ⓘ Corneal opacity

                                     

ⓘ Corneal opacity

Human cornea is a transparent membrane which allows light to pass through it. The word corneal opacification literally means loss of normal transparency of cornea. The term corneal opacity is used particularly for the loss of transparency of cornea due to scarring. Transparency of the cornea is dependent on the uniform diameter and the regular spacing and arrangement of the collagen fibrils within the stroma. Alterations in the spacing of collagen fibrils in a variety of conditions including corneal edema, scars, and macular corneal dystrophy is clinically manifested as corneal opacity.

                                     

1. Magnitude

Corneal opacity is the 4th main cause of blindness globally 5.1%. Using the World Health Organizations WHO; Geneva, Switzerland blindness definition,1 45 million people worldwide are bilaterally blind, of which 6 to 8 million are blind due to corneal disease. In some African areas, nearly 90% of the total blindness is due to corneal pathology.

                                     

1.1. Magnitude Europe

The prevalence of congenital corneal opacities CCO is estimated to be 3 in 100.000 newborns. This number increases to 6 in 100.000 if congenital glaucoma patients are included. A study of live births in Spain reported that corneal opacities accounted for 3.11% of congenital eye malformations Bermejo et al, 1998. About 4% of keratoplasties done in the pediatric population in Denmark are due to congenital anomalies Hovlykke et al, 2014.

                                     

1.2. Magnitude India

In NPCB survey 2001-2002 Corneal opacity was the 6th major cause of blindness in India, which accounts for 0.9% of total blind population. In the RAAB Rapid Assessment of Avoidable Blindness survey 2006-2007 Corneal opacity including Trachoma was mentioned as the second major cause of blindness, which accounts for 6.5% of total blindness.

                                     

2. Causes

  • Onchocerciasis
  • Xerophthalmia, caused by Vitamin A deficiency
  • Congenital opacities may occur as developmental anomalies or following birth trauma. Causes of congenital corneal opacities include sclerocornea, trauma, ulcer, mucopolysaccharidosis, Peter’s anomaly, congenital hereditary endothelial dystrophy.
  • Corneal ulceration
  • Trachoma
  • Ocular trauma
                                     

3.1. Pediatric Corneal Opacities Congenital Corneal Opacities

  • Cystinosis: Cystinosis is a rare metabolic disease characterized by elevated levels of cystine within the cell. All forms of cystinosis show early deposition of cystine crystals in the cornea, often by the age of 16 months
  • Congenital hereditary endothelial dystrophy CHED: There are 2 forms of congenital hereditary endothelial dystrophy CHED. Commonest is an autosomal recessive form, which is present at birth, but nonprogressive. Nystagmus is seen in association with this form. Another is an autosomal dominant form that occurs within the first few years of life. This form is progressive, but nystagmus is not seen. Deafness and CHED are seen in Harboyan syndrome. The histologic findings are very similar to those seen in pseudophakic/ aphakic bullous keratopathy. The appearance of the cornea is similar to that in congenital glaucoma but without increased corneal diameter and elevated intraocular pressure.
  • Granular Corneal Dystrophy: Two types, Type 1 and Type 2 are there. Both have autosomal dominant inheritance. In Type 1, Discrete crumb-like opacities are seen in the central anterior stroma. While some visual symptoms such as glare and photophobia may occur early in life, visual acuity is not usually affected until the 4th decade for most patients. In Type 2, deposits begin to appear in early childhood in homozygotes or adolescence as tiny whitish dots in the anterior stroma. Over time, these lesions progress into larger stellate, ring, or snowflake-like opacities. Vision loss starts earlier than type1.
  • Congenital hereditary stromal dystrophy CHSD: CHSD is also known as Congenital stromal corneal dystrophy or Congenital stromal dystrophy of the cornea. In this Snowflake, whitish opacities appear throughout the entire cornea. The stromal lamellae are abnormal and may be separated by amorphous deposits. Moderate to severe vision loss may occur due to corneal opacity.
  • Lattice Corneal Dystrophy: Two types of dystrophies are there, type 1 and type 2. Type 1 is also known as Biber-Haab-Dimmer corneal dystrophy, TGFBI type Lattice Dystrophy, or Classic Lattice Dystrophy. Type 2 is also known as Finnish Familial Amyloidosis, Meretoja syndrome, Amyloidosis V, Familial amyloidotic polyneuropathy IV. Both have autosomal dominant inheritance. The opacities are small.
  • Sclerocornea: Sclerocornea is a congenital disorder in which the cornea is opaque and resembles the sclera, making the limbus indistinct. The central cornea is clearer than the periphery.
  • Posterior Polymorphous Corneal Dystrophy PPMD, PPCD: PPCD, also known as Schlichting dystrophy, is an autosomal dominant disorder of the corneal endothelium and Descemet’s membrane. It is usually present in the second or third decade of life. It has the same entity as the first form of CHED. Most cases of PPMD are asymptomatic, and these cases generally do not require treatment. PPMD patients with bilateral, corneal opacities that can affect vision, descemet’s membrane endothelial keratoplasty or penetrating keratoplasty are the treatments of choice to improve vision and to avoid amblyopia.
  • Congenital Anterior Staphyloma: Congenital anterior staphyloma is a rare form of anterior segment dysgenesis that shares similarities with Peters anomaly. It is characterized by an ectatic protrusion of a central opacified cornea lined by uveal tissue. The protrusion extends beyond the plane of the eyelid margins and it can be unilateral or bilateral.
  • Mucopolysaccharidoses: The mucopolysaccharidoses are a group of inherited metabolic diseases caused by the absence or malfunctioning of certain enzymes the body needs to break down molecules called glycosaminoglycans. It is an autosomal recessive disorder. Sometimes, Corneal haze may be present in early life. Treatment options for significant opacities include penetrating keratoplasty and DALK.
  • Peters anomaly: Peters anomaly, also known as iridocorneal adhesions or keratolenticular adhesions, is a posterior corneal defect with an overlying stromal opacity, often accompanied by adherent iris strands Peters anomaly type 1. The size and density of the opacity can range from a mild to dense central leukoma.


