15 minute read
Congenital Cataract Surgery
Tips from Experts
by Tan Sher Lynn
Acongenital cataract is the clouding of the lens of an infant’s eye, which happens before birth or during the first year of life. To enable normal vision development and prevent amblyopia or even blindness, congenital cataracts are typically removed by cataract surgery while the child is still an infant.
During a CyberSight live webinar on congenital cataracts, held in August last year, Dr. Donny Suh, chief of pediatric ophthalmology and adult strabismus, Children’s Hospital and Medical Center, USA, and Dr. Serena Wang, associate professor at UT Southwestern Medical Center, USA, discussed various surgical techniques, instruments and tips for successful congenital cataract surgery.
Dr. Suh on surgical planning and other important considerations
In his practice, Dr. Suh usually operates when the baby is between 4 and 10 months old for unilateral dense congenital cataracts, and between 2 and 3 months old for bilateral dense cataracts. “Studies have shown that the risk of glaucoma is higher when cataract surgery is performed at less than 4 weeks of age,” he shared. “For bilateral cataracts, I usually wait two to four weeks before operating on the other eye. Bilateral surgery on both eyes on the same day is typically not recommended, with the exception of certain countries, where the cost and the risk of anesthesia is high, or when the treatment is not readily available,” Dr. Suh added.
He stressed the importance of pre-surgery planning, which plays a critical role in ensuring surgical success. Factors he takes into consideration when planning for cataract surgery include: anterior chamber depth, size of eye/pupil, location of cataract, trauma, anterior segment dysgenesis, zonules status, and other anatomical abnormalities. Dr. Suh added that there are four factors which can cause a poor prognostic: unilateral cases, microphthalmia, other associated ocular abnormalities and systemic disease (e.g., uveitis).
“In my opinion, the most important aspect of cataract surgery, in pediatric as well as adult patients, is the anterior capsulotomy,” Dr. Suh said. “If you don’t have a good view of the anterior capsule, the surgery could become disastrous in a matter of a second. In order to avoid problems with the lens dislocating, the anterior capsulotomy opening should ideally be 5mm in diameter and the posterior capsule opening should be about 4mm, since the posterior chamber intraocular lenses (PC IOL) diameter is 6mm. If you make the anterior capsule opening bigger than that, there’s a chance of prolapse,” he explained.
Another important consideration is whether or not to place the IOL. “Relative contraindications for IOL placement include chronic inflammatory disease such as juvenile
idiopathic arthritis (JIA), as well as nanophthalmos. I typically place an IOL in children who are 7 months or older and who have a corneal diameter of 9mm or more,” he added.
According to Dr. Suh, the most critical part of cataract surgery is the anterior capsulorhexis as it sets the tone for the entire surgery. “Capsulorhexis is difficult to do in children because the anterior capsule is thinner, elastic, more convex in shape, and tears easily,” he explained. “The anterior chamber is also shallower in a smaller eye. And the sclera is less rigid, with a low IOP. So while you’re manipulating the tools, it can collapse and blur your vision easily.”
He further explained that the anterior surface of the adult lens is fairly flat. So when you’re trying to perform the tear in one direction, there’s a counterforce that’s going towards the opposite direction. “However, in pediatric patients, the anterior surface is pretty convex. When you’re trying to make a tear in one direction, there’s another force — the radial force — that’s going toward the center of the lens, resulting in the net vector force which is slightly diagonal,” Dr. Suh shared. “This is the reason why if you perform a 90-degree tear, it’s easy to tear into the periphery toward the equator and end up with a capsulorhexis that’s just small. To counteract the radial force, we want to tear it at 45 degrees.”
During lensectomy, it is advisable to remove all lens cortex as they tend to have a vigorous inflammatory response. Dr. Suh would typically remove the posterior capsule as well if he cannot perform the YAG laser within one year. “If they’re less than 5 years of age, or if they’re not going to be cooperative with the laser, I will directly perform the posterior capsulotomy and vitrectomy,” he advised.
Dr. Wang on helpful techniques in using surgical equipment
Besides pre-surgery planning, an understanding of the surgical equipment is extremely critical in order to successfully perform congenital cataract surgery. Dr. Serena Wang shared the instruments that she’s been using and the special techniques she has developed for pediatric cataract management over the past 15 years.
