Corneal dystrophies and keratoconus

Ten-year Results after Conventional Corneal Cross-linking in Korean Patients with Progressive Keratoconus

Purpose: To evaluate the long-term effects of conventional corneal cross-linking in patients with progressive keratoconus.Methods: A total of 18 eyes of 9 patients diagnosed with keratoconus were analyzed retrospectively. One eye was diagnosed with progressive keratoconus and conventional corneal crosslinking was performed. The other eye was classified as non-progressive and remained untreated. All patients were assessed with best corrected visual acuity (BCVA), maximum keratometry (Kmax), mean keratometry (Kmean), corneal astigmatism, and corneal thickness. Clinical data were collected before the procedure and at 1, 3, 6 months and 1 to 10 years after the procedure.Results: The BCVA significantly improved from 0.63 ± 0.18 logarithm of the minimum angle of resolution (logMAR) to 0.46 ± 0.25 logMAR at 10 years after conventional corneal crosslinking (p = 0.027). The Kmax and Kmean decreased from 65.90 ± 9.43 D and 52.82 ± 5.16 D to 62.83 ± 8.16 D and 51.52 ± 5.18 D, respectively (p = 0.021, p = 0.028, respectively). Corneal astigmatism decreased from 6.97 ± 2.21 D to 5.53 ± 1.64 D (p = 0.008). The thinnest corneal thickness decreased from 435.11 ± 53.37 μm to 369.22 ± 64.00 μm 1 month after the procedure (p = 0.008), and gradually improved over time. At 10 years, the thinnest corneal thickness increased to 410.11 ± 61.32 μm (p = 0.097). In the untreated eyes, the mean keratometry significantly increased after 4 years of follow-up, but other factors did not change significantly. Although corneal opacity persisted for up to 10 years in 3 eyes of the treatment group, there was no significant difference of BCVA compared to the treated eyes without corneal opacity (p = 0.714).Conclusions: In patients with progressive keratoconus, conventional corneal crosslinking is a safe and effective procedure that suppresses long-term progression.

Correlation between Corneal Endothelial Cell Density and Central Ocular Surface Temperature in Normal and Keratoconus Eyes

PURPOSE

In keratoconus (KC), an increase of the corneal back surface area may result in endothelial cell density (ECD) decrease and an increase of the corneal front surface area in ocular surface temperature (OST) decrease due to increased heat dissipation. Along with these hypotheses, we aimed to analyse the correlation between ECD and central corneal OST in patients with KC and healthy controls.

PATIENTS AND METHODS

A total of 154 eyes with KC (mean age 36.1 ± 12.5 years) and 92 healthy eyes (mean age 36.4 ± 12.8 years) were examined. Corneal front and back surface area at the central 5 mm corneal diameter (FSA and BSA) were calculated based on Pentacam measurement data:FSA or BSA = 2×3.14×R(R-√R²-D/2)²,where R referred to corneal front or back surface radius of curvature and D to the corneal front or back surface diameter (5 mm for the present study), respectively.ECD was determined by specular microscopy (EM-3000) and central corneal OST by thermography (TG-1000).

RESULTS

ECD was significantly lower in KC (2498 ± 356/mm²) patients than in controls (2638 ± 294/mm²; p < .001). FSA (20.35 ± 0.26 mm² vs. 20.17 ± 0.03 mm²) and BSA (20.84 ± 0.58 mm² vs. 20.45 ± 0.08 mm²) were significantly higher in KC patients than in controls (p = .001; p < .001), but the average central corneal OST did not differ significantly between both groups (34.2 ± 0.6°C vs.34.3 ± 0.7°C; p = .62). OST at the corneal centre correlated weakly, positively with ECD (r = 0.2; p < .05), but OST did not correlate with FSA (r = 0.045) or BSA (r = 0.064).

CONCLUSIONS

Endothelial cell density seems to have a mild impact on central ocular surface temperature in keratoconus and normal subjects. This effect is not correlated to the corneal front or back surface area.