                                     

3.2. Pediatric Corneal Opacities Acquired Pediatric Corneal Opacities

  • Congenital or infantile glaucoma: In Congenital glaucoma, the cornea becomes edematous, cloudy, and enlarged. Treatment should be done to reduce Intraocular pressure.
  • Traumatic: Traumatic breaks in Descemet membrane may cause corneal opacity. Injuries to Descemet membrane occur during delivery.
  • Congenital corneal ulcers


                                     

4. Types

Depending on the density, corneal opacity is graded as nebula, macula and leucoma.

Macular corneal opacity

It is a semi-dense opacity produced when scarring involves about half the corneal stroma.

                                     

4.1. Types Nebular corneal opacity

It is a faint opacity which results due to superficial scars involving Bowmans layer and superficial stroma. A nebular corneal opacity allows the details of the iris to be seen through the opacity. A thin, diffuse nebula covering the pupillary area interferes more with vision than a strictly localized dense leucoma, so long as the latter does not block the whole pupillary area. This is because the leucoma stops all the light which falls upon it, whereas the nebula refracts it irregularly, allowing many of the rays to fall upon the retina where they blur the image formed by the regularly refracted rays.

                                     

4.2. Types Macular corneal opacity

It is a semi-dense opacity produced when scarring involves about half the corneal stroma.

                                     

4.3. Types Leucomatous corneal opacity leucoma simplex

It is a dense white opacity which results due to scarring of more than half of the stroma

  • Corneoiridic scar: If iris tissue is incarcerated and incorporated within the scar tissue, as occurs in healing of a large sloughed corneal ulcer, it is called a corneoiridic scar.
  • Kerectasia: In this condition corneal curvature is increased at the site of opacity bulge due to weak scar.
  • Anterior staphyloma: An ectasia of psuedocornea the scar formed from organised exudates and fibrous tissue covered with epithelium which results after total sloughing of cornea, with iris plastered behind it is called anterior staphyloma.
  • Corneal facet: Sometimes the corneal surface is depressed at the site of healing due to less fibrous tissue; such a scar is called facet.
  • Adherent leucoma: It results when healing occurs after perforation of cornea with incarceration of iris. The iris is adherent to the back of a leucomatous cornea. One of the major complication of adherent leucoma is Secondary glaucoma


                                     

5. Secondary changes in corneal opacity

Secondary changes may be seen in long-standing cases include: hyaline degeneration, calcareous degeneration, pigmentation and atheromatous ulceration.

                                     

6. Complications

Congenital corneal opacity that affecting vision will cause amblyopia. That type of amblyopia is known as form-deprivation amblyopia or amblyopia ex anopsia.



                                     

7.1. Treatment Keratoplasty

Keratoplasty, also known as Corneal transplantation, is a surgical procedure where a damaged or diseased cornea is replaced by donated corneal tissue the graft. This provides good visual results in uncomplicated cases with corneal opacities, where optical iridectomy is not of much use.

