients with diabetic retinopathy. Early Treatment Diabetic Retinopathy Study Report Number 25. Arch Ophthalmol 1999;117:1600-1606.
14. Melki SA, Safar A, Martin J, Ivanova A, Adi M. Potential acuity pinhole: a simple method to measure potential visual acuity in patients with cataracts, comparison to potential acuity meter. Ophthalmology 106;7:1262-1267.
15. Diabetic Retinpoathy Clinical Research Network. A randomized trial comparing intravitreal triamcinolone acetonide and focal/grid photocoagulation for diabetic macular edema. Ophthalmology 2008;115:1447-1449.
16. Diabetic Retinopathy Clinical Research Network, Elman MJ, Aiello LP, et al. Randomized trial evaluating ranibizumab plus prompt or deferred laser or triamcinolone plus prompt laser for diabetic macular edema. Ophthalmology 2010;117:1064-1077.
17. Ghazi NG, Ciralzky JB, Shah SM, Campochiaro PA, Haller JA. Optical coherence tomography findings in persistent diabetic macular edema: the vitreomacular interface. Am J Ophthalmol 2007;144:747-754.
18. Eaton AM, Jaffe GJ, McCuen BW 2nd, Mincey GJ. Condensation on the posterior surface of silicone intraocular lenses during fluid-air exchange. Ophthalmology 1995;102:733-736.
19. Buznego C, Trattler WB. Presbyopia-correcting intraocular lenses. Curr Opin Ophthalmol 2009;20:13-18.