Hypothyroidism is Not Associated with Keratoconus Disease: Analysis of 626 Subjects

Purpose

To analyze the association between hypothyroidism and keratoconus, we examined blood thyroid hormone levels and corneal tomographic parameters in healthy subjects and patients with keratoconus.

Methods

We included 626 subjects (304 left eyes, 49%; 431 males, 69%; age 38.4 ± 14.3 y). Patients with keratoconus were from our Homburg Keratoconus Center (HKC) (n = 463); patients with hypothyroidism were from the Department of Internal Medicine of Saarland Medical University, Homburg/Saar, Germany (n = 75); and healthy subjects were from the Department of Ophthalmology of Saarland University Medical Center (n = 88). We included only one randomly selected eye of each subject and the first examination data.

Exclusion criteria

Previous thyroid medication, previous ocular surgery, and patients with suspected keratoconus (topographic keratoconus classification, [TKC]: 0 < 1). Patient eyes were classified (TKC) with dedicated, instrument-based, keratoconus detection software provided with the Pentacam. TKC = 0 was considered “normal,” and TKCs ≥ 1 were considered keratoconus. Subjects were also classified as euthyroid or hypothyroid, based on blood thyroid hormone status (i.e., TSH, FT3, and FT4). A multiple logistic linear regression model was constructed to determine the effects of age (covariate), gender, and hypothyroidism (effect sizes) on “TKC-positive” disease.

Results

The significance levels for a constant parameter, sex, thyroid condition, and age were p < 0.0001, p < 0.0001, p < 0.0001, and p=0.003, respectively. The odds ratios for age, sex, and hypothyroidism were 0.98, 3.05, and 3.34, respectively. Male sex and a euthyroid condition had significantly positive, clinically relevant effects, and age had a significantly negative, but clinically irrelevant effect on the estimated TKC index.

Conclusions

Keratoconus appeared to occur more often in patients classified as euthyroid than in patients with hypothyroidism. Thus, hypothyroidism alone could not support the development of keratoconus. Based on these results, it should not be mandatory to screen patients with hypothyroidism for keratoconus or patients with keratoconus for hypothyroidism.

Familial association of keratoconus and granular corneal dystrophy: The familial case series

OBJECTIVE:

The aim of the present study was to evaluate the coexistence of bilateral keratoconus and granular corneal dystrophy (GCD) in the members of a family.

METHODS:

A total of 22 patients were examined in four generations of the family tree in this family screening study. Visual acuity test, biomicroscopic examination, and fundus examination were performed in all patients. The diagnosis of granular dystrophy was based on biomicroscopic examination findings. Corneal topography was performed on the patients diagnosed with granular dystrophy and other family members aged >5 years with normal examination findings. Corneal photographs were obtained from all patients with granular dystrophy except one case.

RESULTS:

Keratoconus or subclinical keratoconus was detected in seven cases. In addition, GCD type 1 was found in six of the seven cases. All patients diagnosed with keratoconus and granular dystrophy were females. On the other hand, there was no ophthalmologic problem in the men of the family tree. Although an autosomal dominant inheritance was found, the onset of the disease only in women suggests that there may be a variant expression.

CONCLUSION:

The present study showed an association of GCD and keratoconus in four generations of a family. More research is required to further explain this association.

Comparison of Standard Versus Accelerated Corneal Collagen Cross-Linking for Keratoconus: A Meta-Analysis

Purpose

To systematically compare epithelial-off standard (SCXL) to accelerated corneal collagen cross-linking (ACXL) for the treatment of keratoconus.

Methods

PubMed, Embase, the Cochrane Library, and the US trial registry were searched for trials comparing SCXL and ACXL for keratoconus up to October 2017. Standardized mean differences (SMDs) with 95% confidence intervals (CIs) were calculated. Primary outcomes were changes in uncorrected distance visual acuity, maximum keratometry (Kmax), and mean keratometry (mean K). Secondary outcomes were changes in corrected distance visual acuity, mean refractive spherical equivalent, central corneal thickness (CCT), and endothelial cell density (ECD).

