IOL Power Analysis
Intraoperative measurements can be used to ascertain the power and residual refractive error of patients while undergoing cataract surgery.5446/A462 Researchers in California used the WaveTec Vision ORange system to calculate patients’ intraoperative aphakic spherical equivalent (IASE) data. Researchers found a relationship between the expected lens position (ELP) of the IOL and the IASE, and used these data to calculate the predicted postoperative refraction for different IOLs, which they then compared to the 30-day manifest refraction spherical equivalent. The result? The absolute value prediction error for the 125 eyes measured was 0.49D±0.35D. Such techniques and calculations could help avoid enhancements and IOL exchanges.
Cataract Patients’ Ocular Surface Health
The prevalence of dry eye in patients scheduled to undergo cataract
surgery is higher than generally reported, found researchers across the
country.5411/A427 In this prospective study, nearly half of 49 patients
questioned reported dryness and foreign body sensation. The mean OSDI
score was 28.2, and average tear film break-up time was 4.94 seconds.
Half of the eyes examined had central cornea staining, and 22.8% had a
Schirmer’s score of 5 or less. Researchers note that increased
awareness of dry eye symptoms in these patients can and should result
in increased rates of treatment for symptoms induced or worsened by the
surgical procedure. Make sure to evaluate for dry eye in all cataract
patients and educate them as to the possible treatments that may help
their condition postoperatively.
Cataract Risk Reduction
Looking for a new technique to reduce the risk of cataract development? Try nutrition—specifically, antioxidants and nutraceuticals, report researchers in Canada.1189/D1121 They dissected pig eyes and incubated them in a medium containing ascorbate, either methylthiazolidine or beta-carotine, and either pycnogenol (BCP) or ginseng extract (BCG). Lenses were then exposed to radiation stress and monitored daily. BCP decreased the cataract grade 24 hours after radiation, while BCG increased the cataract grade at two dosage levels. But, methylthiazolidine-treated lenses showed increased protein leakage after both 24 hours and five days. Antioxidant food factors appear to be promising in reducing risk of cataract, though the dosage can play a role in its efficacy.
Type 2 diabetes mellitus is a major risk factor for cataractogenesis, found researchers in India.2082/A122 Through an examination of 5,999 patients, 1,414 individuals who have diabetes were identified. Age- and gender-adjusted prevalence of cataract was 65.7% Bottom line? Closely examine the lenses of all patients with diabetes, because this is such a strong association.
Likewise, which pre-existing ocular conditions create a higher risk of complications during or after cataract surgery? Researchers in London found that risk of mild complication was significantly increased by pre-existing uveitis/synechiae, pseudoexfoliation/phacodonesis, brunescent/white cataract, high myopia, diabetic retinopathy or previous vitrectomy.5392/A408 Risk of moderate complication stemmed from corneal pathology, pseudoexfoliation/phacodonesis, brunescent/white cataract and reduced fundal view/vitreous opacities. Risk of severe opacities was increased by brunescent/white cataract. These results can help eye care practitioners discuss likely outcomes with patients before surgery. Patients with pre-existing conditions need to know how they are impacted, and practitioners should discuss cataract removal before the lens degrades to this stage. Other topics to discuss include uveitis, pseudoexfoliation, phacodonesis and corneal opacities.
Cataract Surgery
Does it make sense to remove bilateral congenital cataracts and implant IOLs in a single session? Greek researchers found that it reduces anesthetic risk and hospital costs, and it allows for immediate visual rehabilitation.5282/A135 This retrospective study examined 16 patients with bilateral congenital cataracts. Mean age at the time of surgery was 36.3 months. All patients underwent bilateral lensectomy and in-the-bag IOL implantation in a single session under general anesthesia. Patients under the age of two underwent primary posterior capsulorrhexis and anterior vitrectomy, while the posterior capsule of older patients was left intact. During two years of follow-up, one eye developed glaucoma, and another developed secondary membranes that required surgical treatment. Otherwise, there were no serious complications. Though bilateral cataract surgery is debated in the adult population, it makes sense for pediatric patients, who are otherwise exposed to two sessions of general anesthesia, multiple hospital stays and increased costs.