Her “cataract tray” comprises the Alfonso lid speculum without tabs, which works well for very small children; a 0.12 forceps (an essential instrument for pediatric cataract surgery) to hold the eyeball and keep it steady; knives, including the super sharp blade (for paracentesis); as well as the 2.5mm keratome and 3.5mm keratome. Another important instrument that she has been using for the past 15 years is micro-incision capsular forceps. “This instrument makes capsulorhexis so much easier and more controlled. As infants’ eyes are very soft and unstable, by keeping the incisions small, it is much easier to operate,’’ Dr. Wang explained, adding that she has two different tips for the forceps: normal scissors and side-cut scissors.
“These instruments are really helpful during complicated cases such as persistent fetal vasculature (PFV) and pupillary membranes, as they help you do the procedure better,” she added.
For bimanual procedures, Dr. Wang prefers to use the 20 gauge irrigation tip, which is more efficient as it helps to remove the cortex faster. “You can also use the 23 or 25 gauge, but I find the 20 gauge best. Whatever gauge you use, you want to choose the same size knife and you want to keep the wound tight in order to have a stable anterior chamber,” she explained.
At the webinar, Dr. Wang also showcased a video where she performed an anterior capsular vitrectorhexis bimanually. “I hold the 20 gauge irrigation cannula on my left hand, while my right hand holds the vitrector. Starting from the periphery, I go all the way across. I like to clean the subincisional first, as that is the most difficult part. The advantage of the bimanual procedure is that you can switch hands. If you’re having trouble getting the subincisional cortex out, you can switch hands and start from the other end to remove the cortex. Before moving to the next step, I clean the periphery again to make sure that everything is removed. In any kind of surgery, the best way is the way that works for you. You will develop your own way as you find out what is the best and most efficient way to do things,” she shared.
During lens aspiration in adults, the nucleus is taken out starting from the center towards the periphery. But in children, due to the gel-like material of the lens, she prefers to start from the periphery using a “swipe clean” method. After that, she proceeds with posterior capsulotomy using the vitrector.
“During surgery, you want to keep the eyes fixated manually to maintain a stable anterior chamber,” Dr. Wang explained. “This is critical in pediatric cataract surgery, as a stable chamber makes the surgery easier.”
Another important thing to take note of, according to Dr. Wang, is to minimize the time you enter and exit the eye. “You don’t want to go in and out of the eye a lot. Every time you do that, you change the anterior chamber pressure, which increases the risk of the chamber collapsing and the posterior vitreous moving forward. Nevertheless, if something unexpected happens during surgery, do not take the instrument out immediately. The first thing to do is to stop and take a deep breath before deciding on the next step,” she concluded.
Editor’s Note:
The CyberSight Lecture on Congenital Cataracts was held on August 21, 2020. Reporting for this story took place during the event.
The Diagnostic Value of Optical Coherence Tomography for
Microbial Keratitis by Konstantin Yakimchuk
Infectious keratitis is an ocular infection caused by various microbes, such as bacteria, fungi and protozoa.
Some of its predisposing conditions include ocular trauma, contact lens wear, diabetes, ocular hypertension and rheumatoid diseases. Meanwhile, its clinical symptoms are hyperemia, pain, vision defects and inflammatory changes.
Diagnosing bacterial keratitis
The choice of specific therapy demands identification of microbes causing keratitis. For bacterial keratitis, standard microbiological analyses are essential for the appropriate diagnosis. Classical Gram and Giemsa stainings provide a rather high specificity. Nevertheless, the culture of corneal scrapings remains a method of choice for diagnosing bacterial keratitis.1 However, microbiological analysis of corneal infection often provides negative results due to an insufficient amount of tissue in corneal specimens. Besides, an analysis might be subjective and the evaluation of therapeutic outcomes is challenging in the early phases.
Several earlier studies have implemented coherence tomography for diagnosis of keratitis and related medical conditions. In particular, several clinical parameters, such as the thickness of corneal infiltration and retrocorneal morphology, were evaluated by coherence tomography in order to estimate the treatment outcomes.2
Overall, anterior segment optical coherence tomography (AS-OCT) has been successfully implemented for visualization, analysis and monitoring the development of corneal inflammation. The process of recovery from corneal infection includes the early decrease of edema followed by declining infiltration.3
More recently, another study4 has identified localized and diffuse necrotic stromal cystic loci as histological patterns specific for fungal keratitis using spectral domain AS-OCT. This method applies infrared light and generates images of ocular tissues by capturing backscattered reflections.