Results

Eleven trials were included. For primary outcomes, SCXL showed a greater reduction in Kmax (SMD 0.32; 95% CI 0.16, 0.48) than ACXL. For secondary outcomes, the decrease in CCT (SMD 0.32; 95% CI 0.03, 0.61) and ECD (SMD 0.26; 95% CI 0.06, 0.46) was less with ACXL than with SCXL. For the other outcomes, there were no statistically significant differences.

Conclusions

SCXL has a greater effect in terms of reduction in Kmax than ACXL, while ACXL induces less reduction in CCT and ECD than SCXL. Further well-designed randomized controlled trials comparing ACXL and SCXL are indicated.

Modulatory effect of different riboflavin compositions on the central corneal thickness of African keratoconus corneas during collagen crosslinking

Purpose:

A pilot investigation to transfer the established corneal collagen crosslinking (CXL) procedure in European eyes into clinically affected African eyes and to optimize the treatment by adapting the riboflavin composition.

Materials and Methods:

CXL was performed in 15 eyes (11 patients) with advanced stages of keratoconus in the Eye Clinic of Bafoussam in the West Region of Cameroon. The following six riboflavin compositions with different portions of active swelling additives were applied: Solution 1 (0.5% methylhydroxypropylcellulose [MHPC]), solution 2 (1.0% MHPC), solution 3 (1.7% MHPC), solution 4 (5% dextran), solution 5 (10% dextran) and solution 6 (no active swelling ingredient). The central corneal thickness (CCT) was measured by ultrasound pachymetry before and after de-epithelialization and at least every 10 min during CXL.

Results:

The application of the riboflavin solutions resulted in the following mean final CCT values: 172 ± 15% using solution 1 (60 min/n = 5); 183 ± 8% using solution 2 (60 min/n = 5); 170% using solution 3 (60 min/n = 1); 80% using solution 4 (45 min/n = 1); 99% using solution 5 (45 min/n = 1) and 150 ± 13% using solution 6 (50 min/n = 2).

Conclusions:

The combination of riboflavin compositions with swelling and stabilizing effects on the corneal stroma seems necessary in African eyes with advanced keratoconus. Further studies are required to confirm these primary results.

Keratoconus associated with Corneal Guttata

Purpose

To describe clinical findings of cases with keratoconus and concomitant corneal guttata.

Setting

Rio de Janeiro Corneal Tomography and Biomechanics Study Group, Brazil.

Materials and methods

In a retrospective study including 138 patients with clinical keratoconus, 22 eyes from 11 (8%) patients with keratoconus were identified with the presence of corneal guttata. Complete ophthalmologic examination was performed in all patients, including Scheimpflug rotation tomography (Pentacam HR, Oculus, Wetzlar, Germany), biomechanical study associated with noncontact tonometry [ocular response analyzer (ORA); Reichert, Depew, USA], and specular microscopy (LSM 12000, Bio-Optics, Oregon, USA). The amount of guttata was correlated with biomechanical and tomographic parameters by nonparametric Spearman test.

Results

The mean age was 51.8 ± 20.9 (from 25 to 81) years, nine patients were female (81.9%). The mean of corrected distance visual acuity was 0.20 (20/32) ± 0.49 [from 0 (20/20) to 1.9 (10/800)] LogMar. Eleven eyes had corneal guttae grade I, six eyes grade II, four eyes grade III, and one eye grade IV. The average central keratometric readings were 44.45 ± 2.54 (from 39.70 to 50.60) for flattest K (K1), 46.08 ± 2.69 (from 42.40 to 53.50) for steepest K (K2) and 45.24 ± 2.52 (from 42.00 to 52.20) for average K (Km). Maximal keratometric value (Kmax) averaged 47.63 ± 3.10 (from 43.5 to 55.8) D. The mean CCT was 482.54 ± 52.13 µm (from 398 to 585) and in the thinnest point 474.45 ± 50.32 µm (from 387 to 577). The mean of pachymetric progression indices were 0.83 ± 0.41 (from 0.2 to 2.03) (PPI Min), 1.24 ± 0.53 (from 0.7 to 2.73) (PPI Avg), and 1.79 ± 0.92 (from 0.88 to 4.67) (PPI Max). The mean of ART Min was 710.54 ± 372.47 (from 190.64 to 1985), of ART Avg was 433.18 ± 140.96 (from 141.75 to 678.37), and of ART Max was 315.64 ± 122.69 (from 102.78 to 539.78). The mean of front and back elevation at the thinnest point (using best fit sphere to 8 mm) was 5.35 ± 6.77 (from −4 to 20) and 19.15 ± 16.41 (from 1 to 50) respectively. Belin-Ambrósio deviation index (BAD D) was 3.05 ± 3 (from −0.34 to 11.55). The mean corneal hysteresis (CH) was 8.23 ± 2.05 (from 4.1 to 10.9), corneal resistance factor (CRF) was 7.67 ± 2.4 (from 3.4 to 11.3). The amount of guttata was statistically correlated with Km and K1 (Spearman, p > 0.05).