What Works for Kidney Stones Works for Cataract
Another pipeline treatment for cataract: high-intensity focus
ultrasound (HIFU).5395/A411 This treatment is similar to the technique
currently used to break down kidney stones. Porcine lenses were
hardened via a soak in 10% formalin and treated with HIFU for one, two
or three minutes. Researchers found that HIFU primarily affects lens
integrity through mechanical shearing. Changes in the center of the
lens include spreading of membrane spaces and vacuole formation.
Femtosecond Laser Usage
A hot topic this year: the multiple uses of the femtosecond laser. From cataract surgery to presbyopic reduction, the femtosecond laser is demonstrating several benefits in a wide variety of procedures.
Cataract surgery with femtosecond laser shows no significant differences from standard phacoemulsification in early clinical outcome data, report researchers in Florida and Mexico.5394/A410 After the procedure, best-corrected visual acuity and IOP remained very similar, and complications (e.g., IOP rise) occurred and resolved at the same rate. If the intended benefits of laser cataract surgery (e.g., consistent capsulotomy and reduced phaco energy during lens extraction) can be realized, femtosecond laser treatment for cataract will have no adverse effect on clinical outcomes.
Also, an OCT-guided femtosecond laser system may be beneficial for cataract surgery.5445/A461 Such a system could greatly improve precision and reproducibility for surgeons, allowing for improved centration of IOLs and correction of residual astigmatism.
Femtosecond laser may also show some benefit for other conditions, such as presbyopia. But, power levels and other factors are still a concern. Even so, femtosecond laser treatment of the crystalline lens for presbyopia does not induce cataract in pigs up to six months after surgery, found researchers in Germany.811/D1013 Ten middle-aged pigs whose lenses had sclerotic nuclei underwent femtosecond laser treatment over a volume of 5mm x 5mm x 3.5mm centered within the lens. Follow-up at one week, one month, three months and six months confirmed that no cataract had been induced. Slit lamp and Schiempflug images confirmed this. Also, even at six months, the laser treatment grid was still clearly visible, with no signs of change around the spots. So, researchers note that the energy used for the femtosecond laser, just above that of the recommended treatment threshold, might be sufficient for permanent change to the crystalline lens structure.
Such treatment also shows promise in reducing lens stiffness, thereby improving the lens’ natural accommodative abilities.810/D1012 Compression studies show repeatable reduction in lens stiffness, and animal studies, such as the one above, show minimal likelihood of cataract formation. Such treatment could extend the functional time of the lens before presbyopic correction is needed.
Femtosecond laser techniques also prove beneficial in other refractive surgeries, such as deep anterior lamellar keratoplasty (DALK).1122/D944 DALK is a viable alternative to a full-thickness penetrating keratoplasty in cases of keratoconus, and combining DALK with a femtosecond laser’s zigzag incisional pattern results in a biomechanically stable wound and excellent apposition of Descemet’s membrane. And, acuity and astigmatism levels are comparable to full-thickness femtosecond laser keratoplasty.
Postoperative Care
Barring complications, the earliest time after cataract surgery that objective refraction and corneal swelling stabilize is during the third week post-op, found researchers in Spain.3941/A163 In this prospective study of 74 eyes, researchers measured refraction and central corneal thickness at 24 hours, one week, two weeks, three weeks and four weeks. No differences were found between three and four weeks in corneal swelling, and refraction was found to stabilize generally between the second and third weeks post-op.
So, when comanaging cataract patients, it is best to wait until the one-month post-op visit to begin considering optical correction for any residual refractive error. Wait for both the refraction and the swelling to stabilize before proceeding.
But, even if the surgery is uncomplicated, there are still risk factors to monitor. Young myopes are more at risk for a steroid response following uncomplicated cataract surgery than other patient demographics, report researchers in Boston and San Francisco.4563/A621 In this retrospective chart review of more than 1,600 eyes, all patients received topical 1% prednisolone acetate postoperatively and were followed at one day and within the first month post-op. Of this cohort, 38 eyes were diagnosed as steroid responders. Younger age and longer axial length were associated with a higher risk of steroid response—particularly for an IOP rise to greater than 40mm Hg. So when comanaging, keep a close eye on patients that fit these parameters.