In the recent issue of Acta Medica Portuguesa, Dr. Mariana Almeida Oliveira et al., of Coimbra Hospital and University Center in Coimbra, Portugal, have considered AS-OCT to be an effective method to analyze bacterial keratitis.5
According to the authors, Spectralis® (Heidelberg Engineering, Inc., Heidelberg, Germany) OCT model S3300 (with anterior segment module) was performed on the patients enrolled in the study. Potential noise was reduced by averaging the images and angle variation. Following the scan, the patients were treated with antibiotics. In their study, Oliveira et al. aimed to identify specific patterns of microbial keratitis in patients diagnosed with bacterial, fungal or parasitic ocular infections.
A safer choice during the COVID-19 pandemic
Dr. Khor Wei Boon, a senior consultant with the Cornea and External Disease Service and the Refractive Surgery Service of Singapore National Eye Centre (SNEC), was invited to comment on the article of Dr. Oliveira and co-authors. According to Dr. Khor, “AS-OCT is an important instrument for anterior segment specialists, such as cornea, refractive and glaucoma surgeons. To date, the role of AS-OCT imaging in microbial keratitis has largely been used to demonstrate the extent of the infection, the depth of corneal thinning in advanced infections, and to monitor treatment progression.”
As for the safety of AS-OCT, Dr. Khor confirmed that “as a non-contact form of anterior segment imaging, it is comfortable for the patient and also very safe, which is especially important in this age of COVID-19.”
Identifying morphological patterns
Did the patients enrolled in the study have any risk factors? Ocular trauma and usage of contact lenses were the most common risk factors. Several patients had chronic diseases, such as diabetes and hypothyroidism. How does this study contribute to the current knowledge of microbial keratitis? By analyzing patients diagnosed with either bacterial keratitis, the authors have identified nine morphological patterns using the results of the scan.
Among the identified patterns, the presence of solitary hyperreflective stromal lesions and edema indicated a more positive prognosis of keratitis, while pan-corneal inflammation correlated with more aggressive pathogens. In particular, corneal infiltration and edema have previously been found in microbial keratitis.5 Notably, infiltration and edema have been observed in nearly all keratitis patients at early stages. Furthermore, hyperreflective stromal edema was associated with better prognosis and might, therefore, indicate a low degree of keratitis severity.
In the present paper, Oliveira et al. found these two patterns in nearly all patients in the initial stages of keratitis. Another pattern, corneal thinning, a serious symptom related to corneal melting, has been detected in severe bacterial keratitis caused by such pathogens as Pseudomonas aeruginosa and Streptococcus pneumoniae. In addition, hyperreflective lesions associated with the intact epithelium were observed by Oliveira et al. in Staphylococcus aureus-mediated
keratitis. Thus, AS-OST can be applied to estimate the size of hyperreflective loci and evaluate corneal thickness.
Detecting patterns of fungal and protozoan keratitis
In addition to bacterial infection, have the authors identified any specific patterns of fungal and protozoan keratitis? The authors reported that localized necrotic stromal cysts, which might be associated with necrosis, are not specific for fungal keratitis. On the contrary, such stromal cysts were found in both severe bacterial and fungal keratitis. For instance, Oliveira et al. observed cystic spaces in patients with keratitis induced by Citrobacter braakii.
As for fungal infections, a previous study6 has detected hyperreflective dots in the corneal epithelium without spreading into the stroma in microsporidial keratitis. In addition, the dissemination of fungal abscesses into the anterior chamber was reported to be specific for the late stages of fungal keratitis.7 In Oliveira’s study, retrocorneal plaques were found in both fungal and bacterial keratitis.
When it comes to findings specific for early protozoan infections, Oliveira et al. have identified similar patterns, such as hyperreflective stromal loci related to local edema and specific to the early stage of the Acanthamoeba infection. The hyperreflective features were observed mostly in the subepithelial tissue and might be associated with protozoan cysts. These observations were in line with earlier findings of hyperreflective round lesions representing Acanthamoeba cysts.8 Another study has previously suggested that advanced stromal inflammation can be considered as a predictor of severity of Acanthamoeba-induced ocular infection.
Limitations and alternatives
Did the study have any weaknesses or limitations? Due to a cross-sectional design of the experiments, the authors were not able to evaluate the temporal sequence of corneal symptoms. Furthermore, the specimen size was too small to perform a statistical evaluation.