Conclusion

Keratoconus and cornea guttata can coexist in the same patient. This association can camouflage corneal thinning and protrusion associated with ectasia, but elevation, relational thickness, along with combined tomographic indices and biomechanical properties are altered. The diagnosis should be considered in the complete ophthalmic examination, including corneal topography, and tomographic characterization, along specular documentation of corneal endothelium.

How to cite this article

Ramos IC, Belin MW, Valbon BF, Luz A, Pimentel LN, Caldas DL, Ambrósio R Jr. Keratoconus associated with Corneal Guttata. Int J Kerat Ect Cor Dis 2012;1(3):173-178.

[Granular corneal dystrophy treated with deep anterior lamellar keratoplasty: comparing histological analysis and optical coherence tomography]

Granular corneal dystrophy is a rare autosomal dominant disease. It is characterized by breadcrumb-like granular opacities in the central corneal stroma. The mutation has been localized in the TGFβI gene, which codes for keratoepithelin, an adhesion protein found in corneal epithelium and stroma. We report the case of granular corneal dystrophy in a 60-year-old man complaining of reduced visual acuity. Slit-lamp examination revealed multiple opacities in the central stroma of his left eye, and recurrent deposits in his other eye 13 years after penetrating keratoplasty. An anterior segment optical coherence tomography (Visante(®) OCT) was used to determine the location of deposits, then a deep anterior lamellar keratoplasty was performed in his left eye. The depth of the deposits revealed by Visante(®) OCT correlated well with the postsurgical histological findings. Visante(®) OCT can therefore help choose between phototherapeutic keratectomy and lamellar keratoplasty, techniques that are less invasive than penetrating keratoplasty, which is advantageous since this dystrophy is known to recur after surgery.

The association of keratoconus with immune disorders

PURPOSE

To evaluate the association between keratoconus (KC) and immune disorders (IDs).

METHODS

A retrospective observational case-control study of all the members in the Central District of Clalit Health Services in Israel who were diagnosed to have KC (years 2000-2007; n = 426) and 1704 age- and gender-matched controls. We calculated the prevalence of the following IDs: rheumatoid arthritis, ulcerative colitis, arthropathy, amyloidosis, systemic lupus erythematosus, celiac disease, multiple sclerosis, myasthenia gravis, polymyalgia rheumatica, idiopathic thrombocytopenic purpura, Crohn disease, Hashimoto thyroiditis, autoimmune hepatitis, irritable bowel syndrome, asthma, and environmental allergy. The odds ratio (OR) of having IDs among patients with KC was compared with controls.

RESULTS

The association between KC and the following IDs was statistically significant: rheumatoid arthritis [OR = 8.1; 95% (confidence interval) CI: 1.5-44.2], ulcerative colitis (OR = 12.1; CI: 1.3-116), autoimmune chronic active hepatitis (OR = 6; CI: 1.01-36), Hashimoto thyroiditis (OR = 2.0; CI: 1.2-3.3), arthropathy (OR = 1.4; CI: 1.1-1.8), asthma (OR = 2.1; CI: 1.4-3.2), environmental allergy (OR = 1.3; CI: 1.02-1.75), and irritable bowel syndrome (OR = 5; CI: 2.1-12.1). Two autoimmune diseases, multiple sclerosis (OR = 2; CI: 0.2-22) and Crohn disease (OR = 1.6; CI: 0.3-8.3), were more prevalent among patients with KC but did not reach statistical significance.