On that note, a new use for a steroid standby may be to decrease post-op inflammation. Researchers in New York and Minnesota found that Lotemax (loteprednol etabonate 0.5%, Bausch + Lomb) effectively reduces or even resolves anterior chamber inflammation and pain following cataract surgery. More than 800 patients were evaluated in twin studies. Lotemax was efficacious in resolving post-op inflammation in 23.9% of cases in one study and in 31.5% in the other. Nearly three-quarters of patients in both groups ranked it as causing no pain at day eight. Fewer patients who took Lotemax required rescue medication—68 vs. 128 in one study and 62 vs. 132 in the other. Lotemax ointment is soon to be FDA-approved for post-cataract surgery usage. This ointment may be beneficial for nighttime care regimens, as an adjunctive treatment to daytime medication.
Along the same lines, melatonin has shown beneficial effects as an anti-inflammatory medication post-cataract surgery in dogs.1990/D1027 In non-diabetic canines, melatonin treatment results did not differ from those obtained with dexamethasone at two and seven days post-op. At 20 days post-op, the melatonin group’s inflammation rates were lower. In diabetic dogs, melatonin performed better than carprofen at all examined time points.
Post-refractive surgery corneal haze may develop secondary to smoking, report researchers in Texas.2859/D1006 In this retrospective review of 25,313 refractive surgery (PRK, LASIK, LASEK) patients, 157 patients in total developed more than mild corneal haze. While smoking preference was equal in most subgroups of the haze and control groups, one subgroup demonstrated a significant trend of increased incidence of smoking and corneal haze: -5.00D or greater myopes. Educate patients of the risk of haze if they fall into this category and are considering refractive surgery.
Keratoprosthesis Usage
The Boston Type I Keratoprosthesis, essentially an artificial cornea, is an option for patients who are not otherwise candidates for penetrating keratoplasty.1150/D972 But, it is still a “high risk” procedure, say researchers; risks range from poor postoperative vision to prosthesis removal. Patients included in the small study cohort had corneal dystrophy, prior failed penetrating keratoplasty, pemphigoid, herpetic keratitis and pre-phthisical eyes in hypotony. In 18 of the 24 patients, pre-op visual acuity was less than hand motion. Postoperatively, the best outcomes had acuity of better than 20/60 (14 of 24 eyes). Seven patients experienced complications—three necessitated prothesis removal, four developed retro-optical membranes, and one had a retinal detachment.
So, this artificial cornea is an option for high-risk patients, though the surgery itself is not without risks.
The researchers in Boston concurrently extracted patient’s cataracts and placed IOLs and Boston Type I Keratoprostheses successfully, and they recommend this procedure for its overall favorable outcome.1139/D961 Patients were indicated for this “K-Pro Triple” procedure because of herpes zoster neurotrophic keratitis, keratoconus with corneal neovascularization, Peter’s anomaly, corneal ulceration (presumably secondary to chronic steroid use) and corneal neovascularization of unclear etiology. Three of these seven patients had a history of well-controlled glaucoma. Postoperatively, follow-up ranged from 1.5 to 22 months. Final acuity ranged from 20/30 to 20/89, with one case at 20/200 due to postoperative cystoid macular edema. Other complications include worsened glaucoma, retroprosthesis membrane, posterior capsular opacification, mild tearing and pain. This novel use of the prosthesis allows for better outcomes for high-risk patients. n
Lens Refilling
Refilling the human lens can significantly change its power and diameter, report researchers from Australia, Florida and India.808/D1010 They removed the contents of 13 postmortem lenses and filled the capsular bag with a flexible polymer gel. Lens diameter, ciliary body diameter, power, and changes in lens diameter and power all increased after refilling:
• Lens diameter: from 9.01mm±0.41mm to 9.05mm±0.48mm.
• Ciliary body diameter: 11.38mm±0.61mm to 11.51mm±0.95mm.
• Lens power: 21.79D±2.72D to 25.79D±3.49D.
Also, the maximum lens stretching force decreased after refilling from 8.93g±1.17g to 7.80g±0.70g.
These findings raise the possibility of gel injection for cataract surgery after removing the cataractous lens and possibly restoring some accommodation. But, the gel polymer expanded the capsular bag more than a crystalline lens could, so cautious measurement would be necessary.