Are there any alternatives to AS-OCT? Dr. Khor Wei Boon has suggested that “the use of confocal microscopy for the diagnosis of Acanthamoeba keratitis and fungal keratitis is well established. However, some of the drawbacks of confocal microscopy include the following: it requires contact with the ocular surface, it is dependent on the ophthalmologist’s experience in interpreting the images, and the confocal images are taken from only a very small area on the cornea.”
An effective tool in the analysis of microbial keratitis
In conclusion, Oliveira et al. have demonstrated an effective application of AS-OCT for the analysis of bacterial keratitis. Thus, AS-OCT can be used for quantification and analysis of microbial keratitis. The authors have identified several histological features unique for different types of microbial keratitis.
In conclusion, Dr. Khor said: “The article by Oliveira and colleagues has systematically documented the ASOCT findings of patients with microbial keratitis and tried to correlate it to specific pathogens. While it is very interesting work, larger studies need to be performed to see if these findings are replicable in other centers.” He added that although the diagnosis of microbial keratitis will still depend on a thorough history and clinical examination and the use of appropriate microbiological investigations, such as microscopic examination and cultures, AS-OCT might efficiently facilitate the assessment of inflammation in corneal layers and related prognosis.
REFERENCES:
1. Kim, E. et al. Prospective comparison of microbial culture and polymerase chain reaction in the diagnosis of corneal ulcer. Am J Ophthalmol. 2008;146(5):714-723. 2. Konstantopoulos A, Kuo J, Anderson D, Hossain P. Assessment of the use of anterior segment optical coherence tomography in microbial keratitis. Am J Ophthalmol. 2008;146(4):534-542. 3. Konstantopoulos A, Yadegarfar G, Fievez M, Anderson DF, Hossain P. In vivo quantification of bacterial keratitis with optical coherence tomography. Invest Ophthalmol Vis Sci. 2011;52(2):1093-1097. 4. Soliman W, Fathalla AM, El-Sebaity DM, Al-Hussaini AK. Spectral domain anterior segment optical coherence tomography in microbial keratitis. Graefes Arch Clin Exp Ophthalmol. 2013;251(2):549553. 5. Oliveira MA, et al. Anterior Segment Optical Coherence Tomography in the Early Management of
Microbial Keratitis: A Cross-Sectional Study. Acta Med Port. 2020;33(5):318-325. 6. Thanathanee O, Laohapitakvorn S, Anutarapongpan O, Suwan-Apichon O, Bhoomibunchoo C. Anterior
Segment Optical Coherence Tomography Images in Microsporidial Keratoconjunctivitis. Cornea. 2019;38(8):943-947. 7. Vemuganti GK, et al. Evaluation of agent and host factors in progression of mycotic keratitis: A histologic and microbiologic study of 167 corneal buttons. Ophthalmology. 2002;109(8):1538-1546. 8. Yamazaki N, et al. In vivo imaging of radial keratoneuritis in patients with Acanthamoeba keratitis by anterior-segment optical coherence tomography. Ophthalmology. 2014;121(11):2153-2158.
Contributing Doctor
Dr. Khor Wei Boon is a senior consultant with the Cornea and External Disease Service, as well as the Refractive Surgery Service of SNEC; head of the SNEC Eye Clinic at Sengkang Hospital; and the clinical director of Health Insights, the dataanalytics unit of SNEC. He completed his residency in ophthalmology with SNEC, and is a fellow of the Royal College of Surgeons of Edinburgh and the Academy of Medicine, Singapore. He then furthered his subspecialty training in cornea and refractive surgery with Professor Donald Tan in SNEC in 2011, and with Dr. Terry Kim and Dr. Alan Carlson at the Duke University Eye Center in North Carolina, USA, in 2012-2013. In 2006, Dr. Khor was part of the team of ophthalmologists that investigated an outbreak of Fusarium keratitis associated with a specific contact lens solution in Singapore. His published findings contributed to the worldwide alert over what was eventually found to be a global epidemic. In the same year, he, along with the rest of the team, was awarded Singapore’s first Minister of Health Award for Outstanding Performance in Public Health for his contributions. He has been published in respected peer-reviewed journals and has made presentations at numerous scientific meetings, both locally and internationally. His clinical and educational interests are in corneal infections, ocular allergies, lamellar corneal transplantation and the use of technology in ophthalmic education.
khor.wei.boon@singhealth.com.sg