CONCLUSION

Some strong associations between KC and several immune conditions of autoimmune diseases and allergic IDs may point to the role of the immune system in the pathogenesis of KC.

Keratoconus: a review

Keratoconus is the most common primary ectasia. It usually occurs in the second decade of life and affects both genders and all ethnicities. The estimated prevalence in the general population is 54 per 100,000. Ocular signs and symptoms vary depending on disease severity. Early forms normally go unnoticed unless corneal topography is performed. Disease progression is manifested with a loss of visual acuity which cannot be compensated for with spectacles. Corneal thinning frequently precedes ectasia. In moderate and advance cases, a hemosiderin arc or circle line, known as Fleischer's ring, is frequently seen around the cone base. Vogt's striaes, which are fine vertical lines produced by Descemet's membrane compression, is another characteristic sign. Most patients eventually develop corneal scarring. Munson's sign, a V-shape deformation of the lower eyelid in downward position; Rizzuti's sign, a bright reflection from the nasal area of the limbus when light is directed to the limbus temporal area; and breakages in Descemet's membrane causing acute stromal oedema, known as hydrops, are observed in advanced stages. Classifications based on morphology, disease evolution, ocular signs and index-based systems of keratoconus have been proposed. Theories into the genetic, biomechanical and biochemical causes of keratoconus have been suggested. Management varies depending on disease severity. Incipient cases are managed with spectacles, mild to moderate cases with contact lenses and severe cases can be treated with keratoplasty. This article provides a review on the definition, epidemiology, clinical features, classification, histopathology, aetiology and pathogenesis, and management and treatment strategies for keratoconus.

Ultrastructural analysis of collagen fibrils and proteoglycans in keratoconus

PURPOSE

To investigate ultrastructural alterations in the distribution of collagen fibrils (CFs) and proteoglycans (PGs) in the keratoconus cornea.

METHODS

Four normal corneas (donor age 24-75 years) and four severe and one mild keratoconus corneas (donor age 24-47 years) were fixed in 2.5% glutaraldehyde containing 0.05% cuprolinic blue dye for electron microscopy. Analyses were carried out on approximately 39 000 CF and 66 000 PG filaments in the anterior, middle and posterior stroma, using analySIS soft imaging software.

RESULTS

In severe keratoconus, stromal lamellae were seen to undulate in most regions, whereas in mild keratoconus only the middle and posterior lamellae were affected. In keratoconus corneas the mean diameter and interfibrillar spacing of CFs was reduced in all zones (p < 0.0001) and the CF and PG number density and area fractions were significantly increased (p < 0.0001) compared with in normal corneas and were higher (p < 0.0001) in the corneas with severe keratoconus than in that with mild keratoconus. The lamellae contained microfibrils (8-9 nm wide) and, in addition, PGs embedded within CFs. Degenerate keratocytes containing PGs were found in all keratoconus corneas.

CONCLUSIONS

These studies suggest that as keratoconus progresses, the PG content of the stroma increases, whereas fibril diameter is reduced. The altered stromal content of PGs may influence CF diameters and their organization in keratoconus, weakening lateral cohesion and resulting in significant disorder of CF packing.

Six-year Experience With Excimer Laser Surgery for Primary Keratoconus in Russia

PURPOSE

To report our results using PRK combined with PTK to treat keratoconus.

METHODS

Forty-one patients (70 eyes) underwent PRK+PTK with a Nidek EC-5000 excimer laser. PRK included spherical or cylindrical ablations, or both. PRK ablation zone diameter was 6.00 mm. PTK was performed with an ablation zone diameter of 8.00 mm and a transition zone of 9 mm. PTK ablation zone was decentered toward the cone apex, according to corneal topography.