  • Penetrating keratoplasty PK: PK is a full-thickness corneal transplant procedure, in which a trephine of an appropriate diameter is used to make a full-thickness resection of the patients cornea, followed by placement of a full-thickness donor corneal graft. Interrupted and/or running sutures are placed in radial fashion at equal tension to minimize post-operative astigmatism. Later, the sutures are removed selectively to reduce the amount of astigmatism.
  • Superficial Anterior Lamellar Keratoplasty SALK: Superficial Anterior Lamellar Keratoplasty is of two types, Microkeratome-assisted Superficial Anterior Lamellar Keratoplasty and Sutureless Femtosecond Laser-Assisted Anterior Lamellar Keratoplasty FALK. SALK is done to treat anterior stromal corneal opacities developing after penetrating keratoplasty PK. It avoids open-globe surgery and exposure to endothelial rejection associated with repeat PK, and visual rehabilitation is considerably quicker.
  • Sutureless Femtosecond Laser-Assisted Anterior Lamellar Keratoplasty FALK: In this technique a femtosecond laser is used to create the lamellar cut in the recipient with donor corneas. Donor cut is adjusted according to the depth of the lesions with an additional 10–20% thickness adjusted to compensate for donor tissue swelling. Then the recipient’s scarred corneal tissue is removed and replaced with the corneal donor lenticule. A modified method of FALK was reported by Bonfadini et al. using Ziemer femtosecond laser with 2 different dissection depths: midstromal > 250 μm of posterior residual corneal bed thickness and pre-Descemet approximately 50 μm of posterior residual corneal bed thickness with the same principals described above.
  • Lamellar keratoplasty LK: The lamellar keratoplasty involves selective removal and replacement of diseased corneal layers while leaving healthy layers in place.
  • Microkeratome-assisted Superficial Anterior Lamellar Keratoplasty: in Microkeratome-assisted superficial anterior lamellar keratoplasty, a microkeratome is used to cut a superficial lamella from the recipient cornea, then a lamella of the same thickness is obtained from the donor cornea and is sutured into the recipient corneal bed.
  • Anterior Lamellar Keratoplasty ALK: Lamellar keratoplasty LK targets partial or lamellar replacement of diseased corneal tissue. ALK preserves the posterior stroma. The advantages of ALK include reducing the risk of endothelial graft rejection, retaining structural integrity, and reducing potential intraoperative complications associated with open sky procedures.
  • Other Modifications: Modifications to big bubble technique have been applied in unusual cases such as a cornea with radial keratotomy incisions, descemetocele, and healed hydrops.
  • Dissection with Anwar’s Big Bubble Technique: The big bubble technique described by Anwar and Teichmann in 2002. The cornea is trephined and dissected at a depth of approximately 60–80%. Air is injected paracentrally through a 27- or 30-gauge needle or specially designed cannula producing" big bubble” separation of DM from stroma. Entry into this space followed by removal of stromal tissue involves a process that meticulously protects and preserves DM.
  • Surgical Techniques
  • Closed Dissection Melles Technique: Melles et al. described a closed dissection technique in 1999 that begins by exchanging aqueous with air.
  • Dissection with Hydrodelamination: Sugita and Kondo described the technique of intrastromal fluid injection. Partial trephination and lamellar keratectomy are followed by injecting saline into the stromal bed using a 27-gauge needle. The saline induces stromal fiber swelling, which facilitates fine manipulation with forceps. This will reduce the risk of DM rupture.
  • Direct Open Dissection: This method was first described by Anwar in 1972. Partial trephination is followed by lamellar dissection, originally accomplished using a rounded 69 Beaver blade and more recently with a Martinez dissecting spatula or a variety of dissecting blades. Risk of Descemet’s membrane rupture is more in this technique.
  • Big Bubble Technique Combined with Femtosecond laser Trephination: This technique was first described by Suwan-Apichon et al. in 2006 and later by Price Jr. et al. and Farid and Steinert in 2009. The technique offers" zigzag” or" mushroom” configured wound construction in both patient and donor directed at reducing postoperative astigmatism, improving wound strength, and allowing earlier suture removal.
  • Deep Anterior Lamellar Keratoplasty DALK: DALK aims to remove and replace total or near-total corneal stroma while preserving healthy endothelium of the recipient. DALK reduce the risk of endothelial graft rejection.


                                     

7.2. Treatment Optical iridectomy

Optical iridectomy creates a clear entrance pupil, improving vision in patients with segmental corneal opacities. An area of clear peripheral cornea can produce retinal images compatible with good visual acuity. It may be performed in cases with central macular or leucomatous corneal opacities, provided vision improves with pupillary dilatation.

                                     

7.3. Treatment Phototherapeutic keratectomy PTK

Excimer laser phototherapeutic keratectomy PTK is useful in superficial nebular corneal opacities.

                                     

7.4. Treatment Coloured contact lens

Cosmetic coloured contact lens gives a very good cosmetic appearance in an eye with ugly scar having no potential for vision. Presently, this is considered above tattooing of the cornea for cosmetic purposes.

                                     

7.5. Treatment Tattooing of scar

Keratopigmentation or corneal tattooing is a procedure used for centuries to improve the cosmetic appearance of corneal scars. Tattooing will not improve vision. For tattooing procedure Indian black ink, gold or platinum may be used.

                                     

7.6. Treatment Techniques

  • Femto-assisted corneal tattooing FACT: A femtosecond laser is used to make a superficial corneal pocket into which tattoo ink is injected. The procedure enables the ink to last longer and achieve more uniform cosmetic results.
  • Staining method: Direct application of tattoo ink to anterior surface of cornea. Benefits include fast procedure with uniform dye application. Risk of fading is a main drawback.
  • Lamellar keratectomy technique: Benefits include longer retention of pigment and lower risk of recurrent corneal erosions.
  • Impregnation method: Tattoo pigment is directly introduced into the corneal tissue by needle puncture. Benefit is longer retention of pigment but more difficult and time consuming procedure. Irregularly placed pigment deposits can cause light scatter.