RESULTS

Refractive results: UCVA increased from 0.07 +/- 0.003 to 0.76 +/- 0.03 (69.2% of eyes had uncorrected visual acuity of 1.0); mean BSCVA increased from 0.70 +/- 0.03 to 0.83 +/- 0.04; myopia decreased from a mean 5.32 +/- 0.62 D to 1.55 +/- 0.30 D and astigmatism decreased from a mean 3.25 +/- 0.53 D to 1.75 +/- 0.25 D. Therapeutic results: Keratoconus progression was stopped in 91.43% of eyes with a mean follow-up of 3.5 years and maximum follow-up of 6 years.

CONCLUSION

PRK+PTK with the Nidek EC-5000 excimer laser was an excellent option for patients with primary keratoconus.

Keratolysis Following Excimer Laser Phototherapeutic Keratectomy in a Patient With Keratoconus

PURPOSE

We report a case of keratolysis following phototherapeutic keratectomy (PTK) for a subepithelial nodule in a patient with keratoconus.

METHODS

A 29-year-old male with keratoconus who became contact lens intolerant because of a raised subepithelial nodule was treated with excimer laser phototherapeutic keratectomy (PTK).

RESULTS

The epithelium failed to heal postoperatively, and progressive keratolysis led to a central descemetocele by the eighth postoperative day. The patient was managed with a penetrating keratoplasty.

CONCLUSIONS

Excimer laser phototherapeutic keratectomy has been shown to be an effective treatment for subepithelial nodules in patients with keratoconus. Rapidly progressive keratolysis is a potential complication of this procedure.

Lisch corneal dystrophy is genetically distinct from Meesmann corneal dystrophy and maps to xp22.3

PURPOSE

There is an ongoing discussion whether Lisch corneal dystrophy (band-shaped and whorled microcystic dystrophy of the corneal epithelium) represents a disorder that is different from Meesmann corneal dystrophy. The purpose of this study was to evaluate at the molecular level if Lisch and Meesmann corneal dystrophies are genetically distinct.

METHODS

We examined at the slit lamp a total of 48 members of a family with an aggregation of Lisch corneal dystrophy. Genomic DNA was extracted from leukocytes of the peripheral blood of seven affected and six unaffected members of this family. Mutational hotspots in the cornea-specific keratin genes K3 and K12 were scanned for mutations by single-strand conformation analysis. To test for linkage to the keratin K3 or K12 loci or for X-chromosomal inheritance, six (K3) and four (K12) microsatellite markers each flanking the keratin loci as well as 22 microsatellite markers covering the X-chromosome were typed. Linkage was analyzed using the MLINK and FASTMAP procedures.

RESULTS

A total of 19 trait carriers were identified in six generations of the family. No hereditary transmission from father to son was observed. Linkage was excluded for the keratin K3 and K12 genes. Furthermore, single-strand conformation analysis detected no mutations in these genes. Multipoint linkage analysis revealed linkage with a maximum likelihood of the odds (LOD) score of 2.93 at Xp22.3. Linkage was excluded for Xp22.2 to Xqter.

CONCLUSIONS

Lisch corneal dystrophy is genetically different from Meesmann corneal dystrophy. Evidence was found for linkage of the gene for Lisch corneal dystrophy to Xp22.3.

Treatment of mild to moderate keratoconus with laser in situ keratomileusis

PURPOSE

To evaluate the effectiveness, stability, and complications of laser in situ keratomileusis (LASIK) to treat myopic astigmatism in patients with keratoconus.

SETTING

Buzard Eye Institute, Las Vegas, Nevada, USA.

METHODS

This study included 16 eyes of 9 patients who had keratometric and/or clinical evidence of keratoconus. Mean age was 45 years, and refraction was stable for at least 2 years. Two treatment approaches were evaluated.

RESULTS

Mean preoperative spherical equivalent was -4.23 diopters (D) +/- 2.14 (SD) with a mean steep keratometry of 46.81 +/- 3.07 D. Mean preoperative keratometric cylinder was 3.08 +/- 2.22 D. Mean postoperative keratometric cylinder was 3.00 +/- 4.78 D and mean spherical equivalent, -0.44 +/- 0.86 D. Mean postoperative steep keratometry was 44.12 +/- 7.17 D. Two eyes lost 1 line of best corrected visual acuity (BCVA), 1 eye lost 3 lines, and 2 lost 4 lines. Penetrating keratoplasty (PKP) was scheduled in 3 eyes 1 to 2 years after the primary LASIK.

CONCLUSION

The initial visual results appear promising; but longer term results revealed regression of the refractive outcome in some cases. Moreover, despite improvement in the postoperative spherical equivalent and uncorrected visual acuity in most cases, the risk of loss of BCVA and the necessity of performing PKP in 3 cases lead us not to consider LASIK as a primary solution for keratoconus.

Two distinct kerato-epithelin mutations in Reis-Bücklers corneal dystrophy

PURPOSE

Two patients were diagnosed with Reis-Bücklers corneal dystrophy (RBCD), although the pattern and severity of corneal opacification differed. To see whether there was a genetic basis for these phenotypic variations, we analyzed beta ig-h3, the gene that codes for kerato-epithelin and that contains a mutation (Arg555Gln) that causes RBCD.

METHODS

A 30-year-old man with honeycomb-shaped subepithelial opacities in his central cornea and a 25-year-old man with progressive subepithelial geographic opacities were both considered to have RBCD. We isolated genomic DNA from leukocytes of the two patients and their family members and screened for an Arg555Gln kerato-epithelin mutation. Then we analyzed all exons of the gene using the single-strand conformation polymorphism (SSCP) technique to search for any other kerato-epithelin mutations.

RESULTS

The patient with honeycomb-shaped opacities had an Arg555Gln kerato-epithelin mutation that caused his RBCD, whereas the patient with geographic opacities did not; instead, he had a new kerato-epithelin mutation (Arg124Leu), which cosegregated with his family members.

CONCLUSIONS

The variant of RBCD characterized by honeycomb-shaped opacities is caused by an Arg555Gln kerato-epithelin mutation. On the other hand, a new kerato-epithelin mutation, Arg124Leu, was found to cause the RBCD variant characterized by recurrent epithelial erosions and progressive geographic subepithelial opacification. Codon 124 is a hot spot for kerato-epithelin mutations, where the mutations responsible for three autosomal dominant corneal dystrophies--lattice type I (Arg124Cys), Avellino (Arg124His), and the variant of RBCD with geographic rather than honeycomb opacities (Arg124Leu)--are located.

Keratoconus

Keratoconus is a bilateral noninflammatory corneal ectasia with an incidence of approximately 1 per 2,000 in the general population. It has well-described clinical signs, but early forms of the disease may go undetected unless the anterior corneal topography is studied. Early disease is now best detected with videokeratography. Classic histopathologic features include stromal thinning, iron deposition in the epithelial basement membrane, and breaks in Bowman's layer. Keratoconus is most commonly an isolated disorder, although several reports describe an association with Down syndrome, Leber's congenital amaurosis, and mitral valve prolapse. The differential diagnosis of keratoconus includes keratoglobus, pellucid marginal degeneration and Terrien's marginal degeneration. Contact lenses are the most common treatment modality. When contact lenses fail, corneal transplant is the best and most successful surgical option. Despite intensive clinical and laboratory investigation, the etiology of keratoconus remains unclear. Clinical studies provide strong indications of a major role for genes in its etiology. Videokeratography is playing an increasing role in defining the genetics of keratoconus, since early forms of the disease can be more accurately detected and potentially quantified in a reproducible manner. Laboratory studies suggest a role for degradative enzymes and proteinase inhibitors and a possible role for the interleukin-1 system in its pathogenesis, but these roles need to be more clearly defined. Genes suggested by these studies, as well as collagen genes and their regulatory products, could potentially be used as candidate genes to study patients with familial keratoconus. Such studies may provide the clues needed to enable us to better understand the underlying mechanisms that cause the corneal thinning in this disorder.